Radiation imaging device, radiation imaging system, and processing method of radiation imaging device

Abstract

To generate a radiation image in which the influence of the wave tail of a radiation is reduced.SOLUTION: A radiation imaging device includes a plurality of pixels for generating and accumulating an electric charge based on a radiation. Read-out means executes a first read-out operation for reading out a first offset signal based on the electric charge accumulated in the plurality of pixels during preparation for imaging, a second read-out operation for reading out a radiation signal based on the electric charge accumulated in the plurality of pixels in a period including a period when the radiation imaging device is irradiated with the radiation, after the preparation for imaging is completed, and a third read-out operation for reading out a second offset signal based on the electric charge accumulated in the plurality of pixels, after the second read-out operation. Image generation means generates a radiation image on the basis of a signal obtained by adding a signal obtained by correcting the radiation signal by using the first offset signal and a signal obtained by correcting the second offset signal by using the first offset signal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a radiation imaging device, a radiation imaging system, and a processing method for a radiation imaging device. [Background technology]

[0002] Radiation imaging devices have been put to practical use as imaging devices used in medical image diagnosis and non-destructive testing. Radiation images repeatedly generated at a predetermined cycle by radiation imaging devices contain noise resulting from factors such as dark current flowing through photodiodes, temperature fluctuations resulting from heat dissipation by electronic components, and residual images resulting from previous radiation exposure. To reduce such noise, radiation images are corrected using offset images acquired when the radiation imaging device is not irradiated with radiation.

[0003] To perform this type of imaging, radiation must be irradiated in pulses, but pulsed radiation has a wave tail in the latter half of the pulse, and imaging at high frame rates exceeds the period during which radiation can be irradiated. Since accumulation continues even during the readout period of the radiation image, this causes shading in the image and affects the image of the next frame.

[0004] Patent Document 1 discloses a method for eliminating the influence of radiation wave tails in high frame rate imaging by thinning out irradiation and erasing the influence of wave tails that do not fit within the radiation window by reading in thinned images. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-89002 Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Patent Document 1 can eliminate the impact on the frame capturing the next radiation exposure, but when attempting to acquire an offset image, the offset image must be acquired after the thinned-out reading, making it difficult to increase the frame rate.

[0007] An object of the present disclosure is to enable the generation of radiation images in which the influence of radiation wave tails is reduced. [Means for solving the problem]

[0008] The radiation imaging device is a radiation imaging device, and includes a plurality of pixels arranged to form a plurality of pixel rows and a plurality of pixel columns, the plurality of pixels generating and accumulating charges based on radiation, drive means supplying drive signals to the plurality of pixels for selecting any one of the plurality of pixels, readout means reading out signals based on the charges accumulated in the pixel selected by the drive signal, and image generation means generating a radiation image, wherein the readout means performs a first readout operation to read out a first offset signal based on the charges accumulated in the plurality of pixels during preparation for imaging, and after preparation for imaging is completed, performs a second readout operation to read out a radiation signal based on the charges accumulated in the plurality of pixels during a period including a period during which radiation is irradiated to the radiation imaging device, and after the second readout operation, performs a third readout operation to read out a second offset signal based on the charges accumulated in the plurality of pixels, and the image generation means generates the radiation image based on a signal obtained by correcting the radiation signal using the first offset signal and a signal obtained by correcting the second offset signal using the first offset signal. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to generate a radiological image in which the influence of the wave tail of radiation is reduced. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram illustrating an example of the configuration of a radiation imaging system according to an embodiment. [Figure 2] 1 is an equivalent circuit diagram illustrating an example of the configuration of a radiation detection panel according to an embodiment. [Figure 3] 1A and 1B are diagrams illustrating an example of the structure of a pixel according to an embodiment. [Figure 4] 1A and 1B are diagrams illustrating an example of the operation of a radiation imaging system according to an embodiment. [Figure 5] 1A and 1B are diagrams illustrating examples of a radiation image and an offset image. [Figure 6] 1A and 1B are diagrams illustrating an example of the operation of a radiation imaging system according to an embodiment. [Figure 7] 1A and 1B are diagrams illustrating examples of a radiation image and an offset image. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the following embodiments do not limit the scope of the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily required, and multiple features may be combined arbitrarily. Furthermore, in the drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] (First embodiment) 1 shows an example of the configuration of a radiation imaging system 100 according to the first embodiment. The radiation imaging system 100 is configured to generate an electrical radiation image by electrically capturing an optical image formed by radiation. The radiation is typically X-rays, but may also be α-rays, β-rays, γ-rays, etc. The radiation imaging system 100 includes, for example, a radiation imaging device 110, a computer 120, a display 114, an exposure control device 130, and a radiation generation device 140.

[0013] The radiation generating device 140 starts emitting radiation 160 in accordance with an exposure command (radiation command) from the exposure control device 130. The radiation 160 irradiated from the radiation generating device 140 passes through the subject 150 and enters the radiation imaging device 110. The radiation generating device 140 also stops emitting radiation 160 in accordance with a stop command from the exposure control device 130.

[0014] The radiation imaging device 110 includes a radiation detection panel 111, a control circuit 112, and an image generation circuit 113. The radiation detection panel 111 generates a radiation image according to radiation 160 incident on the radiation imaging device 110, and transmits the generated radiation image to the computer 120.

[0015] The control circuit 112 controls the operation of the radiation detection panel 111. For example, the control circuit 112 generates a stop signal for stopping the radiation generation device 140 from emitting radiation 160, based on an image signal obtained from the radiation detection panel 111. The stop signal is supplied to the exposure control device 130. In response to the stop signal, the exposure control device 130 sends a stop command to the radiation generation device 140.

[0016] The control circuit 112 may be configured with a dedicated circuit such as a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Alternatively, the control circuit 112 may be configured with a combination of a general-purpose processing circuit such as a processor and a storage circuit such as a memory. In this case, the general-purpose processing circuit may execute a program stored in the storage circuit, thereby realizing the functions of the control circuit 112.

