Imaging device

Abstract

To provide an imaging device that can further improve an S / N ratio.SOLUTION: An imaging device 1 comprises: a photo cathode 111 having a photoelectric surface 111a; a solid-state imaging element 112 that detects photoelectron discharged from the photoelectric surface 111a and outputs a detecting signal; a vacuum enclosure 113 that holds the photo cathode 111 and the solid-state imaging element 112, in a vacuum state; and a signal processing part 15 that processes the detection signal outputted from the solid-state imaging element 112. The solid-state imaging element 112 detects photoelectron multiplied by photoelectron driving multiplication when accelerated photoelectron is made to incident. The signal processing part 15 that outputs the detection signal performs binarization processing of a detection signal of each frame on the basis of a first threshold relating to preset signal strength so that presence or absence of photon can be identified, and performs photon counting by adding a binarization signal of each frame subjected to the binarization processing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an imaging device.

Background Art

[0002] Patent Document 1 describes a method of using a filter so as not to be affected by excitation reflected light in fluorescence detection. Patent Document 2 describes a method of synchronizing the timings of excitation / reflected light generation and reading so as not to be affected by excitation reflected light in fluorescence detection.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described fluorescence detection and further in the observation of bioluminescence with a small signal amount, etc., a further improvement in the S / N ratio is required.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide an imaging device capable of further improving the S / N ratio.

Means for Solving the Problems

[0006] An imaging device according to one aspect of the present disclosure includes: [1] a photoelectric conversion unit having a photoelectric surface; a solid-state imaging device that detects photoelectrons emitted from the photoelectric surface and outputs a detection signal; a vacuum housing that holds the photoelectric conversion unit and the solid-state imaging device in a vacuum state; and a signal processing unit that processes the detection signal output from the solid-state imaging device. The solid-state imaging device detects photoelectrons multiplied by electron bombardment multiplication when accelerated photoelectrons are incident thereon, and outputs a detection signal. The signal processing unit performs binarization processing on the detection signal of each frame based on a first threshold related to a signal intensity preset so as to enable discrimination of the presence or absence of photons, and performs photon counting by adding the binarized signals of each frame after the binarization processing.

[0007] In the imaging device according to one aspect of the present disclosure, the photoelectric conversion unit and the solid-state imaging device are held in a vacuum state, and photoelectrons multiplied by electron bombardment multiplication in the solid-state imaging device are detected and a detection signal is output. In this way, by detecting photoelectrons multiplied by electron bombardment multiplication in a vacuum state, a detection signal with little multiplication fluctuation can be output. And in the imaging device according to one aspect of the present disclosure, based on a first threshold set so as to enable discrimination of the presence or absence of photons, binarization processing of the detection signal is performed, and the binarized signals of each frame are added to perform photon counting. As described above, since the detection signal has little multiplication fluctuation and the signal component without noise is appropriately multiplied, the presence or absence of photons can be appropriately discriminated by the binarization processing. And by adding the binarized signals in which the presence or absence of photons is appropriately discriminated and performing photon counting, an imaging image with an improved signal-to-noise ratio can be obtained. As described above, according to the imaging device according to one aspect of the present disclosure, a further improvement in the signal-to-noise ratio can be realized.

[0008] An imaging device according to an aspect of the present disclosure may be the imaging device described in [2] "When the number of frames to be added reaches a preset upper limit number of frames, the signal processing unit deletes the binarized signal of the oldest frame when adding the binarized signal of a new frame". According to such a configuration, it becomes possible to always acquire the signal of the latest frame (the frame of the upper limit number of frames). By this, for example, in bioluminescence observation or the like, it is possible to acquire information on the movement (movement information) of an object.

[0009] An imaging device according to an aspect of the present disclosure may be the imaging device described in [3] "For the detection signal of a predetermined excluded frame, the signal processing unit performs a moving average process or an addition process without performing the binarization process". According to such a configuration, separately from the process of adding the above-described binarized signals, for example, signals related to light of different properties can be acquired by a moving average process or an addition process. By this, it is possible to acquire both signals related to light of different properties while switching them in the same time zone.

[0010] An imaging device according to an aspect of the present disclosure may be the imaging device described in [4] "The signal processing unit multiplies a signal obtained by adding the binarized signals of each frame by a predetermined constant". For example, in bioluminescence observation or the like, since the signal amount is extremely small, the signal amount may be insufficient when generating one image by adding the binarized signals of each frame. In this regard, by multiplying a constant by the signal obtained by adding the binarized signals, the signal amount can be increased, the S / N ratio can be improved, and the contrast of the image can be generated. Note that such a process can be realized only because this method can appropriately separate the noise component and the signal component by the binarization process. That is, when the signal contains a large amount of noise components, the S / N ratio cannot be improved even when a constant is multiplied, but in this method, since the signal contains almost no noise components by the binarization process, only the signal component can be increased by multiplying a constant to improve the S / N ratio.

