Radiation imaging apparatus and radiation imaging system

Abstract

To improve the frame rate of an intermittent offset correction mode, and improve the temperature characteristics of a fixed offset correction mode.SOLUTION: A radiation imaging apparatus comprises reading means that reads electric charges accumulated in a conversion element, and image generation means that generates radiation image data. The reading means is capable of: reading the electric charges accumulated in the conversion element in a first reading time before transmission of a permission signal and generating a first correction signal; after the transmission of the permission signal, reading the electric charges accumulated in the conversion element on the basis of irradiation with radiation and generating a radiation signal; and after the transmission of the permission signal, reading the electric charges accumulated in the conversion element not on the basis of the irradiation with radiation in a second reading time and generating a second correction signal. The image generation means performs correction processing on the radiation signal by using the first correction signal or the second correction signal and generates radiation image data. The second reading time is shorter than the first reading time.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a radiation imaging apparatus and a radiation imaging system. [Background technology]

[0002] Radiography devices capable of displaying radiation images in real time using radiation (e.g., X-rays) transmitted through a subject are becoming increasingly common. Radiography devices using flat panel detectors (FPDs) have also been proposed. FPDs feature a matrix of tiny radiation detectors on a quartz glass substrate. The FPDs consist of a solid-state photodetector sandwiching an amorphous semiconductor between transparent and conductive films, and a scintillator that converts radiation into visible light. Known solid-state photodetectors include those using photodetectors such as CCDs (charge-coupled devices) and CMOSs ​​(complementary metal-oxide semiconductors). Radiation detectors that directly detect radiation using solid-state photodetectors without using scintillators are also known. FPDs detect the amount of radiation irradiated during a given accumulation time as electrical charge. Therefore, if electrical charge unrelated to the radiation exposure is present in the radiation detector during the capture of a radiation image of a subject, this charge will be superimposed on the radiation image as noise, resulting in a degradation of the image quality. For example, an example of charge that becomes noise is residual charge (afterimage) that remains after a previously captured radiographic image due to the characteristics of a solid-state photodetector or scintillator. Another example of charge that becomes noise is dark current, which is caused by charges generated in a solid-state photodetector, mainly due to the influence of temperature. Fixed noise caused by defects inherent in the radiation detector also degrades the image quality of a radiographic image. When capturing a radiographic image of a subject, residual charge and dark current component charges accumulate in proportion to the accumulation time of the image during radiation exposure, degrading the image quality. Therefore, when capturing a radiographic image of a subject, offset correction processing is performed to correct offset components due to residual charge, dark current charge, fixed noise, and the like accumulated during capture. Generally, offset correction processing is performed by using image data acquired by capturing an image without irradiating radiation (unexposed image data) as an offset-corrected image and subtracting the offset-corrected image from the radiographic image.

[0003] There are several methods for such offset correction.

[0004] Patent Document 1 describes (1) an intermittent dark in which radiographic images of a subject are captured alternately with the acquisition of unexposed image data (offset correction data), and the offset correction data is subtracted from the radiographic image. Hereinafter, this may be referred to as intermittent offset correction. It also describes (2) a fixed dark in which offset correction processing is performed by subtracting unexposed image data acquired before capturing a radiographic image of the subject from the radiographic image as offset correction data. Hereinafter, this may be referred to as fixed offset correction. The features of methods (1) and (2) are as follows: In method (1), radiographic images of a subject are captured alternately with the acquisition of unexposed image data (offset correction data), thereby reducing image lag. However, method (1) suffers from the problem of a low frame rate.

[0005] On the other hand, in method (2), offset correction data is acquired before capturing a radiographic image of the subject, which increases the frame rate and enables high-speed continuous imaging, such as video imaging. Furthermore, imaging at a low dose is possible, resulting in a high SNR. However, method (2) has the problem of not being able to sufficiently reduce image lag. Furthermore, the dark current charge accumulated during imaging varies due to the temperature of the radiation detector, imaging conditions, and sensor degradation over time. Therefore, when offset correction data is acquired before capturing a radiographic image of the subject, as in method (2), there is the problem of not being able to obtain sufficient accuracy in the offset correction process. As such, each offset correction method has its own unique characteristics, so it is desirable to be able to select the method based on the imaging technique. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-157939 Summary of the Invention [Problem to be solved by the invention]

[0007] The offset correction methods for the intermittent dark (hereinafter referred to as intermittent offset correction mode) and fixed dark (hereinafter referred to as fixed offset correction mode) described in Patent Document 1 have room for improvement in terms of optimizing the correction method. [Means for solving the problem]

[0008] The present invention aims to improve the frame rate in the intermittent offset correction mode and the stability against temperature changes in the fixed offset correction mode, a communication means for transmitting an authorization signal to an external device to authorize radiation irradiation; a readout means for reading out the charges accumulated in the conversion elements to generate a signal; and an image generating means for generating radiation image data from the signal generated by the readout means, wherein the readout means is capable of reading out the charges accumulated in the conversion elements at a first readout time before the transmission of the authorization signal to generate a first correction signal, reading out the charges accumulated in the conversion elements based on radiation irradiation after the transmission of the authorization signal to generate a radiation signal, and reading out the charges accumulated in the conversion elements based on radiation irradiation after the transmission of the authorization signal to generate a second correction signal, and wherein the image generating means corrects the radiation signal with the first correction signal or the second correction signal to generate radiation image data, and the second readout time is shorter than the first readout time. [Effects of the Invention]

