Radiation detectors and radiation detection systems

Abstract

This technology offers advantages in improving the image quality of radiographic images. [Solution] A radiation detector comprising a plurality of pixels that output pixel signals corresponding to incident radiation, and an A / D converter that performs A / D conversion of the pixel signals, wherein the A / D converter includes a comparator that compares the pixel signals with a signal threshold, and is configured to operate in a plurality of modes, the plurality of modes including a first mode in which A / D conversion of the pixel signals is performed using a first reference signal when the pixel signals are smaller than the signal threshold, and A / D conversion of the pixel signals is performed using a second reference signal when the pixel signals are larger than the signal threshold, the first reference signal is a signal that changes over time in a first voltage range, the second reference signal is a signal that changes over time in a second voltage range, the upper limit of the first voltage range is smaller than the lower limit of the second voltage range, and the signal threshold is set between the upper limit and the lower limit.

Description

Technical Field

[0001] The present invention relates to a radiation detector and a radiation detection system.

Background Art

[0002] In a radiation detector that converts radiation such as X-rays and electron beams into electrical signals, a background component caused by dark current or the like flowing in the sensor is removed from the signal obtained by the sensor, whereby a noise-reduced radiation image can be obtained. Patent Document 1 discloses that in an X-ray imaging system that detects X-rays with a CMOS image sensor, the image signal of each image frame is corrected using a correction coefficient acquired using the image signal of an image frame different from the relevant image frame.

Prior Art Literature

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] Background components such as dark current can vary due to changes in temperature and other factors. When performing continuous imaging while irradiating radiation, the temperature of the radiation detector rises over time, causing the background component to change, and correction using a previously acquired background component may lead to degradation in the image quality of the obtained radiation image.

[0005] An object of the present invention is to provide a technique advantageous for improving the image quality of radiation images.

Means for Solving the Problem

[0006] In view of the above problems, a radiation detector according to an embodiment of the present invention is a radiation detector comprising: a plurality of pixels that output a pixel signal corresponding to incident radiation; and an A / D converter that performs A / D conversion of the pixel signal, wherein the A / D converter includes a comparator that compares the pixel signal with a signal threshold, and is configured to operate in a plurality of modes, the plurality of modes including a first mode in which A / D conversion of the pixel signal is performed using a first reference signal when the pixel signal is smaller than the signal threshold, and A / D conversion of the pixel signal is performed using a second reference signal when the pixel signal is larger than the signal threshold, the first reference signal is a signal that changes over time in a first voltage range, the second reference signal is a signal that changes over time in a second voltage range, the upper limit of the first voltage range is smaller than the lower limit of the second voltage range, and the signal threshold is set between the upper limit and the lower limit. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technology that is advantageous for improving the image quality of radiographic images. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing an example configuration of the radiation detector in this embodiment. [Figure 2] A diagram showing an example of the pixel configuration of the radiation detector in this embodiment. [Figure 3] A diagram illustrating the pixel signals of the radiation detector in this embodiment. [Figure 4] This figure shows a histogram of the pixel output values ​​of the radiation detector in this embodiment. [Figure 5] This figure shows an example configuration of the A / D converter for the radiation detector of this embodiment. [Figure 6] This figure illustrates an example of signal processing for the radiation detector of this embodiment. [Figure 7] A diagram illustrating the method of binarization for the radiation detector of this embodiment. [Figure 8] A flowchart illustrating an example of the processing of the radiation detector in this embodiment. [Figure 9] This figure illustrates an example of signal processing for the radiation detector of this embodiment. [Figure 10] A flowchart illustrating an example of the processing of the radiation detector in this embodiment. [Figure 11] This figure illustrates an example of signal processing for the radiation detector of this embodiment. [Figure 12] A diagram showing an example configuration of the radiation detector in this embodiment. [Figure 13] A diagram showing an example configuration of a radiation detection system including a radiation detector according to this embodiment. [Figure 14] This figure illustrates an example of signal processing for the radiation detector of this embodiment. [Figure 15] A schematic diagram showing an example configuration of the equipment and transmission electron microscope as a radiation detection system including a radiation detector according to this embodiment. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] Referring to Figures 1 to 15(a) and 15(b), a radiation detector according to an embodiment of the present disclosure and a radiation detection system using this radiation detector will be described. In the following description, "radiation" is a concept that includes electromagnetic radiation (X-rays, gamma rays, etc.), particle radiation (electron beams, proton beams, neutron beams, alpha rays, etc.), and non-ionizing radiation (radio waves, microwaves, infrared rays, visible light, etc.). "Radiation detection system" refers to a general system that uses radiation to acquire images of an imaging target (subject, patient in the case of a medical imaging system, etc.) as electronic data. "Image" can be a still image or a moving image.

[0011] In the following embodiments, a radiation detector including a conversion element that converts incident radiation into electric charges, and a radiation detection system using this radiation detector will be described. FIG. 1 is a block diagram illustrating a schematic configuration example of the radiation detector 100 of the present embodiment. The radiation detector 100 can include an imaging unit 101, an output signal processing unit 110, a memory 111, and an external interface (external I / F) 112.

[0012] The imaging unit 101 can include a pixel array 102 having a plurality of pixels 103 arranged in a matrix, a vertical scanning circuit 104, vertical signal lines 105, a column signal processing circuit 106, a column memory 107, a horizontal scanning circuit 108, and a signal processing circuit 109. The vertical scanning circuit 104, the vertical signal lines 105, the column signal processing circuit 106, the column memory 107, and the horizontal scanning circuit 108 are examples of a readout circuit that cooperates to read out pixel signals from each pixel 103 of the pixel array 102 for each frame. The signal processing circuit 109 is an example of a processing circuit that processes the pixel signals read out by the readout circuit. The imaging unit 101 may be, for example, a CMOS image sensor that detects radiation.

[0013] The pixels 103 constituting the pixel array 102 convert incident radiation into electric charges. The configuration of the pixels 103 will be described later. The vertical scanning circuit 104 selects and sequentially scans pixel rows that output pixel signals in the pixel array 102. The vertical signal lines 105 transmit pixel signals from the pixels 103 selected by the vertical scanning circuit 104. The column signal processing circuit 106 processes the pixel signals input from the vertical signal lines 105. The processing performed by the column signal processing circuit 106 includes analog-to-digital (A / D) conversion. Therefore, the column signal processing circuit 106 includes an A / D converter as will be described later. The column memory 107 holds digital signals output from the column signal processing circuit 106. The horizontal scanning circuit 108 scans the column signal processing circuit 106 or the column memory 107 in the direction of the pixel columns to sequentially read out the digital signals for each column. The signal processing circuit 109 is an output circuit that processes the digital signals read out from the column signal processing circuit 106 or the column memory 107 and outputs the processed signals to the outside of the imaging unit 101.

