Radiation imaging apparatus and radiation imaging system

Abstract

A radiation imaging apparatus according to the present disclosure comprises: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts the visible light into a first electric signal; and a signal processing unit that includes a first counter circuit which counts the first electric signal and a second counter circuit which counts a second electric signal output from the first counter circuit. The second counter circuit includes a plurality of counter circuits and is configured so as to count the second electric signal output to a counter circuit selected, from among the plurality of counter circuits, using a count value from the first counter circuit.

Description

Radiation imaging device and radiation imaging system

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

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

[0003] FPDs are classified into integral sensors and photon-counting sensors. Integral sensors measure the total amount of charge generated by incident radiation. In contrast, photon-counting sensors identify the energy (wavelength) of incident radiation and count the number of times radiation is detected for each of multiple energy levels. In other words, photon-counting sensors have energy resolution, and therefore can improve diagnostic capabilities compared to integral sensors.

[0004] Photon counting sensors are further divided into direct and indirect types. Direct types count the number of times radiation is detected by directly detecting radiation energy using CdTe. Indirect types count the number of times radiation is detected by indirectly detecting radiation energy based on visible light generated in a scintillator by incident radiation. In Patent Document 1, the electrical signal of visible light generated in a scintillator by radiation photons is considered to be a single analog signal. The height of the peak in the waveform of this signal changes depending on the energy of the radiation photons. At this time, the energy can be estimated by comparing the peak value in the waveform with a threshold, and the radiation photons can be counted using a counter circuit.

[0005] JP 2017-86901 A

[0006] Here, since such analog electrical signals contain noise due to dark current and the like, there is a possibility that the accuracy of estimating the energy of the radiation photons may decrease.

[0007] Therefore, an object of the disclosed technology is to improve the accuracy of obtaining the energy of radiation photons in a photon-counting sensor.

[0008] The disclosed radiation imaging device comprises: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts the visible light into a first electrical signal; and a signal processing unit that includes: a first counter circuit that counts the first electrical signal; and a second counter circuit that counts 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 a count value by the first counter circuit.

[0009] According to the disclosed technology, it is possible to improve the accuracy of obtaining radiation photon energy in a photon-counting sensor.

[0010] FIG. 1 is a schematic diagram of an example of the configuration of a radiation imaging system according to a first embodiment; FIG. 2 is a schematic diagram of a radiation detection panel of the radiation imaging system according to the first embodiment; FIG. 3 is a schematic diagram of a photoelectric conversion board of the radiation detection panel according to the first embodiment; FIG. 4 is a schematic diagram of a signal processing board of the radiation detection panel according to the first embodiment; FIG. 5 is a schematic diagram of a sub-signal processing circuit of the radiation detection panel according to the first embodiment; FIG. 6 is a schematic diagram of a signal processing circuit configuration of the radiation detection panel according to the first embodiment;

[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. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the disclosed technology, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] In the following description, terms indicating specific directions or positions (for example, "upper," "lower," "right," "left," and other terms including these terms) are used as necessary. The use of these terms is for the purpose of facilitating understanding of the embodiments with reference to the drawings, and the meaning of these terms does not limit the technical scope of the disclosure.

[0013] In this specification, a planar view refers to a view from a direction perpendicular to the light incident surface of the semiconductor layer. A cross-sectional view refers to a surface perpendicular to the light incident surface of the semiconductor layer. When the light incident surface of the semiconductor layer is a rough surface when viewed microscopically, the planar view is defined based on the light incident surface of the semiconductor layer when viewed macroscopically.

[0014] The semiconductor layer has a first surface and a second surface opposite to the first surface, through which light is incident. In this specification, the depth direction is the direction from the first surface toward the second surface of the semiconductor layer on which the APD is disposed. Hereinafter, the "first surface" may be referred to as the "front surface," and the "second surface" may be referred to as the "rear surface."

[0015] In the following description, the anode of the avalanche photodiode (APD) is set to a fixed potential, and a signal is extracted from the cathode side. Therefore, the first conductivity type semiconductor region having majority carriers of charges of the same polarity as the signal charge is an N-type semiconductor region, and the second conductivity type semiconductor region having majority carriers of charges of a polarity opposite to that of the signal charge is a P-type semiconductor region. The disclosed technology also applies when the cathode of the APD is set to a fixed potential and the signal is extracted from the anode side. In this case, the first conductivity type semiconductor region having majority carriers of charges of the same polarity as the signal charge is a P-type semiconductor region, and the second conductivity type semiconductor region having majority carriers of charges of a polarity opposite to that of the signal charge is an N-type semiconductor region. The following description will be given of a case where one node of the APD is set to a fixed potential, but the potentials of both nodes may fluctuate.

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

[0017] First Embodiment First, an example of the configuration of a radiation imaging system according to the first embodiment will be described. Fig. 1A shows an example of the configuration of a radiation imaging system 980 according to this 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 also be alpha rays, beta rays, gamma rays, etc. 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 generating device 984 starts emitting radiation 985 in accordance with an exposure command (radiation command) from the exposure control device 981. The radiation 985 irradiated from the radiation generating device 984 passes through the subject 986 and enters the radiation imaging device 990. The radiation generating device 984 stops emitting the radiation 985 in accordance with a 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. A high voltage and a filament current are supplied to the vacuum tube of the radiation generating unit 101 from the high-voltage generator 107. X-rays are generated by irradiating the anode (target) with thermoelectrons from the cathode (filament).

