Radiation imaging device and radiation imaging system

Abstract

The objective is to improve the accuracy of acquiring the energy of radiation photons in photon-counting type sensors. [Solution] The disclosed radiation imaging apparatus comprises a scintillator that converts radiation into visible light, a photoelectric conversion element that converts the visible light into a first electrical signal, a signal processing unit that includes a first counter circuit for counting the first electrical signal, and a second counter circuit for counting a second electrical signal output from the first counter circuit, wherein the second counter circuit includes a plurality of counter circuits and is configured to count the second electrical signal output to a counter circuit selected from the plurality of counter circuits using the count value from the first counter circuit.

Description

Technical Field

[0001] The disclosed technology relates to a radiation imaging apparatus and a radiation imaging system.

Background Art

[0002] As a radiation imaging apparatus that captures a radiation image using radiation (such as X-rays) transmitted through a subject, an FPD (Flat Panel Detector) capable of displaying a radiation image in real time has been proposed. The FPD arranges a minute radiation detector, which is formed by laminating a solid-state photodetector in which an amorphous semiconductor is sandwiched between a transparent conductive film and a conductive film and a scintillator that converts radiation into visible light, in a matrix pattern on a quartz glass substrate. Also known are those using a photodetector such as a CCD (Charge-Coupled Device), CMOS (Complementary Metal-Oxide Semiconductor), APD (Avalanche PhotoDiode), or SPAD (Single-Photon Avalanche Diode) as the solid-state photodetector.

[0003] [[ID=I6]]There are an integrating type sensor and a photon counting type sensor as the FPD. The integrating type sensor measures the total amount of charge generated by the incidence of radiation. In contrast, the photon counting type sensor discriminates the energy (wavelength) of the incident radiation and counts the number of detections of radiation for each of a plurality of energy levels. That is, since the photon counting type sensor has an energy resolution, it can improve the diagnostic ability compared to the integrating type sensor.

[0004] Photon counting sensors can be further divided into direct and indirect types. Direct sensors count the number of radiation detections by directly detecting the energy of the radiation using CdTe. Indirect sensors count the number of radiation detections by indirectly detecting the energy of the radiation based on the visible light generated in a scintillator due to the incidence of radiation. Patent Document 1 considers the electrical signal of visible light generated in a scintillator by radiation photons as a single analog signal. The peak height (peak value) of this signal changes depending on the energy of the radiation photons. At this time, the energy can be estimated by thresholding the peak value in the waveform, and the radiation photons can be counted in a counter circuit. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-86901 [Overview of the project] [Problems that the invention aims to solve]

[0006] In this case, such analog electrical signals contain noise due to dark currents, which can reduce the accuracy of estimating the energy of radiation photons.

[0007] Therefore, the purpose of the disclosed technology is to improve the accuracy of acquiring the energy of radiation photons in photon counting type sensors. [Means for solving the problem]

[0008] The disclosed radiographic imaging device is, A scintillator that converts radiation into visible light, A photoelectric conversion element that converts the visible light into a first electrical signal, The signal processing unit includes a first counter circuit for counting the first electrical signal and a second counter circuit for counting the second electrical signal output from the first counter circuit. The second counter circuit includes a plurality of counter circuits and is configured to count the second electrical signal output to a counter circuit selected from among the plurality of counter circuits using the count value from the first counter circuit. [Effects of the Invention]

[0009] According to the disclosed technology, the accuracy of acquiring the energy of radiation photons in a photon counting type sensor can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] Configuration example of the radiation imaging system of the first embodiment and schematic diagram of the radiation detection panel [Figure 2] Schematic diagram of the photoelectric conversion substrate of the radiation detection panel in the first embodiment. [Figure 3] Schematic diagram of the signal processing board of the radiation detection panel of the first embodiment. [Figure 4] Example configuration of a sub-signal processing circuit for a radiation detection panel in the first embodiment [Figure 5] Example of signal processing circuit configuration for a radiation detection panel of the first embodiment [Figure 6] Schematic diagram showing the operation of the pixel circuit of the radiation detection panel in the first embodiment. [Figure 7] Schematic diagram showing the operation of the multi-stage counter circuit of the radiation detection panel in the first embodiment. [Figure 8] Plan view of the radiation detection panel of the first embodiment [Figure 9] Diagonal cross-sectional view of the radiation detection panel of the first embodiment. [Figure 10] Schematic diagram of the radiation detection panel of the second embodiment [Figure 11] Schematic diagram of the photoelectric conversion substrate of the radiation detection panel in the second embodiment. [Figure 12] Schematic diagram of the signal processing board of the radiation detection panel according to the second embodiment [Figure 13] Example of the signal processing circuit configuration of the radiation detection panel according to the second embodiment **Mode for Carrying Out the Invention**

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the disclosed technology. A plurality of features are described in the embodiments, but not all of these plurality of features are essential for the disclosed technology, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] In the following description, terms indicating specific directions and positions (for example, "up", "down", "right", "left", and other terms including these terms) are used as necessary. The use of these terms is for facilitating the understanding of the embodiments with reference to the drawings, and the technical scope of the disclosure is not limited by the meanings of these terms. <​​​​​​​​​In the following description, the anode of an avalanche photodiode (APD) is set at a fixed potential, and the signal is taken out from the cathode side. Therefore, the semiconductor region of the first conductivity type having majority carriers with charges of the same polarity as the signal charge is an N-type semiconductor region, and the semiconductor region of the second conductivity type having majority carriers with charges of a polarity different from the signal charge is a P-type semiconductor region. Note that the disclosed technology is also applicable when the cathode of the APD is set at a fixed potential and the signal is taken out from the anode side. In this case, the semiconductor region of the first conductivity type having majority carriers with charges of the same polarity as the signal charge is a P-type semiconductor region, and the semiconductor region of the second conductivity type having majority carriers with charges of a polarity different from the signal charge is an N-type semiconductor region. Hereinafter, the case where one of the nodes of the APD is set at a fixed potential will be described, but the potentials of both nodes may vary.

[0016] In this specification, when the term "impurity concentration" is simply used, it means the net impurity concentration obtained by subtracting the amount compensated by the impurities of the opposite conductivity type. A region where the P-type added impurity concentration is higher than the N-type added impurity concentration is a P-type semiconductor region. Conversely, a region where the N-type added impurity concentration is higher than the P-type added impurity concentration is an N-type semiconductor region.

