Radiation detection device, radiation imaging system, radiation imaging method, program, and storage medium

Abstract

To provide a desired radiation detection device capable of performing global electronic shutter operation and capable of inhibiting a radiation which should not exist from being reflected when imaging a radiation picture with continuous frames.SOLUTION: A radiation detection device comprises: a pixel array in which a plurality of pixels are arranged, the pixels having a photoelectric conversion section for receiving irradiation with radiation to generate electric charge, a charge holding section for holding the electric charge transferred from the photoelectric conversion section, and a floating diffusion section to which the electric charge is transferred from the charge holding section; a reading section for reading pixel signals depending on electric charge existing in floating diffusion sections from the respective pixels; and a signal processing section for processing the read pixel signals. When pixel signals read from an arbitrary pixel of the pixel array in continuous two frames exceed a predetermined value, the signal processing section modifies a pixel signal read from any pixel in a frame preceding temporally of the continuous two frames to a smaller correction value.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a radiation detection device and the like. [Background technology]

[0002] 2. Description of the Related Art Radiation detectors are known that obtain a radiation image by receiving radiation with a semiconductor element such as a CMOS image sensor without passing through a scintillator (wavelength converter).

[0003] Patent Document 1 proposes a method for determining background components at the timing when an image of an imaging target is captured in a radiation detector that captures a radiation image using a CMOS image sensor. This method determines background components contained in multiple pixels in a frame using pixel signal values read out in that frame.

[0004] In the field of CMOS image sensors, sensors are known that can realize a so-called global electronic shutter operation in which a shutter operation is performed simultaneously on all pixels in order to prevent image distortion that occurs when capturing an image of a moving object.

[0005] Patent Document 2 discloses an imaging device capable of global electronic shutter operation, which includes multiple pixels each including a photoelectric conversion unit, a charge retention unit that retains charges transferred from the photoelectric conversion unit, and a floating diffusion unit to which charges are transferred from the charge retention unit. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-160729 [Patent Document 2] Japanese Patent Application Publication No. 2019-9155 Summary of the Invention [Problem to be solved by the invention]

[0007] When a conventional imaging device capable of global electronic shutter operation is used to capture radiation images in successive frames, there are cases where radiation that should not have been present in the captured frames appears in the radiation image.

[0008] Therefore, there has been a demand for a radiation detection device that is capable of performing a global electronic shutter operation and that can prevent radiation that is not present in the captured frames from appearing in the radiation image, even when capturing radiation images in consecutive frames. [Means for solving the problem]

[0009] A first aspect of the present invention is a radiation detection device comprising: a pixel array in which a plurality of pixels are arranged, each pixel having a photoelectric conversion unit that generates charge in response to irradiation with radiation, a charge retention unit that retains charge transferred from the photoelectric conversion unit, and a floating diffusion unit to which charge is transferred from the charge retention unit; a control unit that controls the operation of the pixel array; a readout unit that reads out, from each of the pixels, a pixel signal corresponding to the charge present in the floating diffusion unit; and a signal processing unit that processes the readout pixel signal, wherein the control unit simultaneously transfers charge from the photoelectric conversion unit to the charge retention unit in a plurality of the pixels arranged in the pixel array for each frame, and the signal processing unit, when the pixel signal read out from any pixel in the pixel array in two consecutive frames exceeds a predetermined value, corrects the pixel signal read out from the any pixel in the temporally preceding frame of the two consecutive frames to a smaller correction value.

[0010] A second aspect of the present invention provides a pixel array including a plurality of pixels arranged therein, each pixel having a photoelectric conversion unit that generates charge in response to irradiation with radiation, a charge holding unit that holds the charge transferred from the photoelectric conversion unit, and a floating diffusion unit to which the charge is transferred from the charge holding unit; a control unit that controls the operation of the pixel array; a readout unit that reads out a binarized pixel signal from each pixel of the pixel array in accordance with the charge present in the floating diffusion unit; and a signal processing unit that processes the readout pixel signal, wherein the control unit simultaneously transfers charge from the photoelectric conversion unit to the charge holding unit in the plurality of pixels arranged in the pixel array for each frame, and the signal processing unit simultaneously transfers charge from the photoelectric conversion unit to the charge holding unit in the plurality of pixels arranged in the pixel array in accordance with the charge transferred over a plurality of consecutive frames. When the value of a pixel signal read from the pixel array when not exposed to radiation is taken as a dark signal value, if a region is detected in each of two consecutive frames in which adjacent pixels exist whose read-out pixel signal has a value greater than the dark signal value, one pixel that maintains the pixel signal is selected from the pixels in the region, and for the pixels in the region excluding the one pixel, the value of the read-out pixel signal is corrected to the dark signal value, and if the pixel signal of the same pixel is not the dark signal value in both of the corrected two frames, the pixel signal of the same pixel is replaced with the dark signal value in the temporally preceding frame of the two frames.

[0011] a control unit for controlling the operation of the pixel array; a readout unit for reading out, from each pixel, a pixel signal corresponding to a charge present in the floating diffusion unit; and a signal processing unit for processing the readout pixel signals, wherein the control unit simultaneously transfers charge from the photoelectric conversion unit to the charge processing unit in each of the pixels arranged in the pixel array for each frame; and, when the pixel signal readout from a pixel of the pixel array in two consecutive frames exceeds a predetermined value, the signal processing unit corrects the pixel signal readout from the pixel in a temporally earlier frame of the two consecutive frames to a smaller correction value. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a radiation detection device that is capable of performing a global electronic shutter operation and that can prevent radiation that is not supposed to be present in the captured frames from appearing in the radiographic image even when capturing consecutive frames of radiographic images. [Brief explanation of the drawings]

[0013] [Figure 1] 1A is a block diagram showing a schematic configuration of a radiation detector according to embodiment 1. FIG. 1B is a schematic circuit diagram showing an example of the configuration of a pixel. [Figure 2] FIG. [Figure 3] (a) Schematic diagram of a cross section of a pixel taken along line A-A' in Figure 2. (b) Schematic diagram of a cross section of a pixel with a different memory section configuration. [Figure 4] (a) Schematic diagram of a cross section of a pixel taken along line B-B' in Figure 2. (b) Schematic diagram of a cross section of a pixel with a different element isolation structure. [Figure 5] FIG. 4 is a schematic diagram for explaining the drive timing of the imaging element. [Figure 6] (a) Example of drive pulses for readout operation performed row by row in each frame. (b) Example of drive pulses for global reset operation performed simultaneously on all pixels in each frame. [Figure 7] 3 is a flowchart for explaining a signal processing method according to the first embodiment. [Figure 8] 3A and 3B are schematic diagrams illustrating the trajectory of radiation incident on a pixel and traveling through a semiconductor layer to an adjacent pixel. [Figure 9] 10 is a flowchart illustrating a signal processing method according to the second embodiment. [Figure 10] 10 is a flowchart illustrating a signal processing method according to a third embodiment. [Figure 11] 10 is a flowchart illustrating a signal processing method according to a fourth embodiment. [Figure 12] 10 is a flowchart illustrating a signal processing method according to a fifth embodiment. [Figure 13] FIG. 1 is a diagram for explaining a radiation imaging system incorporating a radiation detector. [Figure 14] (a) Schematic diagram showing a radiation imaging system equipped with a radiation detector. (b) Schematic diagram showing the configuration of a transmission electron microscope (TEM) equipped with a radiation detector. DETAILED DESCRIPTION OF THE INVENTION

[0014] A radiation detection device and the like according to an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely an example, and those skilled in the art can appropriately modify and implement the detailed configuration, for example, without departing from the spirit and scope of the present invention.

[0015] In the drawings referred to in the following description of the embodiments, elements denoted by the same reference numerals have the same functions unless otherwise specified. When a plurality of identical elements are arranged in a drawing, the reference numerals and their descriptions may be omitted.

[0016] Furthermore, the drawings may be represented schematically for the convenience of illustration and explanation, and the shape, size, arrangement, etc. of the elements depicted in the drawings may not necessarily be strictly identical to the actual objects.

[0017] In the following description, the term "radiation" refers to electromagnetic radiation (such as X-rays and gamma rays), particle radiation (such as electron beams, proton beams, neutron beams, and alpha rays), and non-ionizing radiation (such as radio waves, microwaves, infrared rays, and visible light). A "radiation imaging system" generally refers to a system that uses radiation to acquire an image of an imaging target as electronic data. The imaging target would be, for example, an object to be inspected in a non-destructive testing system, or a patient in a medical imaging system. A "radiation detector" is a component of a radiation imaging system, and refers to an image sensor unit that converts a radiation image into an electrical signal and acquires the image as electronic data. An "image" refers to an image that is captured and read out in two or more consecutive frames by a radiation detector.

[0018] When describing the pixel arrangement with reference to the drawings, "row" refers to the horizontal arrangement, and "column" refers to the vertical arrangement. A drawing of the radiation detector seen through from the direction perpendicular to the main surfaces of the semiconductor layers that make up the radiation detector (Z direction) may be referred to as a plan view.