[0017] The image generation circuit 113 stores the signal supplied from the radiation detection panel 111 in a memory and generates a radiographic image based on this signal. The method of generating a radiographic image will be described in detail later. The image generation circuit 113 transmits the generated radiographic image to the computer 120.

[0018] The computer 120 has a control unit that controls the radiation imaging device 110 and the exposure control device 130, a receiving unit that receives radiation images from the radiation imaging device 110, and a signal processing unit that processes radiation images obtained by the radiation imaging device 110. Like the control circuit 112, the control unit, receiving unit, and signal processing unit may each be configured by a dedicated circuit, or may be configured by a combination of a general-purpose processing circuit and a memory circuit.

[0019] In one example, the exposure control device 130 has an exposure switch, and when the user turns on the exposure switch, it sends an exposure command to the radiation generation device 140 and also sends a start notification indicating the start of radiation irradiation to the computer 120. In response to the start notification, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the start of radiation irradiation. When the exposure control device 130 and the computer 120 are not synchronously connected, the radiation detection panel 111 may detect the start of irradiation of radiation 160 based on pixel signals.

[0020] 2 shows an example of the configuration of the radiation detection panel 111. The radiation detection panel 111 includes, for example, a pixel array 200, a drive circuit 210, a readout circuit 220, a buffer circuit 230, and an analog-to-digital (AD) converter 240. The drive circuit 210 and the readout circuit 220 function as peripheral circuits of the pixel array 200.

[0021] The pixel array 200 is configured by, for example, a plurality of pixels P, a plurality of drive lines Vg1 to Vgm, a plurality of signal lines Sig1 to Sign, and a bias line Bs. The drive lines Vg1 to Vgm and the signal lines Sig1 to Sign are collectively referred to as drive lines Vg and signal lines Sig, respectively.

[0022] The plurality of pixels P are arranged to form a plurality of pixel rows and a plurality of pixel columns. A pixel row refers to a group of pixels lined up in the horizontal direction in FIG. 2. A pixel column refers to a group of pixels lined up in the vertical direction in FIG. 2. In one example, the radiation detection panel 111 has a dimension of 17 inches, and the pixel array 200 has approximately 3,000 pixel rows and approximately 3,000 pixel columns.

[0023] Each pixel row of the pixel array 200 is called the first row to the mth row (m is an integer greater than or equal to 1) from the top of FIG. 2, and each pixel column of the pixel array 200 is called the first column to the nth column (n is an integer greater than or equal to 1) from the left of FIG. 2.

[0024] Each pixel P is composed of a combination of one conversion element C and one switch element S. The pixel P located in the i-th row and j-th column of the pixel array 200 is represented as pixel P(i,j). The conversion element C and switch element S included in pixel P(i,j) are represented as conversion element C(i,j) and switch element S(i,j), respectively. For example, pixel P(1,2) represents pixel P located in the first row and second column.

[0025] The conversion element C generates and accumulates electric charges in response to radiation incident on the pixel P. The conversion element C can accumulate not only electric charges in response to radiation, but also electric charges generated by dark current. The generation and accumulation of electric charges by the conversion element C of the pixel P is referred to as the pixel P generating and accumulating electric charges.

[0026] The switch element S is connected between the conversion element C and the signal line Sig corresponding to this conversion element C. For example, the switch elements S(1,1) to S(m,1) are connected between the plurality of conversion elements C(1,1) to C(m,1) and the signal line Sig1, respectively. When the switch element S is turned on, the conversion element C and the signal line Sig are brought into a conductive state, and the charge obtained by the conversion element C (for example, the charge accumulated in the conversion element C) is transferred to the signal line Sig.

[0027] The conversion element C may be, for example, an MIS photodiode that is disposed on an insulating substrate such as a glass substrate and is primarily made of amorphous silicon. Alternatively, the conversion element C may be a PIN photodiode. The conversion element C may be configured as a direct type that directly converts radiation into charges, or as an indirect type that converts radiation into light and then detects this light. In the indirect type, the scintillator may be shared by multiple pixels P.

[0028] The switch element S is composed of a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source and drain). The conversion element C has two main electrodes. One main electrode of the conversion element C is connected to one of the two main terminals of the switch element S, and the other main electrode of the conversion element is connected to a bias power supply Vs via a common bias line Bs. The bias power supply Vs generates a bias voltage.

[0029] The control terminals of the switch elements S of the pixels P in the first row are connected to the drive line Vg1. The control terminals of the switch elements S of the pixels P in the second row are connected to the drive line Vg2. The same applies to the third to mth rows.

[0030] The drive circuit 210 supplies a drive signal to the control terminal of the switch element S of each pixel P through the drive line Vg in accordance with the drive signal supplied from the control circuit 112. The drive signal includes an ON signal (high-level voltage in the following description) for turning on the switch element S, and an OFF signal (low-level voltage in the following description) for turning off the switch element S. The drive circuit 210 includes, for example, a shift register, and this shift register performs a shift operation in accordance with the control signal (for example, a clock signal) supplied from the control circuit 112.

[0031] Supplying an on signal (i.e., a high-level drive signal) to a pixel P is referred to as selecting the pixel P. In other words, the drive signal is a signal for selecting one of the multiple pixels P. The same drive signal is supplied to multiple pixels included in the same pixel row. Selecting multiple pixels included in one pixel row is referred to as selecting that pixel row.

[0032] The readout circuit 220 amplifies and reads out the signal that appears on the signal line Sig by selecting the pixel P with the drive signal. This signal is a signal based on the charge accumulated in the conversion element C of the selected pixel P. Reading out the signal based on the charge accumulated in the conversion element C of the pixel P is referred to as reading out the signal based on the charge accumulated in the pixel P.

