Indirect photon-counting radiography device, radiography system, processing device, estimation method for radiation energy, and program

Abstract

This indirect photon-counting radiography device comprises: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts the visible light into an electric signal; a detection unit that detects an output value of the photoelectric conversion element; and an estimation unit that estimates the energy of incident radiation on the basis of a time trend in the detection result of the detection unit.

Description

Indirect photon counting radiation imaging apparatus, radiation imaging system, processing apparatus, radiation energy estimation method, and program

[0001] The present invention relates to an indirect photon counting radiation imaging apparatus, a radiation imaging system, a processing apparatus, a radiation energy estimation method, and a program.

[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. In the FPD, minute radiation detectors, each formed by laminating 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, are arranged in a matrix on a quartz glass substrate. Examples of the solid-state photodetector include CCD (Charge-Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor). In recent years, apparatuses using photodetectors such as APD (Avalanche PhotoDiode) and SPAD (Single-Photon Avalanche Diode) are also known.

[0003] FPDs include integral sensors and photon counting sensors. The integral sensor measures the total amount of electric charge generated by incident radiation. In contrast, a photon counting sensor identifies the energy (wavelength) of incident radiation and counts the number of radiation detections for each of a plurality of energy levels. That is, since the photon counting sensor has energy resolution, it can improve diagnostic capability compared with an integral sensor.

[0004] Photon counting sensors are further divided into direct type and indirect type. The direct type counts the number of radiation detections by directly detecting radiation energy using CdTe. The indirect type counts the number of radiation detections by indirectly detecting radiation energy based on visible light generated in a scintillator upon incidence of radiation.

[0005] Japanese Patent Publication No. 2017-20912

[0006] Patent Document 1 describes a method for counting and discriminating radiation by identifying the spatial distribution of visible light generated by a scintillator when a single radiation particle is incident. However, since the scintillator emits light for a certain period of time in response to the incident radiation, we have found that there is room for improvement in the accuracy of radiation counting and energy discrimination when measuring the spatial distribution of light.

[0007] The indirect photon counting radiation imaging apparatus of the present invention, which solves the above problems, comprises a scintillator that converts radiation into visible light, a photoelectric conversion element that converts visible light into an electrical signal, a detection unit that detects the output value of the photoelectric conversion element, a measurement unit that measures the time progression of the detection result of the detection unit, and an estimation unit that estimates the energy of the incident radiation based on the detection result and the measurement result of the measurement unit.

[0008] According to the present invention, an indirect photon counting radiation imaging device capable of accurately counting and discriminating radiation energy can be provided.

[0009] Examples of radiation imaging system configurations Schematic diagram of radiation detection panel Schematic diagram of photoelectric conversion board of radiation detection panel Schematic diagram of signal processing board of radiation detection panel Schematic diagram of detection circuit of conventional radiation detection panel Operation timing diagram of detection circuit of conventional radiation detection panel Schematic diagram of detection circuit of radiation detection panel of the first embodiment Operation timing diagram of detection circuit of radiation detection panel of the first embodiment Schematic diagram of detection circuit of radiation detection panel of the second embodiment Operation timing diagram of detection circuit of radiation detection panel of the second embodiment Schematic diagram of detection circuit of radiation detection panel of the third embodiment Operation timing diagram of detection circuit of radiation detection panel of the third embodiment Schematic diagram of detection circuit of radiation detection panel of the fourth embodiment Estimation flow diagram of estimation unit of the fourth embodiment Operation timing diagram of detection circuit of radiation detection panel of the fourth embodiment

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] In the following description, terms indicating specific directions or positions (e.g., "up," "down," "right," "left," and other terms including these) will be used as needed. The use of these terms is for the purpose of facilitating the understanding of embodiments with reference to the drawings, and the meaning of these terms does not limit the technical scope of the present invention.

[0012] In this specification, a plan view refers to viewing a semiconductor layer from a direction perpendicular to the light incident surface. A cross-sectional view refers to a surface perpendicular to the light incident surface of the semiconductor layer. If the light incident surface of the semiconductor layer is rough when viewed microscopically, the plan view is defined based on the light incident surface of the semiconductor layer as viewed macroscopically.

[0013] The semiconductor layer has a first surface and a second surface opposite to the first surface, to which light is incident. In this specification, the depth direction is the direction from the first surface to the second surface of the semiconductor layer in which the APD is arranged. Hereafter, the "first surface" may be referred to as the "front surface" and the "second surface" may be referred to as the "back surface".