[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 according to radiation 985 incident on the radiation imaging device 990 and transmits the generated radiation image to the computer 983. The control circuit 993 controls the operation of the radiation detection panel 991. For example, the control circuit 993 generates a stop signal for stopping the radiation generation device 984 from emitting radiation 985, based on an image signal obtained from the radiation detection panel 991. 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 generation device 984.

[0020] The control circuit 993 may be configured with a dedicated circuit such as a programmable logic device (PLD) such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). Alternatively, the control circuit 993 may be configured with a combination of a general-purpose processing circuit such as a processor and a storage circuit such as a memory. In this case, the function of the control circuit 993 may be realized by the general-purpose processing circuit executing a program stored in the storage circuit.

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

[0022] The computer 983 has 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 radiation images obtained by the radiation imaging device 990. Like the control circuit 993, the control unit 971, the receiving unit 972, and the image processing unit 973 may each be configured with a dedicated circuit or a combination of a general-purpose processing circuit and a memory circuit. In one example, the exposure control device 981 has an exposure switch, and when the user turns on the exposure switch, it sends an exposure command to the radiation generation device 984 and sends a start notification indicating the start of radiation irradiation to the computer 983. In response to the start notification, the computer 983 notifies the control circuit 993 of the radiation imaging device 990 of the start of radiation irradiation. When the exposure control device 981 and the computer 983 are not synchronously connected, the radiation detection panel 991 may detect the start of irradiation of radiation 985 based on pixel signals. The control unit 971 may 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 the radiation image output from the radiation imaging device 990.

[0023] 1B is a diagram showing the configuration of a radiation detection panel 991 in which a scintillator 500 is further laminated on a laminated photoelectric conversion unit 100. Radiation photons 600 are incident on the scintillator 500, and are converted from the radiation photons 600 to visible light photons 700 and multiplied by the scintillator 500. Generally, the scintillator 500 multiplies one radiation photon 600 by approximately 1,000 times, and emits it as several thousand visible light photons. The multiplied visible light photons 700 are incident on the photoelectric conversion unit 100, and are detected as an electrical signal by the photoelectric conversion unit 100.

[0024] The photoelectric conversion unit 100 is formed by stacking and electrically connecting two components, a photoelectric conversion substrate 11 and a signal processing substrate 21. The photoelectric conversion substrate 11 includes a first semiconductor layer having a photoelectric conversion element 102 (described later) and a first wiring structure. The signal processing substrate 21 includes 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 formed by stacking the second semiconductor layer, the second wiring structure, the first wiring structure, and the first semiconductor layer in this order. The photoelectric conversion unit 100 is a back-illuminated photoelectric conversion unit in which visible light photons 700 are incident from the second surface and the signal processing substrate 21 is disposed on the first surface side. Note that the techniques described in each embodiment can also be applied to photoelectric conversion units having a front-illuminated structure and can also be applied to photoelectric conversion units consisting of a single layer rather than a stacked type. In other words, the photoelectric conversion substrate 11 and the signal processing substrate 21 may be formed from a common substrate.

[0025] FIG. 2 is a diagram showing an example of the arrangement of the photoelectric conversion substrate 11. Pixels 901 (picture elements) each having a photoelectric conversion element 102 including an avalanche photodiode (APD) are arranged in a two-dimensional array in a plan view to form a pixel region 12. That is, a plurality of pixels may be arranged in a two-dimensional array. Here, the left-right direction in FIG. 2 is referred to as the "row direction," "horizontal direction," "x direction," etc., and the up-down direction in FIG. 2 is referred to as the "column direction," "vertical direction," "y direction," etc. Furthermore, the direction perpendicular to the plane of FIG. 2 is referred to as the "depth direction," "z direction," etc.

[0026] Fig. 3 is a configuration diagram of the signal processing board 21. It has a sub-signal processing unit 103 and a signal processing unit 902 that process the charges photoelectrically converted by the photoelectric conversion element 102 in Fig. 2, 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. The photoelectric conversion element 102 in Fig. 2 and the sub-signal processing unit 103 in Fig. 3 are electrically connected via connection wiring.

[0027] The vertical scanning circuit unit 110 receives a control pulse (drive control signal) supplied from a control pulse generation unit 115, and supplies the control pulse to each pixel via a drive line 116. The vertical scanning circuit unit 110 uses logic circuits such as a shift register and an address decoder.

[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 provided with a counter, memory, etc., and a visible light photon count value is held in the memory. The visible light photon count value is reset once every time a radiation photon is detected.

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

[0030] In order to read out signals from the memory of each pixel where the count value is held, the horizontal scanning circuit unit 111 inputs a control pulse (read control signal) for sequentially selecting each column to the signal processing unit 902. The read control signal is a control pulse signal supplied from the control pulse generation unit 115.