[0017] (First Embodiment) First, a configuration example of the radiation imaging system according to the first embodiment will be described. FIG. 1(a) is a configuration example of the radiation imaging system 980 according to the present embodiment. The radiation imaging system 980 is configured to generate a radiation image of a subject using radiation. The radiation is typically X-rays, but may be α-rays, β-rays, γ-rays, or the like. The radiation imaging system 980 includes, for example, a radiation imaging device 990, a computer 983, a display 982, an exposure control device 981, and a radiation generation device 984.

[0018] The radiation generator 984 starts irradiating with radiation 985 in accordance with the exposure command (radiation command) from the exposure control device 981. The radiation 985 irradiated from the radiation generator 984 passes through the subject 986 and enters the radiation imaging device 990. The radiation generator 984 stops irradiating with radiation 985 in accordance with the stop command from the exposure control device 981. The radiation generating unit 101 is composed of, for example, a vacuum tube that generates X-rays. High voltage and filament current are supplied to the vacuum tube of the radiation generating unit 101 from the high voltage generator 107. X-rays are generated when thermionic electrons are irradiated from the cathode (filament) toward the anode (target).

[0019] The radiation imaging device 990 includes a radiation detection panel 991, a control circuit 993, and an image generation circuit 992. The radiation detection panel 991 generates a radiation image corresponding to the radiation 985 incident on the radiation imaging device 990 and transmits it to the computer 983. The control circuit 993 controls the operation of the radiation detection panel 991. For example, based on the image signal obtained from the radiation detection panel 991, the control circuit 993 generates a stop signal to stop the irradiation of radiation 985 from the radiation generator 984. The stop signal is supplied to the exposure control device 981. In response to the stop signal, the exposure control device 981 sends a stop command to the radiation generator 984.

[0020] The control circuit 993 may be composed of a dedicated circuit such as a PLD (Programmable Logic Device) like an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Alternatively, the control circuit 993 may be composed of a combination of a general-purpose processing circuit such as a processor and a memory circuit such as memory. In this case, the functions of the control circuit 993 may be realized by the general-purpose processing circuit executing a program stored in the memory circuit.

[0021] The image generation circuit 992 stores the signal supplied from the radiation detection panel 991 in memory and generates a radiation image based on this signal. Details of the radiation image generation method will be described later. The image generation circuit 992 transmits the generated radiation image to the computer 983.

[0022] The computer 983 includes a control unit 971 that controls the radiation imaging device 990 and the exposure control device 981, a receiving unit 972 that receives radiation images from the radiation imaging device 990, and an image processing unit 973 that processes the radiation images obtained by the radiation imaging device 990. The control unit 971, the receiving unit 972, and the image processing unit 973 may each be configured by dedicated circuits, similar to the control circuit 993, or by a combination of general-purpose processing circuits and memory circuits. In one example, the exposure control device 981 has an exposure switch, and when the exposure switch is turned on by the user, it sends an exposure command to the radiation generator 984 and a start notification to the computer 983 indicating the start of radiation irradiation. Upon receiving the start notification, the computer 983 responds to the start notification by notifying the control circuit 993 of the radiation imaging device 990 of the start of radiation irradiation. If the exposure control device 981 and the computer 983 are not synchronously connected, the radiation detection panel 991 may detect the start of radiation irradiation 985 based on pixel signals. The control unit 971 may also include a first control unit that controls the radiation imaging device 990 and a second control unit that controls the exposure control device 981. Here, the computer 983 is an example of an image processing device that processes radiation images output from the radiation imaging device 990.

[0023] Figure 1(b) shows the configuration of a radiation detection panel 991 in which a scintillator 500 is further stacked on a stacked photoelectric conversion unit 100. Radiation photons 600 are incident on the scintillator 500, and the scintillator 500 converts and multiplies the radiation photons 600 into visible light photons 700. Generally, the scintillator 500 multiplies one radiation photon 600 by approximately 1000 times, causing it to emit thousands of visible light photons. The multiplied visible light photons 700 are incident on the photoelectric conversion unit 100 and detected as an electrical signal by the photoelectric conversion unit 100.

[0024] The photoelectric conversion unit 100 is constructed by stacking two components, a photoelectric conversion substrate 11 and a signal processing substrate 21, and electrically connecting them. The photoelectric conversion substrate 11 has a first semiconductor layer having a photoelectric conversion element 102 (described later) and a first wiring structure. The signal processing substrate 21 has a second semiconductor layer having circuits such as a sub-signal processing unit 103 (described later) and a second wiring structure. The photoelectric conversion unit 100 is constructed by stacking the second semiconductor layer, the second wiring structure, the first wiring structure, and the first semiconductor layer in that order. The photoelectric conversion unit 100 is a back-illuminated type photoelectric conversion unit in which visible light photons 700 are incident from the second surface and the signal processing substrate 21 is located on the first surface side. The technology according to each embodiment can also be applied to a photoelectric conversion unit having a front-illuminated structure, and can also be applied to a photoelectric conversion unit consisting of a single layer instead of a stacked type. That is, the photoelectric conversion substrate 11 and the signal processing substrate 21 may be made of a common substrate.

[0025] Figure 2 shows an example of the arrangement of the photoelectric conversion substrate 11. Pixels 901, each having a photoelectric conversion element 102 including an avalanche photodiode (APD), are arranged in a two-dimensional array in a planar view, forming a pixel region 12. That is, multiple pixels may be arranged in a two-dimensional array. Here, the left-right direction in Figure 2 is expressed as "row direction," "horizontal direction," "x direction," etc., and the up-down direction in Figure 2 is expressed as "column direction," "vertical direction," "y direction," etc. Also, the direction perpendicular to the plane of the paper in Figure 2 is expressed as "depth direction," "z direction," etc.

[0026] Figure 3 is a diagram of the signal processing board 21. It includes a sub-signal processing unit 103 and a signal processing unit 902 for processing the charge photoelectrically converted by the photoelectric conversion element 102 in Figure 2, a readout circuit 112, a control pulse generation unit 115 (control signal generation unit), a horizontal scanning circuit unit 111, a signal line 113, a vertical scanning circuit unit 110, and a drive line 116. The photoelectric conversion element 102 in Figure 2 and the sub-signal processing unit 103 in Figure 3 are electrically connected via connecting wiring.

[0027] The vertical scanning circuit section 110 receives control pulses (drive control signals) supplied from the control pulse generation section 115 and supplies control pulses to each pixel via the drive line 116. Logic circuits such as a shift register and an address decoder are used in the vertical scanning circuit section 110.