[0014] The output signal processing unit 110 performs arithmetic processing on the signal output from the imaging unit 101. The memory 111 is a data holding unit (storage area) for performing the arithmetic operations in the output signal processing unit 110, and holds data to be processed and predetermined data. The signal output from the output signal processing unit 110 is output to the outside of the radiation detector 100 through the external I / F unit 112.

[0015] Figure 2 is a diagram showing a configuration example of the pixel 103 shown in Figure 1. The pixel 103 may include a photodiode 201, a floating diffusion capacitor 202, a transfer transistor 203, a reset transistor 204, an amplification transistor 205, and a pixel selection transistor 206.

[0016] The photodiode 201 is a conversion element that converts incident radiation into electric charges. The anode of the photodiode 201 is connected to a reference voltage node, and the cathode is connected to the source of the transfer transistor 203. The drain of the transfer transistor 203 is connected to the source of the reset transistor 204 and the gate of the amplification transistor 205. The connection node FD of the drain of the transfer transistor 203, the source of the reset transistor 204, and the gate of the amplification transistor 205 is a so-called floating diffusion unit. The floating diffusion unit includes a capacitive component (floating diffusion capacitor 202) and has a function as a charge holding unit. In the present embodiment, the conversion element is, for example, the photodiode 201 formed on a semiconductor substrate such as silicon, but is not limited thereto. For example, a conversion element formed of cadmium telluride or cadmium zinc telluride may be used instead of the photodiode 201.

[0017] The drain of the reset transistor 204 and the drain of the amplification transistor 205 are connected to a power supply voltage node 207 to which a power supply voltage is supplied. The source of the amplification transistor 205 is connected to the drain of the pixel selection transistor 206. The source of the pixel selection transistor 206 is connected to the vertical signal line 105. The vertical signal line 105 is connected to a current source.

[0018] The gates of the transfer transistor 203, reset transistor 204, and pixel selection transistor 206 are connected to signal lines that transmit control signals from the vertical scanning circuit 104. Each signal line is a common signal line for the row to which the pixel 103 belongs in the pixel array 102.

[0019] When radiation is incident on pixel 103, the photodiode 201 converts the radiation into electric charge (signal charge) and stores it. Based on the control signal supplied from the vertical scanning circuit 104, the transfer transistor 203 transfers the signal charge stored in photodiode 201 to the floating diffusion unit (connection node FD). The floating diffusion unit holds the charge transferred from photodiode 201 and also holds a voltage corresponding to the amount of charge transferred by charge-voltage conversion using the floating diffusion capacitor 202.

[0020] The amplification transistor 205 amplifies the pixel signal based on the charge held by the floating diffusion section (connection node FD) and outputs it to the pixel selection transistor 206. The pixel selection transistor 206 outputs the pixel signal from the amplification transistor 205 to the vertical signal line 105 based on the control signal supplied from the vertical scanning circuit 104. As a result, a pixel signal corresponding to the radiation incident from the pixel 103 is output. The reset transistor 204 resets the floating diffusion section to a voltage corresponding to the power supply voltage based on the control signal supplied from the vertical scanning circuit 104. In the pixel 103, the transfer transistor 203 may be omitted, and the photodiode 201 and the floating diffusion capacitor 202 may be directly connected.

[0021] Figure 3 is a schematic diagram showing the output of each pixel 103 when the pixel array 102 is irradiated with radiation 301. Pixels 103 that are incident on radiation 301 are colored, while pixels 103 that are not incident on radiation 301 are shown uncolored. Examples of radiation that can be used include X-rays, electron beams, and gamma rays. Depending on the type of radiation being irradiated, an appropriate conversion element such as a photodiode 201 or a wavelength conversion material such as a scintillator should be used.

[0022] Figure 4 shows an example of a histogram of the output values ​​of pixel signals in one frame of the pixel array 102. The horizontal axis represents the output value of the pixel signal output from each pixel 103, and the vertical axis represents the number of pixels. The histogram is distributed across three ranges: the first pixel signal range 401, the second pixel signal range 403 which does not overlap with the first pixel signal range 401, and the third pixel signal range 402 which is between the first and second pixel signal ranges 401 and 403. Therefore, the voltage range of the ramp signal when performing A / D conversion on a pixel signal output from any pixel 103 must be a range that includes the first pixel signal range 401, the second pixel signal range 403, and the third pixel signal range 402, for example, pixel signal range 404. Here, the upper limit of the first pixel signal range 401 is smaller than the lower limit of the second pixel signal range 403. Furthermore, the upper limit of the third pixel signal range 402 is less than or equal to the lower limit of the second pixel signal range 403, and the lower limit of the third pixel signal range 402 is greater than or equal to the upper limit of the first pixel signal range 401. The first pixel signal range 401 is assumed to be the range of output values ​​of the pixel signal of pixel 103 that was not incident on by radiation. The second pixel signal range 403 is assumed to be the range of output values ​​of the pixel signal of pixel 103 that was incident on by radiation.

[0023] Here, the pixel signal is the signal output from pixel 103 in response to the signal charge generated in response to the incident radiation. The pixel signal can change depending on the radiation irradiation conditions such as the type of radiation and acceleration energy, the structure of the conversion element such as the photodiode 201, and the thickness of the substrate of the pixel array 102. When the energy of the radiation is high, the generated signal charge is not constant because it has a statistical probability distribution. In addition, the irradiated radiation may pass through the substrate of the pixel array 102 to adjacent pixels 103 and generate charge. In that case, as shown in pixels 302 and 303 in Figure 3, pixel signals corresponding to the incident radiation may be generated across multiple adjacent pixels.

[0024] On the other hand, the pixel signal of a pixel that was not exposed to radiation (for example, pixel 304 in Figure 3) will have a value equivalent to the pixel signal read out when no radiation is applied. However, the signal value will not be zero, and the output will be superimposed with dark current generated in the photodiode 201, circuit-induced noise and shading, etc. Therefore, the first pixel signal range 401 will have a range of values. Components that occur regardless of whether or not radiation is applied are called background components. Background components can interfere with the detection of signal components caused by radiation and may lead to a decrease in the image quality of the image data acquired by the radiation detector 100.

[0025] Figure 5 shows an example configuration of the A / D converter 500 included in the column signal processing circuit 106. The A / D converter 500 may include a comparator 501, a determination unit 502, a reference signal generation circuit 503, a changeover switch 504, a counter 505, and a digital memory 506.

[0026] The comparator 501 may include two input nodes and one output node. One input node of the comparator 501 is supplied with a pixel signal from the vertical signal line 105. As will be described in detail later, the A / D converter 500 (radiation detector 100) is configured to operate in multiple modes. In the high-speed mode, one of the following signals is supplied to the other input node of the comparator 501 from the reference signal generation circuit 503: a signal threshold, ramp signal Ramp1, or ramp signal Ramp2.