[0031] A signal is output to the signal line 113 from the signal processing unit 902 of the pixel selected by the vertical scanning circuit unit 110 for the selected column. The signal output to the signal line 113 is output via the output circuit 114 to a recording unit or image generation unit 992 external to 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 groups: low energy, medium energy, and high energy radiation photons, and each group is represented by an 8-bit counter, one pixel will be composed of a 24-bit digital value. In Figure 2, the photoelectric conversion elements 102 in the pixel region may be arranged one-dimensionally.

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

[0033] Fig. 4 is an example of a block diagram including the equivalent circuits of Fig. 2 and Fig. 3. In Fig. 4, the photoelectric conversion element 102 having the APD 201 is provided on a photoelectric conversion substrate 11, and the other members are provided on a signal processing substrate 21.

[0034] The APD 201 generates charge pairs in response to incident light through photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 201. A voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode of the APD 201. A reverse bias voltage is supplied to the anode and cathode such that the APD 201 performs avalanche multiplication. With this voltage supplied, the charge generated by the incident light undergoes avalanche multiplication, generating an avalanche current. When a reverse bias voltage is supplied, the APD 201 operates in either a Geiger mode, where the potential difference between the anode and cathode is greater than the breakdown voltage, or a linear mode, where the potential difference between the anode and cathode is near or less than the breakdown voltage. An APD operating in the Geiger mode is called a single-photon avalanche diode (SPAD). For example, the voltage VL (first voltage) is −30 V, and the voltage VH (second voltage) is 1 V. The APD 201 may be operated in either a linear mode or a Geiger mode. A SPAD is preferable because a SPAD has a larger potential difference than a linear mode APD, resulting in a more pronounced effect in terms of withstand voltage.

[0035] The quench element 202 is connected to a power supply that supplies voltage VH and the APD 201. The quench element 202 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, suppressing the voltage supplied to the APD 201 and suppressing avalanche multiplication (quench operation). The quench element 202 also returns the voltage supplied to the APD 201 to voltage VH by passing a current equivalent to the voltage drop caused by the quench operation (recharge operation). Although a passive quench element has been described above, an active quench element (MOS transistor) may be used and the recharge operation may be performed by inputting a clock pulse.

[0036] The sub-signal processing unit 103 has a waveform shaping unit 210 and a counter circuit 211. In this specification, it is sufficient that the sub-signal processing unit 103 has either the waveform shaping unit 210 or the counter circuit 211.

[0037] The waveform shaping unit 210 shapes the potential change of the cathode of the APD 201 obtained when photons are detected, and outputs a pulse signal. For example, an inverter circuit is used as the waveform shaping unit 210. While Fig. 4 shows an example in which one inverter is used as the waveform shaping unit 210, a circuit in which multiple inverters are connected in series, or another circuit that has a waveform shaping effect, may also be used.

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

[0039] The electrical connection may be switched by disposing a switch such as a transistor between the quench element 202 and the APD 201 or between the photoelectric conversion element 102 and the sub-signal processing unit 103. Similarly, the supply of the voltage VH or the voltage VL to the photoelectric conversion element 102 may be electrically switched using a switch such as a transistor.

[0040] 5 is an example of a block diagram including an equivalent circuit of the signal processing unit 902. In this embodiment, a counter circuit 211 that counts visible light photons (hereinafter also referred to as visible light photon counter circuit 211) and radiation photon counter circuits 905, 906, and 907 that count radiation photons are connected in series (multi-stage counter). Here, the counter circuit 211 is an example of a first counter circuit that counts an electrical signal (first electrical signal) converted into visible light by the photoelectric conversion element 102. The radiation photon counter circuits 905, 906, and 907 are an example of a second counter circuit that counts an electrical signal (second electrical signal) 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 FIG. 4 is compared with a threshold value by the comparator 904 and distributed to the radiation photon counter circuits 905, 906, and 907, and the count value of one of the multiple counter circuits is increased depending on the energy of the radiation photons. That is, the second counter circuit may be configured to count the second electrical signal output to a counter circuit selected from the radiation photon counter circuits 905, 906, and 907 using the count value from the first counter circuit. In this case, the selected counter circuit is any one of the radiation photon counter circuits 905, 906, and 907. Here, for example, if the count value from the first counter circuit is equal to or greater than a threshold value, one counter circuit from the plurality of 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 other than the one counter circuit from the plurality of 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 a plurality of different threshold values. The comparison unit 904 is, for example, a comparator. The second counter circuit may count the second electrical signal output to a counter circuit selected from the radiation photon counter circuits 905, 906, and 907 using the comparison result (threshold determination result) by the comparison unit 904. As will be described later, the radiation photon counter circuits 905, 906, and 907 may be configured so that their count values ​​correspond to different radiation photon energies. After one frame period of imaging has elapsed, a control pulse pSEL (selection signal) is supplied from the vertical scanning circuit unit 110 in FIG. 4 to the selection circuit 212 via the drive line 116 in FIG. 5 , which switches between electrical connection and disconnection between the radiation photon counter circuits 905, 906, and 907 and the signal line 113, thereby reading 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 stored count value to the signal line 113 at the timing when a control pulse pSEL (selection signal) is supplied. That is, the selection circuit 212 may be configured to transmit the count values ​​output from each of the multiple counter circuits to the signal line in response to a selection signal from the drive line. The selection circuit 212 may also include, for example, a buffer circuit for outputting a signal.