[0033] The readout circuit 220 includes one amplifier circuit 221 for each signal line Sig. In the example of FIG. 2, the pixel array 200 has n signal lines Sig, and therefore the readout circuit 220 includes n amplifier circuits 221.

[0034] The amplifier circuit 221 includes, for example, an integrating amplifier 222, a variable amplifier 223, a switch element 224, a capacitor 225, and a buffer circuit 226. The switch element 224 and the capacitor 225 form a sample-and-hold circuit. The integrating amplifier 222 includes, for example, an operational amplifier, and an integrating capacitor and a reset switch connected in parallel between the inverting input terminal and output terminal of the operational amplifier. A reference voltage is supplied to the non-inverting input terminal of the operational amplifier from a reference power supply Vref.

[0035] When the reset switch is turned on in response to a control signal RC (reset pulse) supplied from the control circuit 112, the integral capacitance is reset and the potential of the signal line Sig is reset to the reference potential.

[0036] Variable amplifier 223 amplifies the signal from integrating amplifier 222 by a set amplification factor. Sample-and-hold circuit samples and holds the signal from variable amplifier 223. The on / off of switch element 224 that constitutes the sample-and-hold circuit is controlled by control signal SH supplied from control circuit 112. Buffer circuit 226 buffers (impedance converts) the signal from the sample-and-hold circuit and outputs it.

[0037] The readout circuit 220 also includes a multiplexer 227 that selects and outputs signals from the plurality of amplifier circuits 221 in a predetermined order. The multiplexer 227 includes, for example, a shift register, and this shift register performs a shift operation in accordance with a control signal (for example, a clock signal) supplied from the control circuit 112. By this shift operation, one signal from the plurality of amplifier circuits 221 is selected.

[0038] The buffer circuit 230 buffers (converts impedance) the signal output from the multiplexer 227. The AD converter 240 converts into a digital signal the analog signal output from the buffer circuit 230. The output of the AD converter 240, i.e., the pixel signal, is sent to the computer 120.

[0039] 3 schematically shows an example of the cross-sectional structure of one pixel P. The pixel P is formed on an insulating substrate 301 such as a glass substrate. The pixel P has a conductive layer 302, an insulating layer 303, a semiconductor layer 304, an impurity semiconductor layer 305, and a conductive layer 306 on the insulating substrate 301.

[0040] The conductive layer 302 constitutes the gate of a transistor (e.g., a TFT) that constitutes the switch element S. The insulating layer 303 is disposed so as to cover the conductive layer 302. The semiconductor layer 304 is disposed on the portion of the conductive layer 302 that constitutes the gate, with the insulating layer 303 interposed therebetween.

[0041] The impurity semiconductor layer 305 is disposed on the semiconductor layer 304 so as to form two main terminals (source and drain) of a transistor that constitutes the switch element S. The conductive layer 306 forms a wiring pattern connected to the two main terminals (source and drain) of the transistor that constitutes the switch element S. A part of the conductive layer 306 forms a signal line Sig, and another part forms a wiring pattern for connecting the switch element S to the conversion element C.

[0042] The pixel P further includes an interlayer insulating film 307 that covers the insulating layer 303 and the conductive layer 306. The interlayer insulating film 307 is provided with a contact plug 308 for connection to the conductive layer 306 (switch element S).

[0043] The pixel P further includes, in this order, a conductive layer 309, an insulating layer 310, a semiconductor layer 311, an impurity semiconductor layer 312, a conductive layer 313, a protective layer 314, an adhesive layer 315, and a scintillator 316 on the interlayer insulating film 307. An indirect conversion element C is configured by these layers.

[0044] The conductive layer 309 and the conductive layer 313 respectively constitute the lower electrode and the upper electrode of the photoelectric conversion element that constitutes the conversion element C. The conductive layer 313 is made of, for example, a transparent material. The conductive layer 309, the insulating layer 310, the semiconductor layer 311, the impurity semiconductor layer 312, and the conductive layer 313 constitute an MIS sensor as the photoelectric conversion element. The impurity semiconductor layer 312 is formed of, for example, an n-type impurity semiconductor layer. The scintillator 316 is made of, for example, a gadolinium-based material or a CsI (cesium iodide) material, and converts radiation into light.

[0045] Alternatively to the above example, the conversion element C may be configured as a direct-type conversion element that directly converts incident radiation into electric charges. Examples of direct-type conversion elements C include conversion elements whose main material is amorphous selenium, gallium arsenide, gallium phosphide, lead iodide, mercury iodide, CdTe, CdZnTe, etc. The conversion element C is not limited to the MIS type, and may be, for example, a pn-type or PIN-type photodiode.

[0046] 3, when orthogonally projected (seen in a plan view) onto the surface of the insulating substrate 301 on which the pixel array 200 is formed, each of the multiple signal lines Sig overlaps a portion of the conversion element C. This configuration is advantageous in that the area of ​​the conversion element C of each pixel P can be increased.

[0047] An example of a processing method of the radiation imaging system 100 will be described with reference to FIG. 4. The upper part of FIG. 4 shows a timing chart, and the lower part of FIG. 4 shows a signal processing flow. The operation shown in FIG. 4 is started, for example, by an instruction from a user of the radiation imaging system 100. The operation of the radiation imaging system 100 is controlled by the computer 120. The operation of the radiation imaging apparatus 110 is executed by the control circuit 112 under the control of the computer 120. Specifically, the control circuit 112 executes the operation of FIG. 4 by controlling the drive circuit 210 and the readout circuit 220. In the following description, the execution of a specific operation by the control circuit 112 controlling the drive circuit 210 or the readout circuit 220 may be simply expressed as the control circuit 112 executing the specific operation.

[0048] 4 indicates the amount of radiation emitted from the radiation 160 to the radiation imaging device 110. In the timing chart of FIG.

[0049] "Vg1" to "Vg8" in the timing chart of Fig. 4 indicate the levels of the drive signals supplied to the drive lines Vg1 to Vg8 from the drive circuit 210. In the example of Fig. 4, the pixel array 200 includes eight pixel rows, but the number of pixel rows is not limited to this.