[0009] According to the present invention, the frame rate in the intermittent offset correction mode can be improved, and the stability against temperature changes in the fixed offset correction mode can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram illustrating an example of the configuration of a radiation imaging system according to some embodiments. [Figure 2]FIG. 2 is an equivalent circuit diagram illustrating an example of the configuration of a radiation detection panel according to some embodiments. [Figure 3] 3A and 3B are schematic diagrams illustrating examples of pixel structures according to some embodiments. [Figure 4] FIG. 10 is an explanatory diagram of a shooting mode according to some embodiments. [Figure 5] 1A and 1B are diagrams illustrating an example of the operation of a radiation imaging system according to some embodiments. [Figure 6] 1A and 1B are diagrams illustrating an example of the operation of a radiation imaging system according to some embodiments. [Figure 7] FIG. 2 illustrates a readout of a radiation imaging system according to some embodiments. [Figure 8] FIG. 4 is a diagram illustrating temperature characteristics of the radiation imaging system according to some embodiments. [Figure 9] 1A and 1B are diagrams illustrating an example of the operation of a radiation imaging system according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] FIG. 1 shows an example configuration of a radiation imaging system 100 according to some embodiments. 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 and a computer 120 serving as a control device for controlling the system. The computer 120 serving as a control device is capable of acquiring radiation image data from the radiation imaging device 110 and generating a radiation image by performing image processing on the radiation image data. In this embodiment, the system further includes a display 114 for displaying the radiation image generated by the computer 120, 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, an image generation circuit (image generation means) 113, and a communication means 115. The radiation detection panel 111 generates a radiation image signal corresponding to radiation 160 incident on the radiation imaging device 110. The radiation image signal is subjected to offset correction (described below) in the image generation circuit 113 to generate radiation image data, which is then transmitted to the computer 120. The control circuit 112 controls the operation of the radiation detection panel 111. For example, the control circuit 112 generates an enable signal that enables radiation irradiation based on the readiness status of the radiation detection panel 111. The control circuit 112 also generates a stop signal that stops the irradiation of radiation 160 from the radiation generation device 140 based on a signal obtained from the radiation detection panel 111. The enable signal and stop signal are supplied (transmitted) by the communication means 115 to an exposure control device 130, which is an external device. In response to the enable signal and stop signal, the exposure control device 130 sends an irradiation command or a stop command to the radiation generation device 140. It is also possible to set the destination of the permission signal or stop signal sent by the communication means 115 to the computer 120, and send it from the computer 120 to the exposure control device 130. In this case, the computer 120 may also be considered to be an external device.

[0015] The control circuit 112 may be configured with a dedicated circuit such as an FPGA or an ASIC. Note that FPGA stands for Field Programmable Gate Array, and ASIC stands for 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 functions of the control circuit 112 may be realized by the general-purpose processing circuit executing a program stored in the storage circuit.

[0016] The image generation circuit 113, which is an image generation means, stores the signal supplied from the radiation detection panel 111 in a memory and generates radiation image data based on this signal. The method of generating radiation image data will be described in detail later. The image generation circuit 113 transmits the generated radiation image data to the computer 120 via the communication means 115.

[0017] The computer 120 includes a control unit that controls the radiation imaging device 110 and the exposure control device 130, and a receiving unit that receives radiation image data from the radiation imaging device 110. The computer 120 also includes a signal processing unit that processes radiation image data obtained by the radiation imaging device 110. The signal processing unit generates a radiation image by, for example, performing image processing on the obtained radiation image data. Like the control circuit 112, the control unit, receiving unit, and signal processing unit may each be configured with a dedicated circuit or a combination of a general-purpose processing circuit and a memory circuit. In one example, the exposure control device 130 has an exposure switch. When the exposure switch is turned on by a user, the exposure control device 130 sends an exposure command to the radiation generation device 140 and also sends an irradiation start request to the computer 120 to request the start of radiation irradiation. In response to the start request, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the radiation irradiation start request. The control circuit 112 transmits (returns) an irradiation permission signal to the computer 120 or the exposure control device 130 via the communication means 115 depending on the readiness status of the radiation detection panel. 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 with the radiation 160 based on the pixel signal.

[0018] FIG. 2 shows an example of the configuration of a radiation detection panel 111. The radiation detection panel 111 includes, for example, a pixel array 200, a drive circuit 210 serving as a drive means, and a readout circuit 220 serving as a readout means. The drive circuit 210 and the readout circuit 220 function as peripheral circuits of the pixel array 200. The pixel array 200 includes, for example, a plurality of pixels 201, 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. The plurality of pixels 201 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 3000 pixel rows and approximately 3000 pixel columns.