[0042] 6A and 6B are schematic diagrams showing the relationship between the operation of an APD and an output signal. Fig. 6A is a diagram showing the APD 201, quench element 202, and waveform shaping unit 210 of Fig. 4. Here, the input side of the waveform shaping unit 210 is referred to as node A, and the output side is referred to as node B. The upper part of Fig. 6B shows the waveform change of node A, and the lower part shows the waveform change of node B.

[0043] Between time t0 and time t1, a potential difference of VH-VL is applied to the APD 201. When a photon is incident on the APD 201 at time t1, avalanche multiplication occurs in the APD 201, an avalanche multiplication current flows through the quench element 202, and the voltage at node A drops. When the amount of voltage drop further increases and the potential difference applied to the APD 201 decreases, avalanche multiplication in the APD 201 stops, as at time t2, and the voltage level at node A no longer drops below a certain value. Thereafter, between time t2 and time t3, a current that compensates for the voltage drop from voltage VL flows through node A, and at time t3, node A settles to its original potential level. At this time, the portion of the output waveform at node A that exceeds a certain threshold is shaped by the waveform shaping unit 210 and output as a signal at node B.

[0044] Here, the operation of the multi-stage counter in this embodiment will be described. FIG. 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 diagram, 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 FIG. 1B , when one radiation photon is incident on the scintillator, it is emitted 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. For simplicity of explanation, FIG. 7 shows only three count periods of the radiation counter circuit (count periods 710, 720, and 730), and subsequent periods 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] Count period 710 is an example of a case where no radiation photons are incident during the count period. When no radiation photons are incident, no visible light photons are generated. 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 counting by the radiation photon counter circuits 905, 906, and 907. In other words, the count value reset by the first counter circuit may be performed at the count cycle of the second counter circuit.

[0046] Count periods 720 and 730 are examples where incident radiation photons are incident during the count period. In period 720, 722 is the timing at which the radiation photon is incident on the scintillator, and 721 is a group of visible light photons generated in response to the incidence of the radiation photon. In period 730, 732 is the timing at which the radiation photon is incident on the scintillator, and 731 is a group of visible light photons generated in response to the incidence of the radiation photon. Periods 720 and 730 differ in the timing and energy of the radiation photons incident. The number of visible light photons 723 generated at this time is proportional to the energy of the radiation photon. This is because, although phosphors differ depending on the material, the number of visible light photons per unit energy of a radiation photon is fixed. The comparator 904 compares the count value held in the visible light photon counter circuit 211 with a threshold value to identify the radiation energy. The count numbers by the radiation photon counter circuits 905, 906, and 907 are then increased in accordance with the energy of the radiation photon. That is, the radiation photon counter circuits 905, 906, 907 may be configured so that the count values ​​generated by each correspond to different radiation photon energies.

[0047] For example, 30 kV to 60 kV radiation photons are allocated to the radiation photon counter circuit 905, 60 kV to 90 kV radiation photons to the radiation photon counter circuit 906, and 90 kV to 120 kV radiation photons to the radiation photon counter circuit 907. At this time, if the count value of the visible light photons 721 is 200 counts, it is recognized that 80 kV radiation photons have been irradiated, and the count value of the 60 to 90 kV radiation photon counter circuit 906 is incremented by one. If the count value of the visible light photons 731 is 100 counts, it is recognized that 40 kV radiation photons have been irradiated, and the count value of the 30 kV to 60 kV radiation photon counter circuit 905 is incremented by one.

[0048] As described above, in this embodiment, the electrical signal of visible light generated in the scintillator by radiation photons is treated as a plurality of digital signals. This signal is an electrical signal generated by a single visible light photon, and the number of such signals varies depending on the energy of the radiation photon. In this case, the first counter circuit may count each visible light photon. In other words, the count value may be incremented by one each time a visible light photon is detected. Alternatively, the first counter circuit may increment the count value by one when one or more visible light photons are detected within a predetermined period of time.

[0049] The second counter circuit may count the radiation photons by counting the electrical signal output to one of the plurality of counter circuits using the count value from the first counter circuit. This makes it possible to obtain the energy of the radiation photons more accurately, since it is less susceptible to noise caused by dark current and the like, compared to when threshold determination is performed based on the peak height (peak value) of the waveform of the analog signal.

[0050] The operation described in Fig. 7 is repeated for each pixel to generate an image in which radiation energy information is identified based on the count values ​​of radiation photons. For example, the count values ​​of the radiation photon counter circuits 905, 906, and 907 may be assigned to the three primary color hues R (red), G (green), and B (blue), and a color image may be generated in which the count values ​​of each counter circuit represent the degree of hue. In other words, different hues (e.g., R, G, and B) may be assigned to multiple counter circuits, and a color image may be generated in which the count values ​​of each of the multiple counter circuits represent 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.

[0051] Note that the count value of visible light photons varies depending on the configuration of the scintillator and reflective layer, and therefore the threshold is not limited to 100 counts or 200 counts. Similarly, the radiation photon energy intervals allocated to the radiation photon counter circuits 905, 906, and 907 are not limited to 30 kV to 60 kV, 60 kV to 90 kV, and 90 kV to 120 kV. The radiation photon energy may be changed depending on imaging conditions such as the radiation source used, the subject, and the application. The energy intervals are not limited to 30 kV, 60 kV, and 90 kV. The energy allocation range is not limited to 30 kV intervals, and is not limited to equal intervals. Furthermore, although the case where the number of radiation photon counter circuits is three has been described, there may be more or fewer.