[0050] The "periods" in the timing chart of Fig. 4 represent periods during which specific operations are performed. Imaging by the radiation imaging device 110 includes an accumulation period ("A" in Fig. 4) during which an accumulation operation is performed, and a readout period ("R" in Fig. 4) during which a readout operation is performed. During the accumulation period, the control circuit 112 does not select any of the multiple pixels P included in the pixel array 200. Specifically, the drive circuit 210 maintains a state in which an off signal is supplied to each of the drive lines Vg1 to Vg8. As a result, the charge generated in each conversion element C is accumulated in the conversion element C, and at the same time, charge corresponding to the dark current flowing through each conversion element C is also accumulated.

[0051] During the readout period, the control circuit 112 selects each of the multiple pixels P included in the pixel array 200 and reads out a signal from the selected pixel P. Specifically, the drive circuit 210 supplies an ON signal to each of the drive lines Vg1 to Vg8 in sequence. First, the drive circuit 210 supplies an ON signal only to the drive line Vg1. This turns on the switch element S(1,j) (j=1, ..., n), establishing a conductive state between the conversion element C(1,j) and the signal line Sigj, and the charge accumulated in the conversion element C(1,j) is read out to the signal line Sigj.

[0052] Next, the drive circuit 210 supplies an ON signal only to the drive line Vg2, which turns on the switch element S(2,j) and establishes a conductive state between the conversion element C(2,j) and the signal line Sigj, causing the charge stored in the conversion element C(2,j) to be read out to the signal line Sigj.

[0053] The drive circuit 210 repeats this operation up to the drive line Vg8, and the charge based on the charge accumulated in the conversion element C is read out through the signal line Sigj by the readout circuit 220. In the following description, performing a readout operation on a plurality of pixels P means performing a readout operation on each of the plurality of pixels P.

[0054] The operations performed by the radiation imaging device 110 include operations performed during preparation for imaging and operations performed after preparation for imaging is completed. The period after preparation for imaging is completed may include a period during which a radiation image is captured, and may also include a period during which a moving image is captured. The period during which a radiation image is captured may be referred to as an imaging period. As will be described later, radiation 160 does not need to be constantly irradiated onto the radiation imaging device 110 during the imaging period, and radiation 160 may be intermittently irradiated.

[0055] During preparation for imaging, the radiation imaging device 110 is not irradiated with radiation 160. Preparation for imaging may be completed when a predetermined condition is satisfied. The predetermined condition may be, for example, generation of a predetermined number of offset images, which will be described later. In response to completion of preparation for imaging, the radiation imaging device 110 may notify the computer 120 that radiation irradiation is possible.

[0056] After preparation for imaging is completed, radiation 160 is irradiated to the radiation imaging device 110, and a radiation image corresponding to the radiation 160 is generated. As shown in Fig. 4, the radiation 160 may be irradiated to the radiation imaging device 110 as a plurality of pulses. The radiation imaging device 110 may generate a radiation image for each pulse. When the radiation imaging device 110 performs moving image imaging, the radiation image for each pulse may form a frame of the moving image.

[0057] The control circuit 112 alternately performs accumulation operations and readout operations during preparation for imaging. As shown in FIG. 4, an accumulation operation is performed during an accumulation period 411, and signals based on charges accumulated in a plurality of pixels P are read out during the subsequent readout period 412. Similarly, for accumulation periods 413 to 418, the control circuit 112 reads out signals based on charges accumulated during at least the accumulation period during the subsequent readout period. The signals read out from the pixels P during preparation for imaging are used to generate an offset image.

[0058] In a readout period 412, a signal based on the charge accumulated over the time length 401 is read out from the pixel P. The time length 401 is the length of time from the end of the previous readout operation of the pixel P (i.e., from the time the drive signal changes to low level) to the end of the current readout operation of the pixel P (i.e., from the time the drive signal changes to low level again). The same is true for the other time lengths during which charge is accumulated. The time length 401 includes an accumulation period 411. In a readout period 414, a signal based on the charge accumulated over the time length 402 is read out from the pixel P. The time length 402 includes an accumulation period 413.

[0059] During a readout period 412 in preparation for imaging, the readout circuit 220 executes a first readout operation to read out offset signals based on charges accumulated in a plurality of pixels P. Specifically, during preparation for imaging, the readout circuit 220 executes readout operations during a plurality of readout periods 412, 414, and 416 to read out a plurality of offset signals.

[0060] The image generation circuit 113 generates an offset image S based on the offset signals read out from each of the multiple pixels P included in the pixel array 200. The offset image S is expressed as a matrix with m rows and n columns, and the signal read out from pixel P(i,j) is the (i,j) component of this matrix.

[0061] The control circuit 112 repeatedly executes the operations from the accumulation period 411 to the readout period 416.

[0062] After completing preparations for imaging, the control circuit 112 starts capturing moving images (i.e., capturing multiple radiation images). Specifically, the control circuit 112 alternately performs accumulation operations and readout operations. As shown in FIG. 4, the control circuit 112 performs an accumulation operation during an accumulation period 421, and then reads out signals based on the charges accumulated in multiple pixels P during a subsequent readout period 422.

[0063] Similarly, for the accumulation period 423 to the readout period 428, the control circuit 112 reads out, in the subsequent readout period, signals based on the charges accumulated during at least the accumulation period. The signals read out from the pixel P after preparation for imaging is completed are used to generate a radiographic image and an offset image. The signals read out from the pixel P during the readout period 422 are referred to as radiographic signals, and the signals read out from the pixel P during the readout period 424 are referred to as imaging offset signals.