[0027] In high-speed mode, first, the comparator 501 outputs an L-level signal if the level of the signal threshold output from the reference signal generation circuit 503 is lower than the level of the pixel signal supplied from the vertical signal line 105. Also, the comparator 501 outputs an H-level signal if the level of the signal threshold output from the reference signal generation circuit 503 is higher than the level of the pixel signal supplied from the vertical signal line 105. The determination unit 502 controls the reference signal generation circuit 503 to output a ramp signal Ramp1 as a reference signal if the output of the comparator 501 is an L-level signal. Also, the determination unit 502 controls the reference signal generation circuit 503 to output a ramp signal Ramp2 as a reference signal if the output of the comparator 501 is an H-level signal.

[0028] Next, the comparator 501 outputs an L-level signal if the level of the ramp signal Ramp1 or ramp signal Ramp2 output from the reference signal generation circuit 503 is lower than the level of the pixel signal supplied from the vertical signal line 105. Also, the comparator 501 outputs an H-level signal if the level of the ramp signal Ramp1 or ramp signal Ramp2 output from the reference signal generation circuit 503 is higher than the level of the pixel signal supplied from the vertical signal line 105. The toggle switch 504 is synchronized with the reference signal generation circuit 503. The toggle switch 504 is connected to the input of the determination unit 502 when a signal threshold is output from the reference signal generation circuit 503. Also, the toggle switch 504 is connected to the input of the digital memory 506 when the ramp signal Ramp1 or ramp signal Ramp2 is output from the reference signal generation circuit 503.

[0029] The counter 505 starts counting in synchronization with the timing when the signal levels of the ramp signals Ramp1 and Ramp2 supplied from the reference signal generation circuit 503 begin to change. The counter 505 has a function to output a count signal to the digital memory 506, which is the count value at the timing when the output of the comparator 501 switches from L level to H level. The digital memory 506 holds the count signal input from the counter 505.

[0030] Figure 6 shows a time chart illustrating the operation of the reference signal generation circuit 503. The horizontal axis represents time, and the vertical axis represents the output voltage of the reference signal generation circuit 503. Here, the range from voltage V1 to voltage V2-A is defined as the first voltage range 605, the range from voltage V2-B to voltage V3 is defined as the second voltage range 607, and the range from voltage V2-A to voltage V2-B is defined as the third voltage range 606. The reference signal generation circuit 503 of the A / D converter 500 can operate in multiple modes, including normal mode and high-speed mode. The ramp signal 604 indicates the ramp voltage when performing A / D conversion in normal mode. In normal mode, the reference signal generation circuit 503 sweeps the ramp signal in a voltage range that includes the first voltage range 605, the second voltage range 607, and the third voltage range 606, respectively, during period Count1. The ramp signal 604 is a signal that changes over time in a continuous voltage range that includes the first voltage range 605 and the second voltage range 607.

[0031] On the other hand, in high-speed mode, the reference signal generation circuit 503 generates either ramp signal 602 or ramp signal 603, which is different from ramp signal 604. The ramp signals 602 and 603 shown in Figure 6 represent the ramp voltages used in high-speed mode. Ramp signal 602 corresponds to ramp signal Ramp1, and ramp signal 603 corresponds to ramp signal Ramp2. In the period Judge, the reference signal generation circuit 503 outputs a signal threshold 601. If the level of the signal threshold 601 is higher than the level of the signal from the vertical signal line 105, the reference signal generation circuit 503 sweeps ramp signal 602 within the first voltage range 605 in period Count2, according to the control of the determination unit 502. Ramp signal 602 is a signal that changes over time within the first voltage range 605. On the other hand, if the level of the signal threshold 601 is lower than the level of the signal from the vertical signal line 105, the reference signal generation circuit 503 sweeps the ramp signal 603 in the second voltage range 607 according to the control of the determination unit 502. The ramp signal 603 is a signal that changes over time in the second voltage range 607. Here, the signal threshold 601 is set to a voltage value within the third voltage range 606, which is between the upper limit of the first voltage range 605 and the lower limit of the second voltage range 607.

[0032] In the example shown in Figure 6, the voltage slopes of ramp signals 602 and 603 with respect to time in high-speed mode are approximately equal to the voltage slopes of ramp signal 604 with respect to time in normal mode. Here, "approximately equal" means that the differences are within the range of variations due to design-specific parasitic capacitance and resistance, as well as individual variations during mass production. These are empirically within ±5%.

[0033] Thus, the radiation detector 100 of this embodiment can perform both normal mode imaging and high-speed mode imaging using the same imaging unit 101, by switching the drive. As will be described in detail later, for example, by setting the first voltage range 605, the second voltage range 607, and the third voltage range 606 to appropriate conditions in normal mode, A / D conversion can be performed in high-speed mode by narrowing it to the voltage range necessary for binarization, thereby realizing high-speed imaging.

[0034] In the high-speed mode of this embodiment, the first pixel signal range 401 is assumed to correspond to the first voltage range 605, and the second pixel signal range 403 is assumed to correspond to the second voltage range 607. The first voltage range 605 is the range of output values ​​of the pixel signal of a pixel 103 that was not incident on by radiation, and corresponds to the background component. The second voltage range 607 is the output value of the pixel signal of a pixel 103 that was incident on by radiation, and corresponds to the image signal component. The pixel signal output from the pixel 103 is compared with a signal threshold 601 and A / D converted using either the ramp signal 602 or the ramp signal 603. In other words, for the output value of a single pixel signal, the background component can be obtained when the ramp signal 602 is used, and the image signal component can be obtained when the ramp signal 603 is used. Furthermore, the third pixel signal range 402 is assumed to correspond to the third voltage range 606. In particular, when performing counting that binarizes depending on whether or not radiation has been incident, it is sufficient to obtain the background component and the A / D conversion value near the counting threshold 701 described later. For this reason, a third voltage range 606 in which no A / D conversion is performed may exist between the first voltage range 605 and the second voltage range 607.

[0035] Thus, in normal mode, A / D conversion is performed during period Count1, while in high-speed mode, A / D conversion is performed during period Judge and period Count2. In high-speed mode, A / D conversion is performed within a narrower voltage range than in normal mode, depending on the magnitude of the pixel signal output value. As a result, even including period Judge, which compares the pixel signal with the signal threshold, high-speed mode can perform faster A / D conversion than normal mode.

[0036] Here, even if the signal threshold 601 is the same as the upper limit of the first voltage range 605 or the lower limit of the second voltage range 607, and the third voltage range 606 does not exist, in high-speed mode, A / D conversion is performed using only one of the first voltage range 605 or the second voltage range 607. Therefore, even in such cases, high-speed mode can be driven at a higher speed than normal mode.

[0037] In the high-speed mode of this embodiment, the first voltage range 605 is swept as ramp signal 602, and the second voltage range 607 is swept as ramp signal 603. In other words, background components and image signal components can be acquired within the same frame. That is, background components can be calculated that are simultaneous with the imaging of the target object. As a result, the radiation detector 100 of this embodiment is capable of high-speed readout and calculation of background components that are simultaneous with the imaging of the target object.