[0014] In the following description, the anode of the avalanche photodiode (APD) is set to a fixed potential, and the signal is taken from the cathode side. Therefore, the semiconductor region of the first conductivity type, which has majority carriers of the same polarity as the signal charge, is an N-type semiconductor region, and the semiconductor region of the second conductivity type, which has majority carriers of charges with a different polarity than the signal charge, is a P-type semiconductor region. Note that the present invention also applies when the cathode of the APD is set to a fixed potential and the signal is taken from the anode side. In this case, the semiconductor region of the first conductivity type, which has majority carriers of the same polarity as the signal charge, is a P-type semiconductor region, and the semiconductor region of the second conductivity type, which has majority carriers of charges with a different polarity than the signal charge, is an N-type semiconductor region. The following description will focus on the case where one node of the APD is set to a fixed potential, but the potentials of both nodes may fluctuate.

[0015] In this specification, when the term "impurity concentration" is used, it refers to the net impurity concentration after subtracting the amount compensated by reverse-conductivity impurities. The region where the concentration of P-type added impurities is higher than the concentration of N-type added impurities is the P-type semiconductor region. Conversely, the region where the concentration of N-type added impurities is higher than the concentration of P-type added impurities is the N-type semiconductor region.

[0016] (First Embodiment) First, the configuration of the system of the first embodiment will be described.

[0017] Figure 1 shows an example configuration of a radiation imaging system 980 according to one embodiment. The radiation imaging system 980 is configured to generate an electrical radiation image by electrically capturing an optical image formed by 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 and a computer 983. In the preferred embodiment shown in Figure 1, it further includes a display 982, an exposure control device 981, and a radiation generator 984.

[0018] The radiation generator 984 begins irradiating with radiation 985 in accordance with an exposure command (radiation command) from the exposure control device 981. The radiation 985 emitted from the radiation generator 984 passes through the subject 986 and enters the radiation imaging device 990. The radiation generator 984 also stops irradiating with radiation 985 in accordance with a stop command from the exposure control device 981.

[0019] The radiation imaging device 990 is an indirect photon counting type radiation imaging device and 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 is composed of a PLD (Programmable Logic Device), such as an FPGA (Field Programmable Gate Array). Alternatively, it may be composed of a dedicated circuit such as an ASIC (Application Specific Integrated Circuit). Instead, 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] In this embodiment, the computer 983, which is a control device for controlling the radiation imaging device, can also control the exposure control device, in a preferred form. The computer 983 has a control unit for controlling the radiation imaging device 990 and the exposure control device 981, a receiving unit for receiving radiation images from the radiation imaging device 990, and a signal processing unit for processing the radiation images acquired from the radiation imaging device 990. The control unit, receiving unit, and signal processing unit 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. The computer 983 may also receive the output of the radiation counter circuit described later from the radiation imaging device 990 instead of radiation images, and analyze the energy of the radiation irradiated to the radiation imaging device 990. Alternatively, instead of the output of the radiation counter circuit, the computer 983 may receive the output of the visible light counter described later (count value and information on its time progression), and analyze the radiation energy incident on the radiation imaging device 990. In these cases, the configuration of the radiation imaging device 990 can be simplified. Furthermore, the computer 983 does not need to have a control function for the radiation imaging device; in this case, the computer 983 functions as a signal processing device. In this embodiment, 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 of the radiation 985 based on the pixel signal.

[0023] Figure 2 shows the configuration of a radiation detection panel 991 in which a scintillator 200 is further stacked on a stacked photoelectric conversion unit 100. A radiation photon 201 is incident on the scintillator 200, and the scintillator 200 converts and multiplies the radiation photon 201 into a visible light photon 202. Generally, the scintillator 200 multiplies one radiation photon 201 by about 1000 times, causing it to emit thousands of visible light photons.

[0024] The amplified visible light photons 202 are incident on the photoelectric conversion unit 100 and detected as electrical signals in the photoelectric conversion unit 100.

[0025] The photoelectric conversion unit 100 is constructed by stacking and electrically connecting two components: a photoelectric conversion substrate 11 and a signal processing substrate 21. 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 202 are incident from the second surface and the signal processing substrate 21 is arranged on the first surface side. Note that the inventions according to 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 instead of a stacked type.

[0026] Figure 3 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. Here, the left-right direction in Figure 3 is expressed as "row direction," "horizontal direction," "x direction," etc., and the up-down direction in Figure 3 is expressed as "column direction," "vertical direction," "y direction," etc. Also, the direction perpendicular to the plane of the paper in Figure 3 is expressed as "depth direction," "z direction," etc.

[0027] Figure 4 is a diagram showing the configuration 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 3, a readout circuit 112, a control pulse generation unit 115, a horizontal scanning circuit unit 111, a signal line 113, a vertical scanning circuit unit 110, and a drive line 116.

[0028] The photoelectric conversion element 102 in Figure 3 and the sub-signal processing unit 103 in Figure 4 are electrically connected via connecting wiring.

[0029] The vertical scanning circuit section 110 receives control pulses 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.

[0030] The signal output from the photoelectric conversion element 102 is processed by the sub-signal processing unit 103.