[0064] In a readout period 422, a signal based on the charge accumulated over the time length 403 is read out from the pixel P. The time length 403 includes the accumulation period 421. The accumulation period 421 includes the period during which the radiation imaging device 110 is irradiated with radiation 160. Therefore, the time length 403 includes the period during which the radiation imaging device 110 is irradiated with radiation 160. In a readout period 424, a signal based on the charge accumulated over the time length 404 is read out from the pixel P. The time length 404 includes the accumulation period 423. The time length 404 does not include the period during which the radiation imaging device 110 is irradiated with radiation 160.

[0065] Here, pulsed radiation emission has a wave tail in the latter half of the pulse where radiation irradiation remains, so irradiation does not stop during the short accumulation period 421 shown in Figure 4, but continues throughout the readout period 422. As explained above, the signal based on the accumulated charge read out from pixel P is actually accumulated during the time when Vg goes from on to off and then back on again. Therefore, the accumulated radiation dose is greater in rows read out later than in rows read out earlier, resulting in higher output values. As a result, when a two-dimensional image is created, the rows read out later appear relatively brighter, resulting in the image shading shown in Figure 5(a). Figure 5(b) shows an example of the output values ​​of the radiation signal in the row direction of Figure 5(a).

[0066] On the other hand, when the next offset signal is read out, the row read out first has a higher output value than the row read out later due to the accumulation of unintended radiation caused by the radiation wave tail, and when the image is converted into a two-dimensional image, the side read out first appears brighter. This results in image shading as shown in Figure 5(c). Figure 5(d) is an example of the output value of the offset signal in the row direction of Figure 5(c). In this way, the offset signal has the opposite characteristics to the radiation signal.

[0067] During a readout period 422 after preparation for imaging is completed, the readout circuit 220 executes a second readout operation to read out radiation signals based on charges accumulated in multiple pixels P during an accumulation period 421 that includes the period during which radiation 160 is irradiated onto the radiation imaging device 110.

[0068] Furthermore, the readout circuit 220 executes a third readout operation in which an image-capturing offset signal based on the charges accumulated in the plurality of pixels P is read out during a readout period 424 after the second readout operation.

[0069] The image generation circuit 113 generates a radiographic image X based on radiation signals read out from each of the plurality of pixels P included in the pixel array 200. The radiographic image X is expressed as a matrix of m rows and n columns, and the signal read out from pixel P(i,j) is the (i,j) component of this matrix.

[0070] The image generation circuit 113 generates an image capture offset image U based on the image capture offset signals read out from each of the multiple pixels P included in the pixel array 200. The image capture offset image U is expressed as a matrix of m rows and n columns, and the signal read out from pixel P(i,j) is the (i,j) component of this matrix.

[0071] The control circuit 112 repeatedly executes the operations from the accumulation period 421 to the readout period 424. That is, the same operations as those from the accumulation period 421 to the readout period 424 are executed from the accumulation period 425 to the readout period 428. In this way, after preparation for imaging is completed (for example, during imaging of a moving image), the control circuit 112 alternately executes a readout operation for reading out radiation signals and a readout operation for reading out imaging offset signals.

[0072] Next, a method in which the image generating circuit 113 corrects the radiation image X using the offset image S and the imaging offset image U will be described. As described above, the components of the offset image S, the imaging offset image U, and the radiation image X are given by an offset signal, an imaging offset signal, and a radiation signal, respectively. In the following method, the radiation signal is corrected using the offset signal and the imaging offset signal.

[0073] As described above, the control circuit 112 generates an offset image S during preparation for imaging. This generates multiple offset images S. During preparation for imaging, the image generation circuit 113 averages the multiple offset images S to create a single offset image S, which is stored in the memory of the image generation circuit 113 for subsequent processing. By averaging the multiple offset images S in this manner, noise contained in the offset image S can be reduced. The number of offset images S used for averaging may be three, as shown in FIG. 4, or may be more. The number of offset images S used for averaging may be set in advance.

[0074] After preparation for imaging is completed, the image generation circuit 113 generates a radiation image X and an imaging offset image U and stores them in the memory of the image generation circuit 113. The image generation circuit 113 reads out the offset image S from the memory and generates a radiation shading image ("XS" in the figure) by subtracting the offset image S from the radiation image X. The image generation circuit 113 also reads out the offset image S from the memory and generates an offset shading image ("US" in the figure) by subtracting the offset image S from the imaging offset image U.

[0075] As mentioned above, a radiation shading image is an image made up of radiation signals due to charges accumulated from radiation irradiation to readout and noise signals such as dark current flowing through the photodiode. Also, an offset shading image is an image made up of accumulated signals of radiation that did not finish accumulating during the accumulation period and noise signals such as dark current flowing through the photodiode.

[0076] Therefore, the sum of the signals obtained by removing noise signals from the radiation shading image and the offset shading image is a signal obtained by irradiating all of the radiation. Therefore, the image generation circuit 113 adds the radiation shading image and the offset shading image to generate a radiation image X' (=X+U-2S) in which the radiation accumulation time is equal. The image generation circuit 113 transmits the corrected radiation image X' to the computer 120.

[0077] As described above, the image generating circuit 113 generates a radiographic image X' (=X+U-2S) based on an image ("US" in the figure) obtained by adding together a radiographic shading image ("XS" in the figure) obtained by correcting the radiographic image X using the offset image S and an offset shading image ("US" in the figure) obtained by correcting the offset image U at the time of imaging using the offset image S.

[0078] Specifically, the image generation circuit 113 generates a radiographic image X' (=X+U-2S) by adding the difference (=XS) between the radiographic image X and the averaged image of multiple offset images S and the difference (=US) between the offset image U at the time of imaging and the averaged image of multiple offset images S.

[0079] The drive circuit 210 supplies drive signals, such as Vg1 to Vg8, to the plurality of pixels P to sequentially select one of the plurality of pixel rows so that the selection period of each pixel row does not overlap with the selection period of the other pixel rows.

[0080] After preparation for imaging is completed, the readout circuit 220 alternately performs the readout operation in the readout period 422 and the readout operation in the readout period 424. The image generation circuit 113 generates a plurality of radiation images X'.