[0019] The pixel rows of the pixel array 200 are referred to as the first row to the mth row (m is an integer equal to or greater than 1) from the top of the drawing, and the pixel columns of the pixel array 200 are referred to as the first column to the nth column (n is an integer equal to or greater than 1) from the left of the drawing. Each pixel 201 is composed of a combination of one conversion element 202 and one switch element 203. The pixel 201 located in the i-th row and j-th column of the pixel array 200 is referred to as pixel 201(i,j). The conversion element 202 and switch element 203 included in pixel 201(i,j) are referred to as conversion element 202(i,j) and switch element 203(i,j), respectively. For example, pixel 201(1,2) refers to the pixel 201 located in the first row and second column.

[0020] The conversion element 202 generates charges in response to radiation incident on the pixel 201 and accumulates these charges. In other words, the conversion element is capable of accumulating charges for generating a radiographic image. The conversion element 202 can accumulate not only charges in response to radiation but also charges generated by dark current. The generation and accumulation of charges by the conversion element 202 of the pixel 201 is referred to as the pixel 201 generating and accumulating charges.

[0021] The switch element 203 is connected between the conversion element 202 and the signal line Sig corresponding to the conversion element 202. For example, the switch elements 203(1,1) to 203(m,1) are connected between the plurality of conversion elements 202(1,1) to 202(m,1) and the signal line Sig1, respectively. When the switch element 203 is turned on, the conversion element 202 and the signal line Sig are brought into a conductive state, and the charge obtained in the conversion element 202 (e.g., the charge accumulated in the conversion element 202) is transferred to the signal line Sig. The conversion element 202 may be, for example, an MIS-type photodiode disposed on an insulating substrate such as a glass substrate and made primarily of amorphous silicon. Alternatively, the conversion element 202 may be a PIN-type photodiode. The conversion element 202 may be configured as a direct type that directly converts radiation into charge, or as an indirect type that converts radiation into light and then detects the light. In the indirect type, the scintillator may be shared by a plurality of pixels 201.

[0022] The switch element 203 is composed of a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source and drain). In this case, one terminal of the switch 203 is connected to the conversion element 202, and the other terminal is connected to a readout circuit 220, which is a readout means, via a signal line. The conversion element 202 has two main electrodes. One main electrode of the conversion element 202 is connected to one of the two main terminals of the switch element 202, 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.

[0023] The control terminals of the switch elements 203 of the pixels 201 in the first row are connected to the drive line Vg1. The control terminals of the switch elements 203 of the pixels 201 in the second row are connected to the drive line Vg2. The same applies to the third to mth rows.

[0024] The drive circuit 210, which is a drive means, supplies a drive signal to the control terminal of the switch element S of each pixel 201 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 the switch element 203 ON, and an OFF signal (low-level voltage in the following description) for turning the switch element 203 OFF. 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.

[0025] Supplying an on signal (i.e., a high-level drive signal) to a pixel 201 is referred to as selecting the pixel 201. That is, the drive signal is a signal for selecting one of the multiple pixels 201. 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 this pixel row.

[0026] The readout circuit 220, which is a readout means, amplifies and reads out the signal that appears on the signal line Sig by selecting the pixel 201. This signal is based on the charge accumulated in the conversion element 202. Reading out the signal based on the charge accumulated in the conversion element 202 of the pixel 201 is referred to as reading out the signal based on the charge accumulated in the pixel 201.

[0027] The readout circuit 220 includes one amplifier circuit 221 for each signal line Sig. In the example of FIG. 2, since the pixel array 200 has n signal lines Sig, the readout circuit 220 includes n amplifier circuits 221. The amplifier circuits 221 include, for example, an integral amplifier circuit 222, an LPF circuit 223S, an LPF circuit 223N, a switch element 224S, a switch element 224N, a capacitor 225S, a capacitor 225N, and a buffer circuit 226S, a buffer circuit 226N. The switch element 224S and the capacitor 225S form a signal sample-and-hold circuit, and the switch element 224N and the capacitor 225N form a noise sample-and-hold circuit. The integral amplifier circuit 222 converts the charge accumulated in the conversion element 202 into a voltage signal and includes, for example, an operational amplifier and an integral capacitor and a reset switch connected in parallel between the inverting input terminal and the 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. 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. The LPF circuit 223S and the LPF circuit 223N remove noise from the signal from the integral amplifier 222 using a set filter value. The sample-and-hold circuit holds the voltage signal generated by the integral amplifier circuit, and samples and holds the signals from the LPF circuit 223S and the LPF circuit 223N. The on / off of the switch elements 224S and 224N constituting the sample-and-hold circuit is controlled by control signals SHS and SHN supplied from the control circuit 112. The buffer circuits 226S and 226N buffer (convert impedance) the signals from the sample-and-hold circuit and output them.

[0028] 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.

[0029] The AD converter 240 converts into a digital signal the analog signal output from the multiplexer 227. The output of the AD converter 240, that is, the pixel signal (a radiation signal and a correction signal, which will be described later), is sent to the computer 120.

[0030] FIG. 3 schematically illustrates an example of the cross-sectional structure of one pixel 201. The pixel 201 is formed on an insulating substrate 301 such as a glass substrate. The pixel 201 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. The conductive layer 302 forms the gate of a transistor (e.g., a TFT) that constitutes the switch element 203. The insulating layer 303 is disposed so as to cover the conductive layer 302. The semiconductor layer 304 is disposed on a portion of the conductive layer 302 that forms the gate, with the insulating layer 303 interposed therebetween. The impurity semiconductor layer 305 is disposed on the semiconductor layer 304 so as to form two main terminals (source and drain) of the transistor that constitutes the switch element 203. 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 203. A part of the conductive layer 306 constitutes the signal line Sig, and another part constitutes a wiring pattern for connecting the conversion element 202 and the switch element 203.