[0019] In the following description, the analog signal output from each pixel of the radiation detector may be referred to as a pixel signal. Furthermore, a signal obtained by quantizing a pixel signal into two values may be referred to as a binary pixel signal or binarized signal. Furthermore, a signal obtained by quantizing a pixel signal into three or more values may be referred to as a multi-value pixel signal. Furthermore, an image for one frame composed of binary pixel signals may be referred to as a binarized image.

[0020] [Embodiment 1] (Configuration of radiation detection device) 1(a) is a block diagram showing a schematic configuration of a radiation detector 100, which is a radiation detection apparatus according to embodiment 1. The radiation detector 100 includes an image sensor 101, an output signal processing unit 110, a memory unit 111, an external interface unit 112, and a control unit 117. The illustrated functional elements are conceptual functional elements and do not necessarily have to be physically configured as shown in the figure. For example, the specific form of distribution and integration of the functional blocks is not limited to the illustrated example, and all or part of them can be functionally or physically distributed and integrated in any unit depending on the usage situation, etc.

[0021] The image sensor 101 includes a pixel array 102 in which a plurality of pixels 103 are arranged in a matrix, a vertical scanning circuit 104, column signal lines 105, column circuits 106, column memories 107, a horizontal scanning circuit 108, and a DFE 109. Here, DFE stands for Digital Front End. The vertical scanning circuit 104, column signal lines 105, column circuits 106, column memories 107, and horizontal scanning circuit 108 are examples of readout circuits that read out pixel signals from each pixel in the pixel array 102 for each frame. The DFE 109 is an example of a processing circuit that processes the pixel signals read out by the readout circuit. The image sensor 101 is a CMOS image sensor that detects radiation.

[0022] The pixels 103 that make up the pixel array 102 convert incident radiation into electric charges and generate pixel signals; the configuration of the pixels 103 will be described later. The vertical scanning circuit 104 selects pixel rows in the pixel array 102 that will output signals and sequentially switches between the selected rows for scanning. The column signal lines 105 transmit pixel signals from the pixels 103 in the rows selected by the vertical scanning circuit 104. The column circuit 106 processes the pixel signals input from the column signal lines 105. The processing performed by the column circuit 106 includes A / D conversion. The column memory 107 holds digital signals (e.g., multi-level pixel signals) output from the column circuit 106. The horizontal scanning circuit 108 scans the column circuit 106 or the column memory 107 in the pixel column direction to sequentially read out the digital signals for each column. The DFE 109 is an output circuit that processes the digital signals read from the column circuit 106 or the column memory 107 and outputs them to the outside of the image sensor 101.

[0023] The output signal processing unit 110 performs signal processing using the signal output from the imaging element 101. The memory unit 111 is a data storage unit (storage area) for performing signal processing in the output signal processing unit 110, and stores data to be processed and predetermined data. It is desirable that the memory unit 111 has a storage capacity capable of storing image signals for at least two frames. The signal output from the output signal processing unit 110 can be output to the outside of the radiation detector 100 via the external interface unit 112. Furthermore, the output signal processing unit 110 can acquire setting values and the like required for signal processing from the outside via the external interface unit 112.

[0024] The control unit 117 controls the operation of each unit of the radiation detector 100, and also transmits and receives signals relating to operation control between the radiation detector 100 and external devices when configuring a radiation imaging system, which will be described later.

[0025] (Pixel configuration) FIG. 1(b) is a schematic circuit diagram showing an example of the configuration of a pixel 103 that constitutes the pixel array 102 of FIG. 1(a). The pixel 103 is a pixel that has a so-called global shutter function. In the following description, it is assumed that the charge accumulated in the detection diode D1, which is a radiation detection element, is an electron. In this embodiment, all of the transistors provided in the pixel 103 are N-type transistors. However, the charge accumulated in the detection diode D1 may be a hole, in which case the transistor of the pixel 103 may be a P-type transistor. In other words, the definition of the conductivity type in the following description can be changed depending on the polarity of the charge treated as a signal.

[0026] The pixel 103 provided in the radiation detector of this embodiment has a detection diode D1 which is a photoelectric conversion unit, a transfer transistor M5, a charge holding unit C2, a reset transistor M2, an amplification transistor M3, a selection transistor M4, a memory transfer transistor M1, a floating diffusion unit C1, and an overflow transistor M6.

[0027] The transfer transistor M5 is provided in an electrical path between the node to which the charge holding unit C2 and the memory transfer transistor M1 are connected and the detection diode D1. The drain of the reset transistor M2 is supplied with a power supply voltage VRES, and the drain of the amplification transistor M3 is supplied with a power supply voltage VDD. The selection transistor M4 is provided in an electrical path between the amplification transistor M3 and a column signal line 105. The amplification transistor M3 is electrically connected to the column signal line 105 via the selection transistor M4. The floating diffusion unit C1 includes a floating diffusion capacitance provided in the semiconductor substrate and a parasitic capacitance of the electrical path from the memory transfer transistor M1 to the amplification transistor M3 via the floating diffusion. A current source (not shown) connected to the amplification transistor M3, the selection transistor M4, and the column signal line 105 can function as a charge-voltage converter that outputs a voltage signal corresponding to the charge present in the floating diffusion unit C1 to the column signal line 105.

[0028] The memory transfer transistor M1 is provided in the electrical path between the charge holding portion C2 and the floating diffusion portion C1. The charge holding portion C2 includes a floating diffusion capacitance provided in the semiconductor substrate and a parasitic capacitance of the electrical path from the transfer transistor M5 to the memory transfer transistor M1 via the floating diffusion portion. The overflow transistor M6 is provided in the electrical path between the detection diode D1 and the overflow drain 11.

[0029] Each of the signals RES, TX, SEL, GS, and OFD is supplied from the vertical scanning circuit 104 shown in Fig. 1(a). In Fig. 1(b), the pixel row to which the signal is supplied is added to the end of each signal. For example, (m) added to the end of each signal indicates that the signal is supplied to pixels in the mth row.

[0030] (Plan view and cross section of pixel) 2 shows a plan view of a pixel 103 included in the radiation detector 100 according to this embodiment. The pixel has a detector diode section 20 including a detector diode D1, a transfer transistor section 21 including a transfer transistor M5, and a floating diffusion section 22 including a floating diffusion section C1. The pixel also has a reset transistor section 23 including a reset transistor M2, an amplifier transistor section 24 including an amplifier transistor M3, and a select transistor section 25 including a select transistor M4. The pixel also has a memory transfer transistor section 26 including a memory transfer transistor M1, a memory section 27 including a charge storage section C2, and an overflow transistor section 28 including an overflow transistor M6. The pixel also has an overflow drain region 29 including an overflow drain 11.

[0031] 3(a) shows a schematic cross-sectional view of the pixel 103 taken along line A-A' in FIG. 2. A P-type semiconductor region 32 is arranged on an N-type semiconductor substrate 31. In the detection diode section 20, an N-type semiconductor region 33 is arranged so as to form a PN junction with the P-type semiconductor region 32. A P-type semiconductor region 34 is arranged on the surface side of the N-type semiconductor region 33. The P-type semiconductor region 32, the N-type semiconductor region 33, and the P-type semiconductor region 33 form a so-called buried photodiode.

[0032] Similarly, in the memory section 27, an N-type semiconductor region 35 is arranged so as to form a PN junction with the P-type semiconductor region 32. A P-type semiconductor region 36 is arranged on the surface side of the N-type semiconductor region 35, thereby forming a floating diffusion capacitance in the semiconductor substrate.

[0033] 3(a), a memory light-shielding film 40, which is a metal film for blocking parasitic light, is shown in the memory unit 27, but in some cases, the memory light-shielding film 40 may not be provided. The configuration of the memory unit 27 is not limited to the example shown in FIG. 1(a), and may be configured such that an electrode 38 is disposed above an N-type semiconductor region 35 without a P-type semiconductor region 36 being disposed thereon, as shown in FIG. 3(b).

[0034] Electrode 37 is the gate electrode of overflow transistor M6 and is electrically connected to signal OFD(m) shown in FIG. 1(b). Electrode 38 is the gate electrode of the memory transfer transistor and is electrically connected to signal GS(m) shown in FIG. 1(b). Electrode 39 is the gate electrode of transfer transistor M5 and is electrically connected to signal TX(m) shown in FIG. 1(b).

[0035] FIG. 4(a) shows a schematic cross-sectional view of the pixel 103 taken along line B-B' in FIG. 2. Reference numeral 301 in the figure denotes shallow trench isolation (STI) as an element isolation structure, in which an oxide film is embedded in a silicon substrate. The element isolation structure for defining the active region of each pixel is not limited to STI; for example, as shown in FIG. 4(b), it is also possible to use a structure in which isolation is achieved by PN isolation. By adopting such a structure, the effects of element degradation due to charge buildup in the oxide film can be reduced, thereby improving the radiation resistance of the imaging device.

[0036] (Pixel drive timing) 5 is a schematic diagram for explaining the drive timing of the image sensor 101. Time flows from left to right in the diagram, and from the top of the diagram, the exposure period of each frame, the period during which the detection diode D1 accumulates charge, and the period during which the memory (charge holding unit C2) holds charge are shown.

