Optical measuring device and optical measuring method

Abstract

Provided are a light measurement device and a light measurement method capable of completing measurement carried out by an image sensor within a decorrelation time. The light measurement device comprises: a laser source (1); an ultrasonic wave source (2); a camera (3); a control circuit (4); and a data analysis unit (5). The control circuit (4) that controls the emission timing such that a first laser beam and a second laser beam are emitted at a time interval shorter than the time of a single frame of an image sensor (3a), and such that the emission time point of the first laser beam and the emission time point of the second laser beam correspond to different exposure time of continuous frames. The ultrasonic wave source (2) emits an ultrasonic wave such that ultrasonic wave arrives at a measurement position at the emission time point of the first laser beam or the second laser beam. The data analysis unit (5) extracts a signal component modulated by the ultrasonic wave on the basis of a detection signal of the first laser beam and a detection signal of the second laser beam detected by the image sensor (3a).

Description

Technical Field

[0004] , , , , , , ,

[0001] The present disclosure relates to an optical measurement device and an optical measurement method for measuring light modulated by ultrasonic waves.

Background Art

[0002] As a technique for minimally invasive measurement of tissues in a living body, many techniques using light have been developed. For example, by irradiating light from outside the body and measuring the light that propagates through the living body and is emitted, biological information such as morphological information and metabolic information (such as oxygen saturation in blood) of tissues in the living body can be obtained. However, since tissues in the living body are light-scattering media, the light irradiated from outside the body is diffused by the tissues in the living body, resulting in poor spatial resolution and inability to measure deep into the body. Therefore, an optical measurement device using ultrasonic wave-modulated optical tomography (UOT: ultrasound-modulated optical tomography), which combines ultrasonic waves that propagate through the living body with low scattering and light, has been developed (Non-Patent Documents 1 and 2). In UOT, biological information is obtained by measuring light modulated by ultrasonic waves.

[0003] Non-Patent Document 3 discloses that a CCD camera is used to capture a speckle pattern both when convergent pulse ultrasonic waves are irradiated and when they are not irradiated, and the change in the speckle pattern is obtained based on the difference, thereby obtaining information on a local region indicated by ultrasonic waves.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

[0005] However, when measuring tissues within a living organism, the autocorrelation of the measured speckle pattern is lost (called decorrelation) due to random state changes (biological fluctuations) of the tissues within the organism caused by biological activity. As shown in Patent Document 3, if the speckle pattern is captured both with and without ultrasound irradiation and the difference is taken, the output of the difference will be affected by decorrelation.

[0006] While using an image sensor with a short frame time can mitigate the effects of decorrelation, such image sensors are relatively expensive.

[0007] This disclosure was made to solve the aforementioned problem, and aims to suppress the influence of biological fluctuations on the speckle pattern being measured in an optical measurement device and optical measurement method using ultrasonic modulated optical tomography. [Means for solving the problem]

[0008] The optical measurement device disclosed herein comprises a light source that irradiates pulsed laser light into a living body, and a measurement position located at a predetermined depth within the living body. So that it convergesThe system comprises an ultrasonic source that irradiates ultrasound, an image sensor that detects laser light that has passed through a region within the body including the measurement position, a control circuit that controls the irradiation timing of the laser light irradiation from the light source, and a calculation circuit that extracts the signal component modulated by ultrasound from the laser light detected by the image sensor. The control circuit irradiates the first laser light and the second laser light at time intervals shorter than the time of one frame of the image sensor, and controls the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of consecutive frames, respectively. The ultrasonic source irradiates ultrasound so that the ultrasound reaches the measurement position at the irradiation time of the first laser light or the second laser light. The calculation circuit extracts the signal component modulated by ultrasound based on the detection signals of the first laser light and the second laser light detected by the image sensor. Furthermore, the light source can emit laser light with different peak wavelengths, and the time interval between the irradiation of the first and second laser beams is 500 μs or less. .

[0009] The optical measurement method disclosed herein comprises a light source that irradiates pulsed laser light into a living organism, and a measurement position at a predetermined depth within the living organism. So that it converges This is an optical measurement method in an optical measurement device comprising: an ultrasonic source that irradiates ultrasonic waves; an image sensor that detects laser light that has passed through a region in the body including the measurement position; a control circuit that controls the irradiation timing of the irradiation of laser light from the light source; and an arithmetic circuit that extracts a signal component modulated by ultrasonic waves from the laser light detected by the image sensor. The optical measurement method includes the steps of: irradiating a first laser beam and a second laser beam at time intervals shorter than the time of one frame of the image sensor, and controlling the irradiation timing so that the irradiation time of the first laser beam and the irradiation time of the second laser beam correspond to different exposure times of consecutive frames, respectively; irradiating ultrasonic waves from the ultrasonic source so that the ultrasonic waves reach the measurement position at the irradiation time of the first laser beam or the second laser beam; and extracting a signal component modulated by ultrasonic waves based on the detection signal of the first laser beam and the detection signal of the second laser beam detected by the image sensor. Furthermore, the light source can emit laser light with different peak wavelengths, and the time interval between the irradiation of the first and second laser beams is 500 μs or less. . [Effects of the Invention]