[0031] The pixel 201 further includes an interlayer insulating film 307 covering the insulating layer 303 and the conductive layer 306. The interlayer insulating film 307 includes a contact plug 308 for connection to the conductive layer 306 (switch element 203). The pixel 201 further includes, on the interlayer insulating film 307, 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, in this order. These layers form an indirect conversion element 202. The conductive layer 309 and the conductive layer 313 respectively form a lower electrode and an upper electrode of a photoelectric conversion element constituting the conversion element 202. 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 form an MIS sensor as a 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.

[0032] Alternatively, the conversion element 202 may be configured as a direct-type conversion element that directly converts incident radiation into electric charges. Examples of the direct-type conversion element 202 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.

[0033] 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 part of the conversion element 202. This configuration is advantageous in that the area of ​​the conversion element 202 of each pixel 201 can be increased.

[0034] The operation modes of the radiation imaging system 100 will be described with reference to Fig. 4. This embodiment has two imaging modes. Mode A is a first offset imaging mode (hereinafter also referred to as fixed offset correction mode) with a frame rate of 15 fps, which enables low-noise imaging. Mode B is a second offset imaging mode (hereinafter also referred to as intermittent offset correction mode) with a frame rate of 15 fps, which enables imaging with low afterimages. The radiologist performing the imaging can select from the two modes the mode that is most suitable for the imaging purpose.

[0035] In this embodiment, the engineer selects from preset modes, but it may also be possible to change between fixed offset correction mode and intermittent offset correction mode by rewriting a program such as an FPGA.

[0036] Next, an example of operation of the radiation imaging system 100 in the fixed offset correction mode will be described with reference to FIG. 5. The upper part of FIG. 5 shows a timing chart, and the lower part of FIG. 5 shows a signal processing flow. The same applies to FIGS. 6 and 9, which will be described later. The operation shown in FIG. 5 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. 5 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 by controlling the drive circuit 210 or the readout circuit 220 may be simply referred to as the control circuit 112 executing the specific operation.

[0037] 5 indicates whether the radiation imaging device 110 is irradiated with radiation 160. A low level indicates that the radiation 160 is not being irradiated, and a high level indicates that the radiation 160 is being irradiated.

[0038] "Vg1" to "Vg8" in the timing chart of Fig. 5 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. 5, the pixel array 200 includes eight pixel rows, but the number of pixel rows is not limited to this.

[0039] The "period" in the timing chart of FIG. 5 indicates a period during which a specific operation is performed. Imaging by the radiation imaging device 110 includes an accumulation period ("A" in FIG. 5) during which an accumulation operation is performed and a readout period ("R" in FIG. 5) during which a readout operation is performed. The accumulation period marked with "A" may also be referred to as an accumulation time. During the accumulation period, the control circuit 112 does not select any of the multiple pixels 201 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 202 is accumulated in the conversion element 202, and at the same time, charge corresponding to the dark current flowing through each conversion element 202 is also accumulated.

[0040] During the readout period, the control circuit 112 selects each of the multiple pixels 201 included in the pixel array 200 and reads out signals from the selected pixels 201. 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 203(1,j) (j = 1, ..., n), establishing a conductive state between the conversion element 202(1,j) and the signal line Sigj, so that the charge accumulated in the conversion element 202(1,j) is read out to the signal line Sigj. Next, the drive circuit 210 supplies an on signal only to the drive line Vg2. This turns on the switch element 203(2,j) and establishing a conductive state between the conversion element 202(2,j) and the signal line Sigj, so that the charge accumulated in the conversion element 202(2,j) is read out to the signal line Sigj. The drive circuit 210 repeats this operation up to the drive line Vg8, whereby charges based on the charges accumulated in the conversion element 202 are 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 201 means performing a readout operation on each of the plurality of pixels 201.

[0041] The operations performed by the radiation imaging device 110 include operations performed during preparation for imaging before the transmission of the radiation irradiation permission signal, and operations performed after the preparation for imaging is completed after the transmission of the permission signal. The period after the 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, it is not necessary for the radiation imaging device 110 to be constantly irradiated with radiation 160 during the imaging period, and the radiation 160 may be intermittently irradiated.

[0042] During preparation for imaging, the radiation imaging device 110 is not irradiated with radiation 160. Preparation for imaging may be ended when a predetermined condition is satisfied. The predetermined condition may be, for example, generation of a predetermined number of offset image signals, which will be described later. In response to completion of preparation for imaging, the radiation imaging device 110 notifies the computer 120 of an enabling signal indicating that radiation irradiation is possible.

[0043] 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. 5, 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.