[0037] FIG. 6(a) shows an example of drive pulses for a readout operation performed row by row in each frame. Time flows from left to right in the figure. While the RES pulse is high, the reset transistor M2 resets the floating diffusion C1. While the TX pulse is high, the memory transfer transistor M1 transfers charge from the charge storage section C2 to the floating diffusion C1. While the SEL pulse is high, the amplifier transistor M3 and the selection transistor M4 read out a voltage signal corresponding to the charge in the floating diffusion C1 to the column circuit 106 via the column signal line 105. Before and after the charge transfer by the memory transfer transistor M1, noise signals (N reading) and optical signals (S reading) are read out for correlated double sampling (CDS).

[0038] 6(b) shows an example of a drive pulse for a global reset operation that is performed simultaneously on all pixels in each frame. While the GS pulse is high, the transfer transistor M5 transfers the charge detected by the detection diode D1 to the charge storage unit C2. While the OFD pulse is high, the overflow transistor M6 transfers the charge from the detection diode D1 to the overflow drain 11.

[0039] Returning to Figure 5, during the exposure period in which radiation is irradiated, the transfer transistor M5 and overflow transistor M6 are controlled to the OFF state during the "detection diode accumulation period," excluding the "global reset period." As a result, signal charge corresponding to the radiation exposure is accumulated in the parasitic capacitance of the detection diode D1. During the "memory retention period," the transfer transistor M5 and memory transfer transistor M1 are controlled to the OFF state, and the charge retained in the charge retention section C2 is maintained. Then, as shown in the "readout operation," during the "detection diode accumulation period" common to all pixels, a readout operation is performed sequentially on each pixel, pixel row by pixel row.

[0040] (Behavior of radiation incident on a pixel) The present inventor has discovered a phenomenon in which, when a radiation detector capable of global electronic shutter operation captures consecutive frames of radiation images, radiation that should not be present in the captured frames appears in the radiation images. This finding will be described.

[0041] 3(a) illustrates the trajectories of radiation 300 and radiation 300' incident on the detector diode section 20 (detector diode D1). The incident radiation travels through the semiconductor layer while interacting with materials in the pixel, sometimes changing direction, until it escapes from the semiconductor layer or disappears within the semiconductor layer. Like radiation 300', some radiation escapes from the semiconductor layer without passing through any elements other than the detector diode section 20, but like radiation 300, some radiation enters a portion other than the detector diode section 20, for example, the memory section 27 (charge retention section C2).

[0042] As illustrated in the bottom row of Figure 5, when radiation passes through the semiconductor layer along the trajectory shown by radiation 300' at the timing of the exposure period of the (n+1) frame, a signal charge is generated in the detection diode section 20, but the memory section 27 is not affected by the radiation 300'.

[0043] On the other hand, the situation is different when radiation passes through the semiconductor layer along the trajectory shown by radiation 300 at the timing of the exposure period of the (n+1)th frame. Due to the action of the incident radiation 300, signal charge (electrons in this case) is generated and accumulated as a detection signal for the (n+1)th frame in the N-type semiconductor region 33 of the detection diode section 20. When the radiation 300 that has passed through the detection diode section 20 enters the memory section 27, charge may be generated in the N-type semiconductor region 35 of the memory section 27.

[0044] The memory unit 27 stores signal charges transferred after detection in frame (n) by the detector diode unit 20. However, as shown in FIG. 3(a), if radiation irradiated in frame (n+1) enters the memory unit 27 and generates charges, the amount of signal charge stored in frame (n) will fluctuate. For example, even if no radiation is incident on the detector diode unit 20 in frame (n), a kind of false signal may be generated, as if radiation had been incident in frame (n). The inventors have found that if radiation is incident in a subsequent frame of two consecutive frames, this influence can cause a false signal to be generated in the pixel signal of the preceding frame, degrading image quality.

[0045] (Signal processing method) The signal processing method according to this embodiment will be described with reference to the flowchart in Fig. 7. In Fig. 7, each pixel that is a component of the pixel array 102 is represented by a column address x and a row address y. Furthermore, the image signal of the nth frame that has been read out is represented as the "first image," the image signal of the (n+1)th frame that has been read out is represented as the "second image," and the first image signal after signal processing and correction is represented as the "first image'."

[0046] 1(a) performs a determination process to determine whether or not the pixel signal of each pixel in the pixel array 102 exceeds a predetermined value in two consecutive frames. For a pixel determined in the determination process to have its pixel signal exceed the predetermined value in two consecutive frames, the output signal processing unit 110 performs a correction process to correct the pixel signal of the temporally preceding frame of the two consecutive frames to a smaller value.

[0047] The output signal processing unit 110 temporarily stores the pixel signals of the first image and the second image read out as multi-value pixel signals via the DFE 109 in the memory unit 111. Then, in step S1, the pixel signal of an arbitrary pixel in the first image is read out from the memory unit 111, and in step S2, the pixel signal of the second image for the same pixel is read out from the memory unit 111. Note that the output signal processing unit 110 may process steps S1 and S2 in this order, in the reverse order, or simultaneously in parallel.

[0048] Next, in step S3, the output signal processing unit 110 reads out a pre-stored noise judgment value from the memory unit 111. The noise judgment value is a threshold value for distinguishing whether the read-out pixel signal is a noise signal in the dark when no radiation is irradiated, or a signal due to charges generated when incident radiation acts on the semiconductor layer. Note that the signal due to charges generated when incident radiation acts on the semiconductor layer includes not only signals based on signal charges generated in the detection diode unit 20 by the incident radiation, but also false signals based on charges generated when radiation enters the memory unit 27 after incidence.

[0049] The noise judgment value is set as follows and stored in advance in the memory unit 111. First, the control unit 117 reads pixel signals (dark signal values) from the pixel array 102 in a state where the pixel array 102 is not irradiated with radiation for two or more consecutive frames, and stores the signals in the memory unit 111. The level of the signal (dark signal value) read from the pixel array at this time reflects dark noise, such as thermal noise and dark current, that occurs in the pixels when not irradiated with radiation.

[0050] The output signal processing unit 110 reads out pixel signals in the dark from the memory unit 111, calculates an average value, and stores the average value in the memory unit 111. The calculated average value is both the spatial average and the temporal average of dark noise generated within the pixel array.

[0051] The noise judgment value may be any value that can sufficiently distinguish the signal level of dark noise from the signal level caused by irradiated radiation, and may be set based on the dark noise. The noise judgment value is set to a value greater than the average value of dark noise. As a suitable example, the noise judgment value may be set to three times the calculated average value of dark noise. In this case, the probability that the pixel signal of a pixel not irradiated with radiation will exceed the noise judgment value can be reduced to less than 3%, while the signal level caused by irradiated radiation will exceed the noise judgment value with a high probability. The output signal processing unit 110 stores the value three times the calculated average value in the memory unit 111 as the noise judgment value. Note that setting the value three times the average value of dark noise is just an example. An appropriate noise judgment value may be set based on a statistical analysis of the signal levels of implicit noise and false signals to maximize the discrimination ratio between the two.

[0052] The noise judgment value can be set in advance using the method described above before irradiating the object with radiation and capturing an image, but if a long time passes after the noise judgment value is set, the dark noise level of the image sensor may change due to radiation irradiation, etc. Therefore, for example, a dark image may be captured without irradiating radiation immediately before capturing the first image or immediately after capturing the second image, and the noise judgment value may be set based on the captured dark image. In this way, even if the characteristics of the pixels of the radiation detector change over time, the effect of this change can be reduced, thereby improving the accuracy of distinguishing between dark noise and false signals.

[0053] 7, the output signal processing unit 110 reads out the noise judgment value and pixel signal values at the same coordinates (pixels) in the first image and the second image acquired in two consecutive frames from the memory unit 111. Then, the output signal processing unit 110 compares the noise judgment value with each of the pixel signal values.

[0054] For example, if the pixel signal value of the first image is smaller than the noise judgment value but larger than the noise judgment value (step S3: No), the output signal processing unit 110 maintains the pixel signal values of the first image and the second image for that pixel without changing them. This is because, although no radiation was incident on that pixel in the nth frame, radiation was incident on the pixel in the (n+1)th frame along the trajectory of radiation 300' shown in Figure 3(a), and signal charge was generated in the detection diode unit 20 but the memory unit 27 was not affected.

[0055] Furthermore, if both the pixel signal value of the first image and the pixel signal value of the second image are smaller than the noise judgment value (step S3: No), the output signal processing unit 110 leaves the pixel signal values of the first image and the second image unchanged for that pixel, because it is considered that no radiation was incident on that pixel in either the nth frame or the n+1th frame.

[0056] On the other hand, if both the pixel signal value of the first image and the pixel signal value of the second image are greater than the noise judgment value (step S3: YES), the output signal processing unit 110 proceeds to step S4. In step S4, the pixel signal value of the first image for that pixel is corrected to a smaller correction value. Specifically, the pixel signal value of the first image is changed to, for example, the average value of the dark noise described above. This is because, although no radiation was incident on that pixel in the nth frame, radiation was incident on the pixel in the n+1th frame along the trajectory of radiation 300 shown in FIG. 3(a), generating a signal charge in the memory unit 27, and the pixel signal in the nth frame is therefore considered to be a false signal.