[0010] The optical measurement apparatus and optical measurement method disclosed herein irradiate the image sensor with a first laser beam and a second laser beam at time intervals shorter than the time of one frame of the image sensor. Since the first exposure time for irradiation with the first laser beam and the second exposure time for irradiation with the second laser beam are different exposure times for consecutive frames, it is possible to complete the measurement by the image sensor within the decorrelation time, thereby reducing the effects of decorrelation and improving measurement accuracy. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an optical measuring device according to an embodiment. [Figure 2] This is a flowchart showing an optical measurement method according to an embodiment. [Figure 3] This is a timing chart showing the timing of the pulse laser illumination of an optical measuring device according to the embodiment. [Figure 4] This is a schematic diagram showing the lighting configuration of the pulsed laser of an optical measuring device according to an embodiment. [Figure 5] This is a timing chart showing an alternative illumination timing for the pulsed laser of an optical measuring device according to the embodiment. [Figure 6] This is a schematic diagram of a modified measurement system using an optical measuring device according to the embodiment. [Figure 7] This is a block diagram of a modified measurement system. [Modes for carrying out the invention]

[0012] The embodiments will be described in detail below with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0013] [Optical measuring device] In this embodiment, an optical measurement device that measures light modulated by ultrasonic waves in order to minimally invasively measure tissues in a living body will be described below. The optical measurement device according to this embodiment can be applied, for example, to an optical measurement device that minimally invasively measures the brain activity of a subject by near-infrared spectroscopy (NIRS: near-infrared spectroscopy). Of course, the optical measurement device according to this embodiment can also be applied to a measurement device that measures the oxygen saturation in blood, etc., in addition to an optical measurement device that measures brain activity by near-infrared spectroscopy.

[0014] FIG. 1 is a schematic diagram of an optical measurement device 10 according to an embodiment. The optical measurement device 10 includes a laser source 1, an ultrasonic source 2, a camera 3, a control circuit 4, and a data analysis unit 5. Note that the control circuit 4 and the data analysis unit 5 can be configured on one computer (not shown), and external devices such as a memory and a printer can be connected as necessary. Also, the laser source 1, the ultrasonic source 2, the camera 3, etc. can be integrally configured, and they and the control circuit 4 can be integrally configured so as to be wearable by a subject.

[0015] The laser source 1 is a light source that irradiates laser light into the living body 20, and is, for example, a semiconductor laser element. In this embodiment, the laser source 1 is controlled to generate pulsed laser light (pulse laser light). The laser source 1 irradiates laser light in a wavelength region of near-infrared light with high transmittance to the living body 20 (for example, 780 nm, etc.). The laser light irradiated from the laser source 1 to the living body 20 is scattered by the tissue in the living body 20 and reaches the measurement position as shown in FIG. 1. Also, the laser source 1 can irradiate pulsed laser light of about several nanoseconds to several tens of nanoseconds.

[0016] The ultrasonic source 2 is an ultrasonic generator that irradiates ultrasonic waves to a measurement position at a predetermined depth within the living body 20. The ultrasonic source 2 is equipped with a converger 2a to focus the irradiated ultrasonic waves at the measurement position within the living body 20. Here, speckle fluctuations increase with higher ultrasonic sound pressure. Therefore, by focusing the ultrasonic waves at the measurement position within the living body 20 using the converger 2a, the high-sound-pressure region is limited to the measurement position, thereby reducing speckle fluctuations that occur in areas where ultrasonic waves exist other than the measurement position. The ultrasonic waves irradiated from the ultrasonic source 2 may be continuous or pulsed. However, by using pulsed ultrasonic waves irradiated from the ultrasonic source 2, the length of the ultrasonic wave propagation direction can be shortened, and the region where ultrasonic waves exist can be limited to the measurement position. In addition, when pulsed ultrasonic waves are irradiated from the ultrasonic source 2, a delay time is required for the pulsed ultrasonic waves irradiated from the surface of the living body 20 to reach the measurement position. Therefore, it is necessary to control the timing of the emission of ultrasonic waves from ultrasonic source 2 (second timing) so that the pulsed ultrasonic waves reach the measurement position at the same time as the pulsed laser light emitted from laser source 1 reaches the measurement position. Since the distance to the measurement position is sufficiently short relative to the speed of light, the time at which the pulsed laser light emitted from laser source 1 reaches the measurement position is approximately the same as the time at which the pulsed laser light is emitted from laser source 1.