[0031] The sub-signal processing unit 103 is equipped with a counter and memory, and the memory stores the visible light photon count value. The visible light photon count value is reset once each time a radiation photon is detected.

[0032] 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 201. Control pulses are input to the signal processing unit 902 to sequentially select each column in order to read the signal from the memory of each pixel in which the count value is held.

[0033] For the selected column, a signal is output from the signal processing unit 902 of the pixel selected by the vertical scanning circuit unit 110 to the signal line 113.

[0034] The signal output to the signal line 113 is output via the output circuit 114 to an external recording unit or image generation circuit 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 3, the arrangement of photoelectric conversion elements 102 in the pixel region may be arranged in a one-dimensional manner.

[0035] As shown in Figures 3 and 4, a plurality of 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.

[0036] 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 that case, the photoelectric conversion substrate 11 and the signal processing substrate 21 can be tiled in the x and y directions to increase the surface area.

[0037] Furthermore, multiple photoelectric conversion boards 11 and signal processing boards 21 can be stacked in the z-direction on a single wiring board to increase the surface area.

[0038] Figure 5 is a conventional example of a block diagram including the equivalent circuits of Figures 3 and 4. In Figure 4, the pixel 901 having the APD 501 is provided on the photoelectric conversion substrate 11, and the other components are provided on the signal processing substrate 21.

[0039] The APD 501 generates charge pairs corresponding to incident light through photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 501. A voltage VH (second voltage), higher than the voltage VL supplied to the anode from the potential supply means, is supplied to the cathode of the APD 501 via a switch element 502 that functions as a changeover switch. For example, a CMOS transistor is used for the switch element 502. A reverse bias voltage is supplied to the anode and cathode such that the APD 501 performs avalanche multiplication. By supplying such voltages, the charge generated by the incident light undergoes avalanche multiplication, and an avalanche current is generated.

[0040] Furthermore, when a reverse bias voltage is supplied, there are two modes of operation: Geiger mode, in which the potential difference between the anode and cathode is greater than the breakdown voltage, and linear mode, in which the potential difference between the anode and cathode is near or below the breakdown voltage.

[0041] 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 APD501 may operate in linear mode or in Geiger mode. In the case of a SPAD, the potential difference is larger compared to a linear-mode APD, and the voltage withstand capability effect is more pronounced, so it is preferable to use a SPAD.

[0042] The APD 501 is connected to a sampling circuit 510, which consists of a switch element 502 and a waveform shaping unit 503. The sampling circuit 510 is a detection unit capable of detecting the output value, which is the charge generated by the photoelectric conversion element 102, and may be simply referred to as the detection unit below. The waveform shaping unit 503 shapes the potential change of the cathode of the APD 501 obtained when a photon is detected and outputs a pulse signal. Therefore, the sampling circuit 510 detects the presence or absence of charge output from the photoelectric conversion element using the waveform shaping unit 503. The switch element 502 is connected to the APD 501 and a power supply, which is a potential supply means that supplies voltage VH. A reset clock 605 is periodically input to the switch element 502, which returns the potential of the cathode of the APD 501 to voltage VH. The output of the waveform shaping unit 503, which is the detection result of the sampling circuit 510, is connected to a visible light counter 505. The visible light counter 505 counts the number of pulse signals output from the waveform shaping unit 503. The output of the visible light counter 505 is connected to the radiation counter circuit 512. The radiation counter circuit 512 has three counters, one for each energy band of radiation: a low-energy counter 506, a medium-energy counter 507, and a high-energy counter 508. The radiation counter circuit 512 periodically refers to the count value of the visible light counter 505. Then, depending on the count value of the visible light counter 505, it counts using one of the low-energy counter 506, medium-energy counter 507, or high-energy counter 508, and resets the count value of the visible light counter 505. The counters in the radiation counter circuit 512 do not necessarily have to represent three energy bands; there may be fewer or more than three.

[0043] The operation timing of the conventional example will be described with reference to FIG. 6. When 70 keV radiation 610 is incident on the scintillator 200, light is emitted for a certain period of time according to the energy of the radiation, like light emission 620. Visible light photons generated from the scintillator 200 are incident on the APD 501. The cathode potential of the APD 501 drops when visible light photons are incident thereon, and is restored to VH when a reset clock 605 is input. A waveform shaping unit 503 outputs a pulse signal in accordance with the cathode potential of the APD 501. During the light emission 620, visible light photons are incident on the APD 501, and the waveform shaping unit 503 outputs a continuous pulse signal. When the light emission 620 ends and no more visible light photons are incident on the APD 501, no pulse signal is output from the waveform shaping unit 503. The radiation counter circuit 512 refers to the count value of the visible light counter 505 in accordance with the reset cycle 607 of the visible light counter. Then, counting is performed by any one of a low-energy counter 506, a medium-energy counter 507, and a high-energy counter 508 according to the count value. When 70 keV radiation 610 is incident as described above, since the light emission 620 of the scintillator falls within the reset cycle of the visible light counter, radiation counting and energy discrimination can be correctly performed according to the count value of the visible light counter.