[0057] The output signal processing unit 110 performs this series of processes on pixel signals read out from all pixels 103 in the pixel array 102 to create a first image' and stores it in the memory unit 111. In this way, it is possible to obtain the first image', which is a high-quality radiation detection image with reduced influence of aliasing signals, for n frames.

[0058] When the image sensor 101 captures frame n+2 consecutively following frame n+1, the output signal processor 110 executes the processing flow shown in Fig. 7 again, with frame n+1 as the first image and frame n+2 as the second image. This makes it possible to obtain a high-quality radiation detection image with reduced influence of aliasing for frame n+1 as well. The same applies when capturing frames n+3, n+4, etc. consecutively. According to this embodiment, noise can be reduced by removing false signals generated by radiation after it has entered the semiconductor layer, thereby improving image quality.

[0059] The above-described method for removing aliasing signals is particularly effective in a system in which there is little possibility that radiation will be incident on the same pixel in consecutive frames. In a preferred embodiment, the control unit 117 controls the frame rate of imaging and / or the radiation irradiation rate so that the radiation irradiation rate per pixel does not exceed, for example, 0.5 during one frame period (i.e., does not exceed 0.5 / pix / frm).

[0060] Here, the unit of the irradiation rate [ / pix / frm] is the average number of radiation particles or photons incident on one pixel per frame. In this embodiment, the radiation irradiation rate is desirably set to 0.5 / pix / frm or less. In other words, imaging is performed at a low irradiation rate such that the probability of radiation incident on one pixel at a given time is 1 / 2 or less. For example, when using X-rays, the target irradiation rate is 0.5 or less in terms of the average number of photons incident on one pixel per frame. When using electron beams, the target irradiation rate is 0.5 or less in terms of the average number of electrons incident on one pixel per frame. Thus, when imaging is performed by irradiating radiation at a low irradiation rate, if pixel signal values greater than the noise judgment value are read out in two consecutive frames, it is highly likely that the pixel signal of the preceding frame represents a false signal generated in the memory unit 27. Furthermore, when imaging is performed by irradiating radiation at a low irradiation rate, it is possible to continuously acquire binary images that can reduce count loss during counting, as described below.

[0061] As described above, according to this embodiment, when radiographic images are captured in consecutive frames using the global electronic shutter, high-quality radiographic images can be acquired with reduced artifacts that would not be present in the captured frames. The acquired radiographic image is a multi-level digital signal, and the radiation detector 100 can binarize the multi-level digital signal and perform a so-called counting process. For example, as described above, an image is captured under a low irradiation rate, and a binarized image is created from the multi-level digital signal from which artifacts have been removed, in which pixel signal values representing the presence or absence of incident radiation are expressed as 1 or 0. Then, by accumulating multiple consecutive binarized images, the density of the incident radiation can be measured with high accuracy from the gradation values of the accumulated pixels. For specific methods of setting a decision threshold and counting when binarizing a multi-level digital signal, reference can be made to known techniques such as U.S. Patent Publication US2016 / 0309105A1 and International Patent Publication WO2019 / 064632A1.

[0062] Processing to remove aliasing has already been performed at the multi-level digital signal stage, but after binarization processing to express the presence / absence of radiation detection in two values is performed on the multi-level digital signal, frames in which radiation is detected consecutively at the same pixel can be detected and corrected.

[0063] The output signal processing unit 110 may also perform so-called trajectory processing on the binarized radiographic image. In trajectory processing, it is determined whether there are adjacent pixels with a signal level indicating the presence of radiation in the binarized radiographic image of the same frame, and if so, it determines one of the adjacent pixels onto which radiation has entered. Then, it corrects the signals of the adjacent pixels other than the determined pixel to a level indicating the absence of radiation.

[0064] Fig. 8 is a schematic diagram illustrating the trajectory of radiation incident on a pixel and traveling through a semiconductor layer to an adjacent pixel. Fig. 8 illustrates a cross section of two adjacent pixels taken along line B-B' in Fig. 2, but the two adjacent pixels may be adjacent pixels in the row direction (x direction) or adjacent pixels in the column direction (x direction).

[0065] As shown in FIG. 8 , radiation 300R incident on a pixel at coordinates (x, y) may penetrate the semiconductor layer into adjacent pixels, penetrating the detector diode section 20 and memory section 27 of the adjacent pixels and generating charges. That is, radiation 300R incident on a pixel at coordinates (x, y) in frame n+1 may generate spurious signals not only in the pixel signal of that pixel in frame n but also in the pixel signals of adjacent pixels in frames n+1 and / or n. For ease of illustration, a case in which spurious signals are generated in only one adjacent pixel is illustrated here. However, depending on the conditions, radiation may penetrate a wider range of pixels through the semiconductor layer. As a result, a single incident radiation ray may generate a pixel cluster in the readout image of frame n+1 and / or frame n, where a group of pixels has a signal level indicating the presence of radiation. This phenomenon is more pronounced in high-resolution radiation detection devices with a small pixel pitch. It is also pronounced when the semiconductor region of the detector diode is formed thick to increase the detection rate.

[0066] In trajectory processing, a determination is made as to whether there are any adjacent pixels with a signal level indicating the presence of radiation in the binarized radiographic image of the same frame, and if so, one of the adjacent pixels is determined as the pixel on which radiation has entered. Then, the signal levels of the other pixels are corrected to indicate the absence of radiation. Trajectory processing can be performed by a known method.

[0067] [Embodiment 2] A radiation detection apparatus according to embodiment 2 will be described. Explanations of matters common to embodiment 1 will be simplified or omitted. Fig. 9 shows a flowchart for explaining a signal processing method according to embodiment 2.

[0068] In embodiment 1, if both the pixel signal value of the first image and the pixel signal value of the second image are greater than the noise judgment value (step S3 in Figure 7: YES), in step S4, the pixel signal value of the first image for that pixel is replaced with the average value of dark noise.

[0069] In contrast, in this embodiment, as shown in step S4A in FIG. 9 , the pixel signal value of the first image is corrected to a correction value using a method different from that of embodiment 1. In this embodiment, if the determination result in step S3 is YES, the pixel signal value of the pixel in the second image is subtracted from the pixel signal value of the first image, and the difference value is replaced as the pixel signal value of the first image. Note that if the pixel signal value of the second image for that pixel is greater than the pixel signal value of the first image, the difference value will be a negative value. In this case, the pixel signal value of the first image will be replaced with 0. This is effective in suppressing image quality degradation due to false signals when the charge generated in the memory unit 27 due to radiation incident on the semiconductor layer is equal to or smaller than the signal charge generated in the detection diode unit 20.

[0070] According to this embodiment, when radiographic images are captured in successive frames using the global electronic shutter, high-quality radiographic images can be obtained in which false signals that should not be present in the captured frames are reduced. Counting and trajectory processing are the same as in the first embodiment.

[0071] [Embodiment 3] A radiation detection apparatus according to embodiment 3 will be described. Explanations of matters common to embodiment 1 will be simplified or omitted. Fig. 10 shows a flowchart for explaining a signal processing method according to embodiment 3.

[0072] In embodiment 1, if both the pixel signal value of the first image and the pixel signal value of the second image are greater than the noise judgment value (step S3 in Figure 7: YES), in step S4, the pixel signal value of the first image for that pixel is replaced with the average value of dark noise.

[0073] In contrast, in this embodiment, as shown in step S4B in FIG. 10, pixel signal values of the first image are corrected using a method different from that of embodiment 1. In this embodiment, if the determination result in step S3 is YES, the signal value of the pixel in the first image is calculated and replaced using the signal values of the pixels in the first image surrounding the pixel in question. For example, this may be calculated using a commonly used noise smoothing method, such as the average or median value of the signal values of surrounding pixels arranged in a matrix around the target pixel. This enables correction that preserves the effects of output distribution within the screen, such as shading, and can prevent inappropriate correction marks caused by, for example, scratches.

[0074] According to this embodiment, when radiographic images are captured in successive frames using the global electronic shutter, high-quality radiographic images can be obtained in which false signals that should not be present in the captured frames are reduced. Counting and trajectory processing are the same as in the first embodiment.

[0075] [Embodiment 4] A radiation detection apparatus according to embodiment 4 will be described. Explanations of matters common to embodiment 1 will be simplified or omitted. Fig. 11 shows a flowchart for explaining a signal processing method according to embodiment 4.

[0076] 1 converts an analog voltage signal output from each pixel of the pixel array 102 into a multi-level pixel signal quantized into multiple values. The output signal processing unit 110 then removes false signal components contained in the preceding frame image based on the multi-level pixel signal, and further binarizes the multi-level pixel signal after removing the false signal components if necessary.

[0077] In contrast, in this embodiment, the A / D converter included in the column circuit 106 shown in Fig. 1 converts the analog voltage signal output from each pixel of the pixel array 102 into a binary pixel signal quantized into two values. The binarization threshold used in the binary quantization is a threshold for distinguishing whether the level of the readout pixel signal is a noise level in the dark when no radiation is irradiated, or a signal level when signal charge is generated by the incidence of radiation. Note that the signal level when signal charge is generated by the incidence of radiation includes not only a signal level based on the signal charge generated in the detection diode unit 20 by the incident radiation, but also a signal level based on the charge generated when the radiation enters the memory unit 27 after incidence.