[0017] The camera 3 includes an image sensor 3a that detects laser light from the measurement position, and a lens 3b for forming an image on the image sensor 3a. In the optical measurement device 10, since it is necessary to photograph the speckle pattern, instead of a single-element photodetector such as a photomultiplier tube, an image sensor 3a such as a charge-coupled device (CCD) sensor or a complementary metal-oxide-semiconductor (CMOS) sensor, which is a multi-element photodetector, is used. By adopting a CCD sensor or a CMOS sensor for the image sensor 3a, the manufacturing cost of the optical measurement device 10 can be reduced. The speckle pattern is an aggregate of speckle grains (spotted particles) generated by the multiple interference of light multiply scattered inside the tissue in the living body 20. Therefore, it is preferable that the pixel size of the image sensor 3a is smaller than the average size of the speckle grains to be photographed.

[0018] In an image sensor 3a such as a CCD sensor, the frame rate is generally in the range of several tens of frames per second (fps) to several hundreds of fps. In contrast, the frequency of ultrasonic waves is as fast as several megahertz (MHz), and the image sensor 3a cannot follow the changes in ultrasonic waves. Therefore, in the optical measurement device 10, the stroboscopic photography method is used to irradiate the tissue in the living body 20 irradiated with ultrasonic waves with pulsed laser light, and the speckle pattern is photographed with the image sensor 3a in the exposure state. Further, in the optical measurement device 10, the irradiation timing (first timing) at which the laser source 1 irradiates the laser light is controlled so that the measurement can be completed within the decorrelation time so that the autocorrelation of the speckle pattern measured due to the body movement is not lost.

[0019] The control circuit 4 controls the first timing for irradiating laser light from the laser source 1 and the second timing for irradiating ultrasonic waves from the ultrasonic source 2. Specifically, the control circuit 4 includes a control unit 4a and a signal generator 4b. The control unit 4a sets the first timing for irradiating the first laser light and the second laser light at different exposure times in consecutive frames, at time intervals shorter than the time of one frame of the image sensor 3a, based on the frame rate of the image sensor 3a. The control unit 4a also sets the second timing so that ultrasonic waves reach the measurement position at the irradiation time of the second laser light. In this disclosure, it is explained that the control unit 4a controls the timing (second timing) for irradiating ultrasonic waves from the ultrasonic source 2, but the ultrasonic source 2 may control the timing for irradiating ultrasonic waves so that ultrasonic waves reach the measurement position at the irradiation time of the first or second laser light, instead of the control unit 4a. Here, since the laser light is pulsed laser light, it is laser light with a pulse width. Therefore, the irradiation time of the laser light is defined, for example, as the rising edge time of the pulse. Of course, the irradiation time of the laser light may also be defined as, for example, the time of the midpoint of the pulse, or the falling edge time of the pulse.

[0020] The signal generator 4b supplies a drive signal to the laser source 1 to irradiate the first laser beam and the second laser beam at a first timing set by the control unit 4a. The signal generator 4b also supplies a drive signal to the ultrasonic source 2 to irradiate ultrasonic waves at a second timing set by the control unit 4a.

[0021] The data analysis unit 5 is a calculation circuit that extracts the signal component modulated by ultrasound from the laser light detected by the camera 3. Specifically, the data analysis unit 5 extracts the signal component modulated by ultrasound (speckle pattern) based on the detection signals of the first laser light and the second laser light detected by the camera 3. Specifically, the data analysis unit 5 obtains a first speckle pattern that is not modulated by ultrasound from the detection signal of the first laser light, and a second speckle pattern that is modulated by ultrasound from the detection signal of the second laser light. The first and second speckle patterns are speckle patterns captured within a decorrelated time when no biological fluctuations occur. Therefore, the data analysis unit 5 can obtain a speckle pattern with a high signal-to-noise ratio by calculating the difference between the first and second speckle patterns.

[0022] [Optical Measurement Method] A method for obtaining a speckle pattern modulated by ultrasound using an optical measurement device 10 will be described. Figure 2 is a flowchart of the optical measurement method according to the embodiment. Figure 3 is a timing chart showing the ignition timing of the pulse laser of the optical measurement device 10 according to the embodiment.