[0044] The control circuit 112 alternately performs accumulation operations and readout operations during preparation for imaging. As shown in FIG. 5, it performs an accumulation operation during an accumulation period 811, and reads out signals based on the charges accumulated in the multiple pixels 201 during the subsequent readout period 812. Similarly, for accumulation periods 813 to 816, the control circuit 112 reads out signals based on at least the charges accumulated during the accumulation period during the subsequent readout period. The signals (offset correction signals) read out from the pixels 201 during preparation for imaging are used to generate offset image signals. Therefore, the offset correction signals are signals obtained by reading out the charges accumulated in the conversion elements without being based on irradiation with radiation.

[0045] In a readout period 812, a signal based on the charge accumulated over the time length 801 is read out from the pixel 201. The time length 801 is the length of time from when the previous readout operation of the pixel 201 ends (i.e., when the drive signal changes to low level) to when the current readout operation of the pixel 201 ends (i.e., when the drive signal changes to low level again). The same applies to other time lengths during which charge is accumulated. The time length 801 includes an accumulation period (accumulation time) 811. In a readout period 814, a signal based on the charge accumulated over the time length 802 is read out from the pixel 201. The time length 802 includes an accumulation period (accumulation time) 813.

[0046] The image generation circuit 113, which is an image generation means, generates an offset image signal S based on the offset signals read out from each of the plurality of pixels 201 included in the pixel array 200. The offset image signal S is expressed as a matrix of m rows and n columns, and the correction signal (offset signal) read out from pixel 201(i,j) is the (i,j) component of this matrix.

[0047] The control circuit 112 repeatedly executes the operations from the accumulation period 811 to the readout period 812. That is, the same operations as those from the accumulation period 811 to the readout period 812 are executed also from the accumulation period 813 to the readout period 816. In this way, the control circuit 112 executes the operation of reading out the offset signal multiple times during preparation for imaging.

[0048] After preparation for imaging is complete, the control circuit 112 generates an enabling signal to permit irradiation of radiation, transmits the enabling signal to the computer 120 via the communication means 115, and starts capturing moving images (i.e., capturing a plurality of radiation images). Specifically, the control circuit 112 alternately performs accumulation operations and readout operations. As shown in FIG. 5, the control circuit 112 performs an accumulation operation during an accumulation period (accumulation time) 822, and then reads out radiation signals based on the charges accumulated in the plurality of pixels 201 during a subsequent readout period 823. The signals read out from the pixels 201 after preparation for imaging is complete are used to generate a radiation image.

[0049] In a readout period 823, a signal based on the charge accumulated over the time length 803 is read out from the pixel 201. The time length 803 includes an accumulation period (accumulation time) 822. The accumulation period 822 includes a period during which the radiation imaging device 110 is irradiated with radiation 160. Therefore, the time length 803 includes a period during which the radiation imaging device 110 is irradiated with radiation 160. The time length 803 may be equal to the time length 801.

[0050] 5, the signal read out from the pixel 201 during the readout period 823 is referred to as a radiation signal. The radiation signal includes a component corresponding to the radiation 160 irradiated onto the radiation imaging device 110 during the accumulation period 822.

[0051] The image generation circuit 113 generates a radiation image signal X based on radiation signals read out from each of the plurality of pixels 201 included in the pixel array 200. The radiation image signal X is expressed as a matrix of m rows and n columns, and the signal read out from pixel 201(i,j) is the (i,j) component of this matrix.

[0052] The control circuit 112 repeatedly executes the operations from the accumulation period 822 to the readout period 823. In this way, the control circuit 112 executes the readout operation to read out radiation signals after preparation for imaging is completed (for example, during imaging of a moving image).

[0053] Next, a method will be described in which the image generating circuit 113 corrects the radiation image signal X using the offset image signal S. As described above, the components of the offset image signal S and the radiation image signal X are provided by the offset signal (correction signal) and the radiation signal, respectively. Therefore, the radiation signal is corrected using the offset signal (correction signal) to generate radiation image data.

[0054] As described above, the control circuit 112 generates the offset image signal S during preparation for imaging. This generates multiple offset image signals S. During preparation for imaging, the image generation circuit 113 averages the multiple offset image signals S to create a single offset image signal S, which is stored in the memory of the image generation circuit 113 for subsequent processing. By averaging the multiple offset image signals in this manner, noise contained in the offset image signal can be reduced. The number of offset image signals used for averaging may be three, as shown in FIG. 5, or may be four or more. The number of offset image signals used for averaging may be set in advance.

[0055] After preparation for imaging is completed, the image generation circuit 113 generates a radiation image signal X and stores it in the memory of the image generation circuit 113. The image generation circuit 113 reads out the offset image signal S from the memory and subtracts the offset image signal S from the radiation image signal X to generate radiation afterimage image data ("XS" in the figure).

[0056] The image generating circuit 113 transmits the corrected radiation image data XS to the computer 120 .

[0057] In this way, in the fixed offset correction mode, the offset image signal S is averaged over multiple images, making it possible to perform low-noise imaging.

[0058] Next, an example of operation of the radiation imaging device 110 in an intermittent offset correction mode, which differs from the operation in Fig. 5, will be described with reference to Fig. 6. In the operation in Fig. 5, an offset image signal S is acquired and multiple images are averaged during preparation for imaging, but in the intermittent offset correction mode shown in Fig. 6, an offset image signal S is not acquired during preparation for imaging.