[0078] The binarization threshold is set as follows and stored in advance in the memory unit 111. First, the control unit 117 reads out multi-level pixel signals from the pixel array 102 over multiple consecutive frames while the imaging element 101 is not being irradiated with radiation, and stores the signals in the memory unit 111. The levels of the multi-level pixel signals read out from the pixel array at this time reflect dark noise that occurs in pixels in the dark, such as thermal noise and dark current.

[0079] The output signal processing unit 110 reads out from the memory unit 111 the multi-value pixel signals read out over multiple frames from all pixels constituting the pixel array 102, calculates the average value, and stores the average value in the memory unit 111. The calculated average value is both the spatial average and the temporal average of the dark noise.

[0080] The binarization threshold may be any value that can sufficiently separate the signal level of dark noise from the signal level caused by irradiated radiation, and may be set, for example, to three times the calculated average value of dark noise. In this case, the probability that the pixel signal of a pixel not irradiated with radiation will exceed the binarization threshold can be reduced to less than 3%, while the signal level caused by irradiated radiation will exceed the binarization threshold with a high probability. The output signal processing unit 110 stores, for example, a value three times the calculated average value as the binarization threshold (multi-level digital value) in, for example, the DFE 109.

[0081] The multi-level digital value stored in the DFE 109 as the binarization threshold value is converted into an analog voltage by a D / A converter, and is used as a threshold voltage when a comparator (A / D converter) provided in the column circuit 106 binarizes an analog pixel signal.

[0082] In this embodiment, the output signal processing unit 110 temporarily stores the pixel signals of the first image and the second image read out as binary images in the memory unit 111. Then, as shown in Fig. 11 , in step S1C, the pixel signal of an arbitrary pixel in the first image is read out from the memory unit 111, and in step S2C, the pixel signal of the second image for the same pixel is read out from the memory unit 111. Note that the output signal processing unit 110 may process steps S1C and S2C in this order, in the reverse order, or simultaneously in parallel.

[0083] In step S3C, the output signal processing unit 110 determines whether the pixel signal values at the same coordinates (pixels) in the first image and the second image acquired in two consecutive frames are both 1.

[0084] For example, if the pixel signal value of the first image is 0 but the pixel signal value of the second image is 1 (step S3C: No), the output signal processing unit 110 maintains the pixel signal values of the first image and the second image for that pixel without changing them. This is because, although no radiation was incident on that pixel in the nth frame, radiation was incident on the pixel in the (n+1)th frame along the trajectory of radiation 300' shown in FIG. 3(a), and signal charge was generated in the detection diode unit 20, but the memory unit 27 was not affected.

[0085] Furthermore, if the pixel signal value of the first image and the pixel signal value of the second image are both 0 (step S3C: No), the output signal processing unit 110 leaves the pixel signal values of the first image and the second image unchanged for that pixel, because it is considered that no radiation was incident on that pixel in either the nth frame or the n+1th frame.

[0086] On the other hand, if both the pixel signal value of the first image and the pixel signal value of the second image are 1 (step S3C: YES), output signal processing unit 110 proceeds to step S4C and corrects the pixel signal value of the first image for that pixel to 0. This is because, although no radiation was incident on that pixel in the nth frame, radiation was incident on that pixel along the trajectory of radiation 300 shown in Figure 8 in the (n+1)th frame, generating a signal charge in memory unit 27, and the pixel signal in the nth frame is considered to be a false signal.

[0087] The output signal processing unit 110 performs this series of processes on pixel signals read out from all pixels 103 in the pixel array 102 to create a first image' and stores it in the memory unit 111. In this way, a high-quality binary radiation detection image with reduced influence of aliasing can be obtained for n frames.

[0088] When the image sensor 101 captures frame n+2 consecutively following frame n+1, the output signal processor 110 executes the processing flow shown in Fig. 11 again, with frame n+1 as the first image and frame n+2 as the second image. This makes it possible to obtain a high-quality binary radiation detection image with reduced influence of aliasing for frame n+1 as well. The same applies when capturing frames n+3, n+4, and so on consecutively.

[0089] According to this embodiment, when radiographic images are captured in successive frames using the global electronic shutter, a high-quality binary image can be obtained in which aliasing signals that would not be present in the captured frames have been reduced. The binary image thus obtained can be used to perform the trajectory processing and counting processing already described. Because aliasing signals due to radiation that has penetrated the semiconductor layer are removed, it is possible to prevent the incident radiation from being counted as superimposed in the counting process. Therefore, the density of the incident radiation can be measured with high precision from the gradation value of each pixel in the integrated image.

[0090] In this embodiment, the analog voltage signal output from the pixel is directly binarized, so the memory unit 27 of each pixel only needs to have a capacity that can hold a signal charge amount larger than the binarization threshold. This makes it possible to reduce the area of the memory unit 27 in a plan view and reduce an increase in leakage current due to charge-up in the surface oxide film, thereby improving the radiation resistance of the image sensor.

[0091] In the above example, in step S3C, a false signal is determined by detecting whether the pixel signal value of both the first image and the second image is 1 for the same pixel. As an alternative method, a region where adjacent pixels having a pixel signal value of 1 form a cluster may be detected for each successive frame. If at least a portion of the detected region overlaps in successive frames, the entire region where the pixel signal value was 1 in the preceding frame may be determined to be a false signal and corrected to 0. When a single incident ray of radiation causes false signals in a wide range of surrounding pixels, this method can effectively remove the false signal.

[0092] [Embodiment 5] A radiation detection apparatus according to embodiment 5 will be described. Explanations of matters common to embodiment 1 or embodiment 4 will be simplified or omitted. Fig. 12 shows a flowchart for explaining a signal processing method according to embodiment 5.

[0093] In the fourth embodiment, spurious signals are detected and corrected based on two consecutive frames of binary images, and then trajectory processing is performed using the corrected binary images. In contrast, in the present embodiment, the output signal processing unit 110 first performs trajectory processing on each of two consecutive frames of binary images.

[0094] That is, for each frame image, it is detected whether or not there is a pixel cluster in which pixels with a pixel signal value of 1 are adjacent to each other. If a pixel cluster is detected, one pixel from that pixel cluster is determined to be the pixel on which radiation is incident. Then, for pixels in that pixel cluster other than the determined pixel, the pixel signal values are corrected to 0. The binarized image of the nth frame on which trajectory processing has been performed in this way is designated as a first trajectory processed image, and the binarized image of the n+1th frame on which trajectory processing has been performed is designated as a second trajectory processed image, and both are stored in memory unit 111.

[0095] Next, as shown in the procedure in FIG. 12, the output signal processing unit 110 uses the binary image of the nth frame after trajectory processing and the binary image of the (n+1)th frame after trajectory processing to detect and remove aliases from the binary image of the nth frame.

[0096] In step S1D, a pixel signal of an arbitrary pixel in the first trajectory processed image is read from the memory unit 111, and in step S2D, a pixel signal of the second trajectory image for the same pixel is read from the memory unit 111. Note that the output signal processing unit 110 may process steps S1D and S2D in this order, in the reverse order, or simultaneously in parallel.

[0097] In step S3D, the output signal processing unit 110 determines whether the pixel signal values at the same coordinates (pixels) in the first trajectory-processed image and the second trajectory-processed image acquired in two consecutive frames are both 1.

[0098] For example, if the pixel signal value of the first trajectory-processed image is 0 but the pixel signal value of the second trajectory-processed image is 1 (step S3D: No), the output signal processing unit 110 maintains the pixel signal values of the first trajectory-processed image and the second trajectory-processed image for that pixel. This is because, although no radiation was incident on that pixel in the nth frame, radiation was incident on the pixel in the trajectory of radiation 300' shown in Figure 3(a) in the (n+1)th frame, generating a signal charge in the detection diode unit 20 but leaving the memory unit 27 unaffected.

[0099] Furthermore, if the pixel signal value of the first trajectory-processed image and the pixel signal value of the second trajectory-processed image are both 0 (step S3D: No), the output signal processing unit 110 maintains the pixel signal value of the first trajectory-processed image and the second trajectory-processed image for that pixel, because it is considered that no radiation was incident on that pixel in either the nth frame or the n+1th frame.

[0100] On the other hand, if both the pixel signal value of the first image and the pixel signal value of the second image are 1 (step S3D: YES), output signal processing unit 110 proceeds to step S4D and corrects the pixel signal value of the first image for that pixel to 0. This is because, although radiation was not incident on that pixel in the nth frame, radiation was incident on that pixel along the trajectory of radiation 300R shown in FIG. 8 in the (n+1)th frame, generating a signal charge in memory unit 27, and the pixel signal in the nth frame is considered to be a false signal.

[0101] The output signal processing unit 110 performs this series of processes on pixel signals read out from all pixels 103 in the pixel array 102 to create a first trajectory-processed image' and stores it in the memory unit 111. In this way, a high-quality binary radiation detection image with reduced effects of aliasing can be obtained for n frames.