[0044] Next, a case (pile-up) where two radiations are incident during one cycle of the visible light counter reset cycle 607 will be described. When two radiations are incident during one cycle of the reset cycle 607 of the visible light counter, such as 30 keV radiations 611 and 612, the count value of the visible light counter adds up the count values for the two 30 keV radiations 611 and 612. Therefore, it is measured that one radiation having higher energy than the original energy is incident, so that counting and energy discrimination cannot be performed correctly. Furthermore, there may also occur a case where the light emission 623 of the scintillator straddles one cycle of the reset cycle 607 of the visible light counter, like 70 keV radiation 613. In this case, since the count of visible light photons is divided between the reset cycles of the visible light counter, it is measured that two radiations having lower energy than the original energy are incident, so that radiation counting and energy discrimination cannot be performed correctly.

[0045] Figure 7 shows the circuit of the present invention. The only difference from the conventional example is the addition of an estimation unit 504, which functions as an estimation unit. The estimation unit 504 is connected to a waveform shaping unit 503 and a reset clock 605, and the output of the estimation unit 504 is connected to a visible light counter 505. The estimation unit 504 has the function of estimating the range of visible light generated when a single radiation particle enters the scintillator 200, based on the time progression of whether or not visible light is detected. In this embodiment, the estimation unit 504 estimates the range of visible light generated by a single radiation particle using the reset clock 605 and the pulse signal of the waveform shaping unit 503 as the time progression of whether or not visible light is detected. When the estimation unit 504 determines that the incidence of visible light photons has ended, it outputs a counter reset signal 608 to the visible light counter 505. Since the range of visible light generated by a single radiation particle depends on the energy of the radiation, the energy of the incident radiation can be estimated by estimating the range of visible light. Therefore, it can be said that the counter reset signal 608 is output after the energy of the radiation has been estimated. The estimation of the visible light range when a pile-up occurs will be described later. When the visible light counter 505 receives a counter reset signal 608 from the estimation unit 504, it outputs the count value to the radiation counter circuit 512 and resets its own count. The radiation counter circuit 512 counts using one of the counters, the low-energy counter 506, the medium-energy counter 507, or the high-energy counter 508, according to the count value of the visible light counter 505. The counters in the radiation counter 512 do not need to have three energy bands; there may be fewer or more than three.

[0046] The operating timing of the circuit in Figure 7 will be explained using Figure 8. The difference from the conventional example is that a counter reset signal 608 is provided instead of the visible light reset period 607. When 70 keV radiation 610 is incident on the scintillator 200, it emits light for a certain period of time according to the energy of the radiation, as in the light emission 620. Visible light photons generated from the scintillator 200 are incident on the APD 501. The cathode potential of the APD 501 drops when visible light photons are incident on it, and returns to VH when the reset clock 605 is input. The waveform shaping unit 503 outputs a pulse signal according to the cathode potential of the APD 501. During the light emission 620, visible light photons are incident on the APD 501, and the waveform shaping unit 503 outputs a continuous pulse signal. When the light emission 620 ends and visible light photons no longer occur on the APD 501, the waveform shaping unit 503 stops outputting a pulse signal. The estimation unit 504 estimates that the emission from the waveform shaping unit 503 is due to radiation 610 from the moment the pulse signal begins to be output until the pulse signal stops being output and the reset clock 605 next reaches a high level. In this way, it estimates the visible light range 800 generated by the 70 keV radiation 610 and outputs a counter reset signal 608 to the visible light counter 505. Through this operation, the counting and energy discrimination of the 30 keV radiation 611 and 612, and the 70 keV radiation 613 that are incident on the scintillator 200 at the same timing as in Figure 6 can be performed correctly. In other words, the estimation unit 504 can detect continuity from the change in the time progression of the output of the waveform shaping unit 503 and, based on this, estimate the visible light range, i.e., the energy of the incident radiation, thereby performing correct energy discrimination.

[0047] The estimation method of the estimation unit 504 of the present embodiment is not limited to the above content, and the estimation of whether visible light photons are continuously incident may be performed according to any predetermined pattern. In this case, for example, the time transition of the pulse signal output from the waveform shaping unit 503 is compared with the pattern held by the estimation unit, and the range of visible light, that is, the energy of incident radiation is estimated based on the most similar pattern. Further, for example, the counter reset signal 608 may be output at the timing when the reset clock 605 becomes Hi level for the second time after no pulse signal is output from the waveform shaping unit 503.