[0028] The signal output from the photoelectric conversion element 102 is processed by the sub-signal processing unit 103. The sub-signal processing unit 103 is equipped with a counter and memory, and the visible light photon count value is stored in the memory. The visible light photon count value is reset once each time a radiation photon is detected.

[0029] The signal processing unit 902 reads the visible light photon count value from the sub-signal processing unit 103 and estimates the energy of the radiation photon 600. Here, the number of visible light photons is proportional to the energy of the radiation photon. This is because, although it varies depending on the material, the number of visible light photons per unit energy of radiation photons is fixed for phosphors. Therefore, by utilizing the above proportional relationship, the energy of the radiation photon can be obtained by reading the count value of the number of visible light photons.

[0030] The horizontal scanning circuit unit 111 inputs control pulses (read control signals) to the signal processing unit 902 to sequentially select each column in order to read a signal from the memory of each pixel in which the count value is held. The read control signal is a control pulse signal supplied from the control pulse generation unit 115.

[0031] On signal line 113, a signal is output from the signal processing unit 902 of the pixel selected by the vertical scanning circuit unit 110 for the selected column. The signal output on signal line 113 is output via output circuit 114 to an external recording unit or image generation unit 992 of the photoelectric conversion unit 100. Therefore, the generated image is a digital value obtained by estimating and counting the energy of radiation photons from the visible light photon count value output from the pixel. For example, if the output value of one pixel is divided into three types of radiation photons—low energy, medium energy, and high energy—and each is represented by an 8-bit counter, then one pixel will consist of a 24-bit digital value. In Figure 2, the arrangement of photoelectric conversion elements 102 in the pixel region may be arranged in a one-dimensional manner.

[0032] As shown in Figures 2 and 3, multiple signal processing units 902 are arranged in the region that overlaps with the pixel region 12 in a plan view. Then, the vertical scanning circuit unit 110, the horizontal scanning circuit unit 111, the readout circuit 112, the output circuit 114, and the control pulse generation unit 115 are arranged so as to overlap between the edge of the photoelectric conversion substrate 11 and the edge of the pixel region 12 in a plan view. In other words, the photoelectric conversion substrate 11 has a pixel region 12 and a non-pixel region arranged around the pixel region 12. Then, the vertical scanning circuit unit 110, the horizontal scanning circuit unit 111, the readout circuit 112, the output circuit 114, and the control pulse generation unit 115 are arranged in the region that overlaps with the non-pixel region in a plan view. Furthermore, the vertical scanning circuit section 110, the horizontal scanning circuit section 111, the readout circuit 112, the output circuit 114, and the control pulse generation section 115 may be arranged within the pixel area 12. In this case, the photoelectric conversion substrate 11 and the signal processing substrate 21 can be tiled in the x and y directions to increase the area. Alternatively, multiple photoelectric conversion substrates 11 and signal processing substrates 21 can be stacked in the z direction on a single wiring board to increase the area.

[0033] Figure 4 is an example of a block diagram including the equivalent circuits of Figures 2 and 3. In Figure 4, the photoelectric conversion element 102 having the APD201 is provided on the photoelectric conversion substrate 11, and the other components are provided on the signal processing substrate 21.

[0034] The APD201 generates charge pairs corresponding to incident light through photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD201. A voltage VH (second voltage), higher than the voltage VL supplied to the anode, is supplied to the cathode of the APD201. A reverse bias voltage is supplied to the anode and cathode such that the APD201 operates in avalanche multiplication mode. By supplying these voltages, the charge generated by the incident light undergoes avalanche multiplication, generating an avalanche current. When a reverse bias voltage is supplied, there are two modes of operation: Geiger mode, where the potential difference between the anode and cathode is greater than the breakdown voltage, and linear mode, where the potential difference between the anode and cathode is near or below the breakdown voltage. An APD operating in Geiger mode is called a single-photon avalanche diode (SPAD). For example, the voltage VL (first voltage) is -30V and the voltage VH (second voltage) is 1V. The APD201 may be operated in linear mode or Geiger mode. In the case of SPAD mode, the potential difference is larger compared to linear mode APD, and the voltage withstand effect is more pronounced, so SPAD mode is preferred.

[0035] The quench element 202 is connected to the power supply that provides voltage VH and to the APD201. The quench element 202 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, suppressing the voltage supplied to the APD201 and thereby suppressing avalanche multiplication (quench operation). The quench element 202 also works to restore the voltage supplied to the APD201 to voltage VH by flowing the current that compensates for the voltage drop caused by the quench operation (recharge operation). In this explanation, a passive type quench element has been described, but an active type quench element (MOS transistor) may also be used, and the recharge operation may be performed by inputting a clock pulse.

[0036] The sub-signal processing unit 103 includes a waveform shaping unit 210 and a counter circuit 211. In this specification, the sub-signal processing unit 103 may include either the waveform shaping unit 210 or the counter circuit 211.

[0037] The waveform shaping unit 210 shapes the cathode potential change of the APD201 obtained during photon detection and outputs a pulse signal. For example, an inverter circuit can be used as the waveform shaping unit 210. Figure 4 shows an example in which one inverter is used as the waveform shaping unit 210, but a circuit in which multiple inverters are connected in series may be used, or other circuits that have a waveform shaping effect may be used.

[0038] The counter circuit 211 counts the pulse signals output from the waveform shaping unit 210 and holds the visible light photon count value. When a control pulse pRES (reset signal) is supplied to the counter circuit 211, the signal held by the counter circuit 211 is reset. The reset signal is the control pulse pRES supplied from the control pulse generation unit 115. The reset signal may also be supplied via a drive line different from the drive line 116.

[0039] A switch such as a transistor may be placed between the quench element 202 and the APD201, or between the photoelectric conversion element 102 and the sub-signal processing unit 103, to switch the electrical connection. Similarly, the supply of voltage VH or voltage VL to the photoelectric conversion element 102 may be electrically switched using a switch such as a transistor.