[0102] When the image sensor 101 captures frame n+2 consecutively following frame n+1, the output signal processor 110 executes the processing flow shown in Fig. 12 again, treating frame n+1 as the first trajectory-processed image and frame n+2 as the second trajectory-processed image. This makes it possible to obtain a high-quality binary radiation detection image with reduced influence of aliasing for frame n+1 as well. The same applies when capturing frames n+3, n+4, etc. consecutively.

[0103] According to this embodiment, noise can be reduced by removing aliasing signals generated by radiation after it has entered the semiconductor layer, thereby improving image quality. The binary image thus acquired can be used to perform the counting process described above. Because aliasing signals caused by radiation that has entered the semiconductor layer are removed, it is possible to prevent the incident radiation from being counted in a superimposed manner during counting. This makes it possible to measure the density of the incident radiation with high accuracy from the integrated pixel gradation values.

[0104] In the above example, if the signal of the same pixel in the first image after trajectory processing and the second image after trajectory processing is 1, it is determined to be a false signal. However, there may be cases where the identification of the radiation incident pixel by trajectory processing contains an error. Therefore, if the signal of a pixel within a predetermined distance in the first image after trajectory processing and the second image after trajectory processing is 1, it may be determined to be a false signal. The setting of this predetermined distance depends on the device structure of the radiation detector, but it is best to set it in the range of approximately 3 to 10 pixels.

[0105] This embodiment is also effective when a false signal occurs across multiple pixels, and can be suitably implemented when aiming to increase the resolution or detection rate of an imaging device.

[0106] [Embodiment 6] A radiation imaging system according to embodiment 6 will be described. Explanations of matters common to embodiments 1 to 5 will be simplified or omitted.

[0107] (Configuration of Radiation Imaging System) A radiation imaging system 913 incorporating the radiation detector according to any one of the first to fifth embodiments will be described with reference to Fig. 13. Fig. 13 is a schematic block diagram showing an example of the configuration of the radiation imaging system 913 according to this embodiment. The radiation imaging system 913 according to this embodiment includes, for example, the radiation detector 100 shown in Fig. 1(a), a radiation source 914, an exposure control unit 915, and a computer 916.

[0108] The radiation source 914 starts emitting radiation in response to a command to start exposure from the exposure control unit 915. The radiation emitted from the radiation source 914 passes through the imaging target and directly or indirectly enters the image sensor 101 of the radiation detector 900. The radiation source 914 stops emitting radiation in response to a stop command from the exposure control unit 915.

[0109] The radiation detector 100 includes a control unit 117 that controls the frame rate of imaging and the radiation irradiation rate. The control unit 117 generates a stop signal for stopping the irradiation of radiation from the radiation source 914 based on a signal output from the image sensor 101. The stop signal is transmitted to an exposure control unit 915, which sends a stop command to the radiation source 914 in response to the transmitted stop signal.

[0110] If the irradiation rate of the radiation emitted from the radiation source 914 is high, the probability that two or more rays of radiation will be incident on the same pixel within one frame period of the image increases. In this case, when acquiring a binary pixel signal, if the analog pixel signal is A / D converted to multi-value and then binarized using a fixed threshold, even a pixel that has been hit by two or more rays of radiation will be counted as 1, which may result in a count loss.

[0111] Therefore, in a preferred embodiment, the control unit 117 controls the imaging frame rate and the radiation irradiation rate so that the radiation irradiation rate per pixel does not exceed, for example, 0.5 during one frame period (i.e., does not exceed 0.5 / pix / frm).

[0112] Here, the unit [ / pix / frm] is the average number of radiation particles or photons incident per pixel per frame. In this embodiment, the radiation irradiation rate is set to 0.5 / pix / frm or less. In other words, imaging is performed at a low irradiation rate such that the probability of radiation incident on one pixel at a given time is 1 / 2 or less. For example, when using X-rays, the target irradiation rate is 0.5 or less in terms of the average number of photons incident per pixel per frame. When using electron beams, the target irradiation rate is 0.5 or less in terms of the average number of electrons incident per pixel per frame. In this way, by performing imaging at a low irradiation rate, it is possible to obtain a binary image that can reduce count loss during counting.

[0113] The control unit 117 can be configured, for example, by a PLD (abbreviation for Programmable Logic Device) such as an FPGA (abbreviation for Field Programmable Gate Array), or an ASIC (abbreviation for Application Specific Integrated Circuit), or a general-purpose computer with a built-in program, or a combination of all or part of these.

[0114] The computer 916 controls, for example, the radiation detector 100 and the exposure control unit 915, receives radiation image data from the external interface unit 112, and performs processing to display the data as a radiation image.

[0115] The control unit 117 may be disposed separately from the radiation detector 100. For example, the computer 916 may have the functions of the control unit 117. The computer 916 may also function as an input unit for the user to input conditions for capturing a radiographic image.

[0116] As an example, the exposure control unit 915 includes an exposure switch, and when the user turns on the exposure switch, an exposure command is sent from the exposure switch to the radiation source 914, and a start notification indicating the start of radiation emission is sent to the computer 916. In response to the start notification, the computer 916 notifies the control unit 117 of the radiation detector 100 of the start of radiation irradiation. In response to this, the control unit 117 controls the image sensor 101 to generate a signal corresponding to the incident radiation.

[0117] The radiation detector 100 continuously captures a plurality of frame images while performing a global shutter operation during the period when the radiation source 914 is emitting radiation. The radiation imaging system according to this embodiment can remove spurious signals generated by radiation after it has entered the semiconductor layer of the imaging element, thereby making it possible to acquire high-quality radiation images.

[0118] [Embodiment 7] As a seventh embodiment, another example of a radiation imaging system incorporating a radiation detector will be described with reference to FIGS. 14(a) and 14(b).

[0119] 14(a) shows an apparatus EQP as a radiation imaging system including a radiation detector 100. The radiation detector 100 includes an imaging element 101, which is a semiconductor device, as well as a package PKG for mounting the imaging element 101.

[0120] The package PKG may include a base on which the imaging element 101 is fixed, a cover such as glass facing the imaging element 101, and connecting members such as bonding wires or bumps that connect terminals provided on the base to terminals provided on the imaging element 101. The imaging element 101 has a pixel array 102 in which pixels 103 are arranged in a matrix, and a peripheral area around the pixel array 102. Peripheral circuits (for example, a vertical scanning circuit 104 and a DFE 109) may be provided in the peripheral area.

[0121] The equipment EQP may further include at least one of an optical system OPT, a control device CTRL, a processing device PRCS, a display device DSPL, a memory device MMRY, and a mechanical device MCHN. The optical system OPT focuses radiation on the radiation detector 100 and is, for example, a lens, a shutter, or a mirror. The optical system OPT may focus particle beams, such as electron beams or proton beams, on the radiation detector 100 depending on the type of radiation being handled. The control device CTRL controls the radiation detector 100 and is, for example, an ASIC. The processing device PRCS processes signals output from the radiation detector 100 and is a device such as a CPU or ASIC that constitutes an AFE (analog front end) or a DFE (digital front end). The display device DSPL is an EL display device or a liquid crystal display device that displays information obtained by the radiation detector 100 in the form of a visible image or the like. The memory device MMRY is a magnetic device or a semiconductor device that stores information obtained by the radiation detector 100. The memory device MMRY is a volatile memory such as an SRAM or a DRAM, or a non-volatile memory such as a flash memory or a hard disk drive. The mechanical device MCHN has a moving or propelling part such as a motor or engine.

[0122] The device EQP displays the signal output from the radiation detector 100 on the display device DSPL and transmits the signal to the outside via a communication device (not shown) included in the device EQP. For this purpose, the device EQP preferably further includes a memory device MMRY and a processing device PRCS in addition to the memory circuit and arithmetic circuit included in the radiation detector 100. The mechanical device MCHN may be controlled based on the signal output from the radiation detector 100. The device EQP shown in FIG. 14(a) may be a medical device such as an endoscope or a radiological diagnostic device, a measuring device such as a distance sensor, or an analytical device such as an electron microscope.

[0123] 14(b) is a schematic diagram showing the configuration of a transmission electron microscope (TEM) as an example of the equipment EQP. The equipment EQP as an electron microscope has an electron beam source 1202 (electron gun), an illumination lens 1204, a vacuum chamber 1201 (optical tube), an objective lens 1206, a magnifying lens system 1207, and a camera 1209 as the radiation detector 100.

[0124] An electron beam 1203, which is an energy beam emitted from an electron beam source 1202, is focused by an irradiation lens 1204 and irradiated onto a sample S, which is held in a sample holder and serves as an analysis target. The space through which the electron beam 1203 passes is formed by a vacuum chamber 1201 (optical column), and this space is maintained at a vacuum. The radiation detector 100 is disposed so as to face the vacuum space through which the electron beam 1203 passes. The electron beam 1203 that has passed through the sample S is magnified by an objective lens 1206 and a magnifying lens system 1207 and projected onto the radiation detector 100. An electron optical system for irradiating the sample S with the electron beam is called an irradiation optical system, and an electron optical system for forming an image of the electron beam that has passed through the sample S on the radiation detector 100 is called an imaging optical system.

