Medical control device and medical observation system

Abstract

This medical control device 9 comprises: a light source control unit 941 that controls the operation of a light source device 3 that emits first light, and first excitation light and second excitation light that respectively excite substances included in an observation target; an imaging control unit 942 that controls the operation of an imaging device 5 that images each of return light of the first light, return light of the first excitation light, and return light of the second excitation light from the observation target; and a mode switching unit 943 that switches to any one mode among a plurality of modes. The light source control unit 941 controls the operation of the light source device 3 such that the light emission patterns of the first light, the first excitation light, and the second excitation light differ among the plurality of modes.

Description

Medical control device and medical observation system The present disclosure relates to a medical control device and a medical observation system. Conventionally, a medical observation system has been known that irradiates an observation target (a subject such as a person) with visible light such as excitation light, which is narrow-band light emitted from a light source device, or white light, which is broadband light, and observes fluorescence emitted from substances contained in the observation target by the irradiation of the excitation light (hereinafter referred to as observation target fluorescence) (see, for example, Patent Document 1). According to such fluorescence observation, it is possible to grasp a tissue state that is difficult to recognize through the observation target fluorescence. Therefore, fluorescence observation can be used for various purposes and applications such as specifying a lesion part. Japanese Patent Application Laid-Open No. 2021-132695 By the way, there is a need to observe not only one type of observation target fluorescence but also observation target fluorescence in a plurality of different wavelength bands. In the medical observation system described in Patent Document 1, it is possible to observe one type of observation target fluorescence, but it is not possible to observe observation target fluorescence in a plurality of different wavelength bands. Therefore, there is a demand for a technique that can satisfactorily observe observation target fluorescence in a plurality of different wavelength bands. The present disclosure has been made in view of the above, and an object thereof is to provide a medical control device and a medical observation system that can satisfactorily observe observation target fluorescence in a plurality of different wavelength bands. In order to solve the above-described problems and achieve the object, a medical control device according to the present disclosure includes a light source control unit that controls the operation of a light source device that emits first light, first excitation light, and second excitation light that respectively excite substances contained in an observation target, an imaging control unit that controls the operation of an imaging device that images return light of the first light, return light of the first excitation light, and return light of the second excitation light from the observation target, and a mode switching unit that switches to any one of a plurality of modes, and the light source control unit controls the operation of the light source device such that emission patterns of the first light, the first excitation light, and the second excitation light are different between the plurality of modes. Furthermore, the medical observation system according to this disclosure comprises a light source device that emits a first light and a first excitation light and a second excitation light that excite substances contained in an object to be observed, respectively; an imaging device that images the return light of the first light, the return light of the first excitation light, and the return light of the second excitation light from the object to be observed, respectively; and a medical control device that controls the operation of the light source device and the operation of the imaging device, respectively. The medical control device comprises a light source control unit that controls the operation of the light source device, an imaging control unit that controls the operation of the imaging device, and a mode switching unit that switches to one of a plurality of modes. The light source control unit controls the operation of the light source device so that the emission patterns of the first light, the first excitation light, and the second excitation light differ in the plurality of modes. According to the medical control device and medical observation system described herein, multiple types of fluorescence in different wavelength bands can be observed effectively. Figure 1 is a diagram showing the configuration of a medical observation system according to Embodiment 1. Figure 2 is a block diagram showing the configuration of a camera head and a control device. Figure 3 is a diagram showing a first example of light source control and imaging control in the first mode. Figure 4 is a diagram showing a second example of light source control and imaging control in the first mode. Figure 5 is a diagram showing a first example of light source control and imaging control in the second mode. Figure 6 is a diagram showing a second example of light source control and imaging control in the second mode. Figure 7 is a diagram showing light source control and imaging control in the third mode. Figure 8 is a diagram showing a first example of light source control and imaging control in the first mode according to Embodiment 2. Figure 9 is a diagram showing a second example of light source control and imaging control in the first mode according to Embodiment 2. Figure 10 is a diagram showing a first example of light source control and imaging control in the second mode according to Embodiment 2. Figure 11 is a diagram showing a second example of light source control and imaging control in the second mode according to Embodiment 2. Figure 12 is a diagram showing a third example of light source control and imaging control in the second mode according to Embodiment 2. Figure 13 is a diagram showing light source control and imaging control in the third mode according to Embodiment 2. Figure 14 is a diagram showing a first example of light source control and imaging control in the first mode according to Embodiment 3. Figure 15 is a diagram showing a second example of light source control and imaging control in the first mode according to Embodiment 3. Figure 16 is a diagram showing a first example of light source control and imaging control in the second mode according to Embodiment 3. Figure 17 is a diagram showing a second example of light source control and imaging control in the second mode according to Embodiment 3. Figure 18 is a diagram showing a first example of light source control and imaging control in the third mode according to Embodiment 3. Figure 19 is a diagram showing a second example of light source control and imaging control in the third mode according to Embodiment 3. Figure 20 is a diagram showing a third example of light source control and imaging control in the third mode according to Embodiment 3. Figure 21 is a diagram showing a fourth example of light source control and imaging control in the third mode according to Embodiment 3. Figure 22 is a diagram showing a fifth example of light source control and imaging control in the third mode according to Embodiment 3. Figure 23 shows a sixth example of light source control and imaging control in the third mode according to Embodiment 3. Figure 24 shows the configuration of a medical observation system according to Embodiment 4.Figure 25 is a diagram illustrating light source control and imaging control in the first mode according to Embodiment 4. Figure 26 is a diagram illustrating a first example of light source control and imaging control in the second mode according to Embodiment 4. Figure 27 is a diagram illustrating a second example of light source control and imaging control in the second mode according to Embodiment 4. Figure 28 is a diagram illustrating light source control and imaging control in the third mode according to Embodiment 4. Figure 29 is a diagram illustrating a modification 1 of Embodiment 1. Figure 30 is a diagram illustrating a modification 1 of Embodiment 1. Figure 31 is a diagram illustrating a modification 2 of Embodiment 2. Figure 32 is a diagram illustrating a modification 2 of Embodiment 2. Figure 33 is a diagram illustrating a modification 3 of Embodiment 3. Figure 34 is a diagram illustrating a modification 3 of Embodiment 3. Figure 35 is a diagram illustrating a modification 3 of Embodiment 3. Figure 36 is a diagram illustrating a modification 3 of Embodiment 3. Figure 37 is a diagram illustrating a modification 3 of Embodiment 3. Figure 38 is a diagram illustrating a modification 3 of Embodiment 3. Figure 39 is a diagram illustrating a modification 4 of Embodiment 4. Figure 40 is a diagram illustrating a modification 4 of Embodiment 4. Figure 41 illustrates a modification 4 of Embodiment 4. Figure 42 illustrates a modification 5 of Embodiments 1 to 4. Figure 43 illustrates a modification 7 of Embodiments 1 to 4. Figure 44 illustrates a modification 8 of Embodiments 1 to 4. Figure 45 illustrates a modification 9 of Embodiments 1 to 4. Figure 46 illustrates a modification 9 of Embodiments 1 to 4. The embodiments for implementing this disclosure (hereinafter referred to as "embodiments") will be described below with reference to the drawings. However, the embodiments described below do not limit this disclosure. Furthermore, the same parts are denoted by the same reference numerals in the drawings. (Embodiment 1) [Configuration of the medical observation system] Figure 1 is a diagram showing the configuration of the medical observation system 1 according to Embodiment 1. In this embodiment 1, the medical observation system 1 is a medical endoscopic system that uses an endoscope to observe the target OB (inside the body). As shown in Figure 1, this medical observation system 1 comprises an insertion unit 2, a light source device 3, a light guide 4, a camera head 5, a first transmission cable 6, a display device 7, a second transmission cable 8, a control device 9, and a third transmission cable 10. In this embodiment 1, the insertion section 2 is made of a rigid endoscope. That is, the insertion section 2 has an elongated shape that is entirely rigid, or partially flexible with the rest being rigid, and is inserted into the observation target OB. Inside this insertion section 2, there is an optical system made of one or more lenses that collects the reflected light (image of the subject) from the observation target OB. Furthermore, an excitation light cut filter 22 (Figure 1) is provided at the base end (eyepiece 21) of the insertion section 2 to partially, substantially, or completely suppress the first and second excitation lights, which will be described later, included in the focused reflected light (subject image). The excitation light cut filter 22 is not limited to the insertion section 2; it may also be installed inside the camera head 5. One end of the light guide 4 is connected to the light source device 3. The light source device 3 then supplies light to the one end of the light guide 4 under the control of the control device 9. As shown in Figure 1, the light source device 3 comprises a first light source 31, a second light source 32, and a third light source 33. The first light source 31 emits first light (broadband light such as white light (visible light), or narrowband light such as red light, green light, or blue light) that includes at least a portion of the visible light wavelength band. Examples of the configuration of the first light source 31 include a configuration including a white LED (Light Emitting Diode), or a configuration including three light sources that emit red light, green light, and blue light respectively, and an optical element that combines the red light, green light, and blue light. The first light source 31 may be made of an LED or a semiconductor laser. The number of first light sources 31 may be one or more. In the following, the first light emitted from the first light source 31 may be referred to as visible light. The second light source 32 emits a first excitation light that excites the substance contained in the object being observed OB. The second light source 32 may be composed of an LED or a semiconductor laser. There may be one or more second light sources 32. Furthermore, the second light source 32 may emit light that includes at least a portion of the visible light wavelength band, or it may emit light in the invisible light wavelength band such as infrared or ultraviolet light. The third light source 33 emits a second excitation light to excite the substance contained in the object OB being observed. The third light source 33 may be an LED or a semiconductor laser. There may be one or more third light sources 33. Furthermore, the third light source 33 may emit light that includes at least a portion of the visible light wavelength band, or it may emit light in the invisible light wavelength band such as infrared or ultraviolet light. In the following, the first and second excitation lights may be collectively referred to as "excitation light." In this embodiment 1, a configuration is provided in which three light sources (first to third light sources 31 to 33) are used to emit visible light and first and second excitation light, respectively, but the invention is not limited to this configuration. For example, a configuration may be adopted in which only one light source is provided and visible light and first and second excitation light are emitted by switching the wavelength using a wavelength-adjusting optical element (filter, etc.). Alternatively, for example, a configuration may be adopted in which two light sources are provided and visible light and first and second excitation light are emitted by switching the wavelength using a wavelength-adjusting optical element (filter, etc.). Here, examples of substances contained in the observed object OB that are excited by the first and second excitation light include drugs and fluorescent dyes applied to the observed object OB, or fluorescent substances derived from the observed object OB that constitute the observed object OB itself. Examples of the above-mentioned drugs administered to the observed OB include "5-ALA (PP-IX)", "ADS780WS", "ADS830WS", "aggregation-induced emission dots allophycocyanin (APC)", "boron-dipyrromethane (BODIPY)", "CLR 1502", "Flavins", "fluorescamine", "Fluorescein", "fluoro-gold", "green fluorescence protein", "ICG (indocyanine green)", "IRDye 78", "IR-PEG nanoparticles", "Isothiocyanate", "rose bengal", "SGM-101", and "trypan blue". Furthermore, the fluorescent dyes mentioned above that can be applied to the observed OB include: "coumarine", "Cy3", "DyLight547", "GE3126", "metal nanoclusters", "oxacarbocyanine", "Rhodamine", "Riboflavin", "fluorescein", "AlexaFluor 488", "AlexaFluor660", "AlexaFluor680", "AlexaFluor700", "Cy5", "Cy5.5", "Dy677", "Dy682", "Dy752", "DyLight647", "HiLyte Fluor 647", "HiLyte Fluor 680", "IRDye 700DX", "methylene blue", "Porphyrins", "Porphysomes", "VivoTag-680", "VivoTag-S680", "AlexaFluor750", "AlexaFluor790", "carbocyanine", "conjugated copolymers", "CW800-CA", "Cy7", "Cy7.5", and "cyanine". Examples include "dyes", "Dy780", "HiLyte Fluor 750", "Indocarbocyanine", "IR-786", "IRDye 800CW", "IRDye 800RS", "IRDye 800BK", "Nervelight", "OTL-38 (Pafolacianine)", "Polymethine", "VivoTag-S750", "ASP5354", "Xanthene", and "LUM-015". Furthermore, examples of fluorescent substances derived from the observed OB that constitute the observed OB itself include "collagen," "elastin," and "NADH." In this embodiment 1, the light source device 3 is configured separately from the control device 9, but it is not limited to this configuration, and it may also be configured to be housed in the same housing as the control device 9. Alternatively, the control device 9 may be divided into two, and the light source device 3 may be housed in the housing of one of the two control devices 9. One end of the light guide 4 is detachably connected to the light source device 3. The other end of the light guide 4 is detachably connected to the insertion section 2. The light guide 4 transmits light (visible light and first and second excitation light) supplied from the light source device 3 from one end to the other and supplies it to the insertion section 2. The light (visible light and first and second excitation light) supplied to the insertion section 2 is emitted from the tip of the insertion section 2 and irradiates the object to be observed OB. When visible light is irradiated onto the object to be observed OB, the reflected light of the visible light from the object to be observed OB is focused by the optical system in the insertion section 2. When the first excitation light is irradiated onto the object to be observed OB, the reflected light of the first excitation light from the object to be observed OB is focused by the optical system in the insertion section 2. The reflected light of the first excitation light includes the first excitation light reflected from the observation target OB, as well as the first fluorescence (hereinafter referred to as the first observation target fluorescence) emitted from a substance contained in the observation target OB when the first excitation light irradiates the observation target OB and excites that substance. Furthermore, when the observation target OB is irradiated with a second excitation light, the reflected light of the second excitation light from the observation target OB is focused by the optical system in the insertion section 2. The reflected light of the second excitation light includes the second excitation light reflected from the observation target OB, as well as the second fluorescence (hereinafter referred to as the second observation target fluorescence) emitted from a substance contained in the observation target OB when the second excitation light irradiates the observation target OB and excites that substance. In the following, the first and second observation target fluorescence may be collectively referred to as the observation target fluorescence. The camera head 5 corresponds to the imaging device according to this disclosure. This camera head 5 is detachably connected to the eyepiece 21 of the insertion section 2. The camera head 5, under the control of the control device 9, captures the reflected light (reflected visible light, reflected light of the first excitation light, and reflected light of the second excitation light) from the observation target OB focused by the insertion section 2 and generates a pixel signal. Hereinafter, for the sake of explanation, this pixel signal may be referred to as the captured image. The detailed configuration of camera head 5 will be explained later in the section titled "Camera Head Configuration". One end of the first transmission cable 6 is detachably connected to the control device 9 via connector CN1 (Figure 1). The other end of the first transmission cable 6 is detachably connected to the camera head 5 via connector CN2 (Figure 1). The first transmission cable 6 transmits captured images and the like output from the camera head 5 to the control device 9, and transmits control signals, synchronization signals, clock signals, and power, etc., output from the control device 9 to the camera head 5, respectively. Furthermore, the captured images and other data transmitted from the camera head 5 to the control device 9 via the first transmission cable 6 may be transmitted as optical signals or as electrical signals. The same applies to the transmission of control signals, synchronization signals, and clock signals from the control device 9 to the camera head 5 via the first transmission cable 6. The display device 7 is composed of a display using liquid crystal or organic EL (Electro Luminescence), and under the control of the control device 9, it displays an image based on a video signal from the control device 9. One end of the second transmission cable 8 is detachably connected to the display device 7. The other end of the second transmission cable 8 is detachably connected to the control device 9. The second transmission cable 8 transmits the video signal processed by the control device 9 to the display device 7. The control device 9 corresponds to the medical control device described herein. This control device 9 is composed of a CPU (Central Processing Unit), an FPGA (Field-Programmable Gate Array), etc., and comprehensively controls the operation of the light source device 3, the camera head 5, and the display device 7. The detailed configuration of the control device 9 will be explained later in the section titled "Configuration of the Control Device". One end of the third transmission cable 10 is detachably connected to the light source device 3. The other end of the third transmission cable 10 is detachably connected to the control device 9. The third transmission cable 10 transmits control signals from the control device 9 to the light source device 3. [Camera head configuration] Next, we will explain the configuration of the camera head 5. Figure 2 is a block diagram showing the configuration of the camera head 5 and the control device 9. As shown in Figure 2, the camera head 5 comprises a lens unit 51, a prism 52, an imaging unit 53, and a communication unit 54. The lens unit 51 is composed of one or more lenses. The lens unit 51 then focuses the reflected light (subject image) from the observation target OB, which has been focused in the insertion section 2, onto the imaging surfaces of the first and second image sensors 531 and 532, respectively. The prism 52 separates the reflected light (subject image) from the observation target OB via the lens unit 51 into light of two different wavelength bands: first and second. The light of the first wavelength band is light of a wavelength band excluding at least a portion of the wavelength bands of the first and second observation target fluorescence, and includes at least a portion of the visible light wavelength band. Hereinafter, the light of the first wavelength band will be referred to as the normal subject image. The light of the second wavelength band is light of a wavelength band excluding at least a portion of the wavelength bands of the visible light, and includes at least a portion of the wavelength bands of the first and second observation target fluorescence. Hereinafter, the light of the second wavelength band that includes at least a portion of the wavelength band of the first observation target fluorescence will be referred to as the first fluorescence subject image. Furthermore, the light of the second wavelength band that includes at least a portion of the wavelength band of the second observation target fluorescence will be referred to as the second fluorescence subject image. The prism 52 then propagates the normal subject image toward the first image sensor 531. Furthermore, the prism 52 propels the first and second fluorescent subject images toward the second image sensor 532. The imaging unit 53 captures images of the observation target OB under the control of the control device 9. As shown in Figure 2, the imaging unit 53 comprises a first image sensor 531, a second image sensor 532, and a signal processing unit 533. The number of image sensors constituting the first image sensor 531 may be one or more. Similarly, the number of image sensors constituting the second image sensor 532 may be one or more. The first and second image sensors 531 and 532 receive the subject image and convert it into an electrical signal (analog signal). These first and second image sensors 531 and 532 are composed of a CMOS (Complementary Metal Oxide Semiconductor), which is a rolling shutter type image sensor in which multiple pixels are arranged in a two-dimensional