[0038] Furthermore, for example, in high-speed mode, the signal processing circuit 109 may calculate correction data by subtracting the background component from the pixel signal that has undergone A / D conversion using the ramp signal 603. In this case, the radiation detector 100 can also output the correction data externally. For example, the signal processing circuit 109 corrects the pixel signals that have undergone A / D conversion using the ramp signal 603 from among the pixel signals output from multiple pixels 103 in a single frame, based on the pixel signals that have undergone A / D conversion using the ramp signal 602. For example, the signal processing circuit 109 may use the mode, median, or mean value of the multiple pixel signals that have undergone A / D conversion using the ramp signal 602 as the background component. The correction of the background component may be performed by the output signal processing unit 110 instead of the signal processing circuit 109. In this way, the radiation detector 100 can provide the background component data and the net image data with the background component removed to, for example, other devices in a radiation detection system including the radiation detector 100.

[0039] Thus, the radiation detector 100 can remove background components during imaging without using calibration methods such as acquiring pixel signals while not irradiating with radiation at a time separate from the imaging of the target object to acquire background components. However, this does not preclude the use of calibration methods to remove noise other than the background components removed by the method of this embodiment.

[0040] The background component of the pixel signal output from multiple pixels 103 can change for various reasons. For example, changes in ambient temperature during imaging or temperature changes associated with the operation of the radiation detector 100 can cause changes in the dark current generated in the pixels 103, resulting in fluctuations in the background component. The radiation detector 100 of this embodiment can acquire background components simultaneously with imaging, even in imaging where temporal fluctuations of the background component tend to be a problem, thereby obtaining more accurate image data.

[0041] The radiation detector 100 of this embodiment can also be applied to counting operations that binarize a pixel 103 arranged in a pixel array 102 depending on whether or not radiation has entered it. Figure 7 is a diagram in which a determination threshold 701 for binarizing the pixel signals output from multiple pixels 103 is added to the histogram of Figure 4. For example, the signal processing circuit 109 binarizes the pixel signals that have been A / D converted using the ramp signal 603 from the pixel signals output from multiple pixels 103 by comparing their magnitudes using the determination threshold 701. In other words, the radiation detector 100 of this practical embodiment can binarize while removing background components that are simultaneous with the imaging of the target being imaged.

[0042] Figure 8 is a flowchart showing the processing performed by the radiation detector 100 during binarization. In S801, the first voltage range 605 of the reference signal, the ramp signal 602, is set. In S802, the second voltage range 607 of the reference signal, the ramp signal 603, is set. The first voltage range 605 and the second voltage range 607 may be set using, for example, previously acquired image data. Alternatively, the first voltage range 605 and the second voltage range 607 may be selected manually or automatically from multiple types of settings depending on the radiation irradiation conditions. Furthermore, S801 may be performed before S802, or the first voltage range 605 and the second voltage range 607 may be set simultaneously.

[0043] During imaging, charge is accumulated in each pixel 103 of the pixel array 102 while radiation is being irradiated from the radiation source of the radiation detection system incorporating the radiation detector 100. In S803, the pixel signal is read out from each pixel 103 for each frame. In S804, a judgment threshold 701 is set. The judgment threshold 701 may be obtained (calculated) from previously acquired image data, or it may be obtained in real time from image data obtained from the most recent frame. Next, using the judgment threshold 701 set in S804, the pixel signal that has been A / D converted using the ramp signal 603 in the second voltage range 607 is binarized. In S806, the binarized data of each pixel 103 is output externally from the radiation detector 100. By outputting the binarized data externally from the radiation detector 100, it is possible to reduce the number of output ports of the radiation detector 100, reduce the output clock rate, and reduce the amount of data processing outside the radiation detector 100. As a result, the cost of the radiation detector 100 and the radiation detection system including the radiation detector 100 can be reduced.

[0044] The voltage range for A / D conversion in high-speed mode S801 and S802 is set by the reference signal generation circuit 503 as described above. S803 can be executed by the vertical scanning circuit 104 and horizontal scanning circuit 108 described above, and a control circuit that controls the control timing for them. S804 to S806 are executed by the signal processing circuit 109.

[0045] In this embodiment, the signal processing circuit 109 within the imaging unit 101 is described as performing steps S804 to S806. In other words, in the high-speed mode of this embodiment, the imaging unit 101 can be equipped with a function for deriving and removing background components on-chip, that is, on the same substrate as the pixel array 102 and the column signal processing circuit 106. This simplifies the subsequent processing from the output signal processing unit 110 onward. As a result, the radiation detector 100 can be made smaller and less expensive. However, this is not the only option, and the deriving and removal of background components in steps S804 to S806 may be performed outside the imaging unit 101, such as in the output signal processing unit 110. Furthermore, a program for causing a computer to execute some or all of steps S801, S802, and S804 to S806 may be stored in a non-transient storage medium readable by a computer, and the computer may be allowed to execute the program. This can improve user convenience.

[0046] The signal level changes of the ramp signals 602 and 603, which are reference signals generated by the reference signal generation circuit 503, do not necessarily have to be continuous; they may be stepwise. Furthermore, the signal level changes do not necessarily have to be linear with respect to time; they may be curvilinear with respect to time. Also, the voltage ranges of ramp signals 602 and 603 may be further divided. Moreover, the A / D converter 500 is not limited to the Slope type; successive approximation or ΔΣ types can also be employed. By selecting the voltage range and resolution for A / D conversion in accordance with the principles of this disclosure, the effects of this disclosure can be obtained.

[0047] Figure 9 shows a modified version of the time chart illustrating the operation of the reference signal generation circuit 503 shown in Figure 6. The horizontal axis represents time, and the vertical axis represents the output voltage of the reference signal generation circuit 503. The difference from the operation shown in Figure 6 is that the resolution of ramp signals 901 and 902 used in high-speed mode is different from the resolution of ramp signals 602 and 603. In the operation shown in Figure 6, it was explained that the slope of the voltage change with respect to time for ramp signals 602 and 603 used in high-speed mode is the same as the slope of ramp signal 604 used in normal mode. On the other hand, in the operation shown in Figure 9, the slope of the voltage change with respect to time for ramp signals 901 and 902 used in high-speed mode is different from the slope of ramp signal 604 used in normal mode, and specifically, it is greater than the slope of ramp signal 604. As a result, by increasing the slope of the voltage change with respect to time for ramp signals 901 and 902 and lowering the resolution, A / D conversion is possible in shorter periods Count2-A and 2-B than the period Count2 shown in Figure 6.

[0048] Furthermore, in the operation shown in Figure 9, the first voltage range 903 of the ramp signal 901 and the second voltage range 904 of the ramp signal 902 are narrower than the first voltage range 605 of the ramp signal 602 and the second voltage range 607 of the ramp signal 603. This can be achieved, for example, by obtaining the approximate voltage range between the background component and the image signal component in advance. In particular, when performing counting, it is sufficient to obtain the background component and an A / D conversion value near the counting judgment threshold 701. Therefore, by narrowing the first voltage range 903 and the second voltage range 904, faster A / D conversion can be achieved.