[0052] The count period 711 of the visible light photon counter circuit 211 is preferably set to a value with a sufficient margin for the amount of light emitted by the scintillator so that multiple visible light photons do not become incident within one period. Similarly, the count period 712 of the radiation photon counter circuit is preferably set to a value with a sufficient margin for the radiation exposure conditions so that multiple radiation photons do not become incident within one period (pile-up). Also, it is preferably set to a value with a sufficient margin for the light emission of the scintillator so that multiple counts do not occur during the radiation photon emission period. Alternatively, it is preferable to use a scintillator whose light emission period is sufficiently short relative to the count period 712 of the radiation photon counter circuit.

[0053] (Example of SPAD Structure) Here, Fig. 8 and Fig. 9 show the structure of the photoelectric conversion substrate 11 (sensor substrate) of the photoelectric conversion unit. Fig. 8 is a plan view showing the configuration of the pixel region, and schematically shows the semiconductor layer 300 of the photoelectric conversion substrate 11 as viewed from the first surface side. Fig. 9 is a cross-sectional view taken along line A-A (diagonal direction) in Fig. 8.

[0054] As shown in FIG. 8 , a plurality of APDs 201 are arranged in a two-dimensional array in the row direction (horizontal direction in FIG. 8 ) and the column direction (vertical direction in FIG. 8 ) in the semiconductor layer 300. For convenience of illustration, FIG. 8 depicts only nine APDs 201 arranged in three rows and three columns. However, in an actual product, for example, hundreds of thousands to millions of APDs 201 are formed. Each APD 201 corresponds to one pixel. The semiconductor layer 300 is provided with an isolation portion 330, which is an isolation structure for reducing crosstalk between adjacent APDs 201. The isolation portion 330 is formed in a lattice pattern by a plurality of row-direction isolation portions 330X extending in the row direction and a plurality of column-direction isolation portions 330Y extending in the column direction. An APD 201 is arranged in each of the sections divided by the lattice-shaped isolation portions 330. In this embodiment, the section corresponding to one pixel has a substantially square shape in a plan view. The boundaries of the sections are arranged to overlap the isolation portions 330, for example. The cathode wiring contact plug 326 formed in the wiring structure 320 is disposed approximately in the center of the pixel (section), and the anode wiring contact plugs 324 are disposed at the four corners of the pixel. That is, in this embodiment, four anode contact plugs 324 are provided for one pixel.

[0055] As shown in FIG. 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 surface of the semiconductor layer 300 facing the wiring structure 320 is referred to as the first surface, and the surface opposite the first surface is referred to as the second surface. The semiconductor layer 300 is made of, for example, silicon. A fixed charge film 310, an insulating film 311, a planarization film 312, and the like are stacked in this order on the second surface of the semiconductor layer 300, and microlenses 313 corresponding to each pixel are further provided above them. That is, the photoelectric conversion unit of this embodiment has a so-called back-illuminated structure in which light enters the semiconductor layer 300 from the second surface side. The second surface is sometimes referred to as the light incident surface. Although FIG. 9 shows the microlenses 313, their provision is not essential. Furthermore, the following structure can be applied to the light incident surface. For example, a concave-convex structure, such as at least one or more concave or convex portions, is arranged on the second surface, which is the light incident surface. The concave-convex structure is formed by the silicon constituting 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 disposed in a recess provided in the semiconductor layer 300. An interface having a refractive index difference that is not parallel to the second surface is formed. With this configuration, incident light is diffracted, thereby improving sensitivity to light in the infrared region.

[0056] The fixed charge film 310 is made of a dielectric material having a negative fixed charge and is disposed over the entire second surface of the semiconductor layer 300. The material of the fixed charge film 310 is 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 be configured with multiple layers. The insulating film 311 is disposed over the entire second surface on the fixed charge film 310. Suitable examples of the insulating film 311 include a silicon oxide film, a silicon oxynitride film, and a silicon nitride film. The insulating film 311 may be configured with multiple layers. Although not shown, in addition to the planarization film 312, a filter layer such as a color filter or an infrared light blocking filter may be provided on the second surface side of the semiconductor layer 300.

[0057] The wiring structure 320 is a structure in which multiple layers of wiring 321, 322, and 323, via plugs 325 and 327 that connect the wirings, a contact plug 324 for an anode wiring, a contact plug 326 for a cathode wiring, and the like are arranged in an insulating layer 329. The lower surface of the wiring structure 320 (the surface opposite to the semiconductor layer 300) is a bonding surface with the signal processing substrate 21, and a plurality of bonding portions 328 are provided on the bonding surface.