[0040] Figure 5 is an example of a block diagram including the equivalent circuit of the signal processing unit 902. In this embodiment, a counter circuit 211 for counting visible light photons (hereinafter also referred to as the visible light photon counter circuit 211) and radiation photon counter circuits 905, 906, and 907 for counting radiation photons are connected in series (multi-stage counter). Here, the counter circuit 211 is an example of a first counter circuit that counts electrical signals (first electrical signals) converted into visible light by the photoelectric conversion element 102. The radiation photon counter circuits 905, 906, and 907 are examples of a second counter circuit that counts electrical signals (second electrical signals) output from the counter circuit 211, and are also examples of multiple counter circuits included in the second counter circuit. The count value of visible light photons held in the counter circuit 211 of the sub-signal processing unit 103 shown in Figure 4 is compared with a threshold value by the comparison unit 904 and distributed to the radiation photon counter circuits 905, 906, and 907, where the count value of one of the multiple counter circuits is increased according to the energy of the radiation photons. That is, the second counter circuit may be configured to count the second electrical signal output to the counter circuit selected using the count value from the first counter circuit among the radiation photon counter circuits 905, 906, and 907. In this case, the selected counter circuit is one of the radiation photon counter circuits 905, 906, and 907. Here, for example, if the count value from the first counter circuit is greater than or equal to the threshold value, one of the multiple counter circuits may be selected. Also, for example, if the count value from the first counter circuit is less than the threshold value, a counter circuit different from one of the multiple counter circuits may be selected.

[0041] Here, the comparison unit 904 is an example of a comparison unit that compares the count value of the first counter circuit with at least one of several different thresholds. The comparison unit 904 is, for example, a comparator. The second counter circuit may count the second electrical signal output to the counter circuit selected using the comparison result (threshold determination result) from the comparison unit 904 among the radiation photon counter circuits 905, 906, and 907. Furthermore, as will be described later, the radiation photon counter circuits 905, 906, and 907 may be configured so that their respective count values ​​correspond to the energies of radiation photons. After the duration of one frame of imaging, a control pulse pSEL (selection signal) is supplied from the vertical scanning circuit unit 110 in Figure 4 to the selection circuit 212 via the drive line 116 in Figure 5, switching the electrical connection between the radiation photon counter circuits 905, 906, and 907 and the signal line 113, and reading out the count value. The selection circuit 212 may receive and temporarily store the count values ​​output from the radiation photon counter circuits 905, 906, and 907, respectively. Furthermore, the selection circuit 212 may transmit each of the stored count values ​​to the signal line 113 when a control pulse pSEL (selection signal) is supplied. In other words, the selection circuit 212 may be configured to transmit the count values ​​output from each of the multiple counter circuits to the signal line according to the selection signal from the drive line. The selection circuit 212 may also include, for example, a buffer circuit for outputting signals.

[0042] Figures 6A and 6B schematically illustrate the relationship between the operation of the APD and the output signal. Figure 6A is an excerpt of the APD 201, quench element 202, and waveform shaping unit 210 from Figure 4. Here, the input side of the waveform shaping unit 210 is denoted as nodeA, and the output side as nodeB. The upper part of Figure 6B shows the waveform change at nodeA, and the lower part shows the waveform change at nodeB.

[0043] Between time t0 and time t1, a potential difference of VH-VL is applied to APD201. When a photon is incident on APD201 at time t1, avalanche multiplication occurs in APD201, an avalanche multiplication current flows through the quench element 202, and the voltage at nodeA drops. As the voltage drop increases further and the potential difference applied to APD201 decreases, the avalanche multiplication of APD201 stops as at time t2, and the voltage level at nodeA stops dropping below a certain value. Subsequently, between time t2 and time t3, a current flows through nodeA to compensate for the voltage drop from voltage VL, and at time t3, nodeA settles to its original potential level. At this time, any portion of the output waveform at nodeA that exceeds a certain threshold is waveform-shaped by the waveform shaping unit 210 and output as a signal at nodeB.

[0044] Here, the operation of the multi-stage counter in this embodiment will be described. Figure 7 is a schematic diagram showing the operation of the visible light photon counter circuit 211 and the radiation photon counter circuits 905, 906, and 907. In the figure, 711 is the count period of the visible light photon counter circuit 211, and 712 is the count period of the radiation photon counter circuits 905, 906, and 907. As explained in Figure 1(b), when one radiation photon enters the scintillator, it emits light as thousands of visible light photons. Therefore, the count period 711 of the visible light photon counter circuit 211 is shorter than the count period 712 of the radiation visible light photon circuits 905, 906, and 907. In Figure 7, for the sake of simplicity, only three count periods (count periods 710, 720, and 730) of the radiation counter circuit are shown, and subsequent counts are omitted. Note that the count period of the first counter circuit may be several hundred to several thousand times the count period of the second counter circuit.

[0045] The count period 710 is an example where no radiation photons are incident during the count period. If no radiation photons are incident, no visible light photons are generated either. Therefore, the count value of the visible light photon counter circuit 211 is 0, and the count values ​​of the radiation photon counter circuits 905, 906, and 907 do not increase. The count value of the visible light photon counter circuit 211 is reset at the timing of the counts of the radiation photon counter circuits 905, 906, and 907. In other words, the reset of the count value by the first counter circuit may be performed at the count period of the second counter circuit.

[0046] Counting periods 720 and 730 are examples of cases where incident radiation photons are incident during the counting period. In period 720, 722 is the timing when the radiation photon is incident on the scintillator, and 721 is the group of visible light photons generated in response to the incident radiation photon. In period 730, 732 is the timing when the radiation photon is incident on the scintillator, and 731 is the group of visible light photons generated in response to the incident radiation photon. Periods 720 and 730 differ in the timing and energy of the incident radiation photon. The number of visible light photons 723 generated at this time is proportional to the energy of the radiation photon. This is because, although it varies depending on the material, the number of visible light photons per unit energy of a radiation photon is fixed for phosphors. The count value held in the visible light photon counter circuit 211 is compared with a threshold value in the comparison unit 904 to identify the energy of the radiation. Then, the count numbers of the radiation photon counter circuits 905, 906, and 907 are increased according to the energy of the radiation photon. In other words, the radiation photon counter circuits 905, 906, and 907 may be configured so that the count values ​​they provide correspond to different energy levels of radiation photons.

[0047] For example, radiation photons in the 30kV to 60kV range are distributed to radiation photon counter circuit 905, radiation photons in the 60kV to 90kV range are distributed to radiation photon counter circuit 906, and radiation photons in the 90kV to 120kV range are distributed to radiation photon counter circuit 907. In this case, if the count value of visible light photon 721 is 200 counts, it is identified that 80kV radiation photons have been irradiated, and the count value of 60-90kV radiation photon counter circuit 906 is increased by 1 count. If the count value of visible light photon 731 is 100 counts, it is recognized that 40kV radiation photons have been irradiated, and the count value of 30kV-60kV radiation photon counter circuit 905 is increased by 1 count.