[0081] (Second embodiment) Next, an example of operation of the radiation imaging apparatus 110 according to the second embodiment, which differs from the operation described above in Fig. 4, will be described with reference to Fig. 6. Fig. 6 shows an example of a method for obtaining an image of a limited range by validating only some output signals near the center, rather than an image based on signals output from all pixels P of the radiation detection panel 111, in order to increase the frame rate when capturing moving images.

[0082] The upper part of Fig. 6(a) shows a timing chart, and the lower part of Fig. 6(a) shows the signal processing flow. Fig. 6(b) is a diagram explaining the image effective area when the radiation detection panel 111 is operated as shown in Fig. 6(a), with the shaded area being the area where normal values ​​are not output and the area near the center being the image effective area of ​​the image that is actually desired to be obtained. In Fig. 6, Vg3 to Vg6 will be described as columns corresponding to the effective area.

[0083] The drive circuit 210 sequentially supplies ON signals to drive lines Vg1 to Vg6, and when supplying Vg7, which falls outside the effective area, it simultaneously supplies an ON signal to Vg1 for the next image. Next, when supplying Vg8, it simultaneously supplies an ON signal to Vg2 for the next image. It sequentially supplies ON signals to Vg3 to Vg6, and as before, when supplying Vg7, it also supplies an ON signal to Vg1 for the next image, repeating this process.

[0084] The drive circuit 210 supplies drive signals Vg1 to Vg8 to the plurality of pixels P to sequentially select one or more pixel rows on a pixel row basis so that the selection periods of one or more pixel rows at the beginning of the plurality of pixel rows overlap with the selection periods of one or more pixel rows at the end of the plurality of pixel rows.

[0085] After preparation for imaging is complete, radiation 160 is irradiated to the radiation imaging device 110. However, by irradiating the radiation 160 during the invalid region, i.e., the period from when Vg1 is on to when Vg2 is off, imaging at a high frame rate becomes possible.

[0086] As in the first embodiment, an offset image S is generated during preparation for imaging, and a radiographic image X and an offset image U at the time of imaging are generated after preparation for imaging is completed. However, by limiting the images to only the effective area, the memory consumption of the image generation circuit 113 can be reduced.

[0087] (Third embodiment) If the scintillator 316 has been exposed to strong radiation in the previous imaging, burn-in occurs, resulting in a so-called afterimage. The afterimage causes a signal level higher than normal in both the radiation image X and the imaging offset image U.

[0088] Therefore, the method of simply adding the radiographic image X and the imaging offset image U, as described in the first and second embodiments, further increases the signal level in the area where the afterimage remains.

[0089] FIG. 7(a) is an example of a radiographic image X with an afterimage, and FIG. 7(b) is an example of a normal radiographic image X and an example of output values ​​of radiation signals in the row direction of a row with an afterimage area.

[0090] Figure 7(c) is an example of the offset image U at the time of shooting when there is an afterimage, and Figure 7(d) is an example of the normal case of the offset image U at the time of shooting and an example of the output value of the offset signal at the time of shooting in the row direction of the row where there is an afterimage area.

[0091] FIG. 7(e) shows an example of a radiographic image X' corrected using the radiographic image X and the offset image U at the time of capture, and FIG. 7(f) shows an example of a normal radiographic image X' and an example of signal output values ​​in the row direction of a row where an afterimage area exists.

[0092] As shown in Figure 7(d), the signal of the afterimage area is characterized by being output at a high value even in an offset image that is not exposed to radiation, with an output value that is 2 to 10 times that of a normal pixel. Therefore, it is easy to determine the afterimage area, and since the afterimage area is an output in which an offset corresponding to the afterimage is added to the original output, the image generation circuit 113 can infer and correct the value of the pixel determined to be in the afterimage area from the output values ​​of other parts.

[0093] One method of inferring this is to consider the radiation image X and the subsequent offset image U at the time of imaging as a set, infer the difference between the average value of the residual image area for each row in the offset image U at the time of imaging and the average value of the other areas, and subtract the same amount from the same location.

[0094] Furthermore, afterimages resulting from exposure to strong radiation in the previous imaging have the characteristic of disappearing as imaging time passes. Therefore, the afterimage area is determined from the offset image U at the time of the first imaging, and in subsequent afterimage corrections, corrections can be made to the respective afterimage areas for each combination of the acquired radiographic image X and the offset image U at the time of imaging so that the values ​​are approximately equal to the values ​​in the normal area of ​​that image.

[0095] The image generation circuit 113 determines, as residual image pixels, pixels in the offset image U at the time of imaging that have pixel values ​​exceeding a threshold value. The image generation circuit 113 then corrects the pixel values ​​of the residual image pixels in the offset image U at the time of imaging based on the pixel values ​​of pixels other than the residual image pixels in the offset image U at the time of imaging. The image generation circuit 113 also corrects the pixel values ​​of the residual image pixels in the radiographic image X based on the pixel values ​​of pixels other than the residual image pixels in the radiographic image X.

[0096] After preparation for imaging is completed, the readout circuit 220 alternately executes the readout operation in the readout period 422 and the readout operation in the readout period 424 .

[0097] The image generation circuit 113 determines as residual image pixels those pixels in the first imaging offset image U that have pixel values ​​exceeding a threshold. Then, for each imaging offset image U from the first imaging onwards, the image generation circuit 113 corrects the pixel values ​​of the residual image pixels in the imaging offset image U based on the pixel values ​​of pixels other than residual image pixels in the imaging offset image U. Furthermore, for each radiographic image X from the first imaging onwards, the image generation circuit 113 corrects the pixel values ​​of the residual image pixels in the radiographic image X based on the pixel values ​​of pixels other than residual image pixels in the radiographic image X.

[0098] The image generation circuit 113 corrects the image U and the radiation image X by subtracting the difference between the average pixel value of the residual image pixels and the average pixel value of the pixels other than the residual image pixels from the pixel values ​​of the residual image pixels for each pixel row.