[0023] First, the optical measurement device 10 sets a first timing for irradiating laser light from the laser source 1 and a second timing for irradiating ultrasonic waves from the ultrasonic source 2 using the control unit 4a (step S101). The first timing is the timing for igniting the pulsed laser to realize optical measurement by UOT using the camera 3 with the image sensor 3a within the decorrelation time. Specifically, as shown in Figure 3, the first timing is the timing at which the image sensor 3a switches frames, and two pulsed laser beams, the first laser beam and the second laser beam, are irradiated onto the laser source 1 at a time interval shorter than the time of one frame of the image sensor 3a. Furthermore, in the first timing, the irradiation time of the first laser beam and the irradiation time of the second laser beam correspond to different exposure times of consecutive frames, respectively. The irradiation time of the first laser beam corresponds to the exposure time of the first frame (first exposure time), and the irradiation time of the second laser beam corresponds to the exposure time of the second frame (second exposure time).

[0024] Here, the time for one frame of the image sensor 3a includes the exposure time and the readout time of the data captured during that exposure time. The period during which the frame signal is ON is the exposure time, and the period during which the frame signal is OFF is the readout time. The time interval between the irradiation of the first laser beam and the second laser beam is also called the pulse interval. This pulse interval should be less than or equal to the decorrelation time. The decorrelation time is generally known to be less than 1 ms, and it is preferable to calculate the average value of the decorrelation times of multiple subjects and set the pulse interval to, for example, 500 μs or less.

[0025] As described later, the optical measuring device 10 controls the timing of laser beam irradiation by the control unit 4a so that the timing of laser beam irradiation corresponds to the exposure times of different frames. Specifically, the control unit 4a pre-synchronizes the laser source 1, ultrasonic source 2, and camera 3 using a signal output from the signal generator 4b (for example, a synchronization signal), and controls the laser source 1 to irradiate laser beam at timings corresponding to the exposure times of different frames. Of course, in addition to synchronously controlling the laser source 1, ultrasonic source 2, and camera 3, the control unit 4a may also determine that the exposure times of the frames are different and control the timing of laser beam irradiation. For example, the control unit 4a may determine the exposure times of different frames using frame-by-frame signals output from the camera 3 (for example, a trigger signal) and control the timing of laser beam irradiation.

[0026] The period during which the first and second laser beams are lit (the period during which the laser drive signal is ON) is also called the pulse lighting time. By making the pulse lighting time shorter than the period of the ultrasound (for example, less than 1 / 8 of the period of the ultrasound), the optical measuring device 10 can measure within a time width in which the speckle fluctuations caused by the ultrasound can be considered to be stationary. Therefore, the optical measuring device 10 can obtain a direct difference between a speckle pattern that is not modulated by ultrasound and a speckle pattern modulated by ultrasound under certain conditions, enabling measurement with a high signal-to-noise ratio. However, if the pulse lighting time is made shorter than the period of ultrasound, the amount of light that can be detected by the image sensor 3a decreases. In order to obtain an amount of light that can be detected by the image sensor 3a, it is preferable to configure the first and second laser beams to include multiple pulsed laser beams.

[0027] Figure 4 is a schematic diagram showing the pulse laser illumination configuration of the optical measuring device 10 according to the embodiment. In Figure 4(a), a first laser beam containing one pulsed laser beam is irradiated in the first frame, and a second laser beam containing one pulsed laser beam is irradiated in the second frame. The time interval (pulse interval) between the first and second laser beams is 10 μs. The pulse illumination time of the first and second laser beams is shorter than the period of the ultrasound, as shown in Figure 4(a). The first and second laser beams shown in Figure 3 employ the pulse laser illumination configuration shown in Figure 4(a), but the pulse laser illumination configurations shown in Figures 4(b) and 4(c), which will be described below, may also be employed.

[0028] In Figure 4(b), a first laser beam containing four pulsed laser beams is emitted in the first frame, and a second laser beam containing four pulsed laser beams is emitted in the second frame. The time interval (pulse interval) from the first pulsed laser beam of the first laser beam to the fourth pulsed laser beam of the second laser beam is 10 μs. The pulse duration of each pulsed laser beam of the first laser beam and the pulsed laser beam of the second laser beam is shorter than the period of the ultrasound, as shown in Figure 4(b). However, the sum of the pulse durations of the four pulsed laser beams is four times the pulse duration in Figure 4(a), thus increasing the amount of light that can be detected by the image sensor 3a. However, since the four pulsed laser beams are emitted so as to be at the same peak position of each ultrasound, a speckle pattern modulated by the portion of the ultrasound at the same peak position is obtained, and optical measurement is possible without being affected by the speckle pattern modulated by the portion of the ultrasound other than that peak. Note that the number of pulsed laser beams included in the first and second laser beams is not limited to four; any number is acceptable.