[0059] The control circuit 112 alternately performs accumulation operations and readout operations. Specifically, after transmitting an enable signal permitting radiation irradiation, the control circuit 112 performs accumulation operations during an accumulation period (accumulation time) 911, as shown in FIG. 6 . During the subsequent readout period 912, signals based on charges accumulated in the plurality of pixels 201 are read out. The radiation imaging device 110 is irradiated with radiation 160 during the accumulation period 911, and during the subsequent readout period 912, signals (radiation signals) based on charges generated by the radiation accumulated in the plurality of pixels 201 are read out. The image generation circuit 113 generates a radiation image signal X based on the radiation signals read out from each of the plurality of pixels 201 included in the pixel array 200.

[0060] Thereafter, during an accumulation period 913, the radiation imaging device 110 is not irradiated with radiation 160, and signals based on charges generated by dark currents and afterimages accumulated in the plurality of pixels P are read out. In other words, after the transmission of the enable signal, charges accumulated in the conversion elements are read out without being irradiated with radiation. The image generation circuit 113 generates an offset image signal S based on the offset signals read out from each of the plurality of pixels 201 included in the pixel array 200.

[0061] Next, a description will be given of a method in which the image generating circuit 113 corrects the radiation image signal X using the offset image signal S. As described above, the components of the offset image signal S and the radiation image signal X are provided by the offset signal and the radiation signal, respectively.

[0062] The image generation circuit 113 generates a radiation image signal X and stores it in the memory of the image generation circuit 113. The image generation circuit 113 also generates an offset image signal S and stores it in the memory of the image generation circuit 113. The image generation circuit 113 reads out the radiation image signal X and the offset image signal S from the memory, and generates radiation afterimage image data ("XS" in the figure) by subtracting the offset image signal S from the radiation image signal X.

[0063] The image generating circuit 113 transmits the corrected radiation image data XS to the computer 120 .

[0064] In this way, in imaging in the intermittent offset correction mode, offset correction is performed using the offset image signal S obtained immediately after the radiographic image signal X is obtained. Therefore, if the radiographic image signal X contains an afterimage, the offset correction is performed using the offset image signal S that is temporally close to the radiographic image signal X, so that the afterimage component can be corrected.

[0065] Next, detailed driving for reading out one row will be described with reference to FIGS. 7(a) and 7(b) and FIG.

[0066] The difference between Figure 7(a) and Figure 7(b) is that Figure 7(a) sequentially reads out the drive lines Vg1 to Vg3 one row at a time, whereas Figure 7(b) simultaneously reads out two rows of drive lines Vg1 and Vg2, drive lines Vg3 and Vg4, and drive lines Vg5 and Vg6. Figure 7 explains the time to read out one row, but in the following explanation, the drive in which two rows of drive lines Vg1 and Vg2 are simultaneously read out, as in Figure 7(b), will also be explained as the time to read out one row.

[0067] First, when the reset switch is turned on in response to a control signal RC (reset pulse) supplied from the control circuit 112 to the amplifier circuit 221, the integral capacitance is reset and the potential of the signal line Sig is reset to the reference potential.

[0068] After resetting the integrating capacitor, a control signal SHN is output to sample the KTC noise appearing at the output of the integrating amplifier 222. The switch 224N is turned on and off, and the KTC noise is sampled in the capacitor 225N.

[0069] Next, an ON signal is supplied from the drive circuit 210 to the drive line Vg1 of the first row. When the switch element 203 is turned ON, the conversion element 202 and the signal line Sig are brought into a conductive state, and the charge obtained by the conversion element 202 is transferred to the signal line Sig and input to the amplifier circuit 221. The input charge is converted into a voltage signal by the integral amplifier circuit 222 and output.

[0070] Next, the control signal SHS is output, the switch 224S is turned on and off, and the signal from the conversion element 202 output by the integral amplifier circuit 222 is sampled in the capacitor 225S.

[0071] Thereafter, the voltage signals held in the capacitors 225N and 225S are sequentially sent by the multiplexer 227 to the AD converter 240 and converted into digital signals.

[0072] The time Z for reading out one row shown in Fig. 7 is configured as the time described above. In this embodiment, the time Z for reading out one row is changed depending on the offset correction mode. Specifically, in the fixed offset correction mode (first offset imaging mode) of mode A, the readout time is, for example, 40 us, and in the intermittent offset correction mode (second offset imaging mode) of mode B, the readout time is, for example, 30 us.

[0073] Figure 8(a)(b) shows the time Z to read one row and its effect on temperature fluctuations.

[0074] Fig. 8(a) shows the fluctuation of the digital value output from the AD converter 240 when the time Z for reading out one row is 30 us, and Fig. 8(b) shows the fluctuation of the digital value output from the AD converter 240 when the time Z for reading out one row is 40 us.

[0075] 8(a) and 8(b) both show the change in the digital value output from the AD converter 240 when the ambient temperature of the radiation imaging apparatus 110 is changed by 10° C. over time m.