[0011] The imaging device according to one aspect of the present disclosure may be the imaging device according to any one of [1] to [4], wherein "the signal processing unit specifies the number of photons based on a second threshold related to a signal intensity preset so as to enable identification of the number of photons". Thus, in addition to the first threshold for identifying the presence or absence of photons, a second threshold is set so as to enable identification of the number of photons, and the number of photons is specified based on the second threshold, whereby a signal including two or more photons can be identified. Note that such processing can be realized only because of this method with little signal multiplication fluctuation.

[0012] The imaging device according to one aspect of the present disclosure may be the imaging device according to any one of [1] to [5], wherein "the signal processing unit excludes a frame with an abnormal number of photons from addition targets based on a third threshold related to a signal intensity preset so as to enable identification of an abnormal number of photons". For example, in bioluminescence or the like, since the amount of light emission is extremely small, it is almost impossible for a signal with a large number of photons (for example, three or more photons) to enter one frame. When such a large number of photons are detected, it is highly likely that they are abnormal values such as cosmic ray noise. By setting the third threshold so as not to count values above a specific signal intensity as abnormal values, the influence of abnormal noise can be canceled. Note that such processing can be realized only because of this method with little signal multiplication fluctuation.

Advantages of the Invention

[0013] According to the imaging device according to the present disclosure, a further improvement in the S / N ratio can be realized.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] [First Embodiment] Hereinafter, the first embodiment of the present invention will be described in detail with reference to the drawings. In the respective figures, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted.

[0016] FIG. 1 is a diagram schematically showing the configuration of an imaging apparatus 1 according to the first embodiment. The imaging apparatus 1 is, for example, an apparatus for observing bioluminescence (bioluminescence) with an extremely small signal amount. As luminescence phenomena, in addition to bioluminescence, there are fluorescence, chemiluminescence, and the like. Bioluminescence is a phenomenon in which a living organism generates and emits light. Fluorescence is a phenomenon in which a living organism that has absorbed energy by irradiation with excitation light and has become in an excited state emits light. Chemiluminescence is a phenomenon in which a living organism that has become in an excited state by a chemical reaction emits light. For example, in fluorescence observation, while increasing the excitation intensity increases the fluorescence intensity, damage to the living organism (such as cells) and autofluorescence increase, which may cause a problem of a decrease in quantification in the observation. In this regard, in bioluminescence observation, since excitation light is not required and light damage to the living organism (cells) does not occur, long-time imaging is possible. Also, in bioluminescence observation, since background light due to autofluorescence is suppressed, only the signal value can be stably acquired and quantification in the observation can be ensured. On the other hand, in bioluminescence observation, the amount of light emission (signal amount) is extremely weak, and it may be difficult to improve the S / N ratio. The imaging apparatus 1 according to the present embodiment employs a method for improving the S / N ratio even in such weak bioluminescence observation (details will be described later).

[0017] As shown in FIG. 1, the imaging device 1 includes an objective lens 2, a filter 3, an electron - implanted camera 10, a high - voltage controller 20, a PC (personal computer) 30, and a monitor 40. Hereinafter, the imaging device 1 will be described assuming that it observes bioluminescence from the cell S.

[0018] The objective lens 2 is a lens that condenses the bioluminescence from the cell S in the direction of the electron - implanted imaging sensor 11 of the electron - implanted camera 10. The bioluminescence condensed by the objective lens 2 enters the electron - implanted imaging sensor 11 of the electron - implanted camera 10 through the filter 3.

[0019] The electron - implanted camera 10 includes an electron - implanted imaging sensor 11, a drive unit 12, a control unit 13, a high - voltage power supply 14, a signal processing unit 15, and an interface 16.

[0020] As shown in FIG. 2, the electron - implanted imaging sensor 11 includes a photocathode 111 (photoelectric conversion unit), a solid - state imaging device 112 having an electron - implanted multiplication function, and a vacuum housing 113. In this embodiment, the solid - state imaging device 112 is an EB - CMOS (Electron Bombarded - Complementary Metal - Oxide - Semiconductor). The vacuum housing 113 is a housing that holds the photocathode 111 and the solid - state imaging device 112 in a vacuum state. The vacuum housing 113 has an incident window 113a through which the light condensed by the objective lens 2 enters. The light incident from the incident window 113a reaches the photoelectric surface 111a of the photocathode 111.