[0048] (Second Embodiment) When a timer is provided, the difference from the first embodiment lies in that the timer manages the input timing of the reset clock 605 input to the switch element 502. Differences from the first embodiment will be described with reference to FIG. 9. The output of the waveform shaping unit 503 is connected to a timer 509 and an estimation unit 504. When a pulse signal is output from the waveform shaping unit 503, the timer 509 outputs a Hi-level signal for a fixed period. The output of the timer 509 and the output of the reset clock 605 are connected to an AND circuit, and the reset clock 605 is input to the switch element 502 only while the timer 509 outputs a Hi-level signal. That is, the timer 509 has a function of instructing the input of the reset clock 605 to the switch element 502, and operates the switch element 502 only during the fixed period in which it outputs a Hi-level signal. In the present embodiment, an AND circuit and the timer 509 are added to the input unit of the switch element 502 in FIG. 7 of the first embodiment, and the logical product of the output of the reset clock 605 and the output of the timer 509 is input to the switch element 502. The estimation unit 504 estimates the range of visible light generated by one piece of radiation using the output of the waveform shaping unit 503 and the input 1001 of the switch element as the time transition of presence / absence of visible light detection.

[0049] The operating timing of the circuit in Figure 9 will be explained using Figure 10. The difference from the first embodiment is the addition of a timer 509 and an input 1001 to the switch element. When 70 keV radiation 610 is incident on the scintillator 200, it emits light for a certain period of time depending on the energy of the radiation, as shown in the light emission 620. Visible light photons generated from the scintillator 200 are incident on the APD 501. The cathode potential of the APD 501 drops when visible light photons are incident on it, and returns to VH when the reset clock 605 is input. The waveform shaping unit 503 outputs a pulse signal according to the cathode potential of the APD 501. The timer 509 outputs a Hi-level signal for a certain period of time, triggered by the first pulse signal output by the waveform shaping unit 503. The logical AND of the output of the timer 509 and the reset clock 605 becomes the input 1001 to the switch element. During the light emission 620, visible light photons are incident on the APD 501, and the waveform shaping unit 503 outputs a continuous pulse signal. When the light emission 620 ends and visible light photons no longer incident on the APD 501, the waveform shaping unit 503 stops outputting a pulse signal. The estimation unit 504 determines the time from when the signal started to be output from the waveform shaping unit 503 until the signal stopped being output and the reset clock 605 next went to a high level. It then estimates that this period corresponds to the visible light range 800 generated by the 70 keV radiation 610 and outputs a counter reset signal 608 to the visible light counter 505. By instructing the operation of the switch element 502 for a certain period in this way, power consumption can be reduced. Also, the output period of the high-level signal of the timer 509 shown in Figure 10 of this embodiment is just an example and can be set to any period.

[0050] (Third Embodiment) When there are multiple photoelectric conversion elements, the difference from the first and second embodiments is that the pixel 901 has multiple APDs, and each APD has a sampling circuit, that is, it has multiple sampling circuits. The difference from the first and second embodiments will be explained using Figure 11. Here, only the difference from Figure 9 will be explained.

[0051] The cathode electrode of APD 501a is connected to a sampling circuit 510a, which consists of a switch element 502a and a waveform shaping unit 503a. The cathode electrode of APD 501b is connected to a sampling circuit 510b, which consists of a switch element 502b and a waveform shaping unit 503b. The estimation unit 504 receives the logical OR of the waveform shaping units 503a and 503b and the input 1001 of the switch element. The timer 509 receives input from the waveform shaping units 503a and 503b. The visible light counter 505 is connected to the waveform shaping units 503a and 503b and counts the pulse signals from the two waveform shaping units.

[0052] Next, the operating timing of the circuit in Figure 11 will be explained using Figure 12. When 70 keV radiation 610 is incident on the scintillator 200, it emits light for a certain period of time according to the energy of the radiation, as shown in the emission 620. Visible light photons generated from the scintillator 200 are incident on APD 501a and APD 501b. The cathode potentials of APD 501a and APD 501b drop when visible light photons are incident on them, and are returned to VH when the reset clock 605 is input to the input 1001 of the switch element. The waveform shaping units 503a and 503b output pulse signals according to the cathode potentials of APD 501a and APD 501b. The timer 509 outputs a Hi-level signal for a certain period of time, triggered by the first pulse signal output by the waveform shaping unit 503a, and the reset clock 605 is input to the switch element. When the light emission 620 ends and visible light photons no longer incident on APD 501a and APD 501b, pulse signals are no longer output from the waveform shaping units 503a and 503b. The estimation unit 504 determines the time from when the signal started to be output from the waveform shaping unit 503a until the signal stopped being output and the input 1001 of the switch element next became high level. The estimation unit 504 estimates that this period corresponds to the visible light range 800 generated by the 70 keV radiation 610 and outputs a counter reset signal 608 to the visible light counter 505. By detecting visible light photons with multiple APDs within a pixel in this way, pile-up can be suppressed more effectively than when a single APD detects visible light photons. The number of APDs is not limited to that shown in Figure 11 of this embodiment; a pixel 901 may have more than two APDs. Furthermore, each APD may have its own visible light counter.