[0125] The electron beam source 1202 is controlled by an electron beam source controller 1211. The illumination lens 1204 is controlled by an illumination lens controller 1212. The objective lens 1206 is controlled by an objective lens controller 1213. The magnifying lens system 1207 is controlled by a magnifying lens system controller 1214. The sample holder control mechanism 1205 is controlled by a holder controller 1215, which controls the drive mechanism of the sample holder.

[0126] An electron beam 1203 transmitted through the sample S is detected by a direct detector 1200 of a camera 1209. An output signal from the direct detector 1200 is processed by a signal processing device 1216 and an image processing device 1218 serving as a processing device PRCS, and an image signal is generated. The generated image signal (transmitted electron image) is displayed on an image display monitor 1220 and an analysis monitor 1221, which correspond to a display device DSPL.

[0127] The camera 1209 is provided below the device EQP. The camera 1209 has a direct electron detector 1200. The direct electron detector 1200 corresponds to the image sensor 101 in any of the first to fifth embodiments. The camera 1209 is provided inside the camera 1209 so that at least a portion of the camera 1209 is exposed to the vacuum space formed by the vacuum chamber 1201.

[0128] The electron beam source controller 1211, the irradiation lens controller 1212, the objective lens controller 1213, the magnifying lens system controller 1214, and the holder controller 1215 are each connected to an image processor 1218. This allows mutual data exchange to set the imaging conditions of the electron microscope. For example, the electron beam irradiation rate can be set to 0.5 electron / pix / frm or less. In this case, the electron beam source controller 1211 and the image processor 1218 function as control means for controlling the radiation irradiation rate. Drive control of the sample holder and setting of the observation conditions for each lens can be performed using signals from the image processor 1218.

[0129] The operator prepares a sample S to be photographed and sets the photographing conditions using an input device 1219 connected to the image processing device 1218. Predetermined data is input to the electron beam source control device 1211, the illumination lens control device 1212, the objective lens control device 1213, and the magnifying lens system control device 1214, respectively, to obtain the desired acceleration voltage, magnification, and observation mode. The operator also inputs conditions such as the number of consecutive field-of-view images, the photographing start position, and the specimen holder movement speed into the image processing device 1218 using the input device 1219 such as a mouse, keyboard, or touch panel. The image processing device 1218 may be designed to automatically set the conditions without relying on operator input.

[0130] The direct detector 1200 as a radiation detector continuously captures a plurality of frame images while performing a global shutter operation during the period when the electron beam source 1202 is emitting electron beams. The radiation imaging system according to this embodiment can remove false signals generated by the electron beam after it has entered the semiconductor layer of the imaging element, and therefore can acquire radiation images of high image quality. The radiation imaging system described above in embodiment 7 is merely an example, and the radiation detectors described in embodiments 1 to 5 may be applied to other systems.

[0131] [Other embodiments] The present invention is not limited to the above-described embodiments and examples, and many modifications are possible within the technical spirit of the present invention. For example, the above-described different embodiments may be combined in whole or in part.

[0132] In the first to fifth embodiments, an example has been described in which the output signal processing unit 110 and the memory unit 111 in the radiation detector 100 are configured separately from the image sensor 101. In other words, an example has been described in which the process of removing aliasing signals generated by radiation after it has entered the semiconductor layer of the image sensor 101 is performed on a chip separate from the image sensor 101. However, the process of detecting and correcting aliasing signals does not necessarily have to be performed outside the image sensor 101. For example, the output signal processing unit 110 and the memory unit 111 for detecting and correcting aliasing signals may be mounted on the same chip (e.g., semiconductor substrate) as the image sensor 101. Conversely, image signals of successive frames may be transmitted from the radiation detector 100 to an external computer via the external interface unit 112, and the computer may use the image signals to perform the process of detecting and correcting aliasing signals.

[0133] In the first to fifth embodiments, the determination process of determining whether a pixel signal exceeds a predetermined value in two consecutive frames is performed on a digital signal after A / D conversion of the pixel signal read from the pixel array. However, it is also possible to perform the determination process and correction process on an analog signal using an analog computing unit that can operate on an analog signal or an analog memory that can store an analog signal.

[0134] The radiation detection element of a pixel of the radiation detection device may be a conversion element such as a detection diode formed on a semiconductor substrate such as silicon, or may be a conversion element made of cadmium telluride or cadmium zinc telluride. The radiation detector may be a detector using a SPAD (single photon avalanche diode).

[0135] The radiation detection device to which the present invention can be applied is not limited to the exemplified embodiments, and may be, for example, a front-side illuminated or back-side illuminated type radiation receiving unit. The radiation detection device may also be a stacked type in which a semiconductor chip including a radiation receiving unit and a semiconductor chip including a logic unit are stacked.

[0136] The present invention also includes a program capable of executing the signal processing method and radiation imaging method described above. The present invention also includes a computer-readable recording medium on which the program is recorded.

[0137] The present invention can also be realized by supplying a program that realizes one or more functions of the embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0138] This specification discloses at least the following: [Item 1] a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a pixel signal corresponding to the charge present in the floating diffusion unit from each of the pixels; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; when the pixel signal read out from any pixel of the pixel array in two consecutive frames exceeds a predetermined value, the signal processing unit corrects the pixel signal read out from the any pixel in a temporally preceding frame of the two consecutive frames to a smaller correction value; A radiation detection device characterized by: [Matter 2] a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to the photoelectric conversion unit of the arbitrary pixel in an arbitrary frame, and the radiation penetrates the charge storage unit of the arbitrary pixel to generate charges, and a pixel signal read out from the arbitrary pixel as a pixel signal of a frame immediately before the arbitrary frame is a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal. 2. The radiation detection device according to item 1. [Matter 3] a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to the photoelectric conversion unit of the arbitrary pixel, and the radiation penetrates the charge storage unit of the arbitrary pixel to generate charges, a pixel signal read out from the arbitrary pixel in accordance with charges transferred from the charge storage unit to the floating diffusion unit is defined as a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal. 2. The radiation detection device according to item 1. [Matter 4] a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to a pixel adjacent to the arbitrary pixel in an arbitrary frame, and the radiation penetrates the charge storage portion of the arbitrary pixel to generate a charge, and a pixel signal read out from the arbitrary pixel as a pixel signal of a frame immediately before the arbitrary frame is a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal. 2. The radiation detection device according to item 1. [Matter 5] the predetermined value is greater than an average value of pixel signals read out from each of the pixels when the pixel array is not irradiated with radiation for two or more consecutive frames. 5. The radiation detection device according to any one of items 1 to 4, [Matter 6] the pixel array is driven such that the average number of radiation photons or particles incident on each pixel per frame is 0.5 or less; 6. The radiation detection device according to any one of items 1 to 5, [Matter 7] The readout unit a charge-voltage converter that converts the charge present in the floating diffusion portion of each pixel into a voltage signal and reads it out; an A / D converter that converts the read voltage signal into a digital signal; 7. The radiation detection device according to any one of items 1 to 6, [Matter 8] the A / D converter converts the voltage signal into a digital signal with three or more values, the correction value is set based on a value obtained by reading out a voltage signal from the pixel array in advance and converting it into a digital signal by the A / D converter when the pixel array is not irradiated with radiation over a plurality of consecutive frames. 8. The radiation detection device according to item 7. [Matter 9] the A / D converter converts the voltage signal into a digital signal with three or more values, the correction value is a difference value between the digital signal of the arbitrary pixel in a temporally subsequent frame of the two consecutive frames and the digital signal of the arbitrary pixel in the temporally preceding frame. 8. The radiation detection device according to item 7. [Matter 10] the A / D converter converts the voltage signal into a digital signal with three or more values, the signal processing unit calculates the correction value using the digital signals of neighboring pixels of the arbitrary pixel in the temporally preceding frame. 8. The radiation detection device according to item 7. [Matter 11] the A / D converter converts the voltage signal into a digital signal with three or more values, the signal processing unit binarizes the ternary or greater digital signal that has been converted into the correction value for the temporally preceding frame. 8. The radiation detection device according to item 7. [Matter 12] the A / D converter performs binarization processing to convert the voltage signal into a binary signal; the correction value is a value of a binary signal obtained by previously reading a voltage signal read from the pixel array when the pixel is not irradiated with radiation over a plurality of consecutive frames and converting the voltage signal into a digital signal by the A / D converter. 8. The radiation detection device according to item 7. [Matter 13] When the pixel array is not irradiated with radiation over a plurality of consecutive frames, the value of the binary signal read out from the pixel array is a dark signal value. The signal processing unit When an area in which pixels having a binary signal greater than the dark signal value are adjacently present is detected in the temporally preceding frame, one pixel that maintains the binary signal is selected from the pixels in the area, and the values of the binary signals of the pixels in the area other than the one pixel are corrected to the dark signal value. 13. The radiation detection device according to item 11 or 12. [Matter 14] a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a binarized pixel signal from each pixel of the pixel array in accordance with the charge present in the floating diffusion unit; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; The signal processing unit When the pixel array is not irradiated with radiation over a plurality of consecutive frames, the pixel signal values read out from the pixel array are dark signal values, When detecting an area in which adjacent pixels exist, each of which has a pixel signal having a value greater than the dark signal value, for each of two consecutive frames, selecting one pixel from among the pixels in the area for maintaining the pixel signal, and correcting the values of the pixel signals read out from the pixels in the area other than the one pixel to the dark signal value; If the pixel signal at the same pixel in both of the two frames after correction is not the dark signal value, the pixel signal at the same pixel in the temporally preceding frame of the two frames is replaced with the dark signal value. A radiation detection device characterized by: [Matter 15] the signal processing unit is disposed on a chip on which the pixel array is formed, 15. The radiation detection device according to any one of items 1 to 14. [Matter 16] the signal processing unit is disposed outside a chip on which the pixel array is formed. 15. The radiation detection device according to any one of items 1 to 14. [Matter 17] A radiation detection device according to any one of items 1 to 16, a radiation source that irradiates the imaging target with radiation; A radiation imaging system comprising: [Matter 18] the radiation source controls the radiation irradiation rate so that the average number of radiation photons or particles incident on each pixel per frame is 0.5 or less; 18. The radiation imaging system according to item 17. [Matter 19] a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a pixel signal corresponding to the charge present in the floating diffusion unit from each of the pixels; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; when the pixel signal read out from any pixel of the pixel array in two consecutive frames exceeds a predetermined value, the signal processing unit corrects the pixel signal read out from the any pixel in a temporally preceding frame of the two consecutive frames to a smaller correction value; A radiation imaging method comprising: [Matter 20] 20. A program for causing a signal processing unit to execute the radiation imaging method according to item 19. [Matter 21] 21. A computer-readable recording medium having the program according to item 20 recorded thereon. [Explanation of symbols]