[0048] In this embodiment, the visible light electrical signals generated by radiation photons in a scintillator are treated as multiple digital signals. Each signal is an electrical signal from a single visible light photon, and the number of signals changes according to the energy of the radiation photon. In this case, the first counter circuit may count each visible light photon individually. The second counter circuit may count the radiation photons by using the count value from the first counter circuit to count the electrical signals output to any of the multiple counter circuits. This makes it less susceptible to noise such as dark current compared to thresholding the peak height (peak value) in the waveform of the analog signal, thus allowing for more accurate acquisition of the energy of radiation photons.

[0049] The operation described in Figure 7 is repeated for each pixel to generate an image that identifies the energy information of the radiation based on the count value of the radiation photons. For example, the count values ​​of radiation photon counter circuits 905, 906, and 907 may be assigned to the hues of three primary colors R (red), G (green), and B (blue), and a color image may be generated in which the count value of each counter circuit represents the degree of hue. That is, multiple counter circuits may be assigned different hues (e.g., R, G, B), and a color image may be generated in which the count value of each of the multiple counter circuits represents the degree of hue. In this case, the multiple counter circuits may be configured to include a counter circuit corresponding to R, a counter circuit corresponding to G, and a counter circuit corresponding to B.

[0050] Note that the count value of visible light photons varies depending on the configuration of the scintillator and reflective layer, so the threshold is not limited to 100 counts or 200 counts. Similarly, the energy intervals of radiation photons assigned to radiation photon counter circuits 905, 906, and 907 are not limited to 30kV to 60kV, 60kV to 90kV, or 90kV to 120kV. The energy of radiation photons may be changed depending on the radiation source used, the subject, the application, and other imaging conditions. The energy intervals are not limited to 30kV, 60kV, and 90kV. The energy assignment range is not limited to 30kV intervals, nor is it necessarily equal intervals. Also, although the explanation described the case with three radiation photon counter circuits, there may be more or fewer.

[0051] Furthermore, it is preferable that the count period 711 of the visible light photon counter circuit 211 be set to a value that has a sufficient margin over the amount of light emitted by the scintillator so that multiple visible light photons do not occur within one period. Similarly, it is preferable that the count period 712 of the radiation photon counter circuit be set to a value that has a sufficient margin over the radiation exposure conditions so that multiple radiation photons do not occur within one period (pile-up). It is also preferable that the count period 712 of the radiation photon counter circuit be set to a value that has a sufficient margin over the light emitted by the scintillator so that multiple counts do not occur during the light emission period of a radiation photon. Alternatively, it is preferable to use a scintillator with a sufficiently short light emission period relative to the count period 712 of the radiation photon counter circuit.

[0052] (An example of SPAD structure) Here, Figures 8 and 9 show the structure of the photoelectric conversion substrate 11 (sensor substrate) of the photoelectric conversion unit. Figure 8 is a plan view showing the configuration of the pixel region, schematically showing the semiconductor layer 300 of the photoelectric conversion substrate 11 as viewed from the first surface side. Figure 9 is a cross-sectional view along line AA (diagonal direction) of Figure 8.

[0053] As shown in Figure 8, multiple APD201s are arranged in a two-dimensional array in the row direction (left-right direction in Figure 8) and column direction (up-down direction in Figure 8) of the semiconductor layer 300. In Figure 8, for illustrative purposes only, nine APD201s in a 3x3 arrangement are depicted, but in an actual product, for example, hundreds of thousands to millions of APD201s are formed. One APD201 corresponds to one pixel. The semiconductor layer 300 is provided with separation sections 330, which are separation structures to reduce crosstalk between adjacent APD201s. The separation sections 330 are formed in a grid shape by multiple row-direction separation sections 330X extending in the row direction and multiple column-direction separation sections 330Y extending in the column direction. An APD201 is arranged in each of the sections separated by this grid-shaped separation section 330. In this embodiment, the section corresponding to one pixel has a roughly square shape in plan view. The boundaries of the sections are provided so as to overlap, for example, the separation sections 330. The cathode wiring contact plug 326 formed on the wiring structure 320 is positioned approximately in the center of the pixel (section), while the anode wiring contact plugs 324 are positioned at the four corners of the pixel. In other words, in this embodiment, four anode contact plugs 324 are provided for each pixel.

[0054] As shown in Figure 9, the photoelectric conversion substrate 11 (sensor substrate) has a structure in which a semiconductor layer 300 and a wiring structure 320 are stacked. The side of the semiconductor layer 300 facing the wiring structure 320 is called the first surface, and the side opposite the first surface is called the second surface. The semiconductor layer 300 is made of silicon, for example. On the second surface of the semiconductor layer 300, a fixed charge film 310, an insulating film 311, a planarization film 312, etc., are stacked in order, and a microlens 313 corresponding to each pixel is provided above them. In other words, the photoelectric conversion unit of this embodiment has a so-called back-illuminated structure in which light is incident on the semiconductor layer 300 from the second surface side. The second surface is sometimes called the light incident surface. In Figure 9, a microlens 313 is provided, but it is not necessarily required. Furthermore, the following structure can be applied to the light incident surface. For example, at least one recess or convex structure can be arranged on the second surface, which is the light incident surface. The uneven structure can be made of silicon that constitutes the semiconductor layer 300 and other materials. For example, an insulator such as a silicon oxide film, a silicon oxynitride film, or a silicon nitride film is placed in a recess provided in the semiconductor layer 300. An interface with a refractive index difference that is not parallel to the second surface is formed. With this configuration, the incident light is diffracted, which can improve sensitivity to light in the infrared region.

[0055] The fixed charge film 310 is made of a dielectric material having a negative fixed charge and is arranged across the entire second surface of the semiconductor layer 300. The material of the fixed charge film 310 can be selected from, for example, hafnium oxide, aluminum oxide, zirconium oxide, titanium oxide, tantalum oxide, and ruthenium oxide, with aluminum oxide or hafnium oxide being preferred. The fixed charge film 310 may consist of multiple layers. The insulating film 311 is arranged on the fixed charge film 310 across the entire second surface. The insulating film 311 can preferably be, for example, a silicon oxide film, a silicon oxynitride film, or a silicon nitride film. The insulating film 311 may also consist of multiple layers. Although not shown in the figures, in addition to the planarization film 312, a filter layer such as a color filter or an infrared light cut filter may be provided on the second surface side of the semiconductor layer 300.