[0021] The photocathode 111 is a photoelectric conversion unit having a photoelectric surface 111a. The photoelectric surface 111a converts incident light into photoelectrons. The photocathode 111 is made, for example, in the form of a semiconductor layer and may be a crystalline photoelectric surface having a single crystal structure (e.g., a III-V semiconductor such as GaAs, or a II-VI semiconductor such as CdTe). Also, the photocathode 111 may be an alkali photoelectric surface having a polycrystalline structure such as SbK2Cs, SbRb2Cs, SbCs3, SbNa3, SbNaKRbCs, SbNaKCs, SbNa2KCs, etc. The photocathode 111 is electrically connected to the electrode 118, and a predetermined potential is applied to the photocathode 111 (photoelectric surface 111a) through the electrode 118. Photoelectrons emitted from the photoelectric surface 111a of the photocathode 111 are radiated into a vacuum and detected by the solid-state imaging device 112.

[0022] The solid-state imaging device 112 is an imaging device that detects photoelectrons emitted from the photoelectric surface 111a and outputs a detection signal. The solid-state imaging device 112 detects photoelectrons multiplied by electron bombardment multiplication when photoelectrons accelerated by having energy corresponding to the potential difference between the photocathode 111 and the solid-state imaging device are incident, and outputs a detection signal. The solid-state imaging device 112 is electrically connected to the lead pin 120 through the bonding wire 119. The solid-state imaging device 112 is provided so as to face the photocathode 111, and is provided at the end opposite to the end where the photocathode 111 is provided within the vacuum housing 113. The solid-state imaging device 112 may be, for example, a back-side illumination type (BSI: Back Side Illumination) CMOS. The detection signal output from the solid-state imaging device 112 is input to the signal processing unit 15 provided outside the vacuum housing 113. The voltage applied to the solid-state imaging device 112 and the gain obtained as the detection signal are generally in a proportional relationship. By adjusting the potential difference between the photoelectric surface 111a of the photocathode 111 and the solid-state imaging device 112, a desired gain can be obtained. Note that the EB-CMOS (solid-state imaging device 112) may be replaced with an EB-CCD (Electron-Bombarded Charge-Coupled Device).

[0023] FIG. 3(a) is a graph showing the signal detected in sCMOS (scientific CMOS), and FIG. 3(b) is a graph showing the signal detected in EB-CMOS. The sCMOS in FIG. 3(a) is illustrated as a configuration for comparison with the electron-impact camera 10. In FIGS. 3(a) and (b), the horizontal axis represents time, and the vertical axis represents the signal amount. In FIGS. 3(a) and (b), the portion where the signal amount is small indicates noise such as read noise and dark current generated within the solid-state imaging device 112. The sCMOS shown in FIG. 3(a) reduces noise by suppressing dark current through cooling and reducing read noise, thereby improving the S / N ratio. On the other hand, sCMOS does not have a multiplication function and cannot increase the signal component. In this regard, as shown in FIG. 3(b), in EB-CMOS, the S / N ratio is improved by multiplying only the signal component that does not include noise (read noise and dark current noise) derived from the driving of the solid-state imaging device 112 by the above-described gain. Such EB-CMOS can achieve a higher S / N ratio than sCMOS in measurements under ultra-low illuminance (for example, in the photon counting region where the average number of photons detected by one pixel per frame is less than a single photon).

[0024] Returning to FIG. 1, the driving unit 12 is a circuit for driving the electron-impact imaging sensor 11. The control unit 13 is configured to change various settings in the electron-impact imaging sensor 11, and changes the number of pixels and the field of view, for example, by processes such as binning and sub-array. The high-voltage power supply 14 is a power supply for applying voltage to the photocathode 111a and the solid-state imaging device 112 for generating an electron-impact multiplication gain. The voltage of the high-voltage power supply 14 is adjusted by the high-voltage controller 20.

[0025] The signal processing unit 15 processes the detection signal output from the solid-state imaging device 112. The signal processing unit 15 performs binarization processing on the detection signal of each frame based on a first threshold value related to a signal intensity preset so as to enable identification of the presence or absence of photons, and performs photon counting by adding the binarized signals of each frame after the binarization processing.

[0026] As shown in FIG. 1, the signal processing unit 15 outputs a Live signal, an output of the binarized signal after the binarization processing, and an output of a photon counting signal obtained by adding the binarized signals. The Live signal is a raw signal that has not been subjected to any special processing on the detection signal. Such a Live signal is used, for example, when acquiring a moving average image (rolling average image).

[0027] The binarization processing will be described with reference to FIGS. 4 and 5. The signal processing unit 15 preliminarily has a luminance value (signal intensity) at the time of photon incidence as a first threshold value so that the presence or absence of photons can be identified. The first threshold value is set to a luminance value that cannot be reached in the case of "no photons" (only noise) and is assumed to always be reached in the case of "photons present". By performing binarization depending on whether or not the first threshold value is exceeded, the presence or absence of photons can be appropriately identified for each frame. As shown in the lowermost row of FIG. 4, for a frame in which the signal intensity is greater than the first threshold value, the signal processing unit 15 determines that "photons are present" and sets it to "1", and for a frame in which the signal intensity is less than the first threshold value, it determines that "photons are absent" and sets it to "0". As shown in FIG. 4, although the signal includes dark current and readout noise, since the first threshold value is set to a luminance value that cannot be reached in the case of only noise of "no photons" as described above, the presence or absence of photons can be appropriately identified even when noise is taken into account.