[0076] As shown in Figures 8(a) and 8(b), when the outside temperature of the radiation imaging device 110 changes, it can be seen that the change in the digital value output from the AD converter 240 is smaller when the time Z for reading out one row is longer. The pixel array 200, drive circuit 210, and readout circuit 220 are composed of semiconductor elements and passive elements, and their characteristics change with temperature. Therefore, the temporal response of the semiconductor elements and passive elements also changes, so extending the time Z for reading out one row improves stability against temperature changes.

[0077] In particular, the time from when the drive circuit 210 supplies an ON signal or OFF signal to the drive line Vg until the signal sample-and-hold circuit holds the voltage in response to the control signal SHS has a large effect (corresponding to periods X and Y in FIG. 7). This is because the voltage of the ON signal supplied to the drive line Vg is high at 10 V or more, and the voltage of the OFF signal is low at −5 V or less, so the effect of amplitude is particularly large.

[0078] In this embodiment, the time Z for reading one row is shorter in the intermittent offset correction mode, which is the second offset correction mode, than in the fixed offset correction mode, which is the first offset imaging mode. In the fixed offset correction mode, the offset image signal S is acquired during preparation for imaging, leaving a gap between this and the acquisition of the radiation image signal X. Therefore, if there is a temperature change during this period, artifacts will occur in the XS image after offset correction. On the other hand, in the intermittent offset correction mode, the offset image signal S is acquired immediately after the acquisition of the radiation image signal X. Therefore, since the offset image signal can be acquired with almost no change in temperature, artifacts are less likely to occur in the XS image after offset correction.

[0079] Furthermore, in the intermittent offset correction mode, two images, a radiation image signal X and an offset image signal S, are acquired to create one frame of image signal, which reduces the frame rate. However, as in this embodiment, the frame rate can be improved by shortening the time Z required to read out one row in the intermittent offset correction mode.

[0080] As described above, in the fixed offset correction mode, the time Z for reading one row is increased to improve stability against temperature changes, and in the intermittent offset correction mode, the frame rate can be improved by shortening the time Z for reading one row.

[0081] Next, a third offset shooting mode (hereinafter referred to as intermittent hybrid offset correction mode) that combines the fixed offset correction mode and the intermittent offset correction mode will be described with reference to FIG.

[0082] The control circuit 112 alternately executes accumulation operations and readout operations before transmitting an enable signal that authorizes radiation irradiation (during preparation for imaging). As shown in FIG. 9, an accumulation operation is executed during an accumulation period (accumulation time) 411, and signals based on charges accumulated in the plurality of pixels 201 are read out during the subsequent readout period 412. Similarly, for accumulation periods (accumulation times) 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 201 during preparation for imaging are used to generate offset image signals.

[0083] In a readout period 412, a signal based on the charge accumulated over the time length 401 is read out from the pixel 201. The time length 401 is the length of time from when the previous readout operation of the pixel 201 ends (i.e., when the drive signal changes to low level) to when the current readout operation of the pixel 201 ends (i.e., when the drive signal changes to low level again). The same applies to other time lengths during which charge is accumulated. The time length 401 includes an accumulation period (accumulation time) 411. In a readout period 414, a signal based on the charge accumulated over the time length 402 is read out from the pixel 201. The time length 402 includes an accumulation period (accumulation time) 413.

[0084] 9, the accumulation period (accumulation time) 413 is shorter than the accumulation period (accumulation time) 411. As a result, the time length 402 is shorter than the time length 401. Therefore, the signal read out from the pixel 201 during the readout period 412 is referred to as a long-time offset signal, and the signal read out from the pixel 201 during the readout period 414 is referred to as a short-time offset signal.

[0085] The image generation circuit 113 generates a long-term offset image signal S based on the long-term offset signals read out from each of the multiple pixels 201 included in the pixel array 200. The long-term offset image signal S is expressed as a matrix with m rows and n columns, and the signal read out from pixel 201(i,j) is the (i,j) component of this matrix. The image generation circuit 113 generates a short-term offset image signal T based on the short-term offset signals read out from each of the multiple pixels 201 included in the pixel array 200. The short-term offset image T is expressed as a matrix with m rows and n columns, and the signal read out from pixel 201(i,j) is the (i,j) component of this matrix.

[0086] The control circuit 112 repeatedly executes the operations from the accumulation period 411 to the readout period 414. That is, the same operations as those from the accumulation period 411 to the readout period 414 are also executed from the accumulation period 415 to the readout period 418. In this way, the control circuit 112 alternately executes a readout operation for reading out a long-time offset signal and a readout operation for reading out a short-time offset signal during preparation for imaging.

[0087] After preparation for imaging is complete, the control circuit 112 generates an enable signal that permits radiation irradiation and transmits it to the computer 120 via the communication means 115, and starts capturing moving images (i.e., capturing a plurality of radiographic images). Specifically, the control circuit 112 alternately executes accumulation operations and readout operations. As shown in FIG. 9 , the control circuit 112 executes an accumulation operation during an accumulation period (accumulation time) 421, and then reads out signals based on the charges accumulated in the plurality of pixels 201 during the subsequent readout period 422. Similarly, for accumulation periods 423 to 428, the control circuit 112 reads out signals based on at least the charges accumulated during the accumulation period during the subsequent readout period. The signals read out from the pixels 201 after preparation for imaging is complete are used to generate radiographic image signals and offset image signals.