[0099] In the above-described embodiment, the pixel array 200 includes only pixels P used to generate radiographic images. Alternatively, the pixel array 200 may include pixels used for purposes other than generating radiographic images, such as pixels used for automatic exposure control.

[0100] As described above, according to the first to third embodiments, the radiation imaging apparatus 110 can acquire radiographic images at a high frame rate while reducing the influence of the wave tail of radiation.

[0101] (Other embodiments) The present disclosure can also be realized by a process in which a program that realizes one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device read and execute the program. The present disclosure can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0102] It should be noted that the above-described embodiments merely illustrate specific examples of implementing the present disclosure, and the technical scope of the present disclosure should not be construed as being limited by these embodiments. In other words, the present disclosure can be implemented in various forms without departing from its technical concept or main features.

[0103] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) A radiation imaging device, a plurality of pixels arranged to form a plurality of pixel rows and a plurality of pixel columns, the pixels generating and accumulating charges based on radiation; a driving means for supplying a driving signal to the plurality of pixels to select one of the plurality of pixels; a readout means for reading out a signal based on the charge accumulated in the pixel selected by the drive signal; an image generating means for generating a radiation image; The reading means performing a first readout operation to read out a first offset signal based on the charges accumulated in the plurality of pixels during preparation for imaging; after preparation for imaging is completed, a second readout operation is performed to read out radiation signals based on charges accumulated in the plurality of pixels during a period including a period during which radiation is irradiated to the radiation imaging device; After the second readout operation, a third readout operation is performed to read out a second offset signal based on the charges accumulated in the plurality of pixels; a radiation imaging device characterized in that the image generating means generates the radiation image based on a signal obtained by adding together a signal obtained by correcting the radiation signal using the first offset signal and a signal obtained by correcting the second offset signal using the first offset signal. (Configuration 2) The radiation imaging device according to configuration 1, wherein the image generating means generates the radiation image based on an image obtained by adding together an image obtained by correcting an image based on the radiation signal using an image based on the first offset signal and an image obtained by correcting an image based on the second offset signal using an image based on the first offset signal. (Configuration 3) The radiation imaging device according to configuration 2, wherein the image generating means generates the radiation image by adding a difference between an image based on the radiation signal and an image based on the first offset signal and a difference between an image based on the second offset signal and an image based on the first offset signal. (Configuration 4) the readout means reads out a plurality of first offset signals by executing a plurality of first readout operations during preparation for imaging; 4. The radiation imaging device according to configuration 2 or 3, wherein the image generating means generates the radiation image by adding a difference between an image based on the radiation signal and an image based on averaging the plurality of first offset signals, and a difference between an image based on the second offset signal and an image based on averaging the first offset signals. (Configuration 5) the readout means alternately executes the second readout operation and the third readout operation after preparation for imaging is completed; 5. The radiation imaging apparatus according to any one of configurations 1 to 4, wherein the image generating means generates a plurality of radiation images. (Configuration 6) The radiation imaging device according to any one of configurations 1 to 5, wherein the driving means supplies a driving signal to the plurality of pixels for sequentially selecting one of the plurality of pixel rows so that the selection period of each pixel row does not overlap with the selection period of another pixel row. (Configuration 7) The radiation imaging device according to any one of configurations 1 to 5, wherein the driving means supplies to the plurality of pixels a driving signal for sequentially selecting one or more pixel rows on a pixel row basis so that a selection period for one or more pixel rows at the beginning of the plurality of pixel rows overlaps with a selection period for one or more pixel rows at the end of the plurality of pixel rows. (Configuration 8) The image generating means A pixel having a pixel value exceeding a threshold in the image based on the second offset signal is determined as an afterimage pixel; correcting pixel values ​​of the residual image pixels in the image based on the second offset signal based on pixel values ​​of pixels other than the residual image pixels in the image based on the second offset signal; The radiation imaging device according to configuration 2, wherein pixel values ​​of residual image pixels in the image based on the radiation signal are corrected based on pixel values ​​of pixels other than residual image pixels in the image based on the radiation signal. (Configuration 9) the readout means alternately executes the second readout operation and the third readout operation after preparation for imaging is completed; The image generating means a pixel having a pixel value exceeding a threshold value in an image based on the second offset signal obtained by the first third readout operation is determined as an afterimage pixel; correcting pixel values ​​of residual pixels in an image based on the second offset signal based on pixel values ​​of pixels other than residual pixels in an image based on the second offset signal for each of the third readout operations from the first readout operation onward; 9. The radiation imaging device according to configuration 8, wherein, for each of the second readout operations from the first readout onward, pixel values ​​of residual image pixels in the image based on the radiation signal are corrected based on pixel values ​​of pixels other than residual image pixels in the image based on the radiation signal. (Configuration 10) 10. The radiation imaging device according to configuration 8 or 9, wherein the image generating means corrects, for each of the image based on the second offset signal and the image based on the radiation signal, by subtracting, from the pixel values ​​of the residual image pixels for each pixel row, a difference between an average value of the pixel values ​​of the residual image pixels and an average value of the pixel values ​​of pixels other than the residual image pixels. (Configuration 11) The radiation imaging device according to any one of configurations 1 to 10, a radiation generating device that irradiates radiation; A radiation imaging system comprising: (Method 1) a plurality of pixels arranged to form a plurality of pixel rows and a plurality of pixel columns, the pixels generating and accumulating charges based on radiation; a driving means for supplying a driving signal to the plurality of pixels to select one of the plurality of pixels; a readout means for reading out a signal based on the charge accumulated in the pixel selected by the drive signal; and an image generating means for generating a radiation image, the readout means performs a first readout operation to read out a first offset signal based on charges accumulated in the plurality of pixels during preparation for imaging; the readout means, after preparation for imaging is completed, executes a second readout operation to read out radiation signals based on charges accumulated in the plurality of pixels during a period including a period during which radiation is irradiated to the radiation imaging device; the readout means performs a third readout operation after the second readout operation to read out a second offset signal based on the charges accumulated in the plurality of pixels; a processing method for a radiation imaging apparatus, characterized in that the image generating means generates the radiation image based on a signal obtained by adding a signal obtained by correcting the radiation signal using the first offset signal and a signal obtained by correcting the second offset signal using the first offset signal. [Explanation of symbols]