[0028] FIG. 4 is a diagram for explaining the characteristics of the electron-multiplied camera 10 as compared with an sCMOS camera and a cooled CCD camera. Since the sCMOS camera does not have a multiplication function, it cannot multiply only the signal components, and thus cannot identify the presence or absence of photons by the first threshold value described above. Also, for the cooled CCD camera, since it cannot increase only the signal components compared to noise such as read noise, it cannot identify the presence or absence of photons by the first threshold value described above. In contrast, in the electron-multiplied camera 10 according to the present embodiment, since only the signal components are multiplied, the presence or absence of photons can be appropriately identified based on the first threshold value.

[0029] FIG. 5 is a diagram for explaining the characteristics of the electron-multiplied camera 10 as compared with an imaging device in which an image intensifier is combined with an imaging element (CMOS camera). As a sensor having a signal multiplication function, there is an image intensifier, and a configuration of an imaging device in which an optical signal multiplied and output by the image intensifier is imaged by a CMOS camera can be considered. However, as shown in the upper diagram of FIG. 5, the optical signal multiplied by the image intensifier has a large fluctuation, and there are cases where the presence or absence of photons cannot be appropriately identified (cannot be appropriately binarized) by the first threshold value when imaging by the CMOS camera. If appropriate binarization cannot be performed, there is a risk that an image with a low S / N and a granular appearance will be obtained. In this regard, as shown in the lower diagram of FIG. 5, in the electron-multiplied camera 10, since the photoelectrons multiplied by electron multiplication in a vacuum state are detected, there is little multiplication fluctuation in the detection signal, and the presence or absence of photons can be appropriately identified by the first threshold value. Note that in the drawings after FIG. 5 (FIGS. 5, 7, 8), the dark current and the read noise are shown together without distinction.

[0030] FIG. 6(a) is a diagram showing an example of a Live image, FIG. 6(b) is a diagram showing an example of a moving average image, and FIG. 6(c) is a diagram showing an example of a photon counting image. The images shown in FIGS. 6(a) to 6(c) are images acquired by the electron bombardment type camera 10, and show an example of an image acquired at an exposure time of 20 msec and 500 V. The Live image shown in FIG. 6(a) is an image acquired from a Live signal (raw signal) for one frame. Since the illumination is low, almost nothing that can be associated with the signal is seen. When such images are added, the S / N ratio becomes extremely poor.

[0031] The moving average image shown in FIG. 6(b) is an image acquired from the Live signal. As described above, since an appropriate image cannot be acquired with the Live signal, moving average can be adopted as a method for improving the S / N ratio. However, under extremely low illumination such as bioluminescence, even if about 15,000 frames are added, noise components will also be acquired proportionally, so the S / N ratio cannot be significantly improved as shown in FIG. 6(b).

[0032] On the other hand, the photon counting image shown in FIG. 6(c) is acquired by canceling noise components (dark current, readout noise) and adding signal components. Therefore, for example, by integrating signals for 15,000 frames, only the signal component (S) is added, and the S / N ratio can be made extremely high.

[0033] Returning to FIG. 1, the signal processing unit 15 may multiply a signal obtained by adding the binarized signals of each frame by a predetermined constant. As described above, the binarized signals subjected to the binarization process are added for an arbitrary number of frames to obtain one image. At this time, the darker the light emission from the cell S, which is a bioluminescence sample, the less the signal amount will be when finally forming an image. Therefore, as a method for generating the contrast of the image, the signal processing unit 15 multiplies the final signal obtained by adding the binarized signals by a predetermined constant. As described above, since the noise component and the signal component are appropriately separated by the binarization process, by multiplying the signal obtained by adding the binarized signals by a predetermined constant, it is possible to increase almost only the signal component. As a result, the S / N ratio in the final image can be improved. Note that the signal processing unit 15 may multiply a signal at an arbitrary timing by a predetermined constant, not only the final signal obtained by adding the binarized signals. For example, in the case of bioluminescence, when the light emission is extremely weak, in order to confirm at an arbitrary stage whether an appropriate signal is detected when binarizing such a weak signal, it is preferable to multiply the signal at an arbitrary timing by a constant and confirm. From this, the signal processing unit 15 may multiply a signal at an arbitrary timing by a predetermined constant.