[0058] The semiconductor layer 300 includes 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 are added by ion implantation or 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 a 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 a second conductivity type (P-type in this embodiment). The first semiconductor region 301 is a semiconductor region of a first conductivity type (N-type in this embodiment) and is provided on the first surface of the semiconductor layer 300. As shown in FIG. 8 , the first semiconductor region 301 in this embodiment is formed in a circular shape in the center of a pixel (section) in a plan view. A cathode contact plug 326 is connected to the center position of the first semiconductor region 301. The fifth semiconductor region 305 is a semiconductor region of a second conductivity type (P-type in this embodiment) and is disposed on the light incident side (closer to the second surface) than the first semiconductor region 301. The fifth semiconductor region 305 is formed in a layer shape at a predetermined depth so as to divide the first conductivity type epitaxial layer in one pixel (section) into upper and lower parts. The periphery of the fifth semiconductor region 305 is in contact with an isolation portion 330 that surrounds the pixel. The first conductivity type epitaxial layer located closer to the first surface than the fifth semiconductor region 305 is the sixth semiconductor region 306, and the first conductivity type epitaxial layer located closer to the second surface is the eighth semiconductor region 308. The first conductivity type first semiconductor region 301 and the second conductivity type fifth semiconductor region 305 form an avalanche multiplication unit AM through a PN junction. Signal charges generated in the eighth semiconductor region 308 by photoelectric conversion are collected in the avalanche multiplication unit AM. In order to improve the sensitivity of the APD 201, it is preferable to increase the size of the eighth semiconductor region 308, which corresponds to the sensitive region. The seventh semiconductor region 307 is a first conductivity type semiconductor region formed around the first semiconductor region 301.The seventh semiconductor region 307 is also formed in a circular shape in a plan view. 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 first semiconductor region 301 has the highest impurity concentration, and the seventh semiconductor region 307 has an impurity concentration between the first semiconductor region 307 and the sixth semiconductor region 306. This ensures electrical connection between the cathode and the first semiconductor region 301 (i.e., the APD 201). The seventh semiconductor region 307 also serves as a guard ring for electric field relaxation. The ninth semiconductor region 309 is a buried layer of the second conductivity type provided over the entire second surface of the semiconductor layer 300. The ninth semiconductor region 309 serves to suppress noise from the second surface side. Furthermore, the ninth semiconductor region 309 can be supplied with a voltage VL from the anode wiring via the second semiconductor region 302. In this case, a potential gradient for collecting charges can be formed.

[0059] Second Embodiment In the first embodiment, single visible light photons and radiation photons are counted one by one in order to estimate the radiation energy with high accuracy. Here, counting losses can occur when the light emitted by the scintillator spans multiple pixels or when the processing speed of the signal processing circuit is insufficient. Therefore, in the second embodiment, a configuration is shown in which partitions are provided in the scintillator in order to suppress counting losses of visible light photons and radiation photons and estimate the radiation energy with high accuracy. Specifically, as will be described later, a pixel scintillator configuration is shown in which the scintillators are separated by partitions provided in accordance with the pixels 901 of the photoelectric conversion unit 100. Note that a description of parts common to the first embodiment will be omitted.

[0060] A configuration for reducing count losses of visible light photons caused by the light emission of the scintillator spanning across pixels will be described with reference to Fig. 10. Fig. 10 is a diagram showing the configuration of a radiation detection panel 991 in which a scintillator 501 is further stacked on a stacked-type photoelectric conversion unit 100.

[0061] The scintillator 501 is a pixel scintillator (or partition phosphor) separated to correspond to the pixels 901 of the photoelectric conversion unit 100. By using a pixel scintillator, it is possible to reduce the incidence of visible light photons 700 on adjacent pixels, and to count the number of visible light photons 700 resulting from one radiation photon in one pixel.

[0062] Materials suitable for the scintillator 501 include CsI:Tl, CsI, Lu3Al5O12:Ce, PbWO4, Gd3Al2Ga3O12:Ce, (Lu,Y)2SiO5:Ce, and Gd2O2S:Tb(Pr), which have good radiation stopping properties and respond at 1 us or less.

[0063] A pixel scintillator is made by forming a metal reflective layer on a partition substrate made by penetrating a silicon wafer using a through-silicon via (TSV) process, and then filling it with scintillator material. In addition to using a silicon wafer, the partition substrate can also be formed by depositing polyimide resin (PI). Other methods for filling the scintillator material include heating and melting the scintillator material, or powdering the scintillator material and mixing it with a binder resin. When using a scintillator material that deliquesces in humidity, such as CsI, it is recommended to use ALPET, a composite material made by laminating aluminum foil and polyester film, as the moisture-proof layer. Furthermore, when laminating the moisture-proof layer to the partition substrate, laminating a reflective layer made of a hot-melt sheet containing TiO2 can achieve both moisture resistance and reflective performance.

[0064] 11 to 13, a configuration for reducing count losses of visible light photons due to insufficient processing speed of the signal processing circuit will be described. By dividing pixels into subpixels and dispersing visible light photons in the spatial direction, the burden on processing speed is reduced and count losses of visible light photons are reduced.

[0065] 11 is a diagram showing an example of the arrangement of the photoelectric conversion substrate 11. Pixels 901, each of which includes subpixels 101, each having a photoelectric conversion element 102 including an avalanche photodiode (APD), are arranged in five rows and five columns, forming a two-dimensional array in a plan view to form a pixel region 12. That is, each of the plurality of pixels may be composed of a plurality of subpixels, and each of the plurality of subpixels may have a photoelectric conversion element and a first counter circuit. Furthermore, the size of each of the plurality of pixels may be several tens to several hundreds of μm, and each of the plurality of pixels may be composed of several hundreds to several thousands of subpixels.