[0029] In Figure 4(c), the first laser beam, containing one pulsed laser beam, is emitted in the first frame, and the second laser beam, also containing one pulsed laser beam, is emitted in the second frame. The time interval (pulse interval) between the first and second laser beams is 10 μs. However, the pulse duration for both the first and second laser beams is 4 μm, which corresponds to the length of four ultrasonic cycles, as shown in Figure 4(c). Because the pulse duration is the length of four ultrasonic cycles, the amount of light that can be detected by the image sensor 3a increases. However, since the first and second laser beams are superimposed with speckle patterns modulated by four ultrasonic cycles, a time average of the speckle pattern modulated by four ultrasonic cycles is obtained.

[0030] Returning to Figure 3, the second timing is the timing at which the ultrasonic source 2 is irradiated with ultrasound so that the ultrasound reaches the measurement position at the irradiation time of the second laser beam. Specifically, as shown in Figure 3, the second timing is the timing at which the ultrasonic source 2 irradiates pulsed ultrasound before the ultrasonic delay time from the irradiation time of the second laser beam. The ultrasonic delay time can be calculated from the distance from the ultrasonic source 2 to the measurement position. Also, since the ultrasound irradiated by the ultrasonic source 2 is pulsed ultrasound, the period during which the ultrasound is irradiated (the period during which the ultrasonic drive signal is ON) is also called the ultrasonic pulse width. Of course, the ultrasound irradiated by the ultrasonic source 2 is not limited to pulsed ultrasound, but may also be continuous ultrasound.

[0031] Furthermore, although Figure 3 explains that ultrasound is irradiated in accordance with the time when the second laser beam irradiates the measurement position, ultrasound may also be irradiated in accordance with the time when the first laser beam irradiates the measurement position. When ultrasound is irradiated in accordance with the time when the first laser beam irradiates the measurement position, the second timing is the timing at which the ultrasound source 2 is instructed to irradiate ultrasound so that the ultrasound reaches the measurement position at the irradiation time of the first laser beam. The ultrasound source 2 should irradiate ultrasound so that the ultrasound reaches the measurement position in accordance with either the irradiation time of the first laser beam or the irradiation time of the second laser beam.

[0032] Returning to Figure 2, the optical measuring device 10 supplies a laser drive signal from the signal generator 4b to the laser source 1 based on the first timing set by the control unit 4a, causing the laser source 1 to emit the first laser light (step S102).

[0033] Next, the optical measuring device 10 supplies an ultrasonic drive signal from the signal generator 4b to the ultrasonic source 2 based on the second timing set by the control unit 4a, causing the ultrasonic source 2 to emit ultrasonic waves (step S103).

[0034] Next, the optical measuring device 10 supplies a laser drive signal from the signal generator 4b to the laser source 1 based on the first timing set by the control unit 4a, causing the laser source 1 to emit a second laser beam (step S104).

[0035] Next, the optical measuring device 10 extracts the ultrasonically modulated signal component from the speckle patterns of the two detected frames in the data analysis unit 5 (step S105). The data analysis unit 5 obtains a first speckle pattern that is not ultrasonically modulated from the detection signal of the first laser beam, and a second speckle pattern that is ultrasonically modulated from the detection signal of the second laser beam. By calculating the difference between the first speckle pattern and the second speckle pattern, the data analysis unit 5 can extract a signal component (speckle pattern) with a high signal-to-noise ratio.

[0036] [Variations in lighting timing] The time for one frame of the image sensor 3a shown in Figure 3 includes the exposure time and the readout time of the data captured during that exposure time. However, the configuration of one frame of an image sensor varies depending on the type of sensor and the readout method, and is not limited to the configuration shown in Figure 3. Figure 5 is a timing chart showing a different lighting timing of the pulse laser of the optical measuring device 10 according to the embodiment. The time for one frame of the image sensor shown in Figure 5 includes the exposure time and the readout time of the data captured in the frame prior to that exposure time. In the image sensor shown in Figure 5, the data captured during the first exposure time of the first frame is read out during the readout time of the second frame. Therefore, in the second frame, the second exposure time of the second frame and the readout time for reading the data from the first frame occur at the same time.

[0037] In the first timing shown in Figure 5, two pulsed laser beams, the first laser beam and the second laser beam, are irradiated at a time interval shorter than the time of one frame of the image sensor. Also, in the first timing shown in Figure 5, the first exposure time for irradiation with the first laser beam and the second exposure time for irradiation with the second laser beam are the exposure times of different frames. The first exposure time is the exposure time of the first frame, and the second exposure time is the exposure time of the second frame.