[0034] In addition, the signal processing unit 15 may specify the number of photons based on a second threshold related to the signal intensity preset so as to enable identification of the number of photons. In the photon counting using the first threshold described above, the presence or absence of photons is identified. Such a first threshold can be said to be a threshold for canceling noise components. In addition to this, by providing a second threshold which is a threshold for identifying the number of photons, it becomes possible to distinguish between one photon and two photons. In the case of bioluminescence, since it is unlikely that three or more photons enter one frame, the second threshold is, for example, a luminance value for distinguishing between one photon and two photons. Therefore, as shown in FIG. 7, the second threshold is set to a luminance value that cannot be reached in the case of "one photon" and is assumed to always be reached in the case of "two photons". Also, the second threshold is set to a luminance value larger than the first threshold. Whether the number of photons is "1" or "2" can be identified depending on whether or not the second threshold is exceeded.

[0035] In addition, the signal processing unit 15 may exclude frames with an abnormal number of photons from the addition target based on a third threshold related to the signal intensity preset so as to enable identification of an abnormal number of photons. As described above, in the case of bioluminescence, it is unlikely that three or more photons enter one frame, and when three or more photons are detected, it is extremely likely that they are abnormal values such as cosmic ray noise. Therefore, as shown in FIG. 8, by setting a luminance value that cannot be reached when it is less than "three photons" and is assumed to always be reached when it is "three photons" or more as the third threshold, frames (noise) with an abnormal number of photons can be appropriately identified. Then, the frames with the abnormal number of photons can be appropriately excluded from the addition target. Here, the frames to be added are the frames used to form an image.

[0036] The signal processing unit 15 outputs the Live signal, the binarized signal, and the photon counting signal obtained by adding the binarized signals of each frame to the PC 30 via the interface 16. The interface 16 is a device for connecting the signal output from the signal processing unit 15 to the subsequent device (here, the PC 30).

[0037] The PC 30 includes an image input board 31 and software 32. The image input board 31 has a function of imaging the signal from the signal processing unit 15. An example of the result of imaging each signal is as shown in FIGS. 6(a) to 6(c) for example. The software 32 performs various processes related to the image. The software 32 outputs the image to the monitor 40. The monitor 40 is a display device for displaying the image.

[0038] (Operational effects) Next, the operational effects of the imaging device 1 according to the present embodiment will be described.

[0039] The imaging device 1 according to the present embodiment includes a photocathode 111 having a photoelectric surface 111a, a solid-state imaging device 112 that detects photoelectrons emitted from the photoelectric surface 111a and outputs a detection signal, a vacuum housing 113 that holds the photocathode 111 and the solid-state imaging device 112 in a vacuum state, and a signal processing unit 15 that processes the detection signal output from the solid-state imaging device 112. The solid-state imaging device 112 detects photoelectrons multiplied by electron bombardment multiplication when accelerated photoelectrons are incident, and outputs a detection signal. The signal processing unit 15 performs binarization processing on the detection signal of each frame based on a first threshold related to a signal intensity set in advance so that the presence or absence of photons can be identified, and performs photon counting by adding the binarized signals of each frame after the binarization processing.

[0040] In the imaging device 1 according to the present embodiment, the photocathode 111 and the solid-state imaging device 112 are held in a vacuum state, and in the solid-state imaging device 112, photoelectrons multiplied by electron bombardment multiplication are detected and a detection signal is output. In this way, by detecting photoelectrons multiplied by electron bombardment multiplication in a vacuum state, a detection signal with little multiplication fluctuation can be output. And in the imaging device 1 according to the present embodiment, based on a first threshold value set so as to enable identification of the presence or absence of photons, binarization processing of the detection signal is performed, and the binarization signals of each frame are added to perform photon counting. As described above, for the detection signal, there is little multiplication fluctuation and the signal component without noise is appropriately multiplied, so the presence or absence of photons can be appropriately identified by the binarization processing. Then, by adding the binarization signals in which the presence or absence of photons is appropriately identified and performing photon counting, an imaging image with an improved S / N ratio can be obtained. As described above, according to the imaging device 1 according to the present embodiment, a further improvement in the S / N ratio can be realized.

[0041] The signal processing unit 15 may multiply a signal obtained by adding the binarization signals of each frame by a predetermined constant. For example, in bioluminescence observation or the like, since the signal amount is extremely small, the signal amount may be insufficient when an image is generated by adding the binarization signals of each frame. In this regard, by multiplying a constant by the signal obtained by adding the binarization signals, the signal amount can be increased, the S / N ratio can be improved, and the contrast of the image can be generated. Note that such processing can be realized only by this method in which the noise component and the signal component can be appropriately separated by the binarization processing. That is, when the signal contains a large amount of noise components, the S / N ratio cannot be improved even when a constant is multiplied, but in this method, since the signal contains almost no noise components by the binarization processing, only the signal component can be increased by multiplying a constant and the S / N ratio can be improved.