[0066] 12 is a configuration diagram of the signal processing board 21. It has a sub-signal processing unit 103 that processes the charges photoelectrically converted by the photoelectric conversion element 102 in FIG. 11, a signal processing unit 902 that combines signals from the sub-signal processing unit 103 into a signal 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.

[0067] The photoelectric conversion element 102 in FIG. 11 and the sub-signal processing unit 103 in FIG. 12 are electrically connected via connection wiring provided for each sub-pixel.

[0068] The vertical scanning circuit unit 110 receives a control pulse (drive control signal) supplied from a control pulse generation unit 115, and supplies the control pulse to each pixel via a drive line 116. The vertical scanning circuit unit 110 uses logic circuits such as a shift register and an address decoder.

[0069] The signals output from the photoelectric conversion elements 102 of the sub-pixels are processed by a sub-signal processing unit 103. The sub-signal processing unit 103 is provided with a counter, memory, etc., and a visible light photon count value is held in the memory. The visible light photon count value is reset once every time a radiation photon is detected.

[0070] The signal processing unit 902 reads out and integrates the visible light photon count values ​​of the 5 rows and 5 columns of the sub-signal processing units 103 to estimate the energy of the radiation photons 600. For example, if the total of the visible light photon count values ​​of the 5 rows and 5 columns is 100 counts, it is recognized that 40 kV radiation photons 600 have been irradiated, and the count value of the 30 kV to 60 kV radiation photons is incremented by one. If the total of the visible light photon count values ​​of the 5 rows and 5 columns is 200 counts, it is recognized that 80 kV radiation photons have been irradiated, and the count value of the 60 to 90 kV radiation photons is incremented by one.

[0071] In order to read out signals from the memory of each pixel in which the radiation photon count value is held, the horizontal scanning circuit unit 111 inputs control pulses (read control signals) that sequentially select each column to the signal processing unit 902. The read control signals are control pulse signals supplied from the control pulse generation unit 115.

[0072] A signal from the signal processing unit 902 of the pixel selected by the vertical scanning circuit unit 110 for the selected column is output to the signal line 113. The signal output to the signal line 113 is output via the output circuit 114 to a recording unit or image generation unit 992 external to 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 the multiple sub-pixels. For example, if the output value of one pixel is divided into three groups: 30 to 60 kV radiation photons, 60 to 90 kV radiation photons, and 90 to 120 kV radiation photons, and each group is represented by an 8-bit counter, then one pixel will be composed of a 24-bit digital value.

[0073] 11, the photoelectric conversion elements 102 may be arranged one-dimensionally in the pixel region. 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 a plurality of photoelectric conversion elements 102, and signal processing may be performed sequentially. Note that the block diagrams including the equivalent circuits in FIGS. 11 and 12 have the same configuration as FIG. 4 of the first embodiment, and therefore description thereof will be omitted.

[0074] Fig. 13 is an example of a block diagram including an equivalent circuit of the signal processing unit 902. The sub-signal processing units 103 shown in Fig. 4 are arranged in five rows and five columns, and the visible light photon count values ​​held in the counter circuits 211 of the sub-signal processing units 103 are added up in an accumulator 903. A comparator 904 compares the accumulated visible light photon count value with a threshold value and distributes it to a 30 kV to 60 kV radiation photon counter circuit 905, a 60 kV to 90 kV radiation photon counter circuit 906, and a 90 kV to 120 kV radiation photon counter circuit 907, and the counter is incremented according to the energy of the radiation photons. After one frame period of imaging has elapsed, a control pulse pSEL (selection signal) is supplied from the vertical scanning circuit unit 110 in FIG. 12 to the selection circuit 212 via the drive line 116 in FIG. 13 , which switches between electrical connection and disconnection between the 30 kV to 60 kV radiation photon counter circuit 905, the 60 kV to 90 kV radiation photon counter circuit 906, and the 90 kV to 120 kV radiation photon counter circuit 907 and the signal line 113, thereby reading out the count values. 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 stored count value 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 in response to the selection signal from the drive line. The selection circuit 212 also includes, for example, a buffer circuit for outputting a signal.

[0075] (Other Embodiments) The disclosed technology can also be realized by executing the following process. That is, the disclosed technology can also be realized by providing software (programs) that realize one or more functions of the various embodiments described above to a system or device via a network or a storage medium, and having a computer (or a CPU, MPU, etc.) of the system or device read and execute the programs. The computer has one or more processors or circuits, and may include multiple separate computers or a network of multiple separate processors or circuits to read and execute 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 data flow processor (DFP), or a neural processing unit (NPU).

[0076] The disclosed technology may include the following configurations.

[0077] (Configuration 1) A radiation imaging device comprising: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts the visible light into a first electrical signal; and a signal processing unit including: a first counter circuit that counts the first electrical signal; and a second counter circuit that counts 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 a count value by the first counter circuit.

[0078] (Configuration 2) The radiation imaging device according to Configuration 1, wherein the first counter circuit counts visible light photons by counting the first electrical signal, and the second counter circuit counts radiation photons by counting the second electrical signal.