[0038] In Figure 5, the period during which the exposure signal is ON is the exposure time, and the period during which the readout signal is ON is the readout time. In addition, in the first and second laser beams shown in Figure 5, the pulse interval is less than or equal to the decorrelation time, and the pulse illumination time is shorter than the ultrasonic period.

[0039] [Application to brain function measurement devices] The optical measurement device 10 according to this embodiment can be applied to a measurement device for measuring brain function, and can measure the subject's brain activity minimally invasively using near-infrared spectroscopy. When applying the optical measurement device 10 to a measurement device for measuring brain function, the laser source 1, ultrasound source 2, and camera 3 shown in Figure 1 are placed on the surface of the subject's head. In other words, the living body 20 shown in Figure 1 is the surface of the subject's head. As a result, the optical measurement device 10 can measure the subject's brain activity minimally invasively, and the activity state near the brain surface can be visualized in real time using functional near-infrared spectroscopy (fNIRS).

[0040] Laser source 1 is configured to irradiate the measurement position from the surface of the subject's head with the first and second laser beams shown in Figure 3. Laser source 1 includes, for example, a semiconductor laser and is configured to irradiate multiple wavelengths of laser light (for example, three wavelengths of light at 780 nm, 805 nm, and 830 nm) in the near-infrared wavelength range, which has high biopenetration potential. Camera 3 includes an image sensor such as a CCD sensor and detects the laser light from the measurement position. Camera 3 outputs an electrical signal corresponding to the detected light. Ultrasound source 2 irradiates the measurement position on the subject's head with ultrasound.

[0041] The data analysis unit 5 then analyzes the changes in hemoglobin levels (oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin) associated with brain activity based on the speckle pattern measured by the camera 3. This allows the optical measurement device 10 to minimally invasively acquire changes in hemoglobin levels associated with brain activity, i.e., changes in blood flow and the activation state of oxygen metabolism.

[0042] [Differentiation] When applying the optical measurement device 10 to a measurement system for measuring brain function, the system may be configured to irradiate the subject's head with measurement light from multiple measurement probes placed on the subject's head, and to receive the measurement light scattered within the brain of the subject's head. Figure 6 is a schematic diagram of a modified measurement system 100 using the optical measurement device according to the embodiment. Figure 7 is a block diagram of the modified measurement system 100.

[0043] As shown in Figure 6, the measurement system 100 for measuring brain function is configured as a brain function imaging device that can minimally invasively measure the brain activity of subject P and visualize the activity state near the brain surface in real time using functional near-infrared spectroscopy. The measurement system 100 also consists of, for example, a main unit 10A attached to subject P and a data analysis unit 5, which is a computer that receives and analyzes the data measured by the main unit 10A via wireless communication.

[0044] As a result, in the measurement system 100, the subject P is not confined to the vicinity of the data analysis unit 5 during brain function measurement, and the subject P can move freely while carrying the main unit 10A, making it possible to perform brain function measurement in an environment closer to everyday life.

[0045] The main unit 10A consists of a laser source 1, an ultrasonic source 2, a camera 3, and a control circuit 4. The measurement system 100 also includes a holder 6 that is attached to the head of the subject P and includes multiple mounting parts 61 for attaching a light transmitting probe 6a, a light receiving probe 6b, and an ultrasonic probe 6c. The light transmitting probe 6a, the light receiving probe 6b, and the ultrasonic probe 6c are each attached to the holder 6 on the head of the subject P and positioned on the surface of the subject P's head.

[0046] The light transmitting probe 6a is connected to the laser source 1 via an optical fiber and irradiates the subject P's head surface to the measurement position with the first and second laser beams shown in Figure 3. The light receiving probe 6b is connected to the camera 3 via an optical fiber and detects the laser beam from the measurement position. The ultrasonic probe 6c is connected to the ultrasonic source 2 via wiring and irradiates the subject P's head surface to the measurement position with ultrasound.

[0047] The laser source 1 is configured to irradiate the head of subject P with a first laser beam and a second laser beam from the light transmitting probe 6a via an optical fiber. The laser source 1 includes, for example, a semiconductor laser and is configured to irradiate multiple wavelengths of laser light in the near-infrared wavelength region, which has high biopenetration. The camera 3 includes an image sensor such as a CCD sensor and is configured to acquire and detect light incident on the light receiving probe 6b via an optical fiber. The camera 3 outputs an electrical signal corresponding to the detected light. The ultrasonic source 2 irradiates ultrasound to a measurement position on the head of subject P from the ultrasonic probe 6c.