[0053] (Fourth Embodiment) Detection by Peak Value Unlike the first to third embodiments, this embodiment converts the signal from visible light photons generated by the scintillator 200 into a voltage signal, and estimates the energy of the radiation photons from the peak value of the voltage signal. The circuit of this embodiment will be explained using Figure 13. Pixel 901 has multiple APDs, each APD connected to a resistor 1300. The terminal of each resistor opposite the cathode electrode of the APD is connected to the node of the pixel output 1302. The pixel output 1302 is also connected to VH via the resistor 1301. When visible light photons are incident on an APD in pixel 901, current flows from VH through the resistor 1301 and the pixel output 1302 to the APD that has been incident on the visible light. As a result, the potential of the pixel output 1302 drops. The amount of potential fluctuation of the pixel output 1302 changes according to the number of APDs that have been incident on the visible light. The potential fluctuation of the pixel output 1302 is input to the sampling circuit 510. The sampling circuit 510 has a low-energy waveform shaping unit 1303, a medium-energy waveform shaping unit 1304, and a high-energy waveform shaping unit 1305. Each waveform shaping unit has a threshold voltage set and outputs a signal according to the potential fluctuation of the pixel output 1302. In other words, each waveform shaping unit corresponds to a different energy band. The sampling circuit 510 may have fewer or more waveform shaping units than three. Also, although Figure 13 shows an example in which the sampling circuit 510 is composed of multiple waveform shaping units, it is not limited to this, and a separate sampling circuit may be provided for each energy band. The estimation unit 504 estimates the range of visible light generated by a single radiation based on the time transition of the output of each waveform shaping unit, estimates whether or not a pileup occurs, and estimates the energy of the radiation. The estimation unit 504 can estimate whether or not a pileup occurs, and also estimates the energy of the radiation as in the embodiment described above, and outputs the estimated energy of the radiation to the correction unit 1306.

[0054] The correction unit 1306 corrects the radiation energy estimated by the estimation unit 504 when a pile-up occurs. Then, it sends a signal to one of the counters, the low-energy counter 506, the medium-energy counter 507, or the high-energy counter 508, according to the radiation energy, and counts the number of radiation particles. The estimation unit 504 may not estimate the radiation energy and may only output whether or not a pile-up occurs, and the correction unit 1306 may not send a signal to the radiation counter circuit 512 when a pile-up occurs and may not count the corresponding radiation.

[0055] Using Figure 14, the estimation flow of the estimation unit 504 when two radiation sources arrive will be explained. First, under condition 1400, it is determined whether the output of the high-energy waveform shaping unit 1305 reached a high level twice while the output of the low-energy waveform shaping unit 1303 was at a high level. If true, operation 1410 is performed. Note that the period during which the output of the waveform shaping unit is at a high level means the period during which the sampling circuit detects the presence of an output from the APD. Operation 1410 estimates that a pile-up exists and estimates the range of visible light generated by each radiation source. The range of visible light generated by the first radiation source is estimated to be the period from when the output of the low-energy waveform shaping unit 1303 reached a high level until the output of the high-energy waveform shaping unit 1305 reached a high level for the second time. Furthermore, the range of visible light generated by the second radiation is estimated to be the period from when the output of the high-energy waveform shaping unit 1305 reaches a Hi level for the second time until the output of the low-energy waveform shaping unit 1303 reaches a Lo level. Next, operation 1411 is performed. Operation 1411 estimates the energy of the second radiation. The energy of the radiation is estimated according to the length of time during which the output of the high-energy waveform shaping unit 1305 is at a Hi level for the second time. Next, operation 1412 is performed. Operation 1412 subtracts the energy of the radiation corresponding to the threshold of the medium-energy waveform shaping unit 1304 from the estimated energy of the second radiation. For this reason, the estimation unit 504 outputs the information on the occurrence of the pileup, the energy of the first radiation, and the estimated energy of the second radiation to the correction unit 1306. The correction unit 1306 corrects the energy of the second radiation according to the output of the estimation unit 504. Subsequently, a signal is sent to one of the counters—the low-energy counter 506, the medium-energy counter 507, or the high-energy counter 508—according to the estimation result of the estimation unit 504 and the energy of the second radiation after correction, and the number of radiation particles is counted.