[0056] The wiring structure 320 is a structure in which multiple layers of wiring 321, 322, 323, via plugs 325, 327 for connecting the wirings, anode wiring contact plug 324, cathode wiring contact plug 326, etc. are arranged within the insulating layer 329. The lower surface of the wiring structure 320 (opposite the semiconductor layer 300) is the bonding surface with the signal processing substrate 21, and multiple bonding portions 328 are provided on the bonding surface.

[0057] The semiconductor layer 300 has a first semiconductor region 301, a second semiconductor region 302, a third semiconductor region 303, a fourth semiconductor region 304, a fifth semiconductor region 305, a sixth semiconductor region 306, a seventh semiconductor region 307, an eighth semiconductor region 308, and a ninth semiconductor region 309. Each semiconductor region is a region to which impurities have been added by ion implantation, or a region to which impurities have been added during the fabrication and epitaxial growth of the semiconductor substrate. Here, the first semiconductor region 301, the sixth semiconductor region 306, the seventh semiconductor region 307, and the eighth semiconductor region 308 are semiconductor regions of the first conductivity type (N-type in this embodiment). The second semiconductor region 302, the third semiconductor region 303, the fourth semiconductor region 304, the fifth semiconductor region 305, and the ninth semiconductor region 309 are semiconductor regions of the second conductivity type (P-type in this embodiment). The first semiconductor region 301 is a semiconductor region of the first conductivity type (N-type in this embodiment) and is provided on the first surface of the semiconductor layer 300. As shown in Figure 8, the first semiconductor region 301 in this embodiment is formed in a circular shape in the center of the pixel (partition) in a plan view. The cathode contact plug 326 is connected to the center of the first semiconductor region 301. The fifth semiconductor region 305 is a semiconductor region of the second conductivity type (P-type in this embodiment) and is located on the light incident side (closer to the second surface) than the first semiconductor region 301. The fifth semiconductor region 305 is formed in layers to a predetermined depth so as to divide the epitaxial layer of the first conductivity type in one pixel (partition) into upper and lower halves. The periphery of the fifth semiconductor region 305 is in contact with the separation portion 330 surrounding the pixel. The epitaxial layer of the first conductivity type located on the first surface side of the fifth semiconductor region 305 is the sixth semiconductor region 306, and the epitaxial layer of the first conductivity type located on the second surface side is the eighth semiconductor region 308. The first semiconductor region 301 of the first conductivity type and the fifth semiconductor region 305 of the second conductivity type form an avalanche multiplication region AM by a PN junction. The signal charge generated in the eighth semiconductor region 308 by photoelectric conversion is collected in the avalanche multiplication region AM. To improve the sensitivity of the APD201, it is preferable to increase the size of the eighth semiconductor region 308, which corresponds to the sensitivity region. The seventh semiconductor region 307 is a semiconductor region of the first conductivity type formed around the first semiconductor region 301.The seventh semiconductor region 307 is also formed in a circular shape when viewed from above. Here, the impurity concentrations of the first semiconductor region 301, the seventh semiconductor region 307, and the sixth semiconductor region 306 are set to satisfy the relationship: first semiconductor region 301 > seventh semiconductor region 307 > sixth semiconductor region 306. That is, the impurity concentration of the first semiconductor region 301 is the highest, and the impurity concentration of the seventh semiconductor region 307 is set to be between that of the first semiconductor region 307 and the sixth semiconductor region 306. This ensures an electrical connection between the cathode and the first semiconductor region 301 (i.e., APD201). The seventh semiconductor region 307 also acts as a guard ring for electric field relaxation. The ninth semiconductor region 309 is a second-conductivity type embedding layer provided across the entire second surface of the semiconductor layer 300. The ninth semiconductor region 309 plays a role in suppressing noise from the second surface side. Furthermore, a voltage VL from the anode wiring can be supplied to the ninth semiconductor region 309 via the second semiconductor region 302. In this case, a potential gradient can be formed to collect charge.

[0058] (Second Embodiment) The first embodiment counts each individual visible light photon and radiation photon to estimate the energy of radiation with high accuracy. However, counting errors may occur if the scintillator's emission spans between pixels or if the processing speed of the signal processing circuit is insufficient. Therefore, the second embodiment shows a configuration in which partitions are provided in the scintillator to suppress counting errors of visible light photons and radiation photons and to estimate the energy of radiation with high accuracy. Specifically, as will be described later, the pixel scintillator configuration is shown in which the scintillator is separated by partitions provided according to the pixels 901 of the photoelectric conversion unit 100. Note that the explanation of parts common to the first embodiment will be omitted.

[0059] Figure 10 illustrates a configuration that reduces the loss of visible light photons caused by scintillator emission spanning between pixels. Figure 10 shows the configuration of a radiation detection panel 991 in which a scintillator 501 is further stacked on a stacked photoelectric conversion unit 100.

[0060] The scintillator 501 is a pixel scintillator (or partition phosphor) separated to match the pixel 901 of the photoelectric conversion unit 100. By using a pixel scintillator, the incidence of visible light photons 700 to adjacent pixels is reduced, making it possible to count the number of visible light photons 700 produced by one radiation photon in a single pixel.

[0061] Suitable materials for scintillator 501 include CsI:Tl, CsI, Lu3Al5O12:Ce, PbWO4, Gd3Al2Ga3O12:Ce, (Lu,Y)2SiO5:Ce, and Gd2O2S:Tb(Pr), which exhibit good radiation stopping properties and respond with a response time of 1us or less.

[0062] Pixel scintillators are constructed by forming a metal reflective layer on a partition substrate created by penetrating a Si wafer using a TSV (through-silicon via) process, and then filling it with scintillator material. Besides using Si wafers, the partition substrate can also be formed by depositing polyimide resin (PI). There are also methods for filling the scintillator material, such as heating and melting the material before filling, or using powdered scintillator material mixed with a binder resin before filling. When using a hygroscopic material like CsI as the scintillator material, it is advisable to use ALPET, a composite material made by laminating aluminum foil and polyester film, as a moisture-proof layer. Furthermore, when laminating the moisture-proof layer to the partition substrate, a reflective layer made of a hot-melt sheet containing TiO2 can be used to achieve both moisture resistance and reflective performance.

[0063] Figures 11-13 illustrate a configuration that reduces the loss of visible light photons due to insufficient processing speed in the signal processing circuit. By dividing pixels into subpixels and dispersing visible light photons in the spatial direction, the processing speed burden is reduced, thereby reducing the loss of visible light photons.