[0048] The data analysis unit 5 is configured to analyze changes in hemoglobin levels associated with brain activity based on the speckle pattern measured by the camera 3. This allows the measurement system 100 to minimally invasively acquire changes in hemoglobin levels associated with brain activity, i.e., changes in blood flow and the activation state of oxygen metabolism. In addition, the measurement system 100 is configured to measure brain activity at each measurement point (measurement channel) composed of the light transmitting probe 6a, the light receiving probe 6b, and the ultrasound probe 6c, and to acquire a two-dimensional distribution.

[0049] In the measurement system 100, the ultrasonic probe 6c may be made into an ultrasonic phased array to enable ultrasonic steering and scanning. Also, in the measurement system 100, a bundled fiber may be used for the optical fiber connecting the light receiving probe 6b and the camera 3 for light reception.

[0050] [Aspect] Those skilled in the art will understand that the embodiments described above are specific examples of the following embodiments.

[0051] (Section 1) An optical measuring device according to one embodiment comprises a light source that irradiates pulsed laser light into a living body, an ultrasonic source that irradiates ultrasonic waves to a measurement position at a predetermined depth within the living body, an image sensor that detects the laser light that has passed through a region within the living body including the measurement position, a control circuit that controls the irradiation timing of the laser light irradiation from the light source, and a calculation circuit that extracts a signal component modulated by ultrasonic waves from the laser light detected by the image sensor. The control circuit irradiates the first laser light and the second laser light at time intervals shorter than the time of one frame of the image sensor, and controls the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of consecutive frames, respectively. The ultrasonic source irradiates ultrasonic waves so that the ultrasonic waves reach the measurement position at the irradiation time of the first laser light or the second laser light. The calculation circuit extracts a signal component modulated by ultrasonic waves based on the detection signal of the first laser light and the detection signal of the second laser light detected by the image sensor.

[0052] According to the optical measurement device described in paragraph 1, the first laser beam and the second laser beam are irradiated at time intervals shorter than the time of one frame of the image sensor, and the first exposure time for the first laser beam and the second exposure time for the second laser beam are different exposure times of consecutive frames. Therefore, it is possible to complete the measurement by the image sensor within the decorrelation time, thereby reducing the effect of decorrelation and improving measurement accuracy.

[0053] (Section 2) The optical measuring device described in paragraph 1, wherein the first laser beam and the second laser beam are composed of a plurality of pulsed laser beams.

[0054] According to the optical measuring device described in paragraph 2, multiple pulsed laser beams are irradiated onto the measurement position, thereby increasing the amount of laser light detected by the image sensor.

[0055] (Section 3) The optical measuring device described in paragraph 1 or 2, wherein the pulse illumination time for the first laser beam and the second laser beam is shorter than the period of the ultrasound.

[0056] According to the optical measuring device described in paragraph 3, by making the pulse illumination time shorter than the period of the ultrasound, the speckle fluctuations caused by the ultrasound can be considered to be stationary.

[0057] (Section 4) An optical measuring device as described in any one of paragraphs 1 to 3, wherein the light source can irradiate laser light with different peak wavelengths.

[0058] According to the optical measuring device described in paragraph 4, the light source can emit laser light with different peak wavelengths, making it possible to measure various things such as blood oxygen saturation.

[0059] (Section 5) An optical measuring device as described in any one of paragraphs 1 to 4, wherein the ultrasonic source can irradiate pulsed ultrasonic waves.

[0060] According to the optical measuring device described in Section 5, the ultrasonic source emits pulsed ultrasound, thereby reducing speckle fluctuations caused by ultrasound.

[0061] (Section 6) An optical measuring device as described in any one of paragraphs 1 to 5, wherein the ultrasonic source irradiates ultrasonic waves such that the ultrasonic waves are focused at the measurement position.

[0062] According to the optical measuring device described in Section 6, by irradiating ultrasound so that the ultrasound is focused at the measurement position, speckle fluctuations caused by ultrasound outside the measurement position can be reduced.

[0063] (Section 7) An optical measuring device as described in any one of paragraphs 1 to 6, wherein the time interval between the irradiation of the first laser beam and the second laser beam is 500 μs or less.

[0064] According to the optical measurement device described in Section 7, by setting the time interval between irradiation with the first laser beam and the second laser beam to 500 μs or less, measurement within the decorrelation time becomes easier.

[0065] (Section 8) The optical measuring device described in paragraph 4, wherein the light source can irradiate laser light of multiple wavelengths in the near-infrared wavelength range.

[0066] According to the optical measuring device described in Section 8, by irradiating the light source with laser light of multiple wavelengths in the near-infrared wavelength range, it becomes possible to measure the oxygen saturation level in the blood.