[0042] The signal processing unit 15 may specify the number of photons based on a second threshold value related to the signal intensity preset so as to enable identification of the number of photons. Thus, in addition to the first threshold value for identifying the presence or absence of photons, a second threshold value is set so as to enable identification of the number of photons, and by specifying the number of photons based on the second threshold value, signals including two or more photons can be identified. Note that such processing can be realized only because this method has little signal multiplication fluctuation.

[0043] The signal processing unit 15 may exclude frames with an abnormal number of photons from the addition target based on a third threshold value related to the signal intensity preset so as to enable identification of an abnormal number of photons. For example, in bioluminescence or the like, since the amount of light emission is extremely small, it is almost impossible for a signal with a large number of photons (for example, three or more photons) to enter one frame. When such a large number of photons are detected, there is a high possibility that they are abnormal values such as cosmic ray noise. By setting the third threshold value so as not to count values above a certain specific signal intensity as abnormal values, the influence of abnormal noise can be canceled. Note that such processing can be realized only because this method has little signal multiplication fluctuation.

[0044] As described above, the imaging device 1 according to the first embodiment has been described, but the aspect of the imaging device according to the first embodiment is not limited to the above. FIGS. 9 and 10 are diagrams schematically showing the configuration of an imaging device according to a modification.

[0045] The imaging device 1A shown in Fig. 9 includes a first signal processing unit 15A and a second signal processing unit 15B as components corresponding to the signal processing unit described above. The first signal processing unit 15A is provided inside the electronic drive camera 10. The second signal processing unit 15B is provided outside the electronic drive camera 10. The first signal processing unit 15A performs binarization processing on the detection signal output from the electronic drive imaging sensor 11 based on a first threshold value, and outputs a binarized signal after the binarization processing. The second signal processing unit 15B acquires the binarized signal output from the first signal processing unit 15A via the interface 16, performs photon counting by adding the binarized signals of each frame, and outputs a photon counting signal. In this way, the signal processing unit may be divided into a component that performs binarization processing (the first signal processing unit 15A) and a component that performs addition processing (the second signal processing unit 15B).

[0046] The imaging device 1B shown in Fig. 10 includes a first signal processing unit 15A inside the electronic drive camera 10 and a second signal processing unit 15B outside the electronic drive camera 10 as components corresponding to the signal processing unit in the same manner as the imaging device 1A. In the imaging device 1B, the first signal processing unit 15A only outputs the detection signal (Live signal) to the subsequent stage, and the second signal processing unit 15B performs binarization processing and addition processing. In this way, the functions borne by the two signal processing units may be appropriately selected.

[0047] [Second Embodiment] Next, the second embodiment of the present disclosure will be described with reference to Figs. 11 to 13. In the second embodiment, the points different from the first embodiment will be mainly described, and the descriptions overlapping with the first embodiment will be omitted.

[0048] The imaging device 101 according to the second embodiment includes a signal processing unit 115 as a signal processing unit. The signal processing unit 115 is configured to be capable of executing rolling photon counting in addition to the same processing as the signal processing unit 15 according to the first embodiment. Hereinafter, rolling photon counting will be described.

[0049] In rolling photon counting, when the number of frames to be added reaches the preset upper limit number of frames, the signal processing unit 115 deletes the binarized signal of the oldest frame when adding the binarized signal of a new frame. For example, if 3000 frames are required to obtain sufficient signals (upper limit number of frames: 3000), when acquiring and adding the information of the 3001st frame, the information of the 1st frame is deleted, and when acquiring and adding the information of the 3002nd frame, the information of the 2nd frame is deleted. By acquiring signals in this way, it is always possible to acquire and add signals for the latest 3000 frames.

[0050] Fig. 12 shows an example in which the time for one image (i.e., the upper limit number of frames) is temporarily set to 4, and an example is shown in which the binarized signal of the oldest frame is deleted each time the binarized signal of the latest frame is acquired. In this way, by always acquiring the binarized signals for the latest upper limit number of frames, it is possible to obtain information on the movement (movement information) of an object, for example, in the case of bioluminescence observation.

[0051] Fig. 13(a) is an image of acquiring movement information by the imaging device 101, and Fig. 13(b) is an image of acquiring movement information by a cooled CCD camera. As shown in Fig. 13(b), in the cooled CCD camera, long-time exposure is required to add signals, and an image is acquired in only one frame at a specific moment (for example, a moment at 5-minute intervals). Therefore, an image capturing the movement of cell S, for example, becomes a discontinuous and jumping image. On the other hand, as shown in Fig. 13(a), in the imaging device 101, since the latest image can be acquired at an arbitrary timing of the user, the movement of cell S over time can be captured.