manner in units of horizontal lines, and a CCD (Charge Coupled Device), which is a global shutter type image sensor, respectively. Here, the first image sensor 531, although not shown in detail in the illustration, is composed of an invalid region where the output signal is not used to generate the captured image, an optical black region (OB region), and an effective pixel region where the normal subject image formed by the lens unit 51 is converted into a pixel signal and output. Similarly, the second image sensor 532 is composed of an invalid region, an optical black region (OB region), and an effective pixel region. The first image sensor 531 then captures a normal subject image via the prism 52 under the control of the control device 9. That is, the first image sensor 531 captures light that includes at least a portion of the visible light wavelength band. For the sake of explanation, the image generated by capturing a normal subject image will be referred to as a normal image below. Furthermore, the second image sensor 532, under the control of the control device 9, captures images of the first and second fluorescent subjects via the prism 52. That is, the second image sensor 532 captures light that includes at least a portion of the wavelength band of the first and second observed fluorescence. For the sake of explanation, the image generated by capturing the first fluorescent subject will be referred to as the first fluorescence image. The image generated by capturing the second fluorescent subject will be referred to as the second fluorescence image. Furthermore, the number of pixels in the normal image and the number of pixels in the first and second fluorescence images may be different or the same. The signal processing unit 533, under the control of the control device 9, performs signal processing on the captured images (analog signals) generated by the first and second image sensors 531 and 532, and outputs the captured images (digital signals). For example, the signal processing unit 533 performs signal processing on the captured image (analog signal) generated by the first and second image sensors 531 and 532, including processing to remove reset noise, processing to multiply the analog signal by an analog gain to amplify the analog signal (hereinafter referred to as analog gain adjustment), and A / D conversion. The communication unit 54 functions as a transmitter that transmits the captured images output sequentially from the imaging unit 53 to the control device 9 via the first transmission cable 6. This communication unit 54 is configured, for example, as a high-speed serial interface that communicates captured images with the control device 9 via the first transmission cable 6 at a transmission rate of 1 Gbps or higher. The communication unit 54 may transmit the normal image, the first fluorescence image, and the second fluorescence image to the control device 9 in sequence, or it may transmit at least two of these three images simultaneously. [Control device configuration] Next, the configuration of the control device 9 will be explained with reference to Figure 2. As shown in Figure 2, the control device 9 includes a communication unit 91, an image memory 92, a processing module 93, a control unit 94, an input unit 95, an output unit 96, and a storage unit 97. The communication unit 91 functions as a receiver that receives captured images sequentially transmitted from the camera head 5 (communication unit 54) via the first transmission cable 6. This communication unit 91 is configured, for example, as a high-speed serial interface that communicates captured images with the communication unit 54 at a transmission rate of 1 Gbps or higher. The image memory 92 is composed of, for example, DRAM (Dynamic Random Access Memory). This image memory 92 can temporarily store multiple frames of captured images that are sequentially output from the camera head 5 (communication unit 54). The processing module 93 processes the captured images that are sequentially transmitted from the camera head 5 (communication unit 54) and received by the communication unit 91, under the control of the control unit 94. As shown in Figure 2, this processing module 93 comprises a memory controller 931, a processing unit 932, and a display control unit 933. The memory controller 931 controls the writing of captured images to the image memory 92 and the reading of captured images from the image memory 92. The captured images read by the memory controller 931 are input to the processing unit 932. The processing unit 932 performs image processing on the input captured image. Examples of such image processing include optical black subtraction (clamping), white balance adjustment, demosaicing, color correction matrix processing, gamma correction, YC processing to convert RGB signals into luminance chromatic difference signals (Y, Cb / Cr signals), digital gain adjustment to multiply digital gain, noise reduction, and filtering to enhance structure. Furthermore, the image processing performed on the normal image, the image processing performed on the first fluorescence image, and the image processing performed on the second fluorescence image may all be different image processing processes, or at least two of the image processing processes may be the same image processing process. The display control unit 933 generates a display image (video signal) for display on the display device 7 based on the captured image after image processing has been performed by the processing unit 932, under the control of the control unit 94. The display control unit 933 then outputs the video signal to the display device 7 via the second transmission cable 8. The control unit 94 is implemented by a controller such as a CPU or MPU (Micro Processing Unit) executing various programs stored in the memory unit 97. It controls the operation of the light source device 3, the camera head 5, and the display device 7, as well as the operation of the entire control device 9. The control unit 94 is not limited to a CPU or MPU; it may also be composed of an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA. As shown in Figure 2, this control unit 94 has the functions of a light source control unit 941, an imaging control unit 942, and a mode switching unit 943. The functions of the light source control unit 941, the imaging control unit 942, and the mode switching unit 943 will be explained later in the section "About Modes". The input unit 95 is configured using operating devices such as a mouse, keyboard, and touch panel, and accepts user operations from a user such as a surgeon. The input unit 95 then outputs an operation signal corresponding to the user operation to the control unit 94. The output unit 96 is configured using a speaker, printer, etc., and outputs various types of information. The memory unit 97 stores programs executed by the control unit 94, information necessary for processing by the control unit 94, and so on. [Challenges of fluorescence observation] Next, I will explain the challenges of fluorescence observation. Hereinafter, the optical path of visible light and the first and second excitation light following the path from the light source device 3 to the light guide 4 to the insertion unit 2 to the observation target OB will be referred to as the first optical path P1 (Figure 1). Furthermore, the optical path of the return light from the observation target OB (return light of visible light, return light of the first excitation light, return light of the second excitation light) following the path from the observation target OB to the insertion unit 2 to the first and second image sensors 531 and 532 will be referred to as the second optical path P2 (Figure 1). In addition, the first and second optical paths P1 and P2 are combined and referred to as the observation optical path P0 (Figure 1). When visible light and the first and second excitation lights propagate through the first optical path P1, and when the reflected light from the observation target OB propagates through the second optical path P2, the member forming the observation optical path P0 (hereinafter referred to as the autofluorescence generating member) is irradiated with visible light, the first and second excitation lights, and the reflected light from the observation target OB, causing autofluorescence (hereinafter referred to as unwanted light) to be generated from the autofluorescence generating member. Examples of the autofluorescence generating member include components contained in multi-component glass such as lenses, organic material components contained in color filters, adhesives used to join lenses, and oil adhering to optical elements such as lenses. Such unwanted light has a wavelength band that includes the wavelength band of the observed fluorescence, which is the light to be observed in fluorescence observation, and becomes noise in the fluorescence observation. Such unwanted light is also generated when the observation target OB is irradiated with visible light or the first and second excitation lights. Furthermore, if the fluorescence of the target object OB is weak, it is necessary to adjust the signal value based on the fluorescence of the target object captured by the second image sensor 532 in order to separate the fluorescence of the target object from the unwanted light mentioned above and perform good fluorescence observation. However, adjusting the signal value based on the fluorescence of the target object is difficult because it is affected by the following (1) to (4). (1) Drugs Generally, the amount of fluorescence light emitted from a drug varies depending on the type and dosage of the drug. The type of drug administered to the observed OB is selected according to the type of OB (cancer, blood, lymph, etc.). Furthermore, in order to image the target fluorescence emitted from the drug in the medical observation system 1, a drug is selected in which the wavelength of the excitation light that excites the drug and the wavelength of the target fluorescence emitted from the drug can be separated. The drugs selected in this way each emit different amounts of target fluorescence. Furthermore, while the intensity of the observed fluorescence can be adjusted by controlling the drug dosage, it is difficult to increase the dosage unnecessarily in order to achieve minimally invasive procedures. In other words, it is difficult to adjust the amount of light emitted from the observed fluorescence by selecting the type of drug and adjusting the dosage. As a result, it is difficult to adjust the signal value based on the observed fluorescence captured by the second image sensor 532 by selecting the type of drug and adjusting the dosage. (2) Subjects of observation The amount of fluorescence emitted from the observed OB varies depending on the location and condition of the OB. Specifically, in the case of an observed OB (observed area) that is prone to drug accumulation, the amount of fluorescence emitted from the observed OB increases. On the other hand, in the case of an observed OB that is prone to drug flow and accumulation, the amount of fluorescence emitted from the observed OB decreases, and the afterglow time also shortens. Furthermore, if the observed OB is a tumor, the amount of fluorescence received by the second image sensor 532 changes depending on its extent, size, and depth. That is, it is difficult to adjust the amount of light of the fluorescence of the observation target according to the type and state of the observation target OB. As a result, it is difficult to adjust the signal value based on the fluorescence of the observation target imaged by the second image pickup device 532 according to the type and state of the observation target OB. (3) Light source device The amount of light of the fluorescence of the observation target varies depending on the amount of excitation light emitted from the light source device 3. In order to increase the amount of excitation light, it may be necessary to adjust the power supplied to the light source device 3. However, the power that can be supplied to the light source device 3 is limited according to the upper limit value of the power for operating the entire medical observation system 1. Further, the amount of excitation light needs to be adjusted in consideration of heat generation in the members constituting the optical path of the excitation light (for example, heat generation between the light guide 4 and the insertion portion 2), correspondence to the laser class, the amount of light energy received by the observation target OB and the surrounding living body (if the amount of light energy is large, there is a risk of leading to burns), or the speed of fading of the fluorescence of the observation target emitted from the drug. Furthermore, the amount of excitation light can also be adjusted by changing the number of excitation light sources mounted on the light source device 3. However, the number of light sources may affect the size of the light source device 3. The size of the light source device 3 may be limited by the size of a cart for carrying the light source device 3 and the like. That is, it is difficult to adjust the amount of light of the fluorescence of the observation target by adjusting the amount of excitation light. As a result, it is difficult to adjust the signal value based on the fluorescence of the observation target imaged by the second image pickup device 532 by adjusting the amount of excitation light. (4) Image pickup device The signal value based on the fluorescence of the observation target generated from the second image pickup device 532 varies depending on the amount of light of the fluorescence of the observation target received by the second image pickup device 532. In order to adjust the signal value based on the fluorescence of the observation target, it is desired to select a second imaging element 532 having sensitivity, configuration, etc. optimal for imaging the fluorescence of the observation target. However, the second imaging element 532 not only outputs an image for fluorescence observation based on the reception of fluorescence of the observation target in a predetermined wavelength band, but may also be required to output an image for normal light observation based on the reception of visible light such as white light. Further, the second imaging element 532 may also be required to output an image for fluorescence observation corresponding to a wide wavelength band or a plurality of wavelength bands among the wavelength bands including visible light and invisible light. Furthermore, even when the same drug is used, the light amount of the fluorescence of the observation target may vary depending on the procedure and the observation target OB, and in such a case, it may also be required to output an image for fluorescence observation corresponding to the change in the light amount of such fluorescence of the observation target. In that case, the second imaging element 532 must select an element capable of corresponding to those observations, and there may be a case where an imaging element with characteristics optimal for imaging fluorescence in a predetermined wavelength band cannot be used. Also, although the second imaging element 532 is disposed inside the camera head 5, due to the size and weight of the camera head 5 suitable for observation, the types including the size of the second imaging element 532 may be restricted. Note that the configuration is not limited to the case where the second imaging element 532 is disposed inside the camera head 5, and even when it is disposed at the tip of a rigid endoscope or a flexible endoscope, due to the size and weight suitable for observation, the types including the size of the second imaging element 532 may be restricted. That is, it is difficult to adjust the signal value based on the fluorescence of the observation target imaged by the second imaging element 532 by selecting the type of the second imaging element 532. As described above, since the signal value based on the fluorescence of the observation target imaged by the second imaging element 532 is determined under the above constraints, it cannot be easily adjusted. In diagnosis and surgery, it is required to suppress the influence of unnecessary light generated due to visible light as much as possible and to make the fluorescence of the observation target observable in a good state. 〔Regarding Modes〕 Next, the modes will be described. The mode switching unit 943 switches the medical observation system 1 to one of the first to third modes in response to user operation on the input unit 95. Here, the first excitation light is the excitation light corresponding to the first drug. The second excitation light is the excitation light corresponding to the second drug. The user then sets the medical observation system 1 to one of the first to third modes by operating the input unit 95, taking into consideration the intensity of the first target fluorescence emitted from the first drug by irradiation with the first excitation light and the intensity of the second target fluorescence emitted from the second drug by irradiation with the second excitation light. The first mode is used when, even if unwanted light is captured in at least one fluorescence image, there is a low possibility of misidentifying the unwanted light as the fluorescence being observed. Furthermore, the second mode is used when, even if unwanted light is captured in at least two fluorescence images, there is a low possibility of misidentifying the unwanted light as the fluorescence being observed. Furthermore, the third mode is used when there is a high possibility of misidentifying unwanted light as the target fluorescence if unwanted light is captured in all fluorescence images. Here, the aforementioned misrecognition can occur not only when the signal value based on unwanted light in the fluorescence image is higher than the signal value based on the observed fluorescence, but also when the signal value based on the unwanted light is lower than the signal value based on the observed fluorescence. The following describes the light source control and imaging control in the first to third modes in order. [Regarding light source control and imaging control in the first mode] Figure 3 shows a first example of light source control and imaging control in the first mode. Figure 4 shows a second example of light source control and imaging control in the first mode. Specifically, Figures 3(a) and 4(a) show the synchronization signal. For example, in the NTSC system, the synchronization signal is a signal with a period of 1 / 60 [s] (frame period). Also, for example, in the PAL system, the synchronization signal is a signal with a period of 1 / 50 [s] (frame period). Figures 3(b) and 4(b) show a period of 1 / 4 of the synchronization signal. Figures 3(c) and 4(c) show the imaging control of the first image sensor 531. The period that contributes to the generation of a normal image by the first image sensor 531 is represented by a rectangular region. In Figures 3(c) and 4(c), for the sake of explanation, the rectangular area is labeled "Visible Light Imaging" to indicate that the reflected visible light is being imaged. Figures 3(d) and 4(d) show the light source control of the first light source 31. The period of visible light emission from the first light source 31 is represented by a rectangular area. In Figures 3(d) and 4(d), for the sake of explanation, the rectangular area is labeled "Visible Light" to indicate that visible light is being emitted. Figures 3(e) and 4(e) show the imaging control of the second image sensor 532. The periods contributing to the generation of the first and second fluorescence images by the second image sensor 532 are represented by rectangular areas, respectively. In Figures 3(e) and 4(e), for the sake of explanation, the rectangular region representing the period contributing to the generation of the first fluorescence image is labeled "Fluorescence 1" to indicate that the reflected light of the first excitation light (the first target fluorescence) is being imaged, and the rectangular region representing the period contributing to the generation of the second fluorescence image is labeled "Fluorescence 2" to indicate that the reflected light of the second excitation light (the second target fluorescence) is being imaged. Figures 3(f) and 4(f) show the light source control of the second and third light sources 32 and 33. The emission periods of the first and second excitation light from the second and third light sources 32 and 33 are represented by rectangular regions, respectively.In Figures 3(f) and 4(f), for the sake of explanation, the words "Excitation Light 1" are written in the rectangular region representing the emission period of the first excitation light, and the words "Excitation Light 2" are written in the rectangular region representing the emission transfer tube of the second excitation light, indicating that the second excitation light is being emitted. As shown in Figures 3 and 4, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by alternately capturing the reflected light of the first excitation light and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner. Here, the normal image and one of the fluorescence images of the first and second fluorescence images are generated during the first frame period of the first and second alternately repeated frame periods. The other fluorescence image of the first and second fluorescence images is generated during the second frame period. Furthermore, the light source control unit 941 emits visible light and one of the first or second excitation lights during the first frame period, and emits the other excitation light during the second frame period. In the case of a rolling shutter type image sensor, a portion of the exposure periods of two consecutive frames overlap. When the emission of visible light and the emission of excitation light occur consecutively, visible light may leak into the fluorescence image, making it difficult to identify the fluorescence being observed. In such cases, the visible light emission time must be set to extend throughout the entire line exposure period of the image sensor. Here, the first example shown in Figure 3 illustrates the light source control and imaging control in a case where, even if visible light is emitted during the period for generating the first fluorescence image, the influence of unwanted light caused by the visible light on the first fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the first observed fluorescence in the first fluorescence image. Therefore, in the first example, as shown in Figure 3, visible light and the first excitation light are emitted during the first frame period T1, and the second excitation light is emitted during the second frame period T2. During the first frame period T1, a normal image and a first fluorescence image are generated. During the second frame period T2, a second fluorescence image is generated. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the first fluorescence image of the two fluorescence images. Furthermore, the second example shown in Figure 4 illustrates light source control and imaging control in a case where, even if visible light is emitted during the period for generating the second fluorescence image, the influence of unwanted light caused by the visible light on the second fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the second observed fluorescence in the second fluorescence image. Therefore, in the second example, as shown in Figure 4, visible light and the second excitation light are emitted during the first frame period T1, and the first excitation light is emitted during the second frame period T2. During the first frame period T1, a normal image and a second fluorescence image are generated. During the second frame period T2, a first fluorescence image is generated. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the second fluorescence image of the first and second fluorescence images. As described above, in the first mode, the light source control unit 941 controls the operation of the light source device 3 with a light emission pattern in which the emission period of one of the first and second excitation lights overlaps with the emission period of the visible light, but the emission period of the other excitation light does not overlap with the emission period of the visible light. Note that the emission periods of one excitation light and the emission period of the visible light do not have to be configured to completely overlap as shown in Figures 3 and 4, as long as at least some of their periods overlap. [Regarding light source control and imaging control in the second mode] The light source control and imaging control in the second mode described below is a light source control and imaging control in which, even if visible light is emitted during the period in which the first and second fluorescence images are generated, the influence of unwanted light caused by said visible light on the first and second fluorescence images is small, and the possibility of misidentifying unwanted light as the observed fluorescence in the first and second fluorescence images is low. First, we will explain a first example of light source control and imaging control in the second mode. Figure 5 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the second mode. As shown in Figure 5, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by alternately capturing the reflected light of the first excitation light and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner. Here, the normal image and the first fluorescence image are generated during the first frame period T1, of the first and second frame periods T1 and T2 which are repeated alternately. The normal image and the second fluorescence image are generated during the second frame period T2, respectively. Furthermore, the light source control unit 941 emits visible light and the first excitation light during the first frame period T1, and emits visible light and the second excitation light during the second frame period T2. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to overlap completely as shown in Figure 5, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (for example, from the latter half of period T1 to the first half of period T2). As a result of the light source control and imaging control described above, unwanted light originating from visible light is included in both the first and second fluorescence images. In the second mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. Figure 6 is a diagram corresponding to Figures 3 and 4, and shows a second example of light source control and imaging control in the second mode. As shown in Figure 6, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated in the first and third frame periods T1 and T3 of the four frame periods T1 to T4, which are repeated in the order of the first to fourth frame periods T1 to T4. The first fluorescence image is generated in the first and fourth frame periods T1 and T4 of the four frame periods T1 to T4. Furthermore, the second fluorescence image is generated in the second and third frame periods T2 and T3 of the four frame periods T1 to T4. Furthermore, as shown in Figure 6, the light source control unit 941 emits visible light during the first and third frame periods T1 and T3, respectively, emits the first excitation light during the first and fourth frame periods T1 and T4, respectively, and emits the second excitation light during the second and third frame periods T2 and T3, respectively. Note that the emission periods of the first and second excitation light and the emission periods of the visible light do not have to overlap completely as shown in Figure 6, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (the period from the latter half of period T1 to the first half of period T2, and the period from the latter half of period T3 to the beginning of period T4), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (the period from period T1 to period T4). Specifically, visible light is emitted during the first frame period T1 of the two first and fourth frame periods T1 and T4 in which the first fluorescence image is generated. Also, visible light is emitted during the third frame period T3 of the two second and third frame periods T2 and T3 in which the second fluorescence image is generated. Therefore, in the second example, the effect of unwanted light caused by visible light is reduced, while the effect of such unwanted light is distributed between the first and second fluorescence images. Note that the order of the four frame periods T1 to T4 is not limited to the order shown in Figure 6; other orders are also acceptable. As described above, in the second mode, the light source control unit 941 controls the operation of the light source device 3 with a light emission pattern in which the emission periods of the first and second excitation light and the emission period of the visible light overlap. [Regarding light source control and imaging control in the third mode] The third mode of light source control and imaging control described below is for situations where, if visible light is emitted during the period for generating the first and second fluorescence images, there is a high possibility that unwanted light caused by the visible light will be misidentified as the target fluorescence in the first and second fluorescence images. Figure 7 is a diagram corresponding to Figures 3 and 4, and shows the light source control and imaging control in the third mode. As shown in Figure 7, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated in the first frame period T1 of three frame periods T1 to T3 that are repeated in the order of first to third frame periods T1 to T3. This first frame period T1 corresponds to the first period in this disclosure. The first fluorescence image is generated in the second frame period T2 of the three frame periods T1 to T3. This second frame period T2 corresponds to the second period in this disclosure. Furthermore, the second fluorescence image is generated in the third frame period T3 of the three frame periods T1 to T3. This third frame period T3 corresponds to the third period in this disclosure. Furthermore, as shown in Figure 7, the light source control unit 941 emits visible light during the first frame period T1, emits the first excitation light during the second frame period T2, and emits the second excitation light during the third frame period T3. That is, no visible light is emitted during the second and third frame periods T2 and T3, when the first and second fluorescence images are generated, respectively. Note that the emission periods for visible light and the first and second excitation lights may be other emission periods, not limited to those shown in Figure 7, as long as they do not overlap with each other. Note that the order of the three frame periods T1 to T3 is not limited to the order shown in Figure 7; other orders are also acceptable. As described above, in the third mode, the light source control unit 941 controls the operation of the light source device 3 with a light emission pattern in which the emission periods of both the first and second excitation light and the emission period of visible light do not overlap. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is not included in either the first or second fluorescence image. Furthermore, the light source control unit 941 controls the operation of the light source device 3 so that the emission patterns of visible light, the first excitation light, and the second excitation light differ between the first to third modes. According to Embodiment 1 described above, the following effects are achieved. The control device 9 according to this embodiment controls the operation of the light source device 3 so that the emission patterns of visible light, the first excitation light, and the second excitation light differ between the first to third modes. In particular, in the first mode, the control device 9 controls the operation of the light source device 3 with an emission pattern in which the emission period of one of the first and second excitation lights overlaps with the emission period of the visible light, while the emission period of the other excitation light does not overlap with the emission period of the visible light. In the second mode, the control device 9 controls the operation of the light source device 3 with an emission pattern in which the emission periods of the first and second excitation lights and the emission periods of the visible light overlap. Furthermore, in the third mode, the control device 9 controls the operation of the light source device 3 with an emission pattern in which the emission periods of both the first and second excitation lights and the emission period of the visible light do not overlap. In other words, by setting the medical observation system 1 to an appropriate mode according to the respective intensities of the first and second target fluorescence, the influence of unwanted light caused by visible light on the first and second fluorescence images can be adjusted, enabling fluorescence observation with improved discriminability between unwanted light and the target fluorescence. Therefore, according to the control device 9 of this embodiment 1, multiple types of target fluorescence in different wavelength bands can be observed well. Furthermore, the control device 9 according to this embodiment 1 switches the medical observation system 1 to one of the first to third modes in response to user operation on the input unit 95. Therefore, the user can switch to the appropriate mode according to the drug being used. In other words, convenience can be improved. (Embodiment 2) Next, Embodiment 2 will be described. In the following description, components similar to those in Embodiment 1 described above will be denoted by the same reference numerals, and their detailed descriptions will be omitted or simplified. In this second embodiment, the light source control and imaging control in the first to third modes are different from the light source control and imaging control described in the first embodiment described above. The light source control and imaging control in the first to third modes according to this second embodiment will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 8 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the first mode according to Embodiment 2. Figure 9 is a diagram showing a second example of light source control and imaging control in the first mode according to Embodiment 2. As shown in Figures 8 and 9, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images, respectively, by alternately capturing the reflected light of the first excitation light and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner. Here, the normal image is generated sequentially during the first frame period T1, which is repeated. The first and second fluorescence images are generated alternately within the first frame period T1, for example, by the high-speed imaging operation of the second image sensor 532, over a period of 1 / 4 of one frame. That is, the normal image and the first and second fluorescence images are generated during the first frame period T1, respectively. Furthermore, the light source control unit 941 emits visible light and one of the first and second excitation lights during a portion of the first frame period T1, respectively, and emits the other excitation light of the first and second excitation lights during the rest of the first frame period T1. Here, the first example shown in Figure 8 illustrates the light source control and imaging control in a case where, even if visible light is emitted during the period for generating the first fluorescence image, the influence of unwanted light caused by the visible light on the first fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the first observed fluorescence in the first fluorescence image. Therefore, in the first example, as shown in Figure 8, visible light and the first excitation light are emitted in the first and third periods T11 and T13, respectively, of the four periods T11 to T14, which are 1 / 4 of one frame within the first frame period T1, and the second excitation light is emitted in the second and fourth periods T12 and T14, respectively. Then, the first fluorescence image is generated in periods T11 and T13. In addition, the second fluorescence image is generated in periods T12 and T14. Furthermore, a normal image is generated in the first frame period T1. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the first fluorescence image of the first and second fluorescence images. Furthermore, the emission period of the first excitation light and the emission period of the visible light do not necessarily have to be a configuration in which all periods completely overlap, as shown in Figure 8, as long as at least some of the periods overlap. Furthermore, the second example shown in Figure 9 illustrates light source control and imaging control in a case where, even if visible light is emitted during the period for generating the second fluorescence image, the influence of unwanted light caused by the visible light on the second fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the second target fluorescence in the second fluorescence image. Therefore, in the second example, as shown in Figure 9, visible light and the second excitation light are emitted during the first and third periods T11 and T13, respectively, which are four periods T11 to T14, each representing one-quarter of a frame within the first frame period T1, while the first excitation light is emitted during the second and fourth periods T12 and T14, respectively. Then, the second fluorescence image is generated during periods T11 and T13. Also, the first fluorescence image is generated during periods T12 and T14. Furthermore, a normal image is generated during the first frame period T1. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the second fluorescence image among the first and second fluorescence images. Furthermore, the emission period of the second excitation light and the emission period of the visible light do not necessarily have to be a configuration in which all periods completely overlap, as shown in Figure 9, as long as at least some of the periods overlap. In the first mode of light source control described above, it is preferable that visible light is emitted at a period of 1 / 120 [s] or less. [Regarding light source control and imaging control in the second mode] The light source control and imaging control in the second mode described below is a light source control and imaging control in which, even if visible light is emitted during the period in which the first and second fluorescence images are generated, the influence of unwanted light caused by said visible light on the first and second fluorescence images is small, and the possibility of misidentifying unwanted light as the observed fluorescence in the first and second fluorescence images is low. First, we will explain a first example of light source control and imaging control in the second mode. Figure 10 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the second mode according to Embodiment 2. As shown in Figure 10, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated sequentially during the first frame period T1, which is repeated. The first and second fluorescence images are generated within the first frame period T1, for example, by the high-speed imaging operation of the second image sensor 532, each for a period of 1 / 4 of one frame. In the example in Figure 10, within the first frame period T1, the first fluorescence image is generated in the first and fourth periods T11 and T14, respectively, out of four periods T11 to T14, each representing 1 / 4 of one frame, and the second fluorescence image is generated in the second and third periods T12 and T13, respectively. Furthermore, as shown in Figure 10, the light source control unit 941 emits visible light during periods T11 and T13, emits the first excitation light during periods T11 and T14, and emits the second excitation light during periods T12 and T13. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to be configured to completely overlap as shown in Figure 10, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (the period from the latter half of period T11 to the first half of period T12, and the period from the latter half of period T13 to the first half of period T14), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (the period from period T11 to period T14). As a result of the light source control and imaging control described above, unwanted light originating from visible light is included in both the first and second fluorescence images. Furthermore, in the second mode, similar to the second example in the second mode described in Embodiment 1 above, the system is configured to reduce the influence of unwanted light originating from visible light while distributing the effects of such unwanted light between the first and second fluorescence images. In the first example of light source control described above, it is preferable that visible light is emitted at a period of 1 / 120 [s] or less. In the second mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. Figure 11 is a diagram corresponding to Figures 3 and 4, and shows a second example of light source control and imaging control in the second mode according to Embodiment 2. As shown in Figure 11, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by alternately capturing the reflected light of the first and second excitation lights with the second image sensor 532 in a time-division manner. Here, the normal image is generated sequentially during the first frame period T1, which is repeated. The first and second fluorescence images are generated within the first frame period T1, for example, by the high-speed imaging operation of the second image sensor 532, each for a period of 1 / 4 of one frame. In the example in Figure 11, within the first frame period T1, the first fluorescence image is generated in the first and third periods T11 and T13, respectively, out of four periods T11 to T14, each representing 1 / 4 of one frame, and the second fluorescence image is generated in the second and fourth periods T12 and T14, respectively. Furthermore, as shown in Figure 11, the light source control unit 941 emits visible light during periods T11 and T14, emits the first excitation light during periods T11 and T13, and emits the second excitation light during periods T12 and T14. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to be configured to completely overlap as shown in Figure 11, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (the period from the latter half of period T11 to the first half of period T12, and the period from the latter half of period T13 to the first half of period T14), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (the period from period T11 to period T14). Furthermore, in the second mode, the light source control and imaging control may be performed not only in the first and second examples described above, but also in the third example shown below. Figure 12 is a diagram corresponding to Figures 3 and 4, and shows a third example of light source control and imaging control in the second mode according to Embodiment 2. As shown in Figure 12, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated sequentially during the first frame period T1, which is repeated. The first and second fluorescence images are generated within the first frame period T1, for example, by the high-speed imaging operation of the second image sensor 532, each for a period of 1 / 4 of one frame. In the example in Figure 12, within the first frame period T1, the first fluorescence image is generated in the first to third periods T11 to T13, and the second fluorescence image is generated in the fourth period T14, which is one-quarter of one frame. Furthermore, as shown in Figure 12, the light source control unit 941 emits visible light during periods T11 and T14, emits the first excitation light during periods T11 to T13, and emits the second excitation light during period T14. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to be completely overlapping as shown in Figure 12, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (e.g., from the latter half of period T13 to the first half of period T14), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (from period T11 to period T14). [Regarding light source control and imaging control in the third mode] The third mode of light source control and imaging control described below is for situations where, if visible light is emitted during the period for generating the first and second fluorescence images, there is a high possibility that unwanted light caused by the visible light will be misidentified as the target fluorescence in the first and second fluorescence images. Figure 13 is a diagram corresponding to Figures 3 and 4, and shows the light source control and imaging control in the third mode according to Embodiment 2. As shown in Figure 13, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, within a first frame period T1 that is repeated sequentially, over a period of 1 / 4 of one frame. The first and second fluorescence images are generated, for example, by the high-speed imaging operation of the second image sensor 532, within a first frame period T1, over a period of 1 / 4 of one frame, respectively. In the example shown in Figure 13, within the first frame period T1, among the four periods T11 to T14, which each represent one-quarter of a frame, a normal image is generated in the first and third periods T11 and T13, respectively. A first fluorescence image is generated in the second period T12, and a second fluorescence image is generated in the fourth period T14. These periods T11 and T13 correspond to the first period in this disclosure. Furthermore, period T12 corresponds to the second period in this disclosure. In addition, period T14 corresponds to the third period in this disclosure. Furthermore, as shown in Figure 13, the light source control unit 941 emits visible light during periods T11 and T13, emits the first excitation light during period T12, and emits the second excitation light during period T14. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 13, but may be other emission periods as long as they do not overlap with each other. Note that the order of the four periods T11 to T14 within the first frame period T1 is not limited to the order shown in Figure 13; other orders are also acceptable. In other words, in the third mode, in order to perform the light source control and imaging control described above, unwanted light originating from visible light is not included in either the first or second fluorescence image. According to Embodiment 2 described above, in addition to the same effects as Embodiment 1 described above, the following effects are achieved. Incidentally, when the medical control device according to this disclosure is combined with an open-field observation device used in abdominal surgery, the user may encounter the problem of visible light flashing in their field of vision. For this reason, it is undesirable to make the visible light emission period unnecessarily large. In this case, it is preferable to set the visible light emission period to 1 / 120 [s] or less. In contrast, the light source control according to this second embodiment can emit visible light at a period of 1 / 120 [s] or less, thereby solving the above-mentioned problems. In the examples shown in Figures 8 to 12, the first image sensor 531 continuously captured the reflected visible light within the first frame period T1. However, the system is not limited to this, and imaging may be performed only during the visible light emission period, as in the example shown in Figure 13. Such continuous imaging is usually performed when there is no influence from excitation light during image observation. (Embodiment 3) Next, Embodiment 3 will be described. In the following description, components similar to those in Embodiment 1 described above will be denoted by the same reference numerals, and their detailed descriptions will be omitted or simplified. In this third embodiment, the light source control and imaging control in the first to third modes are different from the light source control and imaging control described in the first embodiment described above. The light source control and imaging control in the first to third modes according to this embodiment 3 will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 14 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the first mode according to Embodiment 3. Figure 15 is a diagram showing a second example of light source control and imaging control in the first mode according to Embodiment 3. As shown in Figures 14 and 15, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by alternately capturing the reflected light of the first excitation light and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner. Here, the normal image is generated sequentially during the first frame period T1, which is repeated. The first and second fluorescence images are generated alternately within the first frame period T1, for example, by the high-speed imaging operation of the second image sensor 532, over a period of half a frame. That is, the normal image and the first and second fluorescence images are generated during the first frame period T1, respectively. Furthermore, the light source control unit 941 emits visible light and one of the first and second excitation lights during a portion of the first frame period T1, respectively, and emits the other excitation light of the first and second excitation lights during the rest of the first frame period T1. Here, the first example shown in Figure 14 illustrates the light source control and imaging control in a case where, even if visible light is emitted during the period for generating the first fluorescence image, the influence of unwanted light caused by the visible light on the first fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the first observed fluorescence in the first fluorescence image. Therefore, in the first example, as shown in Figure 14, visible light and the first excitation light are emitted during the first half of the two periods T11 and T12 within the first frame period T1, while the second excitation light is emitted during the second half of the period T12. Then, the first fluorescence image is generated during period T11. The second fluorescence image is generated during period T12. Furthermore, a normal image is generated during the first frame period T1. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the first fluorescence image of the two fluorescence images. Furthermore, the emission period of the first excitation light and the emission period of the visible light do not necessarily have to be a configuration in which all periods completely overlap, as shown in Figure 14, as long as at least some of the periods overlap. Furthermore, the second example shown in Figure 15 illustrates light source control and imaging control in a case where, even if visible light is emitted during the period for generating the second fluorescence image, the influence of unwanted light caused by the visible light on the second fluorescence image is small, and there is a low possibility of misidentifying unwanted light as the second target fluorescence in the second fluorescence image. Therefore, in the second example, as shown in Figure 15, visible light and the second excitation light are emitted during the first half of the two periods T11 and T12, which are half of one frame within the first frame period T1, and the first excitation light is emitted during the second half of the period T12. Then, the second fluorescence image is generated during period T11. Also, the first fluorescence image is generated during period T12. Furthermore, a normal image is generated during the first frame period T1. In other words, through the light source control and imaging control described above, unwanted light caused by visible light is included only in the second fluorescence image of the first and second fluorescence images. Furthermore, the emission period of the second excitation light and the emission period of the visible light do not necessarily have to be a configuration in which all periods completely overlap, as shown in Figure 15, as long as at least some of the periods overlap. In the first mode of light source control described above, it is preferable that visible light is emitted at a period of 1 / 120 [s] or less. [Regarding light source control and imaging control in the second mode] The light source control and imaging control in the second mode described below is a light source control and imaging control in which, even if visible light is emitted during the period in which the first and second fluorescence images are generated, the influence of unwanted light caused by said visible light on the first and second fluorescence images is small, and the possibility of misidentifying unwanted light as the observed fluorescence in the first and second fluorescence images is low. First, we will explain a first example of light source control and imaging control in the second mode. Figure 16 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the second mode according to Embodiment 3. As shown in Figure 16, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first exciton and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner (changing the timing of imaging). Here, the normal image is generated in the first and second frame periods T1 and T2, which are repeated alternately. The first and second fluorescence images are generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first frame period T1 and a period of half a frame within the second frame period T2, respectively. In the example shown in Figure 16, the first fluorescence image is generated during the first half of the frame period T1, specifically during the first half of the frame period T11 (T11 and T12), and during the second half of the frame period T22, specifically during the second half of the frame period T2, specifically during the second half of the frame period T2, specifically during the second half of the frame period T2, specifically during the second half of the frame period T21, specifically during the second half of the frame period T22, specifically during the second half of the frame period T2, specifically during the second half of the frame period T21, specifically during the second half of the frame period T22, specifically during the second half of the frame period T2. Furthermore, as shown in Figure 16, the light source control unit 941 emits visible light during periods T11 and T21, emits the first excitation light during periods T11 and T22, and emits the second excitation light during periods T12 and T21. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to be configured to completely overlap as shown in Figure 16, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (the period from the latter half of period T11 to the first half of period T12, and the period from the latter half of period T21 to the first half of period T22), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (the period from period T1 to period T2). As a result of the light source control and imaging control described above, unwanted light originating from visible light is included in both the first and second fluorescence images. Furthermore, in the second mode, similar to the second example in the second mode described in Embodiment 1 above, the system is configured to reduce the influence of unwanted light originating from visible light while distributing the effects of such unwanted light between the first and second fluorescence images. In the first example of light source control described above, it is preferable that visible light is emitted at a period of 1 / 120 [s] or less. In the second mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. Figure 17 is a diagram corresponding to Figures 3 and 4, and shows a second example of light source control and imaging control in the second mode according to Embodiment 2. As shown in Figure 17, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images, respectively, by alternately capturing the reflected light of the first excitation light and the reflected light of the second excitation light with the second image sensor 532 in a time-division manner. Here, the normal image is generated in the first and second frame periods T1 and T2, which are repeated alternately. The first and second fluorescence images are generated alternately in a time-division manner in two periods of half a frame within the first frame period T1, and alternately in a time-division manner in two periods of half a frame within the second frame period T2, for example, by the high-speed imaging operation of the second image sensor 532. In the example shown in Figure 17, the first fluorescence image is generated during the first half of the two periods T11 and T12 within the first frame period T1, specifically during period T11, and during the first half of the two periods T21 and T22 within the second frame period T2, specifically during period T21. Furthermore, the second fluorescence image is generated during the second half of the two periods T11 and T12 within the first frame period T1, specifically during period T12, and during the second half of the two periods T21 and T22 within the second frame period T2, specifically during period T22. Furthermore, as shown in Figure 17, the light source control unit 941 emits visible light during periods T11 and T22, emits the first excitation light during periods T11 and T21, and emits the second excitation light during periods T12 and T22. Note that the emission periods of the first and second excitation light and the emission period of the visible light do not have to be configured to completely overlap as shown in Figure 17, as long as at least some of the periods overlap. For example, the emission period of the visible light may be set to span the emission periods of the first and second excitation light (the period from the latter half of period T11 to the first half of period T12, and the period from the latter half of period T21 to the first half of period T22), or the emission period of the visible light may be set to overlap with all of the emission periods of the first and second excitation light (the period from period T1 to period T2). [Regarding light source control and imaging control in the third mode] The third mode of light source control and imaging control described below is for situations where, if visible light is emitted during the period for generating the first and second fluorescence images, there is a high possibility that unwanted light caused by the visible light will be misidentified as the target fluorescence in the first and second fluorescence images. First, we will describe a first example of light source control and imaging control in the third mode. Figure 18 is a diagram corresponding to Figures 3 and 4, and shows a first example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 18, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, in the first and second frame periods T1 and T2 which are repeated alternately, for half a period of one frame within the first frame period T1 and for half a period of one frame within the second frame period T2. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, for half a period of one frame within the first frame period T1. Furthermore, the second fluorescence image is generated for half a period of one frame within the second frame period T2. In the example shown in Figure 18, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, and during the first half of the two periods T21 and T22 within the second frame period T2, specifically during the first half of the two periods T21 and T22. Additionally, a first fluorescence image is generated during the second half of the two periods T11 and T12 within the first frame period T1, and a second fluorescence image is generated during the second half of the two periods T21 and T22 within the second frame period T2. Furthermore, as shown in Figure 18, the light source control unit 941 emits visible light during periods T11 and T21, emits the first excitation light during period T12, and emits the second excitation light during period T22. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 18, but may be other emission periods as long as they do not overlap with each other. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 18; other orders are also acceptable. In other words, in the first example, in order to perform the light source control and imaging control described above, unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. Figure 19 is a diagram corresponding to Figures 3 and 4, and shows a second example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 19, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half the period of one frame within the first frame period T1 of the first and second frame periods T1 and T2, which are repeated alternately. The first fluorescence image is generated during the period of one frame within the first and second frame periods T1 and T2. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, during half the period of one frame within the second frame period T2. In the example shown in Figure 19, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, specifically during the first half of one frame, period T11. A first fluorescence image is generated during the period of one frame, which is the second half of the two periods T11 and T12 within the first frame period T11, and the first half of the two periods T11 and T12 within the second frame period T2, specifically during period T21. Furthermore, a second fluorescence image is generated during the second half of the two periods T21 and T22 within the second frame period T2, specifically during period T22. Furthermore, as shown in Figure 19, the light source control unit 941 emits visible light during period T11, emits the first excitation light during periods T12 and T21, and emits the second excitation light during period T22. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 19, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of period T11, period T12, T21, and period T22 is not limited to the order shown in Figure 19; other orders are also acceptable. In other words, in the second example, just like in the first example described above, the light source control and imaging control described above are performed, so unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only in the first and second examples described above, but also in the third example shown below. Figure 20 is a diagram corresponding to Figures 3 and 4, and shows a third example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 20, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half the period of one frame within the first frame period T1 of the first and second frame periods T1 and T2 which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, during half the period of one frame within the first frame period T1. Furthermore, the second fluorescence image is generated during the second frame period T2. In the example shown in Figure 20, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, specifically during period T11. The first fluorescence image is generated during the second half of the two periods T11 and T12 within the first frame period T1, specifically during period T12. Furthermore, as shown in Figure 20, the light source control unit 941 emits visible light during period T11, emits the first excitation light during period T12, and emits the second excitation light during the second frame period T2. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 20, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of periods T11, T12, T21, and T22 is not limited to the order shown in Figure 20; other orders are also acceptable. In other words, the third example, like the first and second examples described above, performs the light source control and imaging control described above, so unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only in the first to third examples described above, but also in the fourth example shown below. Figure 21 is a diagram corresponding to Figures 3 and 4, and shows a fourth example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 21, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, within a first frame period T1 that is repeated sequentially, for a period of 1 / 2 of one frame. The first and second fluorescence images are generated, for example, by the high-speed imaging operation of the second image sensor 532, within a first frame period T1, for a period of 1 / 4 of one frame, respectively. In the example shown in Figure 21, within the first frame period T1, a normal image is generated in the first and second periods T11 and T12, which are four periods T11 to T14, each representing one-quarter of a frame. The first fluorescence image is generated in the third period T13, and the second fluorescence image is generated in the fourth period T14. Furthermore, as shown in Figure 21, the light source control unit 941 emits visible light during periods T11 and T12, emits the first excitation light during period T13, and emits the second excitation light during period T14. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 21, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of periods T11, T12, T13, and T14 is not limited to the order shown in Figure 21; other orders are also acceptable. In other words, in the fourth example, just like in the first to third examples described above, the light source control and imaging control described above are performed, so unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only in the first to fourth examples described above, but also in the fifth example shown below. Figure 22 is a diagram corresponding to Figures 3 and 4, and shows a fifth example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 22, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, in a period of 1 / 4 of one frame within a first frame period T1 that is repeated sequentially. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of 1 / 2 of one frame within the first frame period T1. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of 1 / 4 of one frame within the first frame period T1. In the example shown in Figure 22, within the first frame period T1, a normal image is generated in the first period T11, one of four periods T11 to T14, each representing one-quarter of a frame. The first fluorescence image is generated in the second and third periods T12 and T13, and the second fluorescence image is generated in the fourth period T14. Furthermore, as shown in Figure 22, the light source control unit 941 emits visible light during period T11, emits the first excitation light during periods T12 and T13, and emits the second excitation light during period T14. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 22, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of period T11, periods T12 and T13, and period T14 is not limited to the order shown in Figure 22; other orders are also acceptable. In other words, in the fifth example, just like in the first to fourth examples described above, the light source control and imaging control described above are performed, so unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only in the first to fifth examples described above, but also in the sixth example shown below. Figure 23 is a diagram corresponding to Figures 3 and 4, and shows a sixth example of light source control and imaging control in the third mode according to Embodiment 3. As shown in Figure 23, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates first and second fluorescence images by capturing the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, within a first frame period T1 that is repeated sequentially, for a period of 1 / 4 of one frame. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, within a period of 1 / 4 of one frame within the first frame period T1. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, within a period of 1 / 2 of one frame within the first frame period T1. In the example shown in Figure 23, within the first frame period T1, of the four periods T11 to T14, each representing one-quarter of a frame, a normal image is generated in the first period T11, a first fluorescence image is generated in the second period T12, and a second fluorescence image is generated in the third and fourth periods T13 and T14. Furthermore, as shown in Figure 23, the light source control unit 941 emits visible light during period T11, emits the first excitation light during period T12, and emits the second excitation light during periods T13 and T14. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 23, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of periods T11, T12, T13, and T14 is not limited to the order shown in Figure 23; other orders are also acceptable. In other words, in the sixth example, as in the first to fifth examples described above, the light source control and imaging control described above are performed, so unwanted light originating from visible light is not included in either the first or second fluorescence image. According to this embodiment 3 described above, in addition to the same effects as in embodiment 1 described above, the following effects are achieved. According to the light source control and imaging control of this third embodiment, as shown in Figures 14 to 18 and 21 to 23, a normal image can be generated every frame. Therefore, the update cycle of the display image 7 can be accelerated, and a smooth display can be achieved. (Embodiment 4) Next, Embodiment 4 will be described. In the following description, components similar to those in Embodiment 1 described above will be denoted by the same reference numerals, and their detailed descriptions will be omitted or simplified. In the above-described embodiment 1, a configuration was adopted in which two types of drugs, etc., were used to acquire the first and second target fluorescence, which are the fluorescence to be observed. In contrast, this third embodiment employs a configuration that uses three types of drugs, etc., to acquire the first to third target fluorescence, which are the fluorescence to be observed. Figure 24 is a diagram corresponding to Figure 1, and shows the configuration of the medical observation system 1 according to Embodiment 4. In this fourth embodiment, as shown in Figure 24, the light source device 3 has a fourth light source 34 in addition to the first to third light sources 31 to 33. The fourth light source 34 emits a third excitation light that excites the substance contained in the observation target OB. The fourth light source 34 may be composed of an LED or a semiconductor laser. The number of fourth light sources 34 may be one or more. Furthermore, the fourth light source 34 may emit light that includes at least a part of the visible light wavelength band, or it may emit light in the invisible light wavelength band such as infrared light or ultraviolet light. Hereafter, the fluorescence emitted from the substance contained in the observation target OB when the third excitation light is irradiated onto the observation target OB and the substance is excited will be referred to as the third observation target fluorescence. The reflected light of the third excitation light from the observation target OB is focused by the optical system in the insertion section 2. This reflected light of the third excitation light includes the third excitation light reflected by the observation target OB, as well as the fluorescence of the third observation target. Here, of the reflected light of the third excitation light from the observation target OB, the third excitation light is partially, substantially, or completely suppressed by the excitation light cut filter 22. The fluorescence of the third observation target is light in a wavelength band excluding at least a portion of the visible light wavelength band. The light in the second wavelength band separated by the prism 52, which includes at least a portion of the wavelength band of the fluorescence of the third observation target, is referred to as the third fluorescence subject image. The prism 52 then propels the fluorescence subject image toward the second image sensor 532. For the sake of explanation, the image generated by imaging the fluorescence subject image will be referred to as the third fluorescence image below. Next, the mode according to this fourth embodiment will be described. Here, the first excitation light is the excitation light corresponding to the first drug. The second excitation light is the excitation light corresponding to the second drug. Furthermore, the third excitation light is the excitation light corresponding to the third drug. The user then sets the medical observation system 1 to one of the first to third modes by operating the input unit 95, taking into consideration the intensity of the first target fluorescence emitted from the first drug upon irradiation with the first excitation light, the intensity of the second target fluorescence emitted from the second drug upon irradiation with the second excitation light, and the intensity of the third target fluorescence emitted from the third drug upon irradiation with the third excitation light. The following describes the light source control and imaging control in the first to third modes in order. [Regarding light source control and imaging control in the first mode] The light source control and imaging control in the first mode described below is a light source control and imaging control in which, even if visible light is emitted during the period for generating the first fluorescence image, the influence of unwanted light caused by said visible light on the first fluorescence image is small, and there is a low possibility of misidentifying the unwanted light as the first target fluorescence in the first fluorescence image. Figure 25 is a diagram corresponding to Figures 3 and 4, and shows the light source control and imaging control in the first mode according to Embodiment 4. In Figure 25(e), for the sake of explanation, the rectangular region which is the period that contributes to the generation of the third fluorescence image is labeled with the words "Fluorescence 3" to indicate that the reflected light of the third excitation light (the third observed fluorescence) is being imaged. Also, in Figure 25(f), for the sake of explanation, the rectangular region which is the emission period of the third excitation light is labeled with the words "Excitation Light 3" to indicate that the third excitation light is being emitted. As shown in Figure 25, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates the first to third fluorescence images by capturing the reflected light of the first excitation light, the reflected light of the second excitation light, and the reflected light of the third excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated in the first and second frame periods T1 and T2, which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first and second frame periods T1 and T2. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first frame period T1. Furthermore, the third fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532 during a period of half a frame within the second frame period T2. In the example shown in Figure 25, the first fluorescence image is generated during the first half of the two periods T11 and T12, which are half of a frame within the first frame period T1, and during the first half of the two periods T21 and T22, which are half of a frame within the second frame period T2, while the second fluorescence image is generated during the latter half of the period T12, and the third fluorescence image is generated during the latter half of the period T22. Furthermore, as shown in Figure 25, the light source control unit 941 emits visible light and the first excitation light during periods T11 and T21, respectively, emits the second excitation light during period T12, and emits the third excitation light during period T22. Note that the emission periods of visible light and the emission periods of the first excitation light do not have to be completely overlapping as shown in Figure 25; at least some of the periods overlap. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 25; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first fluorescence image among the first to third fluorescence images. [Regarding light source control and imaging control in the second mode] First, we will explain a first example of light source control and imaging control in the second mode. The first example of light source control and imaging control in the second mode shown below is a light source control and imaging control in which, even if visible light is emitted during the period in which the second and third fluorescence images are generated, the influence of unwanted light caused by said visible light on the second and third fluorescence images is small, and there is a low possibility of misidentifying the unwanted light as the observed fluorescence in the second and third fluorescence images. Figure 26 is a diagram corresponding to Figure 25, and shows a first example of light source control and imaging control in the second mode according to Embodiment 4. As shown in Figure 26, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates the first to third fluorescence images by capturing the reflected light of the first excitation light, the reflected light of the second excitation light, and the reflected light of the third excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated in the first and second frame periods T1 and T2, which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first and second frame periods T1 and T2. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first frame period T1. Furthermore, the third fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532 during a period of half a frame within the second frame period T2. In the example shown in Figure 26, the first fluorescence image is generated during the first half of the two periods T11 and T12, which are half of a frame within the first frame period T1, and during the first half of the two periods T21 and T22, which are half of a frame within the second frame period T2, with the second fluorescence image being generated during period T12 and the third fluorescence image being generated during period T22. Furthermore, as shown in Figure 26, the light source control unit 941 emits visible light during periods T12 and T22, emits the first excitation light during periods T11 and T21, emits the second excitation light during period T12, and emits the third excitation light during period T22. Note that the emission periods of visible light and the emission periods of the first and second excitation lights do not have to be completely overlapping as shown in Figure 26; at least some of the periods overlap. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 26; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the second and third fluorescence images out of the first to third fluorescence images. In the second mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. The second example of light source control and imaging control in the second mode shown below is a light source control and imaging control in which, even if visible light is emitted during the period for generating the first to third fluorescence images, the influence of unwanted light caused by said visible light on the first to third fluorescence images is small, and there is a low possibility of misidentifying the unwanted light as the observed fluorescence in the first to third fluorescence images. Figure 27 is a diagram corresponding to Figure 25, and shows a second example of light source control and imaging control in the second mode according to Embodiment 4. As shown in Figure 27, the imaging control unit 942 performs imaging control similar to the imaging control in the first example described above (Figure 25). Furthermore, as shown in Figure 27, the light source control unit 941 emits visible light during the first and second frame periods T1 and T2, respectively, emits the first excitation light during periods T11 and T12, respectively, emits the second excitation light during period T12, and emits the third excitation light during period T22. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 27; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included in all of the first to third fluorescence images. [Regarding light source control and imaging control in the third mode] The light source control and imaging control in the third mode described below are for situations where, if visible light is emitted during the period for generating the first to third fluorescence images, there is a high possibility that unwanted light caused by the visible light will be misidentified as the target fluorescence in the first to third fluorescence images. Figure 28 is a diagram corresponding to Figure 25, and shows a first example of light source control and imaging control in the third mode according to Embodiment 4. As shown in Figure 28, the imaging control unit 942 generates a normal image by capturing the reflected visible light with the first image sensor 531, and generates the first to third fluorescence images by capturing the reflected light of the first excitation light, the reflected light of the second excitation light, and the reflected light of the third excitation light in a time-division manner (changing the timing of imaging) with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during a period of half a frame within the first frame period T1 of the first and second frame periods T1 and T2 which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, during a period of half a frame within the first frame period T1. Furthermore, the second and third fluorescence images are generated, for example, by the high-speed imaging operation of the second image sensor 532, during a period of half a frame within the second frame period T2. In the example shown in Figure 28, within the first frame period T1, a normal image is generated in the first half of the two periods T11 and T12, which represent half of one frame, and the first fluorescence image is generated in the second half of the period T12. Similarly, within the second frame period T2, a second fluorescence image is generated in the first half of the two periods T21 and T22, which represent half of one frame, and the third fluorescence image is generated in the second half of the period T22. Furthermore, as shown in Figure 28, the light source control unit 941 emits visible light during period T11, the first excitation light during period T12, the second excitation light during period T21, and the third excitation light during period T22. Note that the emission periods for visible light and the first to third excitation lights may be other emission periods, not limited to those shown in Figure 28, as long as they do not overlap with each other. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 28; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is not included in any of the first to third fluorescence images. According to this embodiment 4 described above, in addition to the same effects as in embodiment 1 described above, three types of target fluorescence can be observed clearly. Furthermore, in the above-described embodiment 4, if the effects of embodiment 2 (flicker reduction) and embodiment 3 (smooth display) are to be achieved, the control of the first and second frame periods T1 and T2 can be reduced to a single frame period, similar to embodiments 2 and 3 described above. (Other embodiments) While we have described the forms for implementing this disclosure, this disclosure should not be limited to the embodiments described above. In the embodiments 1 to 4 described above, the display control unit 933 may generate a display image from a plurality of captured images (normal image, first to third fluorescence observation images) after image processing has been performed by the processing unit 932, or it may generate a display image from each of the captured images. When generating a display image from a plurality of captured images, a normal image from which noise reduction processing has been performed may be used, or an image obtained by combining a plurality of normal images using HDR (High Dynamic Range), a technique that expresses the range from dark to bright areas by combining a bright image and a dark image, may be used. In the embodiments 1 to 4 described above, the mode switching unit 943 switched the medical observation system 1 to one of the first to third modes in response to user operation to the input unit 95, but it is not limited to this. For example, the mode switching unit 943 determines the rate of drug fading based on the captured image and estimates the drug being used from that fading rate. Then, the mode switching unit 943 switches the medical observation system 1 to one of the first to third modes according to the estimated drug. Furthermore, for example, the mode switching unit 943 identifies a surgical scene based on the captured image and estimates the drugs being used from that surgical scene. Then, the mode switching unit 943 switches the medical observation system 1 to one of the first to third modes according to the estimated drugs. Furthermore, in the above-described embodiment, the following modifications 1 to 9 may also be adopted. (Variation 1) In the first embodiment described above, the second observed fluorescence was light in a wavelength band other than the visible light band (invisible fluorescence), but it is not limited to this. In this modified example 1, the second observed fluorescence is light (visible fluorescence) that includes at least a portion of the visible light wavelength band and is light included in the first wavelength band separated by the prism 52. Therefore, the second fluorescence subject image, which is light in the first wavelength band separated by the prism 52 and which includes at least a portion of the wavelength band of the second observed fluorescence, travels toward the first image sensor 531. The first image sensor 531 then generates a second fluorescence image by capturing the second fluorescence subject image. As described above, visible light and the second target fluorescence are imaged using the same first image sensor 531. Therefore, it is not possible to image visible light and the second target fluorescence simultaneously. The first mode is used when there is a low possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. Furthermore, since it is not possible to image visible light and the second target fluorescence simultaneously, the second mode is not used in this modified example 1. In addition, the third mode is used when there is a high possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. The light source control and imaging control in the first to third modes related to this modified example 1 will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 29 is a diagram illustrating a modification 1 of Embodiment 1. Specifically, Figure 29 corresponds to Figures 3 and 4, and is a diagram illustrating the light source control and imaging control in the first mode according to Modification 1. In Figure 29(c), for the sake of explanation, the rectangular region which is the period that contributes to the generation of the second fluorescence image is labeled with the words "Visible Fluorescence 2 Imaging" to indicate that the reflected light of the second excitation light (second observation target fluorescence (visible fluorescence)) is being imaged. As shown in Figure 29, the imaging control unit 942 alternately captures the reflected visible light and the reflected second excitation light with the first image sensor 531 in a time-division manner to generate a normal image and a second fluorescence image, respectively, and captures the reflected first excitation light with the second image sensor 532 to generate a first fluorescence image. Here, the normal image and the first fluorescence image are generated during the first frame period T1 of the first and second frame periods T1 and T2 which are repeated alternately. The second fluorescence image is generated during the second frame period T2. Furthermore, as shown in Figure 29, the light source control unit 941 emits visible light and the first excitation light during the first frame period T1, and emits the second excitation light during the second frame period T2. Note that the emission period of visible light and the emission period of the first excitation light do not have to be completely overlapping as shown in Figure 29; at least some of the periods overlap. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first fluorescence image out of the first and second fluorescence images. [Regarding light source control and imaging control in the third mode] Figure 30 illustrates a modification 1 of Embodiment 1. Specifically, Figure 30 corresponds to Figure 29 and shows the light source control and imaging control in the third mode according to Modification 1. As shown in Figure 30, the imaging control unit 942 uses the first image sensor 531 to capture the reflected visible light and the reflected second excitation light in a time-division manner (changing the timing of imaging) to generate a normal image and a second fluorescence image, respectively, and also uses the second image sensor 532 to capture the reflected first excitation light to generate a first fluorescence image. Here, the normal image is generated in the first frame period T1 of three frame periods T1 to T3 that are repeated in the order of first to third frame periods T1 to T3. This first frame period T1 corresponds to the first period in this disclosure. The first fluorescence image is generated in the second frame period T2 of the three frame periods T1 to T3. This second frame period T2 corresponds to the second period in this disclosure. Furthermore, the second fluorescence image is generated in the third frame period T3 of the three frame periods T1 to T3. The third frame period T3 corresponds to the third period relating to this disclosure. Furthermore, as shown in Figure 30, the light source control unit 941 emits visible light during the first frame period T1, emits the first excitation light during the second frame period T2, and emits the second excitation light during the third frame period T3. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 30, but may be other emission periods as long as they do not overlap with each other. Note that the order of the three frame periods T1 to T3 is not limited to the order shown in Figure 30; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, if the exposure period of the second image sensor 543 becomes shorter and the intensity of the first observed target fluorescence weakens, the exposure period may be extended, or the brightness of the first fluorescence image may be increased (the intensity of the first observed target fluorescence may be increased) by adjusting the analog gain or digital gain. Even when configured as in the modified example 1 described above, the same effects as those of the embodiment 1 described above are achieved. (Variation 2) In the second embodiment described above, the second observed fluorescence was light in a wavelength band other than the visible light band (invisible fluorescence), but it is not limited to this. In this modified example 2, the second observed fluorescence is light (visible fluorescence) that includes at least a portion of the visible light wavelength band and is light included in the first wavelength band separated by the prism 52. Therefore, the second fluorescence subject image, which is light in the first wavelength band separated by the prism 52 and which includes at least a portion of the wavelength band of the second observed fluorescence, travels toward the first image sensor 531. The first image sensor 531 then generates a second fluorescence image by capturing the second fluorescence subject image. As described above, visible light and the second target fluorescence are imaged using the same first image sensor 531. Therefore, it is not possible to image visible light and the second target fluorescence simultaneously. The first mode is used when there is a low possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. Furthermore, since it is not possible to image visible light and the second target fluorescence simultaneously, the second mode is not used in this modified example 2. In addition, the third mode is used when there is a high possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. The light source control and imaging control in the first to third modes related to this modified example 2 will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 31 is a diagram illustrating a modified example 2 of Embodiment 2. Specifically, Figure 31 corresponds to Figure 29 and is a diagram illustrating the light source control and imaging control in the first mode according to Modified Example 2. As shown in Figure 31, the imaging control unit 942 generates a normal image and a second fluorescence image, respectively, by alternately capturing the reflected visible light and the reflected second excitation light with the first image sensor 531 in a time-division manner, and generates a first fluorescence image by capturing the reflected first excitation light with the second image sensor 532. Here, the normal image and the second fluorescence image are generated alternately in a time-division manner over four periods of 1 / 4 of a frame within a first frame period T1 that is repeated sequentially by the high-speed imaging operation of the first image sensor 531. The first fluorescence image is generated over two periods of 1 / 4 of a frame within the first frame period T1, respectively, by the high-speed imaging operation of the second image sensor 532. In the example shown in Figure 31, within the first frame period T1, the normal image and the first fluorescence image are generated in the first and third periods T11 and T13, respectively, out of four periods T11 to T14, which are 1 / 4 of one frame, and the second fluorescence image is generated in the second and fourth periods T12 and T14, respectively. Furthermore, as shown in Figure 31, the light source control unit 941 emits visible light and the first excitation light during periods T11 and T13, respectively, and emits the second excitation light during periods T12 and T14, respectively. Note that the emission periods of visible light and the emission periods of the first excitation light do not have to be configured to completely overlap as shown in Figure 31, as long as at least some of the periods overlap. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first fluorescence image out of the first and second fluorescence images. Note that the order of the four periods T11 to T14 within the first frame period T1 is not limited to the order shown in Figure 31; other orders are also acceptable. [Regarding light source control and imaging control in the third mode] Figure 32 illustrates a modification 2 of the second embodiment. Specifically, Figure 32 corresponds to Figure 29 and shows the light source control and imaging control in the third mode according to modification 2. As shown in Figure 32, the imaging control unit 942 uses the first image sensor 531 to capture the reflected visible light and the reflected second excitation light in a time-division manner (changing the timing of imaging) to generate a normal image and a second fluorescence image, respectively, and uses the second image sensor 532 to capture the reflected first excitation light to generate a first fluorescence image. Here, the normal image and the second fluorescence image are generated, for example, by the high-speed imaging operation of the first image sensor 531, in a period of 1 / 4 of a frame within a first frame period T1 that is repeated sequentially. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of 1 / 4 of a frame within the first frame period T1. In the example shown in Figure 32, within the first frame period T1, among the four periods T11 to T14, which each represent one-quarter of a frame, a normal image is generated in the first and third periods T11 and T13, respectively. A first fluorescence image is generated in the second period T12, and a second fluorescence image is generated in the fourth period T14. These periods T11 and T13 correspond to the first period in this disclosure. Furthermore, this period T12 corresponds to the second period in this disclosure. In addition, this period T14 corresponds to the third period in this disclosure. Furthermore, as shown in Figure 32, the light source control unit 941 emits visible light during periods T11 and T13, emits the first excitation light during period T12, and emits the second excitation light during period T14. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 32, but may be other emission periods as long as they do not overlap with each other. Note that the order of the four periods T11 to T14 within the first frame period T1 is not limited to the order shown in Figure 32; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is not included in either the first or second fluorescence image. Even when configured as in the modified example 2 described above, the same effects as those of the embodiment 2 described above are achieved. (Variation 3) In the above-described embodiment 3, the second observed fluorescence was light in a wavelength band other than the visible light band (invisible fluorescence), but is not limited to this. In this modified example 3, the second observed fluorescence is light (visible fluorescence) that includes at least a portion of the visible light wavelength band and is light included in the first wavelength band separated by the prism 52. Therefore, the second fluorescence subject image, which is light in the first wavelength band separated by the prism 52 and which includes at least a portion of the wavelength band of the second observed fluorescence, travels toward the first image sensor 531. The first image sensor 531 then generates a second fluorescence image by capturing the second fluorescence subject image. As described above, visible light and the second target fluorescence are imaged using the same first image sensor 531. Therefore, it is not possible to image visible light and the second target fluorescence simultaneously. The first mode is used when there is a low possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. Furthermore, since it is not possible to image visible light and the second target fluorescence simultaneously, the second mode is not used in this modified example 3. In addition, the third mode is used when there is a high possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. The light source control and imaging control in the first to third modes related to this modified example 3 will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 33 illustrates a third modification of Embodiment 3. Specifically, Figure 33 corresponds to Figure 29 and shows a first example of light source control and imaging control in the first mode according to the third modification. As shown in Figure 33, the imaging control unit 942 generates a normal image and a second fluorescence image, respectively, by alternately capturing the reflected visible light and the reflected second excitation light with the first image sensor 531 in a time-division manner, and generates a first fluorescence image by capturing the reflected first excitation light with the second image sensor 532. Here, the normal image and the second fluorescence image are generated, for example, by the high-speed imaging operation of the first image sensor 531, in a period of half a frame within a first frame period T1 that is repeated sequentially. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in a period of half a frame within the first frame period T1. In the example in Figure 33, within the first frame period T1, of the two periods T11 and T12, which are half a frame, the normal image and the first fluorescence image are generated in the first half period T11, and the second fluorescence image is generated in the second half period T12. Furthermore, as shown in Figure 33, the light source control unit 941 emits visible light and the first excitation light during period T11, and emits the second excitation light during period T12. Note that the emission period of visible light and the emission period of the first excitation light do not have to be configured to completely overlap as shown in Figure 33, as long as at least some of the periods overlap. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first fluorescence image out of the first and second fluorescence images. Note that the ratio of the emission periods of the first and second excitation light is not limited to the ratio shown in Figure 33 (1:1), but may be any other ratio. For example, the ratios shown in the second and third examples below may also be used. Figure 34 illustrates a third modification of Embodiment 3. Specifically, Figure 34 corresponds to Figure 29 and shows a second example of light source control and imaging control in the first mode according to the third modification. In the example shown in Figure 34, within the first frame period T1, a normal image and a first fluorescence image are generated in the first three periods T11 to T13, which are four periods T11 to T14, each representing one-quarter of a frame, and a second fluorescence image is generated in the fourth period T14. Furthermore, as shown in Figure 34, the light source control unit 941 emits visible light and the first excitation light during three periods T11 to T13, respectively, and emits the second excitation light during period T14. The emission periods of visible light and the emission periods of the first excitation light do not have to be configured to completely overlap as shown in Figure 34, as long as at least some of the periods overlap. In other words, in the second example, the ratio of the emission period of the first excitation light to the emission period of the second excitation light is "3:1". Figure 35 illustrates a third modification of Embodiment 3. Specifically, Figure 35 corresponds to Figure 29 and shows a third example of light source control and imaging control in the first mode according to the third modification. In the example shown in Figure 35, within the first frame period T1, the normal image and the first fluorescence image are generated in the first period T11, which is one-quarter of one frame, and the second fluorescence image is generated in the second to fourth periods T12 to T14. Furthermore, as shown in Figure 35, the light source control unit 941 emits visible light and the first excitation light during period T11, and emits the second excitation light during three periods T12 to T14. The emission periods of visible light and the emission periods of the first excitation light do not have to be configured to completely overlap as shown in Figure 34, as long as at least some of the periods overlap. In other words, in the second example, the ratio of the emission period of the first excitation light to the emission period of the second excitation light is "1:3". [Regarding light source control and imaging control in the third mode] First, we will describe a first example of light source control and imaging control in the third mode. Figure 36 is a diagram corresponding to Figure 29, and shows a first example of light source control and imaging control in the third mode according to Modification 3. As shown in Figure 36, the imaging control unit 942 uses the first image sensor 531 to capture the reflected visible light and the reflected second excitation light in a time-division manner (changing the timing of imaging) to generate a normal image and a second fluorescence image, respectively, and uses the second image sensor 532 to capture the reflected first excitation light to generate a first fluorescence image. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half a frame period within the first frame period T1 and half a frame period within the second frame period T2, respectively, of the first and second frame periods T1 and T2 which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, during half a frame period within the first frame period T1. Furthermore, the second fluorescence image is generated during half a frame period within the second frame period T2. In the example shown in Figure 36, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, and during the first half of the two periods T21 and T22 within the second frame period T2, specifically during the first half of the two periods T21 and T22. Additionally, a first fluorescence image is generated during the second half of the two periods T11 and T12 within the first frame period T1, and a second fluorescence image is generated during the second half of the two periods T21 and T22 within the second frame period T2. Furthermore, as shown in Figure 36, the light source control unit 941 emits visible light during periods T11 and T21, emits the first excitation light during period T12, and emits the second excitation light during period T22. Note that the emission periods for visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 36, but may be other emission periods as long as they do not overlap with each other. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 36; other orders are also acceptable. In other words, in the first example, in order to perform the light source control and imaging control described above, unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only as in the first example described above, but also as in the second example shown below. Figure 37 is a diagram corresponding to Figure 29, and shows a second example of light source control and imaging control in the third mode according to Modification 3. As shown in Figure 37, the imaging control unit 942 uses the first image sensor 531 to capture the reflected visible light and the reflected second excitation light in a time-division manner (changing the timing of imaging) to generate a normal image and a second fluorescence image, respectively, and uses the second image sensor 532 to capture the reflected first excitation light to generate a first fluorescence image. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half the period of one frame within the first frame period T1 of the first and second frame periods T1 and T2, which are repeated alternately. The first fluorescence image is generated during the period of one frame within the first and second frame periods T1 and T2. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half the period of one frame within the second frame period T2. In the example shown in Figure 37, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, specifically during the first half of one frame, period T11. A first fluorescence image is generated during the period of one frame, which is the second half of the two periods T11 and T12 within the first frame period T11, and the first half of the two periods T11 and T12 within the second frame period T2, specifically during period T21. Furthermore, a second fluorescence image is generated during the second half of the two periods T21 and T22 within the second frame period T2, specifically during period T22. Furthermore, as shown in Figure 37, the light source control unit 941 emits visible light during period T11, emits the first excitation light during periods T12 and T21, and emits the second excitation light during period T22. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 37, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of period T11, period T12, T21, and period T22 is not limited to the order shown in Figure 37; other orders are also acceptable. In other words, in the second example, just like in the first example described above, the light source control and imaging control described above are performed, so unwanted light originating from visible light is not included in either the first or second fluorescence image. In the third mode, light source control and imaging control may be performed not only in the first and second examples described above, but also in the third example shown below. Figure 38 is a diagram corresponding to Figure 29, and shows a third example of light source control and imaging control in the third mode according to Modification 3. As shown in Figure 38, the imaging control unit 942 uses the first image sensor 531 to capture the reflected visible light and the reflected second excitation light in a time-division manner (changing the timing of imaging) to generate a normal image and a second fluorescence image, respectively, and uses the second image sensor 532 to capture the reflected first excitation light to generate a first fluorescence image. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, within a first frame period T1 that is repeated sequentially, for a period of 1 / 2 of one frame. The first and second fluorescence images are generated, for example, by the high-speed imaging operation of the second image sensor 532, within a first frame period T1, for a period of 1 / 4 of one frame, respectively. In the example shown in Figure 38, within the first frame period T1, a normal image is generated in the first and second periods T11 and T12, which are four periods T11 to T14, each representing one-quarter of a frame. The first fluorescence image is generated in the third period T13, and the second fluorescence image is generated in the fourth period T14. Furthermore, as shown in Figure 38, the light source control unit 941 emits visible light during periods T11 and T12, emits the first excitation light during period T13, and emits the second excitation light during period T14. Note that the emission periods for the visible light and the first and second excitation lights are not limited to the emission periods shown in Figure 38, but may be other emission periods as long as they do not overlap with each other. Furthermore, within the first and second frame periods T1 and T2, the order of periods T11, T12, T13, and T14 is not limited to the order shown in Figure 38; other orders are also acceptable. In other words, the third example, like the first and second examples described above, performs the light source control and imaging control described above, so unwanted light originating from visible light is not included in either the first or second fluorescence image. Even when configured as in the modified example 3 described above, the same effects as those of the embodiment 3 described above are achieved. (Variation 4) In the above-described embodiment 4, the second observed fluorescence was light in a wavelength band other than the visible light band (invisible fluorescence), but is not limited to this. In this modified example 4, the second observed fluorescence is light (visible fluorescence) that includes at least a portion of the visible light wavelength band and is light included in the first wavelength band separated by the prism 52. Therefore, the second fluorescence subject image, which is light in the first wavelength band separated by the prism 52 and which includes at least a portion of the wavelength band of the second observed fluorescence, travels toward the first image sensor 531. The first image sensor 531 then generates a second fluorescence image by capturing the second fluorescence subject image. As described above, visible light and the second target fluorescence are imaged using the same first image sensor 531. Therefore, it is not possible to image visible light and the second target fluorescence simultaneously. Of the first and third fluorescence images, the first mode is used when there is a low possibility of misidentifying unwanted light as the first target fluorescence in the first fluorescence image. The second mode is used when there is a low possibility of misidentifying unwanted light as the target fluorescence in both the first and third fluorescence images. Furthermore, the third mode is used when there is a high possibility of misidentifying unwanted light as the target fluorescence in both the first and third fluorescence images. The light source control and imaging control in the first to third modes related to this modified example 4 will be described in order below. [Regarding light source control and imaging control in the first mode] Figure 39 is a diagram corresponding to Figures 25 and 29, and shows the light source control and imaging control in the first mode according to Modification 4. As shown in Figure 39, the imaging control unit 942 generates a normal image and a second fluorescence image by time-division imaging (changing the timing of imaging) of the reflected visible light and the reflected light of the second excitation light with the first image sensor 531, and generates first and third fluorescence images by time-division imaging (changing the timing of imaging) of the reflected light of the first excitation light and the reflected light of the third excitation light with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, in half the period within the first frame period T1 and half the period within the second frame period T2, which are repeated alternately in the first and second frame periods T1 and T2. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in half the period within the first frame period T1 and half the period within the second frame period T2. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the first image sensor 531 during half of the first frame period T1. The third fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532 during half of the second frame period T2. In the example shown in Figure 39, the normal image and the first fluorescence image are generated during the first half of the two periods T11 and T12, which represent half of one frame within the first frame period T1, and during the first half of the two periods T21 and T22, which represent half of one frame within the second frame period T2, respectively. Furthermore, within the first frame period T1, a second fluorescence image is generated in the latter half of the two periods T11 and T12, which represent half of one frame, and within the second frame period T2, a third fluorescence image is generated in the latter half of the two periods T21 and T22, which represent half of one frame, and within the second frame period T2, a third fluorescence image is generated in the latter half of the two periods T21 and T22. Furthermore, as shown in Figure 39, the light source control unit 941 emits visible light and the first excitation light during periods T11 and T21, respectively, emits the second excitation light during period T12, and emits the third excitation light during period T22. Note that the emission periods of visible light and the emission periods of the first excitation light do not have to be configured to completely overlap as shown in Figure 39, as long as at least some of the periods overlap. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first fluorescence image among the first to third fluorescence images. [Regarding light source control and imaging control in the second mode] Figure 40 is a diagram corresponding to Figures 25 and 29, and shows the light source control and imaging control in the second mode according to Modification 4. As shown in Figure 40, the imaging control unit 942 generates a normal image and a second fluorescence image by time-division imaging (changing the timing of imaging) of the reflected visible light and the reflected light of the second excitation light with the first image sensor 531, and generates first and third fluorescence images by time-division imaging (changing the timing of imaging) of the reflected light of the first excitation light and the reflected light of the third excitation light with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, in the first and second frame periods T1 and T2 which are repeated alternately, in the first frame period T1 and the second frame period T2, respectively. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, in the first frame period T1 and the second frame period T2, respectively. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the first image sensor 531 during half of the first frame period T1. The third fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532 during half of the second frame period T2. In the example of Figure 40, a normal image is generated during the first half of the two periods T11 and T12 within the first frame period T1, and during the second half of the two periods T21 and T22 within the second frame period T2, respectively. Also, the first fluorescence image is generated during the first half of the two periods T11 and T12 within the first frame period T1, and during the first half of the two periods T21 and T22 within the second frame period T2, respectively. Furthermore, within the first frame period T1, a second fluorescence image is generated in the latter period T12 of the two periods T11 and T12 within one frame. Also, within the second frame period T2, a third fluorescence image is generated in the latter period T22 of the two periods T21 and T22 within one frame. Furthermore, as shown in Figure 40, the light source control unit 941 emits visible light during periods T11 and T22, emits the first excitation light during periods T11 and T21, emits the second excitation light during period T12, and emits the third excitation light during period T22. Note that the emission periods of visible light and the emission periods of the first and third excitation lights do not have to overlap completely as shown in Figure 40, as long as at least some of the periods overlap. For example, the emission period of visible light may be set to span the emission periods of the first and third excitation lights (from the latter half of period T21 to the first half of period T22), or the emission period of visible light may be set to overlap with all of the emission periods of the first and third excitation lights (from period T21 to period T22). In other words, through the light source control and imaging control described above, unwanted light originating from visible light is included only in the first and third fluorescence images out of the first to third fluorescence images. [Regarding light source control and imaging control in the third mode] Figure 41 is a diagram corresponding to Figures 25 and 29, and shows the light source control and imaging control in the third mode according to Modification 4. As shown in Figure 41, the imaging control unit 942 generates a normal image and a second fluorescence image by time-division imaging (changing the timing of imaging) of the reflected visible light and the reflected second excitation light with the first image sensor 531, and generates first and third fluorescence images by time-division imaging (changing the timing of imaging) of the reflected first excitation light and the reflected third excitation light with the second image sensor 532. Here, the normal image is generated, for example, by the high-speed imaging operation of the first image sensor 531, during half the period of one frame within the first frame period T1 of the first and second frame periods T1 and T2 which are repeated alternately. The first fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532, during half the period of one frame within the first frame period T1. Furthermore, the second fluorescence image is generated, for example, by the high-speed imaging operation of the first image sensor 531 during a period of half a frame within the second frame period T2. The third fluorescence image is generated, for example, by the high-speed imaging operation of the second image sensor 532 during a period of half a frame within the second frame period T2. In the example shown in Figure 41, a normal image is generated in the first half of the two periods T11 and T12, which are half of a frame within the first frame period T1, and the first fluorescence image is generated in the second half of the period T12. Also, in the second frame period T2, a second fluorescence image is generated in the first half of the two periods T21 and T22, which