[0064] Figure 11 shows an example of the arrangement of the photoelectric conversion substrate 11. Pixels 901, each having a photoelectric conversion element 102 including an avalanche photodiode (APD), are arranged in a 5x5 grid, forming a two-dimensional array in plan view, creating a pixel region 12. That is, each of the multiple pixels is composed of multiple subpixels, and each of the multiple subpixels may have a photoelectric conversion element and a first counter circuit. Furthermore, the size of each of the multiple pixels may be several tens to several hundred micrometers, and each of the multiple pixels may be composed of several hundred to several thousand subpixels.

[0065] Figure 12 is a diagram of the signal processing board 21. It includes a sub-signal processing unit 103 that processes the charge photoelectrically converted by the photoelectric conversion element 102 in Figure 11, a signal processing unit 902 that combines the signals from the sub-signal processing unit 103 into signals for each pixel, a readout circuit 112, a control pulse generation unit 115 (control signal generation unit), a horizontal scanning circuit unit 111, signal lines 113, a vertical scanning circuit unit 110, and drive lines 116.

[0066] The photoelectric conversion element 102 in Figure 11 and the sub-signal processing unit 103 in Figure 12 are electrically connected via connection wiring provided for each subpixel.

[0067] The vertical scanning circuit section 110 receives control pulses (drive control signals) supplied from the control pulse generation section 115 and supplies control pulses to each pixel via the drive line 116. Logic circuits such as a shift register and an address decoder are used in the vertical scanning circuit section 110.

[0068] The signal output from the subpixel photoelectric conversion element 102 is processed by the subsignal processing unit 103. The subsignal processing unit 103 is equipped with a counter and memory, and the visible light photon count value is stored in the memory. The visible light photon count value is reset once each time a radiation photon is detected.

[0069] The signal processing unit 902 reads the visible light photon count values ​​from the 5x5 sub-signal processing unit 103, integrates them, and estimates the energy of the radiation photon 600. For example, if the sum of the 5x5 visible light photon count values ​​is 100 counts, it recognizes that 40kV radiation photon 600 has been irradiated, and adds 1 count to the 30kV-60kV radiation photon count value. If the sum of the 5x5 visible light photon count values ​​is 200 counts, it identifies that 80kV radiation photons have been irradiated, and adds 1 count to the 60-90kV radiation photon count value.

[0070] The horizontal scanning circuit unit 111 inputs control pulses (read control signals) to the signal processing unit 902 to sequentially select each column in order to read a signal from the memory of each pixel in which the radiation photon count value is stored. The read control signal is a control pulse signal supplied from the control pulse generation unit 115.

[0071] On signal line 113, a signal is output from the signal processing unit 902 of the pixel selected by the vertical scanning circuit unit 110 for the selected column. The signal output on signal line 113 is output via output circuit 114 to the recording unit or image generation unit 992 outside the photoelectric conversion unit 100. Therefore, the generated image is a digital value obtained by estimating and counting the energy of radiation photons from the visible light photon count values ​​output from multiple subpixels. For example, if the output value of one pixel is divided into three categories: 30-60kV radiation photons, 60-90kV radiation photons, and 90-120kV radiation photons, and each is represented by an 8-bit counter, then one pixel will consist of a 24-bit digital value.

[0072] In Figure 11, the arrangement of photoelectric conversion elements 102 in the pixel region may be arranged in a one-dimensional manner. The function of the signal processing unit does not necessarily need to be provided for each photoelectric conversion element; for example, one signal processing unit may be shared by multiple photoelectric conversion elements 102, and signal processing may be performed sequentially. Note that the block diagrams including the equivalent circuits in Figures 11 and 12 have the same configuration as in Figure 4 of the first embodiment, so their explanation is omitted.

[0073] Figure 13 is an example of a block diagram including the equivalent circuit of the signal processing unit 902. The sub-signal processing units 103 shown in Figure 4 are arranged in a 5x5 grid, and the visible light photon count values ​​held in the counter circuits 211 of each sub-signal processing unit 103 are added together in the integration unit 903. The comparison unit 904 compares the integrated visible light photon count values ​​with a threshold and distributes them to the 30kV-60kV radiation photon counter circuit 905, the 60kV-90kV radiation photon counter circuit 906, and the 90kV-120kV radiation photon counter circuit 907, increasing the counter according to the energy of the radiation photons. After the duration of one frame of imaging has elapsed, a control pulse pSEL (selection signal) is supplied from the vertical scanning circuit section 110 in Figure 12 to the selection circuit 212 via the drive line 116 in Figure 13. This switches the electrical connection between the 30kV~60kV radiation photon counter circuit 905, the 60kV~90kV radiation photon counter circuit 906, the 90kV~120kV radiation photon counter circuit 907 and the signal line 113, and reads out the count value. The selection circuit 212 may receive and temporarily store the count values ​​output from each of the radiation photon counter circuits 905, 906, and 907. The selection circuit 212 may also transmit each of the stored count values ​​to the signal line 113 at the timing when the control pulse pSEL (selection signal) is supplied. In other words, the selection circuit 212 may be configured to transmit the count values ​​output from each of the multiple counter circuits to the signal line according to the selection signal from the drive line. The selection circuit 212 also includes, for example, a buffer circuit for outputting a signal.

[0074] (Other embodiments) Furthermore, the disclosed technology can also be realized by performing the following process: that is, the disclosed technology can also be realized by supplying software (programs) that implement one or more functions of the various embodiments described above to a system or device via a network or storage medium, and the computer (or CPU, MPU, etc.) of that system or device reads and executes the program. The computer may have one or more processors or circuits and may include a network of separate computers or separate processors or circuits for reading and executing computer executable instructions. In this case, the processor or circuit may include a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), or a field-programmable gateway (FPGA). The processor or circuit may also include a digital signal processor (DSP), a dataflow processor (DFP), or a neural processing unit (NPU).

[0075] The disclosed technology may include any of the following components:

[0076] (Composition 1) A scintillator that converts radiation into visible light, A photoelectric conversion element that converts the visible light into a first electrical signal, The signal processing unit includes a first counter circuit for counting the first electrical signal and a second counter circuit for counting the second electrical signal output from the first counter circuit. The radiation imaging apparatus is configured such that the second counter circuit includes a plurality of counter circuits, and counts the second electrical signal output to a counter circuit selected from among the plurality of counter circuits using the count value from the first counter circuit.

[0077] (Configuration 2) The first counter circuit counts visible light photons by counting the first electrical signal, The radiation imaging apparatus according to configuration 1, wherein the second counter circuit counts radiation photons by counting the second electrical signal.