[0052] (Function and effect) Next, the function and effect of the imaging device 101 according to this embodiment will be described.

[0053] In the imaging device 101, when the number of frames to be added reaches the preset upper limit number of frames, the signal processing unit 115 may delete the binarization signal of the oldest frame when adding the binarization signal of a new frame. According to such a configuration, it is possible to always acquire the signal of the latest frame (the frame of the upper limit number of frames). By this, for example, in bioluminescence observation or the like, by saving an image at an arbitrary timing of the user, it is possible to acquire information (movement information) on the movement of the object.

[0054] As described above, the imaging device 101 according to the second embodiment has been described. However, the aspect of the imaging device according to the second embodiment is not limited to the above. FIGS. 14 to 17 are diagrams for explaining an imaging device according to a modification.

[0055] As shown in FIG. 14, in rolling photon counting, instead of saving one frame at a time, it may be saved in a lump for a predetermined number of frames. That is, for example, when the number of frames required for image acquisition is 3000, the binarized and added images may be saved every 1000 frames, and the information for 3000 required for image acquisition may be collected. In FIG. 14, the frames marked as addition I to addition IV are each a frame group of 1000 frames, and the images may be saved in units of these frame groups. When addition and deletion are repeated in rolling photon counting, for example, the 1000 frames of addition I may be deleted and the new 1000 frames of addition IV may be added and saved. According to such a method, compared with the case of saving one frame at a time, since the number of images to be saved becomes 1 / 1000, the data amount can be made 1 / 1000.

[0056] The imaging device 101A shown in FIG. 15 includes a first signal processing unit 115A and a second signal processing unit 115B as components corresponding to the signal processing unit described above. The first signal processing unit 115A is provided inside the electronic drive camera 10. The second signal processing unit 115B is provided outside the electronic drive camera 10. The first signal processing unit 115A performs binarization processing on the detection signal output from the electronic drive imaging sensor 11 based on a first threshold value, and outputs a binarized signal after the binarization processing. Further, the first signal processing unit 115A performs photon counting by adding the binarized signals of each frame, and outputs a photon counting signal. The second signal processing unit 115B performs rolling photon counting in which, when the number of frames to be added reaches a preset upper limit number of frames, the binarized signal of the oldest frame is deleted when adding the binarized signal of a new frame. In this way, the signal processing unit may be divided into a configuration (the first signal processing unit 115A) that performs binarization processing and addition processing and a configuration (the second signal processing unit 115B) that performs rolling photon counting processing.

[0057] The imaging device 101B shown in FIG. 16 includes a first signal processing unit 115A and a second signal processing unit 115B as components corresponding to the signal processing unit described above. The first signal processing unit 115A is provided inside the electronic drive camera 10. The second signal processing unit 115B is provided outside the electronic drive camera 10. The first signal processing unit 15A performs binarization processing on the detection signal output from the electronic drive imaging sensor 11 based on a first threshold value, and outputs a binarized signal after the binarization processing. The second signal processing unit 115B acquires the binarized signal output from the first signal processing unit 15A via the interface 16, performs photon counting by adding the binarized signals of each frame, and outputs a photon counting signal. Further, the second signal processing unit 115B performs rolling photon counting in which, when the number of frames to be added reaches a preset upper limit number of frames, the binarized signal of the oldest frame is deleted when adding the binarized signal of a new frame. In this way, the functions borne by the two signal processing units may be appropriately selected.

[0058] The imaging device 101C shown in FIG. 17 includes, as a configuration corresponding to the signal processing unit, a first signal processing unit 115A within the electronic flash camera 10 and a second signal processing unit 115B outside the electronic flash camera 10. In the imaging device 101C, the first signal processing unit 115A only outputs the detection signal (Live signal) to the subsequent stage, and the second signal processing unit 15B performs binarization processing, addition processing, and photon counting processing. In this way, the functions borne by the two signal processing units may be appropriately selected.

[0059] [Third Embodiment] Next, the third embodiment of the present disclosure will be described with reference to FIGS. 18 to 20. In the third embodiment, the points different from the first and second embodiments will be mainly described, and the descriptions overlapping with the first and second embodiments will be omitted.

[0060] In the imaging device according to the third embodiment, imaging is performed while switching between the above-described rolling photon counting and moving average processing or addition processing at an arbitrary time. When performing bioluminescence observation, the signal processing unit of the imaging device may perform moving average processing or addition processing on the detection signals of predetermined exclusion frames without performing binarization processing, and thus perform fluorescence observation. In this case, the signal processing unit does not add the signals for fluorescence observation to the signals for bioluminescence observation. The signal processing unit adds the bioluminescence signals after fluorescence acquisition while holding the bioluminescence signals before fluorescence acquisition in the memory, thereby storing the bioluminescence image immediately after fluorescence acquisition.