[0067] (Section 9) An optical measurement method according to one embodiment is an optical measurement method in an optical measurement device comprising: a light source that irradiates pulsed laser light into a living body; an ultrasonic source that irradiates ultrasonic waves to a measurement position at a predetermined depth in the living body; an image sensor that detects the laser light that has passed through a region in the living body including the measurement position; a control circuit that controls the irradiation timing of the irradiation of laser light from the light source; and an arithmetic circuit that extracts a signal component modulated by ultrasonic waves from the laser light detected by the image sensor. The optical measurement method includes the steps of: irradiating a first laser light and a second laser light at time intervals shorter than the time of one frame of the image sensor, and controlling the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of consecutive frames, respectively; irradiating ultrasonic waves from the ultrasonic source so that the ultrasonic waves reach the measurement position at the irradiation time of the first laser light or the second laser light; and extracting a signal component modulated by ultrasonic waves based on the detection signal of the first laser light and the detection signal of the second laser light detected by the image sensor.

[0068] According to the optical measurement method described in Section 9, the first laser beam and the second laser beam are irradiated at time intervals shorter than the time of one frame of the image sensor. Since the first exposure time for the first laser beam and the second exposure time for the second laser beam are different exposure times for consecutive frames, it becomes possible to complete the measurement by the image sensor within the decorrelation time, thereby reducing the effects of decorrelation and improving measurement accuracy.

[0069] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0070] 1 Laser source, 2 Ultrasonic source, 2a Focuser, 3 Camera, 3a Image sensor, 3b Lens, 4 Control circuit, 4a Control unit, 4b Signal generator, 5 Data analysis unit, 6 Holder, 6a Light transmitting probe, 6b Light receiving probe, 6c Ultrasonic probe, 10 Optical measuring device, 10A Main unit, 20 Biological device, 61 Mounting unit, 100 Measurement system.

Claims

1. A light source that irradiates pulsed laser light into the living body, An ultrasonic source that emits ultrasound so as to focus at a measurement position at a predetermined depth within the living body, An image sensor that detects the laser light that has passed through the region within the living body including the measurement position, A control circuit for controlling the irradiation timing of irradiating the laser light from the light source, The system includes a calculation circuit that extracts a signal component modulated by the ultrasound from the laser light detected by the image sensor, The aforementioned control circuit is The first laser beam and the second laser beam are irradiated at time intervals shorter than the time of one frame of the image sensor, and the irradiation timing is controlled so that the irradiation time of the first laser beam and the irradiation time of the second laser beam correspond to different exposure times of consecutive frames, respectively. The ultrasonic source irradiates the ultrasonic waves so that they reach the measurement position at the irradiation time of the first laser beam or the second laser beam. The aforementioned arithmetic circuit is Based on the detection signal of the first laser beam and the detection signal of the second laser beam detected by the image sensor, the signal component modulated by the ultrasound is extracted. The light source can irradiate laser light with different peak wavelengths. An optical measuring device in which the time interval between irradiating with the first laser light and the second laser light is 500 μs or less.

2. The first laser beam and the second laser beam are composed of a plurality of pulsed laser beams, The pulse illumination time for the first laser beam and the second laser beam is shorter than the period of the ultrasonic wave. The optical measuring device according to claim 1, wherein the ultrasonic source is capable of irradiating pulsed ultrasonic waves.

3. The optical measuring device according to claim 1 or claim 2, wherein the light source can irradiate laser light of multiple wavelengths in the near-infrared wavelength region.

4. An optical measurement method in an optical measurement device comprising: a light source that irradiates pulsed laser light into a living body; an ultrasonic source that irradiates ultrasonic waves so as to focus at a measurement position at a predetermined depth within the living body; an image sensor that detects the laser light that has passed through the region within the living body including the measurement position; a control circuit that controls the irradiation timing of the irradiation of the laser light from the light source; and a calculation circuit that extracts a signal component modulated by the ultrasonic waves from the laser light detected by the image sensor, wherein The steps include: irradiating the image sensor with a first laser beam and a second laser beam at time intervals shorter than the time of one frame, and controlling the irradiation timing so that the irradiation time of the first laser beam and the irradiation time of the second laser beam correspond to different exposure times of consecutive frames, respectively; The steps include: irradiating the ultrasonic source with ultrasonic waves such that the ultrasonic waves reach the measurement position at the irradiation time of the first laser beam or the second laser beam; The process includes the step of extracting a signal component modulated by ultrasound based on the detection signal of the first laser beam and the detection signal of the second laser beam detected by the image sensor, The light source can irradiate laser light with different peak wavelengths. A photometric measurement method in which the time interval between irradiating with the first laser beam and the second laser beam is 500 μs or less.

Images