[0139] 20. Detector diode section / 21. Transfer transistor section / 22. Floating diffusion section / 23. Reset transistor section / 24. Amplification transistor section / 25. Select transistor section / 26. Memory transfer transistor section / 27. Memory section / 28. Overflow transistor section / 29. Overflow drain region / 31. Semiconductor substrate / 32. P-type semiconductor region / 33. N-type semiconductor region / 34. P-type semiconductor region / 35. N-type semiconductor region / 36. P-type semiconductor region / 37. Electrode / 38. Electrode / 39. Electrode / 40. Memory light-shielding film / 100. Radiation detector / 101. Imaging Element / 102...pixel array / 103...pixel / 104...vertical scanning circuit / 105...column signal line / 106...column circuit / 107...column memory / 108...horizontal scanning circuit / 109...DFE / 110...output signal processing unit / 111...memory unit / 112...external interface unit / 117...control unit / 300, 300', 300R...radiation / C1...floating diffusion unit / C2...charge storage unit / D1...detection diode / M1...memory transfer transistor / M2...reset transistor / M3...amplifying transistor / M4...selection transistor / M5...transfer transistor / M6...overflow transistor

Claims

1. a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a pixel signal corresponding to the charge present in the floating diffusion unit from each of the pixels; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; when the pixel signal read out from any pixel of the pixel array in two consecutive frames exceeds a predetermined value, the signal processing unit corrects the pixel signal read out from the any pixel in a temporally preceding frame of the two consecutive frames to a smaller correction value; A radiation detection device characterized by:

2. a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to the photoelectric conversion unit of the arbitrary pixel in an arbitrary frame, and the radiation penetrates the charge storage unit of the arbitrary pixel to generate charges, and a pixel signal read out from the arbitrary pixel as a pixel signal of a frame immediately before the arbitrary frame is a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal.

2. The radiation detection device according to claim 1.

3. a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to the photoelectric conversion unit of the arbitrary pixel, and the radiation penetrates the charge storage unit of the arbitrary pixel to generate charges, a pixel signal read out from the arbitrary pixel in accordance with charges transferred from the charge storage unit to the floating diffusion unit is defined as a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal.

2. The radiation detection device according to claim 1.

4. a pixel signal read from the arbitrary pixel when the pixel array is not irradiated with radiation for two or more consecutive frames is defined as a first pixel signal; When radiation is irradiated to a pixel adjacent to the arbitrary pixel in an arbitrary frame, and the radiation penetrates the charge storage portion of the arbitrary pixel to generate a charge, and a pixel signal read out from the arbitrary pixel as a pixel signal of a frame immediately before the arbitrary frame is a second pixel signal, the predetermined value is a threshold value that can distinguish between the first pixel signal and the second pixel signal.

2. The radiation detection device according to claim 1.

5. the predetermined value is greater than an average value of pixel signals read out from each of the pixels when the pixel array is not irradiated with radiation for two or more consecutive frames.

2. The radiation detection device according to claim 1.

6. the pixel array is driven such that the average number of radiation photons or particles incident on each pixel per frame is 0.5 or less; 6. The radiation detection device according to claim 1, wherein the radiation detection device is a radiation detector.

7. The readout unit a charge-voltage converter that converts the charge present in the floating diffusion portion of each pixel into a voltage signal and reads it out; an A / D converter that converts the read voltage signal into a digital signal; 6. The radiation detection device according to claim 1, wherein the radiation detection device is a radiation detector.

8. the A / D converter converts the voltage signal into a digital signal with three or more values, the correction value is set based on a value obtained by reading out a voltage signal from the pixel array in advance and converting it into a digital signal by the A / D converter when the pixel is not irradiated with radiation over a plurality of consecutive frames.

8. The radiation detection device according to claim 7.

9. the A / D converter converts the voltage signal into a digital signal with three or more values, the correction value is a difference value between the digital signal of the arbitrary pixel in a temporally subsequent frame of the two consecutive frames and the digital signal of the arbitrary pixel in the temporally preceding frame.

8. The radiation detection device according to claim 7.

10. the A / D converter converts the voltage signal into a digital signal with three or more values, the signal processing unit calculates the correction value using the digital signals of neighboring pixels of the arbitrary pixel in the temporally preceding frame.

8. The radiation detection device according to claim 7.

11. the A / D converter converts the voltage signal into a digital signal with three or more values, the signal processing unit binarizes the ternary or greater value digital signal that has been converted into the correction value for the temporally preceding frame.

8. The radiation detection device according to claim 7.

12. the A / D converter performs a binarization process to convert the voltage signal into a binary signal; the correction value is a value of a binary signal obtained by previously reading a voltage signal read from the pixel array when the pixel is not irradiated with radiation over a plurality of consecutive frames and converting the voltage signal into a digital signal by the A / D converter; 8. The radiation detection device according to claim 7.

13. When the pixel array is not irradiated with radiation over a plurality of consecutive frames, the value of the binary signal read from the pixel array is defined as a dark signal value. The signal processing unit When an area in which pixels having a binary signal greater than the dark signal value are adjacently present is detected in the temporally preceding frame, one pixel that maintains the binary signal is selected from the pixels in the area, and the values of the binary signals of the pixels in the area other than the one pixel are corrected to the dark signal value.

12. The radiation detection device according to claim 11.

14. a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a binarized pixel signal from each pixel of the pixel array in accordance with the charge present in the floating diffusion unit; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; The signal processing unit When the pixel array is not irradiated with radiation over a plurality of consecutive frames, the pixel signal values read out from the pixel array are dark signal values, When detecting an area in which adjacent pixels exist, each of which has a pixel signal having a value greater than the dark signal value, for each of two consecutive frames, selecting one pixel from among the pixels in the area for maintaining the pixel signal, and correcting the values of the pixel signals read out from the pixels in the area other than the one pixel to the dark signal value; If the pixel signal at the same pixel in both of the two frames after correction is not the dark signal value, the pixel signal at the same pixel in the temporally preceding frame of the two frames is replaced with the dark signal value. A radiation detection device characterized by:

15. the signal processing unit is disposed on a chip on which the pixel array is formed, 6. The radiation detection device according to claim 1, wherein the radiation detection device is a radiation detector.

16. the signal processing unit is disposed outside a chip on which the pixel array is formed.

6. The radiation detection device according to claim 1, wherein the radiation detection device is a radiation detector.

17. The radiation detection device according to any one of claims 1 to 5, a radiation source that irradiates the imaging target with radiation; A radiation imaging system comprising:

18. the radiation source controls the radiation irradiation rate so that the average number of radiation photons or particles incident on each pixel per frame is 0.5 or less; 18. The radiation imaging system according to claim 17.

19. a photoelectric conversion unit that generates charges when irradiated with radiation; a charge holding unit that holds charges transferred from the photoelectric conversion unit; a pixel array including a plurality of pixels each having a floating diffusion portion to which charges are transferred from the charge storage portion; a control unit that controls the operation of the pixel array; a readout unit that reads out a pixel signal corresponding to the charge present in the floating diffusion unit from each of the pixels; a signal processing unit that processes the read pixel signals, the control unit simultaneously transfers charges from the photoelectric conversion units to the charge holding units in the plurality of pixels arranged in the pixel array for each frame; when the pixel signal read out from any pixel of the pixel array in two consecutive frames exceeds a predetermined value, the signal processing unit corrects the pixel signal read out from the any pixel in a temporally preceding frame of the two consecutive frames to a smaller correction value; A radiation imaging method comprising:

20. A program for causing a signal processing unit to execute the radiation imaging method according to claim 19.

21. A computer-readable recording medium on which the program according to claim 20 is recorded.

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