[0049] In the operation shown in Figure 9, the slope (resolution) of ramp signal 901 and ramp signal 902 used in high-speed mode are different from each other. However, this is not the only option; for example, ramp signal 901 and ramp signal 902 may sweep the voltage with approximately the same resolution. By obtaining a background component with a resolution equivalent to that of the A / D conversion value of ramp signal 902 from the A / D conversion value of ramp signal 901 and subtracting it, the respective A / D conversion values ​​can be subtracted without gain adjustment.

[0050] Figure 10 is a flowchart showing a modified version of the process performed by the radiation detector 100 during binarization, as explained using Figure 8. The background component changes for various reasons, including, for example, damage to the imaging device due to the cumulative radiation dose known as the total dose effect. Specifically, this could include an increase in dark current in pixel 103 or threshold fluctuations in each transistor located in pixel 103. In other words, an increase in the cumulative radiation dose can cause a shift in the first pixel signal range 401 shown in Figure 4. The binarization process considering the total dose effect will be explained below.

[0051] Steps S801 to S803 are the same as those described above, with the first voltage range 605 and the second voltage range 607 being set, and the pixel signal being read from the pixel 103. Next, in S1004, the judgment threshold 701 shown in Figure 7 is set from the background component read by the ramp signal 602. For example, the signal processing circuit 109 sets the judgment threshold 701 based on the pixel signals output from multiple pixels 103 in the same frame as the pixel signal to be binarized (the pixel signal that is A / D converted using the ramp signal 603), and the pixel signal that has been A / D converted using the ramp signal 602. For example, the signal processing circuit 109 may perform a correction to remove the background component from the judgment threshold 701 obtained from previously captured image data or image data obtained from the most recent frame. After setting the judgment threshold 701, the binarization process is performed in S805 as described above, and the data for each pixel 103 is output in S806.

[0052] Furthermore, after executing step 1006, the radiation detector 100 returns the process from S806 to S803 as shown by line 1007, and by repeating steps S803 to S806, it is possible to set a judgment threshold 701 that corresponds to the increase in the cumulative radiation dose. In other words, even if the first pixel signal range 401 of the radiation detector 100 of this embodiment is shifted, the judgment threshold 701 of the second pixel signal range 403 is shifted by the amount of the shift, thereby enabling binarization processing that follows the fluctuations in the background component.

[0053] In this way, by setting the judgment threshold 701 from the background component obtained from the pixel signal converted using the ramp signal 602, changes in the background component can be corrected. Here, instead of shifting the judgment threshold 701 in S1004, the ramp signals 602 and 603 may be shifted by an amount equivalent to the change. In that case, the increase in the cumulative radiation dose can be removed by subtracting the background component from the image signal component.

[0054] Next, we will explain a process (method) to mitigate the effects of spatial heterogeneity when acquiring background components. Figures 11(a) and 11(b) show the computational filter in this embodiment. Figure 11(a) shows the filter region of the computational filter. In this embodiment, it is possible to obtain a two-dimensional background component by selecting a background component for each pixel.

[0055] As shown in Figure 11(a), for a target pixel 1101 (the pixel of interest) among the pixels 103, a predetermined range 1102 composed of multiple pixels 103 centered on the target pixel 1101 is set as the size of the calculation filter. The background component is obtained from the value of the pixel signal output from each pixel 103 within the filter region of this calculation filter. The judgment threshold 701 may be set using this background component.

[0056] As shown in Figure 11(b), the target pixels 1101 are successively changed on the pixel array 102 and swept two-dimensionally, and for each pixel 103, the background component is acquired using an operational filter within a predetermined range 1102 as shown in Figure 11(a). The sweep direction can be either column-direction or row-direction first. For example, the sweep can be performed in either the row-direction or column-direction depending on the processing characteristics of the signal processing circuit 109.

[0057] Figure 12 shows an example configuration of a radiation detector 100 that acquires background components using an arithmetic filter. Compared to the configuration shown in Figure 1, memory 1214 has been added. Other configurations may be the same as those shown in Figure 1, and the explanation will focus on the differences, while explanations of similarities will be omitted as appropriate.

[0058] In this embodiment, the processing of the operational filter can be performed by the signal processing circuit 109. The filter size (a predetermined range 1102) is set considering the spatial frequencies of the main elements that cause non-uniformity in the background component. Generally, a smaller filter size makes it easier to extract local unevenness and shading components contained in the background component. On the other hand, a larger filter size reduces the possibility that the value calculated as the background component will deviate significantly from the actual background component.

[0059] If the filter size is wide, a memory 1214 such as a line memory or frame memory may be provided in the imaging unit 101 of the radiation detector 100. Pixel signals output from a predetermined range 1102 of pixels 103 from a target pixel 1101, and converted using a ramp signal 602, are stored in the memory 1214. The signal processing circuit 109 sets a determination threshold 701 based on the pixel signals stored in the memory 1214. When the memory 1214 is equipped with a frame memory, the background component can be calculated using a two-dimensional filter. Using a two-dimensional filter allows for accurate calculation of the background component while suppressing the effects of signal components other than the background component and pixel-specific characteristic variations. Furthermore, as described above, performing processing within the radiation detector 100 improves the simultaneity between imaging and correction processing. On the other hand, when the memory 1214 is equipped with a line memory, the background component is calculated using a one-dimensional filter, but the memory size can be reduced. Therefore, it becomes possible to miniaturize the radiation detector 100 (imaging unit 101).

[0060] The memory 1214 is not limited to being located in the imaging unit 101. The memory 1214 may be located outside the imaging unit 101. For example, the memory 1214 may be located in the output signal processing unit 110, and the above-described processing may be performed there.

[0061] In this way, by using an operational filter to acquire the background component for every 103 pixels, it becomes possible to obtain background components that include spatially non-uniform distributions. This improves the accuracy of the image data after subtracting the background component.

[0062] The background component may also include non-uniformity from pixel to pixel. To correct for non-uniformity from pixel to pixel, for example, one could acquire the output of each pixel beforehand in a state where radiation has not been irradiated, save it as a correction value, and subtract the correction value from the pixel signal at the time of imaging. The method for acquiring the background component in this embodiment may be used in combination with such a method for correcting the output of each pixel.

[0063] Figure 13 shows an example configuration of a radiation detection system 1313 incorporating the radiation detector 100 of this embodiment. The radiation detection system 1313 may include the radiation detector 100, a radiation source 1314 that irradiates the radiation detector 100 with radiation, an exposure control unit 1315, and a computer 1316.

[0064] The radiation source 1314 begins irradiating with radiation in accordance with the exposure command supplied by the exposure control unit 1315. The radiation emitted from the radiation source 1314 penetrates the imaging target and enters the imaging unit 101 of the radiation detector 100 directly or indirectly. The radiation source 1314 stops emitting radiation in accordance with the stop command supplied by the exposure control unit 1315.