[0061] FIG. 18 is a diagram schematically showing the configuration for fluorescence observation among the imaging devices according to the third embodiment. The imaging device according to the third embodiment includes, in addition to the configurations provided in the above-described imaging device 1 and imaging device 101, the configuration for fluorescence observation shown in FIG. 18. In the example shown in FIG. 18, as the configuration for fluorescence observation, a dichroic mirror 501 and an excitation filter 502 are provided.

[0062] The excitation filter 502 is an optical element for extracting light of a wavelength necessary for exciting the fluorescent substance from an excitation light source (not shown, for example, a mercury lamp). The excitation filter 502 may be a band-pass filter that transmits only light of a specific wavelength and does not transmit other light. The dichroic mirror 501 is an optical element for separating the excitation light and the fluorescence. The dichroic mirror 501 reflects the light transmitted through the excitation filter 502 and guides it in the direction of the cell S, and transmits the fluorescence emitted from the cell S and guides it in the direction of the filter 3.

[0063] FIG. 19 is a diagram for explaining the switching between the rolling photon counting method and the rolling average method. In the example shown in FIG. 19, in rolling photon counting, the signals for the latest 4 frames are added. However, for a predetermined exclusion frame in which fluorescence observation is performed without photon counting, moving average processing or addition processing is performed instead of binarization processing for fluorescence observation, and it is excluded from the addition target of rolling photon counting. Then, in rolling photon counting, the signal of bioluminescence after fluorescence acquisition is added while holding the signal of bioluminescence before fluorescence acquisition in the memory, and an image of bioluminescence is acquired immediately after fluorescence acquisition.

[0064] FIG. 20(a) is a diagram showing the observation result of bioluminescence, and FIG. 20(b) is a diagram showing the observation result of fluorescence. As shown in FIGS. 20(a) and (b), the luminance value of fluorescence is much higher than that of bioluminescence. Therefore, for example, if simultaneous observation is performed with a CCD or the like, the image of the emission will be blurred and it will not be possible to detect it appropriately. In this regard, by acquiring only fluorescence observation by moving average processing or addition processing separately from rolling photon counting, it is possible to acquire both images of bioluminescence and fluorescence while switching in the same time zone.

[0065] The present disclosure is not limited to the above-described embodiments. For example, with regard to the processing related to image generation, it may be completed (fully implemented) in the signal processing unit. In this case, the configurations such as the above-described PC 30 and monitor 40 may not be provided. Further, the generated image does not necessarily have to be displayed on the monitor in real time, and may be recorded by being output to a USB or the like. With such a configuration, it is possible to appropriately record the image generated in a configuration in which the above-described PC 30 and monitor 40 are not provided. Further, various signal processes such as binarization processing do not have to be performed inside the above-described electronic driving type camera 10, and may be performed by software built in a PC, for example.

Description of Reference Numerals

[0066] 1, 1A, 1B, 101, 101A, 101B, 101C... imaging devices, 15, 15A, 15B, 115, 115A, 115B... signal processing units, 111... photocathode (photoelectric conversion unit), 111a... photoelectric surface, 112... solid-state imaging device, 113... vacuum housing.

Claims

1. A photoelectric conversion unit having a photoelectric surface, a solid-state imaging device that detects photoelectrons emitted from the photoelectric surface and outputs a detection signal, a vacuum housing that holds the photoelectric conversion unit and the solid-state imaging device in a vacuum state, and a signal processing unit that processes the detection signal output from the solid-state imaging device. The solid-state imaging device detects photoelectrons multiplied by electron bombardment multiplication when the accelerated photoelectrons are incident, and outputs the detection signal. The signal processing unit performs binarization processing on the detection signal of each frame based on a first threshold value related to a signal intensity preset so as to enable identification of the presence or absence of photons, and performs photon counting by adding the binarized signals of each frame after the binarization processing. An imaging device.

2. The imaging device according to claim 1, wherein when the number of frames to be added reaches a preset upper limit number of frames, the signal processing unit deletes the binarized signal of the oldest frame when adding the binarized signal of a new frame.

3. The imaging device according to claim 2, wherein the signal processing unit performs moving average processing or addition processing on the detection signal of a predetermined excluded frame without performing the binarization processing.

4. The imaging device according to claim 1, wherein the signal processing unit multiplies a signal obtained by adding the binarized signals of each frame by a predetermined constant.

5. The imaging device according to claim 1, wherein the signal processing unit specifies the number of photons based on a second threshold value related to a signal intensity preset so as to enable identification of the number of photons.

6. The imaging device according to claim 1, wherein the signal processing unit excludes frames with an abnormal number of photons from the addition target based on a third threshold value related to a signal intensity preset so as to enable identification of an abnormal number of photons.

Images