[0056] Next, we will explain the case where condition 1400 is false. If condition 1400 is false, we proceed to condition 1401. In condition 1401, we determine whether the output of the medium-energy waveform shaping unit 1304 reached a high level twice while the output of the low-energy waveform shaping unit 1303 was at a high level. If true, we proceed to condition 1402. In condition 1402, we determine whether the output of the high-energy waveform shaping unit 1305 reached a high level twice. If true, we perform operation 1413; otherwise, we perform operation 1414. Operation 1413 performs the same operation as operation 1411. In operation 1414, we assume that there is a pile-up and estimate the range of visible light generated by each radiation. We estimate that the range of visible light generated by the first radiation is the period from when the output of the low-energy waveform shaping unit 1303 reaches a high level until the output of the medium-energy waveform shaping unit 1304 reaches a high level for the second time. Furthermore, the range of visible light generated by the second radiation is estimated to be from the time the output of the medium-energy waveform shaping unit 1304 reaches a Hi level for the second time until the output of the low-energy waveform shaping unit 1303 reaches a Lo level. Once operations 1413 and 1414 are completed, operation 1415 is performed. In operation 1415, the energy of the radiation corresponding to the threshold of the low-energy waveform shaping unit 1303 is subtracted from the estimated energy of the second radiation. For this reason, the estimation unit 504 outputs information on the occurrence of a pileup, information on which radiation counter to count the first radiation, and the estimated energy of the second radiation to the correction unit 1306. The correction unit 1306 corrects the energy of the second radiation according to the output of the estimation unit 504. After that, a signal is sent to one of the counters, the low-energy counter 506, the medium-energy counter 507, or the high-energy counter 508, according to the estimation result of the estimation unit 504 and the corrected energy of the second radiation, and the number of radiations is counted.

[0057] Finally, let's explain the case where condition 1401 is false. If condition 1401 is false, operation 1416 is performed. In operation 1416, it is estimated that there is no pileup, and the correction unit 1306 outputs information that no pileup has occurred and which of the low-energy counter 506, medium-energy counter 507, and high-energy counter 508 should be used for counting. The correction unit 1306 sends a signal to one of the low-energy counter 506, medium-energy counter 507, or high-energy counter 508 according to the estimation result of the estimation unit 504, and counts the number of radiation particles.

[0058] Using Figure 15, an example of the circuit in Figure 13 and the operating timing in Figure 14 will be explained. Radiation 1500 of 100 keV is incident, and the scintillator emits light according to the energy of the radiation. The potential of the pixel output 1302 changes according to the amount of light emitted by the scintillator, and in response to the change in the potential of the pixel output 1302, a Hi-level signal is output from the low-energy waveform shaping unit 1303, the medium-energy waveform shaping unit 1304, and the high-energy waveform shaping unit 1305. According to the flowchart in Figure 14, since conditions 1400 and 1401 are false, operation 1416 is performed.

[0059] Next, we will explain the case where 100 keV radiation 1501 and 30 keV radiation 1502 are incident as an example of pile-up occurrence. When 100 keV radiation 1501 is incident, the scintillator emits light according to the energy of the radiation, and the potential of the pixel output 1302 changes. In response to the change in the potential of the pixel output 1302, Hi-level signals are output from the low-energy waveform shaping unit 1303, the medium-energy waveform shaping unit 1304, and the high-energy waveform shaping unit 1305. If 30 keV radiation 1502 is incident before the scintillator emission due to 100 keV radiation 1501 has finished, the amount of light emitted by the scintillator increases, and the potential of the pixel output 1302 decreases. In the timing shown in Figure 15, the output of the low-energy waveform shaping unit 1303 outputs a Hi level from the moment 100 keV radiation 1501 is incident and exceeds the threshold until the luminescence of the scintillator due to 30 keV radiation 1502 attenuates and falls below the threshold. The output of the medium-energy waveform shaping unit 1304 outputs a Hi level at the timing of both the incident 100 keV radiation 1501 and the incident 30 keV radiation 1502. The output of the high-energy waveform shaping unit 1305 outputs a Hi level only at the timing of the incident 100 keV radiation 1501. According to the flowchart in Figure 14, since condition 1400 is false, condition 1401 is true, and 1402 is false, operations 1414 and 1415 are performed. With this operation, even when estimating the energy of radiation photons from high values, radiation counting and energy discrimination can be performed correctly regardless of the occurrence of pile-up.

[0060] Furthermore, if the estimation results indicate that a pile-up is occurring, it is advisable to inform the user of this. In this case, the radiation imaging system 980 is equipped with a notification unit that notifies the estimation results of the estimation unit, and a display or speaker can be used as the notification unit. This allows the user to appropriately change the usage of the radiation imaging device 990 and consider the need for measures such as suppressing the occurrence of a pile-up.

[0061] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0062] This application claims priority based on Japanese Patent Application No. 2025-031788, filed on 28 February 2025, and all of its contents are incorporated herein by reference.