[0065] The radiation detector 100 includes a control unit 1317 that controls the imaging frame rate and the radiation irradiation rate. The control unit 1317 may generate a stop signal to stop the irradiation of radiation from the radiation source 1314 based on the signal output from the imaging unit 101. The stop signal is supplied to the exposure control unit 1315, which sends a stop command to the radiation source 1314 in response to the stop signal.

[0066] When performing the binarization process described above, if radiation is detected more than once in a single pixel 103 within a single frame, "1" is output as the binarization output. As a result, a portion of the image signal component is lost. Therefore, for example, the control unit 1317 controls the imaging frame rate and the radiation irradiation rate so that the radiation irradiation rate does not exceed 0.5 / pix / frm. For example, by performing imaging at a relatively low irradiation rate, it is possible to provide an image with improved count loss during counting.

[0067] Here, the unit [ / pix / frm] is the average number of radiation particles or photons incident per frame and per pixel. In this embodiment, the radiation irradiation rate is 0.5 / pix / frm or less. In other words, the radiation source 1314 is controlled at a low irradiation rate such that the probability of radiation incident on one pixel 103 at a given time is 0.5 or less. For example, when using X-rays, the guideline for the irradiation rate is 0.5 or less, based on the average number of photons incident per frame and per pixel. When using electron beams, the guideline for the irradiation rate is 0.5 or less, based on the average number of electrons incident per frame and per pixel.

[0068] The control unit 1317 may be, for example, a Programmable Logic Device (PLD) such as a Field Programmable Gate Array (FPGA), or an Application Specific Integrated Circuit (ASIC). Alternatively, the control unit 1317 may be a general-purpose computer with a program embedded within it. Furthermore, the control unit 1317 may be composed of all or some of these components combined.

[0069] The computer 1316 may, for example, control the radiation detector 100 and the radiation control unit 1315. The computer 1316 may also receive radiation image data from the external I / F unit 112 and process it for display as a radiation image.

[0070] Here, the control unit 1317 may be located separately from the radiation detector 100. For example, the computer 1316 may have the functions of the control unit 1317. Alternatively, the computer 1316 may function as an input unit for the user to input the conditions for capturing radiation images.

[0071] For example, the exposure control unit 1315 has an exposure switch, and when the exposure switch is turned on by the user, it sends an exposure command to the radiation source 1314 and also sends a start notification to the computer 1316 indicating the start of radiation emission. Upon receiving the start notification, the computer 1316 responds by notifying the control unit 1317 of the radiation detector 100 of the start of radiation irradiation. In response, the control unit 1317 causes the imaging unit 101 to generate a signal corresponding to the incident radiation.

[0072] Figure 14 is a flowchart showing the processing performed by the radiation detector 100 incorporated into the radiation detection system 1313. In the operation shown in Figure 14, operations S1401 to S1406 are performed before the high-speed mode imaging (main imaging) described above. In S1401, the A / D converter 500 is set to normal mode. In S1402, the ramp signal 602 is set. During imaging, charge is accumulated in each pixel 103 of the pixel array 102 while radiation is being irradiated from the radiation source 1314 of the radiation detection system 1313. Next, in S1403, the pixel signal is read out from each pixel 103 for each frame. In S1404, the histogram shown in Figure 4 is generated, and the mode of the histogram and the judgment threshold 701 are derived. In S1405, the first voltage range 605 of the ramp signal 602 is set within the range that includes the mode of the histogram. In addition, in S1406, the second voltage range 607 of the ramp signal 603 is set within the range that includes the judgment threshold 701. S1406 may be performed before S1405, or S1405 and S1406 may be performed simultaneously.

[0073] S1407 to S1410 describe the operations during the actual imaging. In S1407, the A / D converter 500 is set to high-speed mode. During imaging, charge is accumulated in each pixel 103 of the pixel array 102 while radiation is being irradiated from the radiation source 1314 of the radiation detection system 1313. In S1408, the pixel signal is read out from each pixel 103 for each frame. In S1409, for example, the mode of the histogram in Figure 4 is used as the background component, and the signal component is binarized using the judgment threshold 701 set in step 1404. In S1410, the binarized data of each pixel 103 is output externally.

[0074] In this embodiment, S1401 and 1407 are set by the A / D converter 500. The voltage range for A / D conversion in S1402, 1405, and 1406 is set by the reference signal generation circuit 503. S1403 and 1408 can be executed by the vertical scanning circuit 104 and horizontal scanning circuit 108 described above, and a control circuit that controls the control timing for them. S1404, 1409, and 1410 are executed by the signal processing circuit 109.

[0075] Furthermore, in this embodiment, the first voltage range 605 of the ramp signal 602, set in S1405, is optimized using the results of prior imaging in S1401 to S1404. In this embodiment, the first voltage range 605 of the ramp signal 602 is set to include the mode of the histogram shown in Figure 4. By using the mode, the impact of output values ​​from pixels outside the voltage range on the image quality of the resulting image can be reduced. However, this is not the only option; in S1404, a median value may be derived instead of the mode of the pixel signal output from pixel 103, and the first voltage range 605 of the ramp signal 602 may be set to include the median value of the histogram. Known algorithms can be used to calculate the median value. For example, to calculate the median value of the pixel signals for each row, the pixel signals for each row can be sorted in descending order using quicksort or similar, and then an intermediate value can be selected from the sorted array. Alternatively, a faster algorithm, such as median of medians (quick select), may be applied. Alternatively, for example, in S1404, the average value of the pixel signal output from pixel 103 may be derived, and the first voltage range 605 of the ramp signal 602 may be set to include the average value of the histogram.

[0076] The creation of the histogram shown in Figure 4, the derivation of the mode of the histogram, the derivation of the judgment threshold 701, and the binarization process may be performed by elements other than the imaging unit 101 of the radiation detector 100. For example, the output signal processing unit 110 may perform the processing in S1404, 1409, and 1410. Furthermore, the mode of the histogram can be derived from previously acquired image data, or it can be derived in real time from the most recently acquired image data.

[0077] Next, other examples of radiation detection systems incorporating the radiation detector 100 will be described with reference to Figures 15(a) and 15(b).

[0078] Figure 15(a) shows the EQP as a radiation detection system equipped with a radiation detector 100. The radiation detector 100 includes an imaging unit 101, which is a semiconductor device, as well as a package PKG for mounting the imaging unit 101.

[0079] The package PKG may include a base on which the imaging unit 101 is fixed, a cover made of glass or the like facing the imaging unit 101, and connecting members such as bonding wires or bumps that connect terminals provided on the base and terminals provided on the imaging unit 101. The imaging unit 101 has a pixel array 102 in which pixels 103 are arranged in a matrix and a peripheral region around it. Peripheral circuits (for example, a vertical scanning circuit 104 or a signal processing circuit 109) can be provided in the peripheral region.