are half of a frame within the second frame period T2, and the third fluorescence image is generated in the second half of the period T22. Furthermore, as shown in Figure 41, the light source control unit 941 emits visible light during period T11, the first excitation light during period T12, the second excitation light during period T21, and the third excitation light during period T22. Note that the emission periods for visible light and the first to third excitation lights may be other emission periods, not limited to those shown in Figure 41, as long as they do not overlap with each other. Note that the order of the four periods T11, T12, T21, and T22 within the first and second frame periods T1 and T2 is not limited to the order shown in Figure 41; other orders are also acceptable. In other words, through the light source control and imaging control described above, unwanted light originating from visible light is not included in any of the first to third fluorescence images. Even when configured as in the modified example 4 described above, the same effects as in the embodiment 4 described above are achieved. In addition, in the above-described modified example 4, if the effects of Embodiment 2 (flicker reduction) and Embodiment 3 (smooth display) are to be achieved, the control of the first and second frame periods T1 and T2 can be reduced to a single frame period, similar to Embodiments 2 and 3 described above. (Variation 5) Figure 42 illustrates a fifth modified example of embodiments 1 to 4. Specifically, Figure 42(a) corresponds to Figure 3(e), and Figure 42(b) corresponds to Figure 3(f). In the embodiments 1 to 4 and the modified examples 1 to 4 described above, the emission of visible light and the first to third excitation light during each emission period may be continuous emission or pulsed emission. Figure 42(b) shows the emission period of the first excitation light, and it is possible to emit the first excitation light continuously during periods T11 to T13 (the figure shown on the left in Figure 42(b)), or to emit the first excitation light in pulses during periods T11, T12, and T13, respectively (the figure shown on the right in Figure 42(b)). Furthermore, in this case, the imaging of the visible light return and the return of the first to third excitation lights may be performed as continuous imaging or as multiple imaging sessions in accordance with the emission of light from the light source. Figure 42(a) shows the imaging control of the return of the first excitation light, and it is possible to continuously image the return of the first excitation light during the period T11 to T13 (the figure shown on the left of Figure 42(a)), or to image the return of the first excitation light during the periods T11, T12, and T13 respectively (the figure shown on the right of Figure 42(a)). Even when configured as in the modified example 5 described above, the same effects as those of embodiments 1 to 4 and modified examples 1 to 4 described above are achieved. (Variation 6) The configurations described in Embodiments 1 to 4 and Modifications 1 to 5 above may also be applied to surgeries and other procedures using the multiple drugs shown in Table 1 below. In Table 1, drugs used are marked with a "○" and drugs not used are marked with a "×". Here, fluorescein emits a target fluorescence of approximately 520 nm when irradiated with excitation light in the wavelength range of approximately 470-480 nm. ALM-488 emits a target fluorescence of approximately 530 nm when irradiated with excitation light in the wavelength range of approximately 488 nm. Furthermore, LUM-015 emits a target fluorescence of approximately 675 nm when irradiated with excitation light in the wavelength range of approximately 650 nm. In addition, 5-ALA emits a target fluorescence of approximately 530-630 nm when irradiated with excitation light in the wavelength range of approximately 405 nm. Furthermore, ICG emits a target fluorescence of approximately 830 nm when irradiated with excitation light in the wavelength range of approximately 805 nm. For example, when performing lymph node dissection during lobectomy for lung cancer, ALM-488 and ICG are used, as shown in Table 1. That is, the left recurrent laryngeal nerve is visualized using ALM-488, and the lymph nodes are visualized using ICG. By visualizing the left recurrent laryngeal nerve and lymph nodes in this way, it is possible to distinguish between the left recurrent laryngeal nerve and the lymph nodes, thereby reducing recurrent laryngeal nerve paralysis during lobectomy. In this case, since two drugs, ALM-488 and ICG, are used, one of the two drugs is excited by one of the first and second excitation lights, and the other drug is excited by the other excitation light. The physician performing the lobectomy can then determine the location of the left recurrent laryngeal nerve and lymph nodes from the image displayed on the display device 7. Furthermore, for example, when performing lateral lymph node dissection during rectal resection for colorectal cancer, ALM-488 and ICG are used as shown in Table 1. That is, ALM-488 is used to visualize neurovascular bundles, and ICG is used to visualize lymph nodes. By visualizing these neurovascular bundles and lymph nodes, it is possible to distinguish between them and reduce urinary dysfunction, defecation dysfunction, male sexual dysfunction, or motor dysfunction caused by nerve damage during rectal resection. In this case, since two drugs, ALM-488 and ICG, are used, one of the two drugs is excited by one of the first and second excitation lights, and the other drug is excited by the other excitation light. The physician performing the rectal resection can then understand the location of the neurovascular bundles and lymph nodes from the image displayed on the display device 7. Furthermore, for example, in malignant tumor resection surgery for pediatric brain tumors, ALM-488 and ICG are used when performing malignant tumor resection, as shown in Table 1. That is, nerves are visualized by using ALM-488, and blood vessels (blood flow) are visualized by using ICG. By visualizing nerves and blood vessels in this way, it is possible to distinguish malignant tumors from nerves and blood vessels, prevent cancer recurrence after malignant tumor resection surgery, and further prevent damage to nerves and blood vessels during malignant tumor resection surgery. In this case, since two drugs, ALM-488 and ICG, are used, one of the two drugs is excited by one of the first and second excitation lights, and the other drug is excited by the other excitation light. The physician performing the malignant tumor resection surgery can then grasp the location of nerves and blood vessels from the image displayed on the display device 7. Furthermore, for example, in mastectomy for breast cancer, when removing malignant tumors or dissecting axillary lymph nodes, ALM-488, LUM-015, and ICG are used as shown in Table 1. Specifically, ALM-488 is used to visualize nerves such as the intercostal brachial nerve and thoracodorsal nerve, LUM-015 is used to visualize malignant tumors, and ICG is used to visualize lymph nodes. By visualizing nerves, malignant tumors, and lymph nodes in this way, it is possible to distinguish between malignant tumors, nerves, and lymph nodes, and reduce nerve damage during mastectomy. In this case, since three drugs, ALM-488, LUM-015, and ICG, are used, one of the three drugs is excited by one of the first to third excitation lights, one of the other two drugs is excited by one of the other two excitation lights, and the remaining drug is excited by the remaining excitation light. Furthermore, the surgeon performing the mastectomy can determine the locations of nerves, malignant tumors, and lymph nodes from the image displayed on the display device 7. Furthermore, for example, when performing brain tumor treatment using photodynamic diagnosis (PDD), ALM-488 and 5-ALA (5-aminolevulinic acid) are used, as shown in Table 1. Specifically, the area near the tumor is visualized by fluorescein, the fluorescent dye of ALM-488, and the tumor cells are visualized by protoporphyrin (PpIX), which is biosynthesized from 5-ALA. By visualizing tumor cells, including the area near the tumor, it is possible to prevent damage during brain tumor treatment and safely remove the tumor. In this case, since two drugs, ALM-488 and 5-ALA, are used, one of the two drugs is excited by one of the first and second excitation lights, and the other drug is excited by the other excitation light. The physician performing the brain tumor treatment can then determine the location of the tumor cells and the area near the tumor from the image displayed on the display device 7. Furthermore, for example, when performing transurethral cystectomy in the surgical treatment of superficial urinary tract cell carcinoma using photodynamic diagnosis, fluorescein and 5-ALA are used as shown in Table 1. That is, the tumor is visualized by PpIX, which is biosynthesized from 5-ALA. However, PpIX has the drawback of visualizing not only the tumor but also highly metabolic inflammatory tissue present in the bladder. Therefore, false positives of highly metabolic inflammatory tissue caused by PpIX are reduced by fluorescein. In this case, since two drugs, fluorescein and 5-ALA, are used, one of the two drugs is excited by one of the first and second excitation lights, and the other drug is excited by the other excitation light. Then, the physician performing the transurethral cystectomy can determine the location of the tumor and the false positives of highly metabolic inflammatory tissue caused by PpIX from the image displayed on the display device 7. Even when adopting the configuration of the modified example 6 described above, the same effects as those of embodiments 1 to 4 and modified examples 1 to 5 described above are achieved. Furthermore, as mentioned above, it is anticipated that multiple different drugs will be used depending on the surgery or procedure. The fluorescence images generated by using these multiple drugs will have different acceptable levels of unwanted light that do not cause misrecognition, even if the combination of drugs and the wavelength range of the drugs are the same, depending on the surgical scene, the observed target (OB), or the situation. By switching between multiple light source control and imaging control methods as described in Embodiments 1 to 4 and Modifications 1 to 5 above, it becomes possible to respond to such various situations. (Variation 7) The medical observation system according to this modified example 7 is a medical observation system that uses a so-called videoscope (flexible endoscope) having an imaging unit on the tip side of the insertion part. For the sake of explanation, the medical observation system 1 according to this modified example 7 will be referred to as medical observation system 1B below. Figure 43 shows a modified example 7 of the embodiment. As shown in Figure 43, the medical observation system 1B includes an endoscope 300B that captures images of the internal organs of the observation site by inserting an insertion part 2B into the body and outputs the captured images, a light source device 3 that emits first light and excitation light from the tip of the endoscope 300B, a control device 9 that processes the captured images output from the endoscope 300B, and a display device 7 that is connected to the control device 9 via a second transmission cable 8 and displays images based on the video signals processed by the control device 9. As shown in Figure 43, the endoscope 300B comprises a flexible, elongated insertion section 2B, an operating section 301 connected to the base end of the insertion section 2B for receiving various operations, and a universal cord 302 extending from the operating section 301 in a direction different from the direction in which the insertion section 2B extends, and containing various cables for connecting to the light source device 3 and the control device 9. As shown in Figure 43, the insertion portion 2B comprises a tip portion 24, a flexible curved portion 25 connected to the base end of the tip portion 24 and composed of a plurality of curved pieces, and a long, flexible pipe portion 26 connected to the base end of the curved portion 25. The tip portion 24 incorporates a configuration substantially similar to that of the camera head 5 described in Embodiment 2 above, although this is not shown in detail. The captured image captured by the tip portion 24 (image sensor) is output to the control device 9 via the operation unit 301 and the universal code 302. Even when adopting the configuration of the modified example 7 described above, the same effects as those of the embodiment described above are achieved. (Variation 8) The medical observation system according to this modified example 8 is a medical observation system that uses a surgical microscope to magnify and image a predetermined field of view of the inside (in vivo) or surface (biological surface) of the subject being observed. For the sake of explanation, the medical observation system 1 according to this modified example 3 will be referred to as medical observation system 1C below. Figure 44 shows a modified example 8 of the embodiment. As shown in Figure 44, the medical observation system 1C comprises a surgical microscope 12 that captures images for observing a subject and outputs the captured images, a control device 9 that processes the captured images output from the surgical microscope 12, and a display device 7 that is connected to the control device 9 via a second transmission cable 8 and displays images based on the video signals processed by the control device 9. As shown in Figure 44, the surgical microscope 12 comprises a microscope unit 121 that magnifies and images minute parts of a subject and outputs the captured image, a support unit 122 connected to the base end of the microscope unit 121 and including an arm that rotatably supports the microscope unit 121, and a base unit 123 that rotatably holds the base end of the support unit 122 and is movable on the floor surface. The control device 9 is installed on the base unit 123, as shown in Figure 44. Although not shown in detail, the base unit 123 also has a light source device 3 that emits the first light and excitation light from the surgical microscope 12 to the object being observed. Furthermore, the base portion 123 may be fixed to the ceiling or wall, etc., to support the support portion 122, rather than being provided movably on the floor. Although not shown in detail in the illustration, the microscope unit 121 incorporates a configuration substantially similar to that of the camera head 5 described in Embodiment 2 above. The image captured by the microscope unit 121 (image sensor) is output to the control device 9 via the first transmission cable 6, which is wired along the support unit 122. Even when adopting the configuration of the modified example 8 described above, the same effects as those of the embodiment described above are achieved. (Variation 9) Figures 45 and 46 illustrate a modified example 9 of the embodiment. Specifically, Figure 45 is a side view of the ring light 15. Figure 46 is a front view of the ring light 15 (left side in Figure 45). In this modified example 9, in addition to the insertion part 2 described in the above-described embodiment, a ring light 15, as shown in Figures 45 and 46, is detachably connected to the camera head 5. That is, depending on the user's usage, the camera head 5 may be connected to either the insertion part 2 or the ring light 15, as shown in Figure 45. Unlike the insertion unit 2, the ring light 15 is not inserted into the observation target OB, but rather supplies first light and excitation light to the surgical unit and captures second light (subject image), which is the reflected light of the first light and excitation light from the surgical unit. As shown in Figures 45 and 46, the ring light 15 comprises an illumination unit 151 and a subject image capture unit 152 that captures the subject image. As shown in Figures 45 and 46, the lighting unit 151 comprises a housing 1511 and a plurality of lighting lenses 1512. The housing 1511 has an annular shape centered on the optical axis Ax. The other end of the light guide 4 is detachably connected to the housing 1511. As shown in Figure 46, the multiple illumination lenses 1512 are arranged at predetermined intervals along the circumferential direction centered on the optical axis Ax on the front end face of the housing 1511. The multiple illumination lenses 1512 each irradiate the surgical area with the first light supplied from the light source device 3 and introduced into the housing 1511 via the light guide 4. The subject image acquisition section 152 extends along the optical axis Ax. Within the subject image acquisition section 152, there is an optical system composed of one or more lenses that focuses the second light (subject image) illuminated by multiple illumination lenses 1512 and transmitted through the surgical section. Furthermore, a connection section 1521 is provided at the base end (right side in Figure 45) of the subject image acquisition section 152. This connection section 1521 is designed (shaped) to be compatible with the eyepiece section 21 in the insertion section 2 and is detachably connected to the camera head 5. Even when adopting the configuration of the modified example 9 described above, the same effects as those of the embodiment described above are achieved. Furthermore, the following configurations also fall within the technical scope of this disclosure. (1) A medical control device comprising: a light source control unit that controls the operation of a light source device that emits a first light and a first excitation light and a second excitation light that excite substances contained in an object to be observed, respectively; an imaging control unit that controls the operation of an imaging device that images the return light of the first light, the return light of the first excitation light, and the return light of the second excitation light from the object to be observed, respectively; and a mode switching unit that switches to one of a plurality of modes, wherein the light source control unit controls the operation of the light source device such that the emission patterns of the first light, the first excitation light, and the second excitation light differ among the plurality of modes. (2) The medical control device according to (1) above, wherein the first light includes at least a portion of the visible light wavelength band. (3) The medical control device according to (1) or (2), wherein the light source control unit controls the operation of the light source device in a light emission pattern in which, in the first mode of the plurality of modes, at least a portion of the emission period of the first excitation light and the emission period of the first light overlap, and the emission period of the second excitation light and the emission period of the first light do not overlap. (4) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object to be observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object to be observed, respectively, wherein the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, wherein the normal image and the first fluorescence image are generated in the same first frame period, and the second fluorescence image is generated in a second frame period different from the first frame period, and the light source control unit emits the first light and the first excitation light in the first frame period, respectively, and emits the second excitation light in the second frame period, as described in (3). (5) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object to be observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object to be observed, respectively, wherein the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, wherein the normal image, the first fluorescence image, and the second fluorescence image are each generated in a first frame period, and the light source control unit emits the first light and the first excitation light in a period of time in the first frame period, respectively, and emits the second excitation light in a period of time different from the aforementioned part in the first frame period, as described in (3). (6) The medical control device according to (5), wherein the light source control unit emits the first light at a period of 1 / 120 [s] or less. (7) The imaging device comprises a first image sensor for imaging the reflected light of the first light and the reflected light of the second excitation light from the object of observation, and a second image sensor for imaging the reflected light of the first excitation light from the object of observation, wherein the imaging control unit causes the first image sensor to time-divisionally image the reflected light of the first light and the reflected light of the second excitation light to generate a normal image and a second fluorescence image, respectively, and causes the second image sensor to image the reflected light of the first excitation light to generate a first fluorescence image, wherein the normal image and the first fluorescence image are generated in the same first frame period, and the second fluorescence image is generated in a second frame period different from the first frame period, and the light source control unit emits the first light and the first excitation light in the first frame period, respectively, and emits the second excitation light in the second frame period, as described in (3). (8) The imaging device comprises a first image sensor for imaging the reflected light of the first light and the reflected light of the second excitation light from the object of observation, and a second image sensor for imaging the reflected light of the first excitation light from the object of observation, wherein the imaging control unit generates a normal image and a second fluorescence image by time-division imaging the reflected light of the first light and the reflected light of the second excitation light with the first image sensor, and generates a first fluorescence image by imaging the reflected light of the first excitation light with the second image sensor, wherein the normal image, the first fluorescence image and the second fluorescence image are generated in a first frame period, and the light source control unit emits the first light and the first excitation light in a part of the first frame period, and emits the second excitation light in a part of the first frame period that is different from the part, as described in (3). (9) The medical control device according to (8), wherein the light source control unit emits the first light at a period of 1 / 120 [s] or less. (10) The medical control device according to (1), wherein the light source control unit controls the operation of the light source device in a light emission pattern in which, in the second mode of the plurality of modes, at least a portion of the emission period of the first excitation light and at least a portion of the emission period of the first light overlap, and at least a portion of the emission period of the second excitation light and at least a portion of the emission period of the first light overlap. (11) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object to be observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object to be observed, respectively, wherein the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, wherein the normal image and the first fluorescence image are generated during the first frame period of the first and second frames which are repeated alternately, and the normal image and the second fluorescence image are generated during the second frame period, respectively, wherein the light source control unit emits the first light and the first excitation light during the first frame period, respectively, and emits the first light and the second excitation light during the second frame period, respectively, as described in (10). (12) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object being observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner. The normal image is generated in two frame periods out of four frames that are repeated in the order of a first frame, a second frame, a third frame, and a fourth frame, respectively, and the first fluorescence The medical control device according to (10), wherein the images are generated in two frame periods in which the normal image is generated, of which the two frame periods in which the normal image is generated are the same, the second fluorescence image is generated in two frame periods in which the first fluorescence image is generated, of which the two frame periods in which the first fluorescence image is generated are different, and the light source control unit emits the first light in the two frame periods for generating the normal image, emits the first excitation light in the two frame periods for generating the first fluorescence image, and emits the second excitation light in the two frame periods for generating the second fluorescence image. (13) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object to be observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object to be observed, respectively, wherein the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, wherein the normal image, the first fluorescence image, and the second fluorescence image are each generated in a first frame period, and the light source control unit emits the first light and the first excitation light in a period of time different from the first frame period, respectively, as described in (10). (14) The medical control device according to (13), wherein the light source control unit emits the first light at a period of 1 / 120 [s] or less. (15) The imaging device comprises a first image sensor for imaging the reflected light of the first light from the object being observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively, and the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, and the normal image, the first fluorescence image, and the second The fluorescence image is generated in a first frame period and a second frame period which are repeated alternately, and the light source control unit emits the first light and the first excitation light for a portion of the first frame period, emits the second excitation light for a portion of the first frame period which is different from the portion, emits the first light and the second excitation light for a portion of the second frame period which is different from the portion, and emits the first excitation light for a portion of the second frame period which is different from the portion, as described in (10) above. (16) The medical control device according to (1), wherein the light source control unit controls the operation of the light source device in the third mode of the plurality of modes with a light emission pattern in which the light emission periods of both the first excitation light and the second excitation light do not overlap with the light emission period of the first light. (17) The medical control device according to (16), wherein the imaging device comprises a first image sensor for imaging the reflected light of the first light from the object to be observed, and a second image sensor for imaging the reflected light of the first excitation light and the reflected light of the second excitation light from the object to be observed, and the imaging control unit generates a normal image by having the first image sensor image the reflected light of the first light, and generates a first fluorescence image and a second fluorescence image by having the second image sensor image the reflected light of the first excitation light and the reflected light of the second excitation light in a time-division manner, and the light source control unit emits the first light in a first period, emits the first excitation light in a second period different from the first period, and emits the second excitation light in a third period different from the first and second periods. (18) The medical control device according to (17), wherein the first period, the second period, and the third period are different frame periods, and the normal image, the first fluorescence image, and the second fluorescence image are generated in different frame periods, respectively. (19) The medical control device according to (17), wherein the normal image, the first fluorescence image, and the second fluorescence image are each generated during a first frame period, and the first period, the second period, and the third period are periods within the first frame period. (20) The medical control device according to (19), wherein the light source control unit emits the first light at a period of 1 / 120 [s] or less. (21) The medical control device according to (16), wherein the imaging device comprises a first image sensor that images the reflected light of the first light and the reflected light of the second excitation light from the object to be observed, and a second image sensor that images the reflected light of the first excitation light from the object to be observed, the imaging control unit generates a normal image and a second fluorescence image by having the first image sensor capture the reflected light of the first light and the reflected light of the second excitation light in a time-division manner, and generates a first fluorescence image by having the second image sensor capture the reflected light of the first excitation light, and the light source control unit emits the first light in a first period, emits the first excitation light in a second period different from the first period, and emits the second excitation light in a third period different from the first and second periods. (22) The medical control device according to (21), wherein the first period, the second period, and the third period are different frame periods, and the normal image, the first fluorescence image, and the second fluorescence image are generated in different frame periods, respectively. (23) The medical control device according to (21), wherein the normal image, the first fluorescence image, and the second fluorescence image are each generated during a first frame period, and the first period, the second period, and the third period are periods within the first frame period. (24) The medical control device according to (23), wherein the light source control unit emits the first light at a period of 1 / 120 [s] or less. (25) A medical observation system comprising: a light source device that emits a first light and a first excitation light and a second excitation light that excite substances contained in an object to be observed, respectively; an imaging device that images the return light of the first light, the return light of the first excitation light, and the return light of the second excitation light from the object to be observed, respectively; and a medical control device that controls the operation of the light source device and the operation of the imaging device, respectively, wherein the medical control device comprises a light source control unit that controls the operation of the light source device, an imaging control unit that controls the operation of the imaging device, and a mode switching unit that switches to one of a plurality of modes, wherein the light source control unit controls the operation of the light source device such that the emission patterns of the first light, the first excitation light, and the second excitation light differ in the plurality of modes. (26) The medical observation system according to (25), wherein the first light is broadband light or narrowband light. (27) The medical observation system according to (25) or (26), wherein the light source device includes a first light source that emits the first light, and the first light source is comprised of one or more. (28) The medical observation system according to any one of (25) to (27), wherein the light source device includes a first light source that emits the first light, and the first light source is composed of an LED or a semiconductor laser. (29) The medical observation system according to any one of (25) to (28), wherein the first excitation light and the second excitation light are each narrowband light. (30) The medical observation system according to any one of (25) to (29), wherein the light source device emits the first light, the first excitation light, and the second excitation light from one light source or two or more light sources. (31) The medical observation system according to any one of (25) to (30), wherein the light source device has one or two light sources and emits the first light, the first excitation light, and the second excitation light by switching wavelengths using a wavelength adjustment optical element. 1, 1B, 1C Medical Observation System 2, 2B Insertion section 3 Light source device 4. Light Guide 5. Camera head 6. First transmission cable 7 Display device 8. Second transmission cable 9. Control device 10. Third transmission cable 12 Surgical microscope 15 Ring Light 21 Eyepiece 22. Excitation light cut filter 24 Tip 25 Curved section 26 Flexible tube section 31. First light source 32. Second light source 33. The third light source 34. The fourth light source 51 Lens Unit 52 Prisms 53 Imaging Unit 54 Communications Department 91 Communications Department 92 Image memory 93 Processing Module 94 Control Unit 95 Input section 96 Output section 97 Memory section 121 Microscope Department 122 Support part 123 Base section 151 Lighting Department 152 Subject Image Capture Unit 300B Endoscope 301 Operation unit 302 Universal Code 531 First image sensor 532 Second image sensor 533 Signal Processing Unit 931 Memory Controller 932 Processing Unit 933 Display Control Unit 941 Light source control unit 942 Imaging Control Unit 943 Mode switching section 1511 enclosure 1512 Illumination Lens 1521 Connection part Ax optical axis CN1, CN2 connectors OB Observation Subjects P0 Observation light path P1 First optical path P2 Second optical path T1 First frame period T2 Second frame period T3 Third frame period T4 Fourth frame period Periods T11-T14, T21, T22

Claims

A light source control unit controls the operation of a light source device that emits a first light and a first excitation light and a second excitation light, respectively, which excite substances contained in the object to be observed. An imaging control unit controls the operation of an imaging device that images the reflected light of the first light, the reflected light of the first excitation light, and the reflected light of the second excitation light from the object of observation, respectively. It includes a mode switching unit that switches to one of several modes, The light source control unit, A medical control device that controls the operation of the light source device such that the emission patterns of the first light, the first excitation light, and the second excitation light differ among the multiple modes. 　 The first light is, A medical control device according to claim 1, comprising at least a portion of the visible light wavelength band. 　 The light source control unit, The medical control device according to claim 1, wherein in the first of the plurality of modes, at least a portion of the emission period of the first excitation light and the emission period of the first light overlap, and the operation of the light source device is controlled with an emission pattern in which the emission period of the second excitation light and the emission period of the first light do not overlap. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The above-mentioned normal image and the above-mentioned first fluorescence image are, Each is generated within the same first frame period, The second fluorescence image is It is generated in a second frame period that is different from the first frame period, The light source control unit, The medical control device according to claim 3, wherein the first light and the first excitation light are emitted during the first frame period, and the second excitation light is emitted during the second frame period. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, Each is generated during the first frame period, The light source control unit, The medical control device according to claim 3, wherein the first light and the first excitation light are emitted during a portion of the first frame period, and the second excitation light is emitted during a period different from the portion of the first frame period. 　 The light source control unit, The medical control device according to claim 5, wherein the first light is emitted at a period of 1 / 120 [s] or less. 　 The imaging device is A first image sensor that captures the reflected light of the first light and the reflected light of the second excitation light from the object being observed, The system comprises a second image sensor that captures the reflected light of the first excitation light from the object being observed, The imaging control unit, The first image sensor captures the reflected light of the first light and the reflected light of the second excitation light in a time-resolved manner to generate a normal image and a second fluorescence image, respectively, and the second image sensor captures the reflected light of the first excitation light to generate a first fluorescence image. The above-mentioned normal image and the above-mentioned first fluorescence image are, Each is generated within the same first frame period, The second fluorescence image is It is generated in a second frame period that is different from the first frame period, The light source control unit, The medical control device according to claim 3, wherein the first light and the first excitation light are emitted during the first frame period, and the second excitation light is emitted during the second frame period. 　 The imaging device is A first image sensor that captures the reflected light of the first light and the reflected light of the second excitation light from the object being observed, The system comprises a second image sensor that captures the reflected light of the first excitation light from the object being observed, The imaging control unit, The first image sensor captures the reflected light of the first light and the reflected light of the second excitation light in a time-resolved manner to generate a normal image and a second fluorescence image, respectively, and the second image sensor captures the reflected light of the first excitation light to generate a first fluorescence image. The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, Each is generated during the first frame period, The light source control unit, The medical control device according to claim 3, wherein the first light and the first excitation light are emitted during a portion of the first frame period, and the second excitation light is emitted during a period different from the portion of the first frame period. 　 The light source control unit, The medical control device according to claim 8, wherein the first light is emitted at a period of 1 / 120 [s] or less. 　 The light source control unit, The medical control device according to claim 1, wherein in the second mode of the plurality of modes, at least a portion of the emission period of the first excitation light and at least a portion of the emission period of the first light overlap, and the operation of the light source device is controlled with an emission pattern in which at least a portion of the emission period of the second excitation light and at least a portion of the emission period of the first light overlap. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The above-mentioned normal image and the above-mentioned first fluorescence image are, Of the first and second frames which are repeated alternately, these are generated during the first frame period, The above-mentioned normal image and the above-mentioned second fluorescence image are, Each of the following is generated during the second frame period: The light source control unit, The medical control device according to claim 10, wherein the first light and the first excitation light are emitted during the first frame period, and the first light and the second excitation light are emitted during the second frame period. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The aforementioned standard image is It is generated during two frame periods of the four frames that are repeated in the order of the first frame, second frame, third frame, and fourth frame. The first fluorescence image is Of the four frames mentioned above, the normal image is generated in two frame periods where only one of the two frame periods in which the normal image is generated is the same. The second fluorescence image is Of the four frames, the first fluorescence image is generated in two frame periods that are different from the two frame periods in which the first fluorescence image is generated. The light source control unit, The medical control device according to claim 10, wherein the first light is emitted during the two frame periods for generating the normal image, the first excitation light is emitted during the two frame periods for generating the first fluorescence image, and the second excitation light is emitted during the two frame periods for generating the second fluorescence image. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, Each is generated during the first frame period, The light source control unit, The medical control device according to claim 10, wherein the first light and the first excitation light are emitted during a portion of the first frame period, and the first light and the second excitation light are emitted during a period different from the portion of the first frame period. 　 The light source control unit, The medical control device according to claim 13, wherein the first light is emitted at a period of 1 / 120 [s] or less. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, It is generated during the first and second frame periods, which alternately repeat, The light source control unit, A medical control device according to claim 10, wherein the first light and the first excitation light are emitted during a portion of the first frame period, the second excitation light is emitted during a period different from the portion of the first frame period, the first light and the second excitation light are emitted during a portion of the second frame period, and the first excitation light is emitted during a period different from the portion of the second frame period. 　 The light source control unit, The medical control device according to claim 1, wherein in the third mode of the plurality of modes, the operation of the light source device is controlled with a light emission pattern in which the light emission periods of both the first excitation light and the second excitation light do not overlap with the light emission period of the first light. 　 The imaging device is A first image sensor that captures the reflected light of the first light from the object being observed, The system includes a second image sensor that captures the reflected light of the first excitation light and the reflected light of the second excitation light from the object being observed, respectively. The imaging control unit, The first image sensor captures the reflected light of the first light to generate a normal image, and the second image sensor captures the reflected light of the first excitation light and the reflected light of the second excitation light in a time-resolved manner to generate a first fluorescence image and a second fluorescence image, respectively. The light source control unit, The medical control device according to claim 16, wherein the first light is emitted during a first period, the first excitation light is emitted during a second period different from the first period, and the second excitation light is emitted during a third period different from the first and second periods. 　 The first period, the second period, and the third period are, They are different frame periods, The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, The medical control device according to claim 17, which is generated in different frame periods. 　 The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, Each is generated during the first frame period, The first period, the second period, and the third period are, The medical control device according to claim 17, which is a period within the first frame period. 　 The light source control unit, The medical control device according to claim 19, wherein the first light is emitted at a period of 1 / 120 [s] or less. 　 The imaging device is A first image sensor that captures the reflected light of the first light and the reflected light of the second excitation light from the object being observed, The system comprises a second image sensor that captures the reflected light of the first excitation light from the object being observed, The imaging control unit, The first image sensor captures the reflected light of the first light and the reflected light of the second excitation light in a time-resolved manner to generate a normal image and a second fluorescence image, respectively, and the second image sensor captures the reflected light of the first excitation light to generate a first fluorescence image. The light source control unit, The medical control device according to claim 16, wherein the first light is emitted during a first period, the first excitation light is emitted during a second period different from the first period, and the second excitation light is emitted during a third period different from the first and second periods. 　 The first period, the second period, and the third period are, They are different frame periods, The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, The medical control device according to claim 21, which is generated in different frame periods. 　 The above-mentioned normal image, the first fluorescence image, and the second fluorescence image are, Each is generated during the first frame period, The first period, the second period, and the third period are, The medical control device according to claim 21, which is a period within the first frame period. 　 The light source control unit, The medical control device according to claim 23, wherein the first light is emitted at a period of 1 / 120 [s] or less. 　 A light source device that emits a first light and a first excitation light and a second excitation light, respectively, which excite substances contained in the object to be observed. An imaging device that captures the reflected light of the first light, the reflected light of the first excitation light, and the reflected light of the second excitation light from the object of observation, respectively. The system includes a medical control device that controls the operation of the light source device and the operation of the imaging device, respectively. The aforementioned medical control device is A light source control unit that controls the operation of the light source device, The imaging control unit controls the operation of the imaging device, It includes a mode switching unit that switches to one of several modes, The light source control unit, A medical observation system that controls the operation of the light source device such that the emission patterns of the first light, the first excitation light, and the second excitation light differ in the plurality of modes. 　 The aforementioned light source device is The medical observation system according to claim 25, wherein the first light, the first excitation light, and the second excitation light are emitted from one light source or two or more light sources. 　 The aforementioned light source device is A medical observation system according to claim 25, having one or two light sources, and emitting the first light, the first excitation light, and the second excitation light, respectively, by switching wavelengths using a wavelength-adjusting optical element.

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