[0079] (Configuration 3) The radiation imaging device according to Configuration 1 or 2, wherein the count period of the first counter circuit is shorter than the count period of the second counter circuit, and the count value of the first counter circuit is reset at the count period of the second counter circuit.

[0080] (Configuration 4) A radiation imaging device according to any one of configurations 1 to 3, configured such that when the count value by the first counter circuit is equal to or greater than a threshold value, one counter circuit of the plurality of counter circuits is selected, and when the count value by the first counter circuit is less than the threshold value, a counter circuit other than the one counter circuit of the plurality of counter circuits is selected.

[0081] (Configuration 5) A radiation imaging device according to any one of configurations 1 to 4, wherein 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 threshold values ​​that are different from each other, and the second counter circuit counts the second electrical signal output to a counter circuit selected from the plurality of counter circuits using a comparison result by the comparison unit.

[0082] (Configuration 6) The radiation imaging device according to any one of Configurations 1 to 5, wherein the pixels each have a photoelectric conversion element, and a plurality of pixels are arranged in a two-dimensional array, and the scintillator is configured as a pixel scintillator by providing a partition wall for each pixel.

[0083] (Configuration 7) The radiation imaging apparatus according to Configuration 6, wherein each of the plurality of pixels is composed of a plurality of sub-pixels, and each of the plurality of sub-pixels has the photoelectric conversion element and the first counter circuit.

[0084] (Configuration 8) The radiation imaging device according to any one of configurations 1 to 7, wherein the photoelectric conversion element is a single photon avalanche diode, and the single photon avalanche diode is connected to a quench element that functions as a load circuit when signals are multiplied by avalanche multiplication.

[0085] (Configuration 9) The radiation imaging apparatus according to any one of configurations 1 to 8, wherein the counting cycle of the first counter circuit is several hundred to several thousand times the counting cycle of the second counter circuit.

[0086] (Configuration 10) The radiation imaging apparatus according to any one of configurations 1 to 9, wherein the plurality of counter circuits are configured so that the count values ​​generated by each of the counter circuits correspond to different energies of radiation photons.

[0087] (Configuration 11) The radiation imaging device 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 values ​​of the respective plurality of counter circuits represent degrees of hue.

[0088] (Configuration 12) The radiation imaging device according to Configuration 11, wherein the different hues are R, G, and B, and 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.

[0089] (Configuration 13) The radiation imaging apparatus according to any one of configurations 1 to 12, further comprising a selection circuit that transmits the count values ​​output from the plurality of counter circuits to a signal line in response to a selection signal from a drive line.

[0090] (Configuration 14) A radiation imaging system comprising: the radiation imaging device according to any one of configurations 1 to 13; a radiation generating device that irradiates radiation toward the radiation imaging device; and an image processing device that processes a radiation image output from the radiation imaging device.

[0091] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are appended.

[0092] This application claims priority based on Japanese Patent Application No. 2024-152994, filed September 5, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A radiation imaging device comprising: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts the visible light into a first electrical signal; and a signal processing unit including: a first counter circuit that counts the first electrical signal; and a second counter circuit that counts 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 of the first counter circuit.

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

3. A radiation imaging device according to claim 1, wherein the count period of the first counter circuit is shorter than the count period of the second counter circuit, and the count value of the first counter circuit is reset at the count period of the second counter circuit.

4. A radiation imaging device as described in claim 1, configured such that when the count value by the first counter circuit is equal to or greater than a threshold value, one counter circuit of the plurality of counter circuits is selected, and when the count value by the first counter circuit is less than the threshold value, a counter circuit other than the one counter circuit of the plurality of counter circuits is selected.

5. The radiation imaging device according to claim 1, wherein 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 threshold values ​​that are different from each other, and the second counter circuit counts the second electrical signal output to a counter circuit selected from the plurality of counter circuits using the comparison result by the comparison unit.

6. The radiation imaging device according to claim 1, wherein the pixels each have a photoelectric conversion element, and a plurality of pixels are arranged in a two-dimensional array, and a partition is provided for each pixel in the scintillator, thereby forming a pixel scintillator.

7. A radiation imaging apparatus according to claim 6, wherein each of the plurality of pixels is composed of a plurality of sub-pixels, and each of the plurality of sub-pixels has the photoelectric conversion element and the first counter circuit.

8. A radiation imaging device according to claim 1, wherein the photoelectric conversion element is a single photon avalanche diode, and the single photon avalanche diode is connected to a quench element that functions as a load circuit when signals are multiplied by avalanche multiplication.

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

10. The radiation imaging apparatus according to claim 1, wherein the plurality of counter circuits are configured so that the count values ​​generated by each of the counter circuits correspond to different radiation photon energies.

11. A 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 values ​​of the respective plurality of counter circuits represent degrees of hue.

12. The radiation imaging device according to claim 11, wherein the different hues are R, G, and B, and 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 the plurality of counter circuits to a signal line in response to a selection signal from a drive line.

14. A radiation imaging system comprising: a radiation imaging device according to any one of claims 1 to 13; a radiation generating device that irradiates radiation toward said radiation imaging device; and an image processing device that processes a radiation image output from said radiation imaging device.

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