[0080] The EQP device may further include at least one of the following: an optical system OPT, a control unit CTRL, a processing unit PRCS, a display device DSPL, a memory device MMRY, and a mechanical device MCHN. The optical system OPT images the radiation onto the radiation detector 100 and is, for example, a lens, shutter, or mirror. Depending on the type of radiation being handled, the optical system OPT may also image particle beams such as electron beams or proton beams onto the radiation detector 100. The control unit CTRL controls the radiation detector 100 and is, for example, an ASIC. The processing unit PRCS processes the signals output from the radiation detector 100 and is a device such as a CPU or ASIC for configuring an AFE (analog front end) or DFE (digital front end). The display device DSPL is an EL display device or liquid crystal display device that displays the 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 semiconductor device that stores the information obtained by the radiation detector 100. The memory device MMRY is a volatile memory such as SRAM or DRAM, or a non-volatile memory such as flash memory or a hard disk drive. The mechanical device MCHN has moving parts or propulsion parts such as motors and engines.

[0081] The EQP device displays the signal output from the radiation detector 100 on the DSPL display device, or transmits it externally via a communication device (not shown) provided by the EQP device. For this purpose, the EQP device may further include a memory device MMRY and a processing device PRCS, separate from the memory circuit and arithmetic circuit of the radiation detector 100. The mechanical device MCHN may be controlled based on the signal output from the radiation detector 100.

[0082] The EQP device shown in Figure 15(a) may be a medical device such as an endoscope or radiological diagnostic equipment, a measuring instrument such as a distance sensor, or an analytical instrument such as an electron microscope.

[0083] Figure 15(b) is a schematic diagram showing the configuration of a transmission electron microscope (TEM) as an example of an EQP instrument. The EQP instrument as an electron microscope includes an electron source 1502 (electron gun), an irradiation lens 1504, a vacuum chamber 1501 (microscope tube), an objective lens 1506, a magnification lens system 1507, and a camera 1509 as a radiation detector 100.

[0084] The electron beam 1503, an energy beam emitted from the electron source 1502, is focused by the irradiation lens 1504 and irradiated onto the sample S, which is held in a sample holder and is the target of analysis. The space through which the electron beam 1503 passes is formed by the vacuum chamber 1501 (lens tube), and this space is maintained under vacuum. The radiation detector 100 is positioned to face the vacuum space through which the electron beam 1503 passes. The electron beam 1503 that has passed through the sample S is magnified by the objective lens 1506 and the magnifying lens system 1507 and projected onto the radiation detector 100. The electron optical system for irradiating the sample S with the electron beam is called the irradiation optical system, and the electron optical system for imaging the electron beam that has passed through the sample S onto the radiation detector 100 is called the imaging optical system.

[0085] The electron source 1502 is controlled by the electron source control device 1511. The irradiation lens 1504 is controlled by the irradiation lens control device 1512. The objective lens 1506 is controlled by the objective lens control device 1513. The magnification lens system 1507 is controlled by the magnification lens system control device 1514. The sample holder control mechanism 1505 is controlled by the holder control device 1515, which controls the drive mechanism of the sample holder.

[0086] The electron beam 1503 that passes through the sample S is detected by the direct detector 1500 of the camera 1509. The output signal from the direct detector 1500 is processed by the signal processing unit 1516 and the image processing unit 1518, which function as the processing unit PRCS, to generate an image signal. The generated image signal (transmitted electron image) is displayed on the image display monitor 1520 and the analysis monitor 1521, which correspond to the display unit DSPL.

[0087] Camera 1509 is located at the bottom of the EQP instrument. Camera 1509 has a direct electron detector 1500, which corresponds to the imaging unit 101. At least a portion of camera 1509 is located inside the camera 1509 so that it is exposed to the vacuum space formed by the vacuum chamber 1501.

[0088] The electron source control device 1511, the irradiation lens control device 1512, the objective lens control device 1513, the magnification lens system control device 1514, and the holder control device 1515 are each connected to the image processing device 1518. This allows for the exchange of data between them to set the imaging conditions of the electron microscope. For example, the electron beam irradiation rate can be set to 0.5 electrons / pix / frm or less. In this case, the electron source control device 1511 and the image processing device 1518 function as control means for controlling the radiation irradiation rate. Signals from the image processing device 1518 allow for the driving control of the sample holder and the setting of observation conditions for each lens.

[0089] The operator prepares the sample S to be photographed and sets the imaging conditions using the input device 1519 connected to the image processing device 1518. The operator inputs predetermined data to the electron source control device 1511, the irradiation lens control device 1512, the objective lens control device 1513, and the magnification lens system control device 1514, respectively, to obtain the desired acceleration voltage, magnification, and observation mode. The operator also inputs conditions such as the number of continuous field images, the starting position for imaging, and the movement speed of the sample holder into the image processing device 1518 using the input device 1519, such as a mouse, keyboard, or touch panel. The image processing device 1518 may also be configured to automatically set the conditions without operator input. The radiation detection system described above is merely an example, and the radiation detector 100 described above may be applied to other systems.

[0090] Furthermore, the above embodiments describe an example in which a method for determining the background component of the pixel signal simultaneously with imaging is applied to a radiation detector or radiation detection system. However, the methods described in each embodiment may also be applied to, for example, an imaging device using a SPAD (single-photon avalanche diode) and an imaging system equipped therewith. By doing so, the background component can be determined simultaneously with imaging and removed from the image data.

[0091] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0092] The disclosures herein include the following radiation detectors and radiation detection systems.

[0093] (Item 1) A radiation detector comprising a plurality of pixels that output pixel signals corresponding to incident radiation, and an A / D converter that performs A / D conversion of the pixel signals, The A / D converter includes a comparator that compares the pixel signal with a signal threshold, and is configured to operate in multiple modes. The plurality of modes include a first mode in which, when the pixel signal is smaller than the signal threshold, A / D conversion of the pixel signal is performed using a first reference signal, and when the pixel signal is larger than the signal threshold, A / D conversion of the pixel signal is performed using a second reference signal. The first reference signal is a time-varying signal in a first voltage range, and the second reference signal is a time-varying signal in a second voltage range. The upper limit of the first voltage range is smaller than the lower limit of the second voltage range. A radiation detector characterized in that the signal threshold is set between the upper limit and the lower limit.

[0094] (Item 2) In the first mode, there exists a third voltage range between the first voltage range and the second voltage range in which A / D conversion is not performed. The upper limit of the third voltage range is less than or equal to the lower limit of the second voltage range. The radiation detector according to item 1, characterized in that the lower limit of the third voltage range is greater than or equal to the upper limit of the first voltage range.

[0095] (Item 3) The radiation detector according to item 1 or 2, characterized in that the slope of the voltage change with respect to time of the first reference signal is equal to the slope of the voltage change with respect to time of the second reference signal.

[0096] (Item 4) A radiation detector according to item 1 or 2, characterized in that the slope of the voltage change with respect to time of the first reference signal and the slope of the voltage change with respect to time of the second reference signal are different from each other.