[0063] 102 Photoelectric conversion element 200 Scintillator 504 Estimation unit 510 Sampling circuit 980 Radiation imaging system 990 Radiation imaging device

Claims

1. An indirect photon counting type radiation imaging device comprising: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts visible light into an electrical signal; a detection unit that detects the output value of the photoelectric conversion element; and an estimation unit that estimates the energy of incident radiation based on the time progression of the detection result of the detection unit.

2. The indirect photon counting type radiation imaging apparatus according to claim 1, characterized in that the estimation unit maintains a time progression pattern and estimates the energy of incident radiation based on a comparison of the time progression of the detection result with the pattern.

3. The indirect photon counting type radiation imaging apparatus according to claim 1, characterized in that the detection unit includes a sampling circuit for detecting the presence or absence of output from the photoelectric conversion element.

4. The indirect photon counting type radiation imaging apparatus according to claim 3, characterized in that the estimation unit estimates the energy of the incident radiation based on the change in the detection result of the sampling circuit.

5. The indirect photon counting type radiation imaging apparatus according to claim 3, characterized in that the estimation unit estimates the energy of incident radiation based on the continuity of the detection results of the sampling circuit.

6. The indirect photon counting type radiation imaging apparatus according to claim 3, characterized in that the detection unit comprises a plurality of sampling circuits, and the estimation unit estimates the energy of incident radiation based on the detection results of the plurality of sampling circuits.

7. The indirect photon counting type radiation imaging apparatus according to claim 1, further comprising a radiation counter that counts the energy of radiation based on the estimation result of the estimation unit.

8. The indirect photon counting type radiation imaging apparatus according to claim 7, characterized in that the radiation counter comprises a plurality of counters that count for each energy band of radiation.

9. The indirect photon counting type radiation imaging apparatus according to claim 3, further comprising a visible light counter for counting the detection results.

10. The indirect photon counting type radiation imaging apparatus according to claim 9, further comprising a reset means for resetting the visible light counter.

11. The indirect photon counting type radiation imaging apparatus according to claim 10, characterized in that the reset means resets the visible light counter after the estimation unit has estimated the energy of the incident radiation.

12. The indirect photon counting type radiation imaging apparatus according to claim 4, further comprising: a potential supply means for supplying potential to the photoelectric conversion element; a changeover switch for switching the connection between the photoelectric conversion element and the potential supply means; and an instruction means for instructing the operation of the changeover switch, wherein the instruction means instructs the operation of the changeover switch for a certain period of time when the sampling circuit detects that a detection result is present.

13. The indirect photon counting type radiation imaging apparatus according to claim 6, characterized in that each of the plurality of sampling circuits corresponds to a different energy band of radiation.

14. The indirect photon counting type radiation imaging apparatus according to 13, characterized in that the estimation unit is capable of estimating whether or not a pileup is occurring, and during a period in which some of the plurality of sampling circuits detect the presence or absence of output from the photoelectric conversion element, if a sampling circuit corresponding to a higher radiation energy band than the some sampling circuits detects a change in the presence or absence of output from the photoelectric conversion element, the estimation unit estimates that a pileup is occurring.

15. The indirect photon counting type radiation imaging apparatus according to claim 14, characterized in that the estimation unit corrects and estimates the energy of the radiation when it estimates that a pile-up has occurred.

16. The indirect photon counting type radiation imaging apparatus according to claim 14, characterized in that the estimation unit does not estimate the energy of the radiation when it estimates that a pile-up has occurred.

17. The indirect photon counting type radiation imaging apparatus according to claim 1, further comprising a notification unit for notifying the estimation results of the estimation unit.

18. The indirect photon counting type radiation imaging apparatus according to claim 1, characterized in that the photoelectric conversion element is a SPAD.

19. A radiation imaging system comprising a radiation imaging device according to claim 1, and a control device that acquires an image signal from the radiation imaging device and processes the acquired image signal.

20. An indirect photon counting type radiation imaging apparatus comprising a scintillator that converts radiation into visible light, a photoelectric conversion element that converts visible light into an electrical signal, and a detection unit capable of detecting the time change of the output value of the photoelectric conversion element, comprising: an acquisition means for acquiring the detection result of the detection unit; and an estimation means for estimating the energy of radiation incident on the indirect photon counting type radiation imaging apparatus based on the detection result acquired by the acquisition means.

21. A method for estimating radiation energy, comprising: an acquisition step of acquiring information regarding the time transition of the output value of a photoelectric conversion element from an indirect photon counting type radiation imaging device comprising: a scintillator that converts radiation into visible light; a photoelectric conversion element that converts visible light into an electrical signal; and a detection unit capable of detecting the time transition of the output value of the photoelectric conversion element; and an estimation step of estimating the energy of radiation incident on the indirect photon counting type radiation imaging device based on the information regarding the time transition of the output value acquired in the acquisition step.

22. A program for causing a computer to function as each means of the processing apparatus described in claim 21.

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