[0078] (Composition 3) The count period of the first counter circuit is shorter than the count period of the second counter circuit. The radiation imaging apparatus according to configuration 1 or 2, wherein the reset of the count value by the first counter circuit is performed by the counting period of the second counter circuit.

[0079] (Composition 4) A radiation imaging apparatus according to any one of configurations 1 to 3, wherein if the count value from the first counter circuit is greater than or equal to a threshold, one of the plurality of counter circuits is selected, and if the count value from the first counter circuit is less than the threshold, a counter circuit different from the one of the plurality of counter circuits is selected.

[0080] (Composition 5) The signal processing unit includes a comparison unit that compares the count value of the first counter circuit with at least one of a plurality of mutually different threshold values. The radiation imaging apparatus according to any one of configurations 1 to 4, wherein the second counter circuit counts the second electrical signal output to the counter circuit selected from among the plurality of counter circuits using the comparison result by the comparison unit.

[0081] (Composition 6) A pixel having the aforementioned photoelectric conversion element, wherein a plurality of pixels are arranged in a two-dimensional array, The radiation imaging apparatus according to any one of configurations 1 to 5, wherein the scintillator is configured as a pixel scintillator by providing a partition wall for each pixel.

[0082] (Composition 7) Each of the aforementioned multiple pixels is composed of multiple subpixels, The radiation imaging apparatus according to configuration 6, wherein each of the plurality of subpixels has the photoelectric conversion element and the first counter circuit.

[0083] (Composition 8) The aforementioned photoelectric conversion element is a single-photon avalanche diode. The radiation imaging apparatus according to any one of configurations 1 to 7, wherein the single-photon avalanche diode is connected to a quench element that functions as a load circuit when the signal is multiplied by avalanche multiplication.

[0084] (Composition 9) A radiation imaging apparatus according to any one of configurations 1 to 8, wherein the counting period of the first counter circuit is several hundred to several thousand times the counting period of the second counter circuit.

[0085] (Composition 10) The radiation imaging apparatus according to any one of configurations 1 to 9, wherein the plurality of counter circuits are configured to have count values ​​corresponding to different energy radiation photons.

[0086] (Composition 11) A radiation imaging apparatus according to any one of configurations 1 to 10, wherein different hues are assigned to the plurality of counter circuits, and a color image is generated in which the count value of each of the plurality of counter circuits represents the degree of hue.

[0087] (Composition 12) The aforementioned different hues are R, G, and B. The radiation imaging apparatus according to configuration 11, wherein the plurality of counter circuits include a counter circuit corresponding to R, a counter circuit corresponding to G, and a counter circuit corresponding to B.

[0088] (Composition 13) A radiation imaging apparatus according to any one of configurations 1 to 12, further comprising a selection circuit that transmits the count values ​​output from each of the plurality of counter circuits to a signal line in accordance with a selection signal from a drive line.

[0089] (Composition 14) A radiation imaging device as described in any one of configurations 1 to 13, A radiation generator that irradiates radiation toward the aforementioned radiation imaging device, An image processing device that processes radiation images output from the radiation imaging device, A radiation imaging system equipped with the following features.

Claims

1. A scintillator that converts radiation into visible light, A photoelectric conversion element that converts the visible light into a first electrical signal, The signal processing unit includes a first counter circuit for counting the first electrical signal and a second counter circuit for counting the second electrical signal output from the first counter circuit. The radiation imaging apparatus is configured such that the second counter circuit includes a plurality of counter circuits, and counts the second electrical signal output to a counter circuit selected from among the plurality of counter circuits using the count value from the first counter circuit.

2. The first counter circuit counts visible light photons by counting the first electrical signal, The radiation imaging apparatus according to claim 1, wherein the second counter circuit counts radiation photons by counting the second electrical signal.

3. The count period of the first counter circuit is shorter than the count period of the second counter circuit. The radiation imaging apparatus according to claim 1, wherein the reset of the count value by the first counter circuit is performed by the count period of the second counter circuit.

4. The radiation imaging apparatus according to claim 1, configured such that when the count value from the first counter circuit exceeds a threshold, one of the plurality of counter circuits is selected, and when the count value from the first counter circuit falls below a threshold, a counter circuit different from the one of the plurality of counter circuits is selected.

5. The signal processing unit includes a comparison unit that compares the count value of the first counter circuit with at least one of a plurality of mutually different threshold values. The radiation imaging apparatus according to claim 1, wherein the second counter circuit counts the second electrical signal output to the counter circuit selected from among the plurality of counter circuits using the comparison result by the comparison unit.

6. A pixel having the aforementioned photoelectric conversion element, wherein a plurality of pixels are arranged in a two-dimensional array, The radiation imaging apparatus according to claim 1, wherein the scintillator is configured as a pixel scintillator by providing a partition wall for each pixel.

7. Each of the aforementioned multiple pixels is composed of multiple subpixels, The radiation imaging apparatus according to claim 6, wherein each of the plurality of subpixels has the photoelectric conversion element and the first counter circuit.

8. The aforementioned photoelectric conversion element is a single-photon avalanche diode. The radiation imaging apparatus according to claim 1, wherein the single-photon avalanche diode is connected to a quench element that functions as a load circuit when the signal is multiplied by avalanche multiplication.

9. The radiation imaging apparatus according to claim 1, wherein the counting period of the first counter circuit is several hundred to several thousand times the counting period of the second counter circuit.

10. The radiation imaging apparatus according to claim 1, wherein the plurality of counter circuits are configured to correspond to different energy levels of radiation photons, with each counter circuit producing a different count value.

11. The radiation imaging apparatus according to claim 1, wherein different hues are assigned to the plurality of counter circuits, and a color image is generated in which the count value of each of the plurality of counter circuits represents the degree of hue.

12. The aforementioned different hues are R, G, and B. The radiation imaging apparatus according to claim 11, wherein the plurality of counter circuits include a counter circuit corresponding to R, a counter circuit corresponding to G, and a counter circuit corresponding to B.

13. The radiation imaging apparatus according to claim 1, further comprising a selection circuit that transmits the count values ​​output from each of the plurality of counter circuits to a signal line in accordance with a selection signal from a drive line.

14. A radiation imaging apparatus according to any one of claims 1 to 13, A radiation generator that irradiates radiation toward the aforementioned radiation imaging device, An image processing device that processes radiation images output from the radiation imaging device, A radiation imaging system equipped with the following features.

Images