[0097] (Item 5) The aforementioned plurality of modes include a second mode that performs A / D conversion of the pixel signal using a third reference signal, The radiation detector according to any one of items 1 to 4, characterized in that the third reference signal is a signal that changes over time in a continuous fourth voltage range including the first voltage range and the second voltage range.

[0098] (Item 6) The radiation detector according to item 5, characterized in that the slope of the voltage change with respect to time of at least one of the first reference signal and the second reference signal is equal to the slope of the voltage change with respect to time of the third reference signal.

[0099] (Item 7) The radiation detector according to item 5, characterized in that the slope of the voltage change with respect to time of the first reference signal and the second reference signal is greater than the slope of the voltage change with respect to time of the third reference signal.

[0100] (Item 8) The system further comprises a processing circuit for processing the signal converted by the aforementioned A / D converter, The radiation detector according to any one of items 1 to 7, characterized in that the processing circuit binarizes the pixel signals, which have been A / D converted using a second reference signal from among the pixel signals output from the plurality of pixels, using a determination threshold.

[0101] (Item 9) The radiation detector according to item 8, characterized in that the processing circuit sets the determination threshold based on a first pixel signal, which is output from the plurality of pixels in the same frame as the pixel signal to be binarized, and which is A / D converted from the pixel signal using the first reference signal.

[0102] (Item 10) The radiation detector according to item 9, characterized in that the processing circuit sets the determination threshold based on the first pixel signal which is output from a predetermined range of pixels from the pixel that outputs the pixel signal to be binarized among the plurality of pixels, and which has been A / D converted using the first reference signal.

[0103] (Item 11) The frame memory further comprises a frame memory for holding the first pixel signal. The radiation detector according to item 10, characterized in that the processing circuit sets the determination threshold based on the first pixel signal held in the frame memory.

[0104] (Item 12) The line memory for holding the first pixel signal is further provided, The radiation detector according to item 10, characterized in that the processing circuit sets the determination threshold based on the first pixel signal held in the line memory.

[0105] (Item 13) The system further comprises a processing circuit for processing the signal converted by the aforementioned A / D converter, The radiation detector according to any one of items 1 to 12, characterized in that the processing circuit corrects the pixel signals output from the plurality of pixels in one frame, which have been A / D converted using the second reference signal, based on the pixel signals which have been A / D converted using the first reference signal.

[0106] (Item 14) The radiation detector according to any one of items 1 to 13, characterized in that the first voltage range is set to include the mode, median, or mean value of the pixel signals output from the plurality of pixels.

[0107] (Item 15) A radiation detector described in any one of items 1 through 14, A radiation source that irradiates the aforementioned radiation detector with radiation, A radiation detection system characterized by comprising the following features.

[0108] (Item 16) The radiation detection system according to item 15, characterized in that the radiation irradiation rate of the radiation source is controlled such that the average number of photons or particles of radiation incident per frame and per pixel is 0.5 or less.

[0109] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of symbols]

[0110] 100: Radiation detector, 103: Pixel, 500: A / D converter, 501: Comparator

Claims

1. A radiation detector comprising a plurality of pixels that output pixel signals corresponding to incident radiation, and an A / D converter that performs A / D conversion of the pixel signals, The A / D converter includes a comparator that compares the pixel signal with a signal threshold, and is configured to operate in multiple modes. The plurality of modes include a first mode in which, when the pixel signal is smaller than the signal threshold, A / D conversion of the pixel signal is performed using a first reference signal, and when the pixel signal is larger than the signal threshold, A / D conversion of the pixel signal is performed using a second reference signal. The first reference signal is a time-varying signal in a first voltage range, and the second reference signal is a time-varying signal in a second voltage range. The upper limit of the first voltage range is smaller than the lower limit of the second voltage range. A radiation detector characterized in that the signal threshold is set between the upper limit and the lower limit.

2. In the first mode, there exists a third voltage range between the first voltage range and the second voltage range in which A / D conversion is not performed. The upper limit of the third voltage range is less than or equal to the lower limit of the second voltage range. The radiation detector according to claim 1, characterized in that the lower limit of the third voltage range is greater than or equal to the upper limit of the first voltage range.

3. The radiation detector according to claim 1, characterized in that the slope of the voltage change with respect to time of the first reference signal is equal to the slope of the voltage change with respect to time of the second reference signal.

4. The radiation detector according to claim 1, characterized in that the slope of the voltage change with respect to time of the first reference signal and the slope of the voltage change with respect to time of the second reference signal are different from each other.

5. The aforementioned plurality of modes include a second mode in which A / D conversion of the pixel signal is performed using a third reference signal, The radiation detector according to claim 1, characterized in that the third reference signal is a signal that changes over time in a continuous fourth voltage range including the first voltage range and the second voltage range.

6. The radiation detector according to claim 5, characterized in that the slope of the voltage change with respect to time of at least one of the first reference signal and the second reference signal is equal to the slope of the voltage change with respect to time of the third reference signal.

7. The radiation detector according to claim 5, characterized in that the slope of the voltage change with respect to time of the first reference signal and the second reference signal is greater than the slope of the voltage change with respect to time of the third reference signal.

8. The system further comprises a processing circuit for processing the signal converted by the A / D converter, The radiation detector according to claim 1, characterized in that the processing circuit binarizes the pixel signals, which have been A / D converted using a second reference signal from among the pixel signals output from the plurality of pixels, using a determination threshold.

9. The radiation detector according to claim 8, characterized in that the processing circuit sets the determination threshold based on a first pixel signal, which is output from the plurality of pixels in the same frame as the pixel signal to be binarized, and which is obtained by A / D conversion of the pixel signal using the first reference signal.

10. The radiation detector according to claim 9, characterized in that the processing circuit sets the determination threshold based on the first pixel signal which is output from a predetermined range of pixels from the pixel that outputs the pixel signal to be binarized among the plurality of pixels, and which has been A / D converted using the first reference signal.

11. The frame memory further comprises a frame memory for holding the first pixel signal. The radiation detector according to claim 10, characterized in that the processing circuit sets the determination threshold based on the first pixel signal held in the frame memory.

12. The system further comprises a line memory for holding the first pixel signal, The radiation detector according to claim 10, characterized in that the processing circuit sets the determination threshold based on the first pixel signal held in the line memory.

13. The system further comprises a processing circuit for processing the signal converted by the A / D converter, The radiation detector according to claim 1, characterized in that the processing circuit corrects the pixel signals output from the plurality of pixels in one frame, which have been A / D converted using the second reference signal, based on the pixel signals which have been A / D converted using the first reference signal.

14. The radiation detector according to claim 1, characterized in that the first voltage range is set to include the mode, median, or mean value of the pixel signals output from the plurality of pixels.

15. A radiation detector according to any one of claims 1 to 14, A radiation source that irradiates the aforementioned radiation detector with radiation, A radiation detection system characterized by comprising the following features.

16. The radiation detection system according to claim 15, characterized in that the radiation irradiation rate of the radiation source is controlled such that the average number of photons or particles of radiation incident per frame and per pixel is 0.5 or less.

Images