[0104] 100 radiation imaging system, 110 radiation imaging device, 200 pixel array

Claims

1. A radiation imaging device, a plurality of pixels arranged to form a plurality of pixel rows and a plurality of pixel columns, the pixels generating and accumulating charges based on radiation; a driving means for supplying a driving signal to the plurality of pixels to select one of the plurality of pixels; a readout means for reading out a signal based on the charge accumulated in the pixel selected by the drive signal; an image generating means for generating a radiation image; The reading means performing a first readout operation to read out a first offset signal based on the charges accumulated in the plurality of pixels during preparation for imaging; after preparation for imaging is completed, a second readout operation is performed to read out radiation signals based on charges accumulated in the plurality of pixels during a period including a period during which radiation is irradiated to the radiation imaging device; After the second readout operation, a third readout operation is performed to read out a second offset signal based on the charges accumulated in the plurality of pixels; a radiation imaging device characterized in that the image generating means generates the radiation image based on a signal obtained by adding together a signal obtained by correcting the radiation signal using the first offset signal and a signal obtained by correcting the second offset signal using the first offset signal.

2. 2. The radiation imaging device according to claim 1, wherein the image generating means generates the radiation image based on an image obtained by adding together an image obtained by correcting an image based on the radiation signal using an image based on the first offset signal and an image obtained by correcting an image based on the second offset signal using an image based on the first offset signal.

3. 3. The radiation imaging device according to claim 2, wherein the image generating means generates the radiation image by adding a difference between an image based on the radiation signal and an image based on the first offset signal and a difference between an image based on the second offset signal and an image based on the first offset signal.

4. the readout means reads out a plurality of first offset signals by executing a plurality of first readout operations during preparation for imaging; 3. The radiation imaging device according to claim 2, wherein the image generating means generates the radiation image by adding a difference between an image based on the radiation signal and an image based on averaging the plurality of first offset signals, and a difference between an image based on the second offset signal and an image based on averaging the first offset signals.

5. the readout means alternately executes the second readout operation and the third readout operation after preparation for imaging is completed; 2. The radiation imaging apparatus according to claim 1, wherein the image generating means generates a plurality of radiation images.

6. 2. The radiation imaging device according to claim 1, wherein the driving means supplies the plurality of pixels with driving signals for sequentially selecting one of the plurality of pixel rows so that a selection period of each pixel row does not overlap with a selection period of another pixel row.

7. 2. The radiation imaging device according to claim 1, wherein the driving means supplies to the plurality of pixels a driving signal for sequentially selecting one or more pixel rows on a pixel row basis so that a selection period of one or more pixel rows at the beginning of the plurality of pixel rows overlaps with a selection period of one or more pixel rows at the end of the plurality of pixel rows.

8. The image generating means a pixel having a pixel value exceeding a threshold in the image based on the second offset signal is determined as an afterimage pixel; correcting pixel values ​​of the residual image pixels in the image based on the second offset signal based on pixel values ​​of pixels other than the residual image pixels in the image based on the second offset signal; 3. The radiation imaging apparatus according to claim 2, wherein pixel values ​​of residual image pixels in the image based on the radiation signal are corrected based on pixel values ​​of pixels other than residual image pixels in the image based on the radiation signal.

9. the readout means alternately executes the second readout operation and the third readout operation after preparation for imaging is completed; The image generating means a pixel having a pixel value exceeding a threshold value in an image based on the second offset signal obtained by the first third readout operation is determined as an afterimage pixel; correcting pixel values ​​of residual pixels in an image based on the second offset signal based on pixel values ​​of pixels other than residual pixels in an image based on the second offset signal for each of the third readout operations from the first readout operation onward; 9. The radiation imaging device according to claim 8, wherein, for each of the first and subsequent second readout operations, pixel values ​​of residual image pixels in the image based on the radiation signal are corrected based on pixel values ​​of pixels other than residual image pixels in the image based on the radiation signal.

10. 9. The radiation imaging device according to claim 8, wherein the image generating means corrects the pixel values ​​of the residual image pixels for each pixel row, for each of the image based on the second offset signal and the image based on the radiation signal, by subtracting from the pixel values ​​of the residual image pixels a difference between an average pixel value of the residual image pixels and an average pixel value of pixels other than the residual image pixels.

11. A radiation imaging device according to any one of claims 1 to 10; a radiation generating device that irradiates radiation; A radiation imaging system comprising:

12. a plurality of pixels arranged to form a plurality of pixel rows and a plurality of pixel columns, the pixels generating and accumulating charges based on radiation; a driving means for supplying a driving signal to the plurality of pixels to select one of the plurality of pixels; a readout means for reading out a signal based on the charge accumulated in the pixel selected by the drive signal; and an image generating means for generating a radiation image, the readout means performs a first readout operation to read out a first offset signal based on the charges accumulated in the plurality of pixels during preparation for imaging; the readout means, after preparation for imaging is completed, executes a second readout operation to read out radiation signals based on charges accumulated in the plurality of pixels during a period including a period during which radiation is irradiated to the radiation imaging device; the readout means performs a third readout operation after the second readout operation to read out a second offset signal based on the charges accumulated in the plurality of pixels; a processing method for a radiation imaging apparatus, characterized in that the image generating means generates the radiation image based on a signal obtained by adding a signal obtained by correcting the radiation signal using the first offset signal and a signal obtained by correcting the second offset signal using the first offset signal.

Images