[0088] In a readout period 422, a signal based on the charge accumulated over the time length 403 is read out from the pixel 201. The time length 403 includes an accumulation period (accumulation time) 421. The accumulation period 421 includes a period during which the radiation imaging device 110 is irradiated with radiation 160. Therefore, the time length 403 includes a period during which the radiation imaging device 110 is irradiated with radiation 160. The time length 403 may be equal to the time length 401. In a readout period 424, a signal based on the charge accumulated over the time length 404 is read out from the pixel 201. The time length 404 includes an accumulation period (accumulation time) 423. The time length 404 does not include a period during which the radiation imaging device 110 is irradiated with radiation 160. The time length 404 may be equal to the time length 402.

[0089] 9, the accumulation period (accumulation time) 423 is shorter than the accumulation period (accumulation time) 421. As a result, the time length 404 is shorter than the time length 403. The signal read out from the pixel 201 during the readout period 422 is referred to as a radiation signal, and the signal read out from the pixel 201 during the readout period 424 is referred to as an imaging offset signal. The radiation signal includes a component corresponding to the radiation 160 irradiated to the radiation imaging device 110 during the accumulation period 421. By making the accumulation period (accumulation time) 423 shorter than the accumulation period (accumulation time) 421, the frame rate of the moving images generated by the radiation imaging device 110 can be improved.

[0090] The image generation circuit 113 generates a radiation image signal X based on radiation signals read out from each of the plurality of pixels 201 included in the pixel array 200. The radiation image signal X is expressed as a matrix of m rows and n columns, and the signal read out from pixel 201(i,j) is the (i,j) component of this matrix. The image generation circuit 113 generates an imaging offset image signal U based on imaging offset signals read out from each of the plurality of pixels 201 included in the pixel array 200. The imaging offset image signal U is expressed as a matrix of m rows and n columns, and the signal read out from pixel 201(i,j) is the (i,j) component of this matrix.

[0091] 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.

[0092] Next, a method will be described in which the image generating circuit 113 corrects the radiation image signal X using the long-term offset image signal S, the short-term offset image signal T, and the imaging offset image signal U. As described above, the long-term offset image signal S, the short-term offset image signal T, the imaging offset image signal U, and the radiation image signal X are respectively provided by the long-term offset signal, the short-term offset signal, the imaging offset signal, and the radiation signal. In the following method, the radiation signal is corrected using the long-term offset signal, the short-term offset signal, and the imaging offset signal.

[0093] As described above, during preparation for imaging, i.e., before transmitting a radiation irradiation enable signal, the control circuit 112 alternately generates the long-term offset image signal S and the short-term offset image signal T. This generates multiple long-term offset image signals S and multiple short-term offset image signals T. During preparation for imaging, the image generation circuit 113 averages the multiple long-term offset image signals S to generate a single long-term offset image signal S and stores the single long-term offset image signal S in its memory for subsequent processing. Similarly, during preparation for imaging, the image generation circuit 113 averages the multiple short-term offset image signals T to generate a single short-term offset image signal T and stores the single short-term offset image signal T in its memory for subsequent processing. Averaging multiple offset image signals in this manner reduces noise contained in the offset image signals. The number of offset image signals used for averaging may be two, as shown in FIG. 9, or may be three or more. The number of offset image signals used for averaging may be set in advance.

[0094] The image generation circuit 113 generates a radiation image signal X and an imaging offset image signal U and stores them in the memory of the image generation circuit 113. The image generation circuit 113 reads out the long-term offset image signal S from the memory and generates a radiation afterimage image signal ("XS" in the figure) by subtracting the long-term offset image signal S from the radiation image signal X. The image generation circuit 113 also reads out the short-term offset image signal T from the memory and generates an offset afterimage image signal ("UT" in the figure) by subtracting the short-term offset image signal T from the imaging offset image signal U.

[0095] The residual image components contained in the radiation residual image signal and the offset residual image signal are proportional to the length of time that charge is accumulated in the pixel 201. Therefore, the image generation circuit 113 multiplies each element of the offset residual image signal by a coefficient k, which is equal to the ratio of the time length 403 to the time length 404 (i.e., the value obtained by dividing the time length 403 by the time length 404). This generates an adjusted residual image signal ("k(UT)" in the figure). The image generation circuit 113 then subtracts the adjusted residual image signal from the radiation residual image signal to generate radiation image data X' (=X-kU+(kT-S)). The radiation image data X' is image data obtained by correcting the radiation image signal X using the long-term offset image signal S, the short-term offset image signal T, the imaging offset image signal U, and the coefficient k. The image generation circuit 113 transmits the corrected radiation image data X' to the computer 120.

[0096] The above-described calculation order for generating radiation image data X' is merely an example, and calculations may be performed in other orders. The radiation image data X', i.e., XSk(UT), is transformed into X-kU+(kT-S). Therefore, the image generation circuit 113 may calculate kT-S using the long-term offset image signal S, the short-term offset image signal T, and the coefficient k during preparation for imaging, and store this value as a correction value in the memory of the image generation circuit 113. The coefficient k may be determined based on a predetermined setting of the timing at which the drive circuit 210 supplies an ON signal to the pixel array 200. During imaging of a moving image, the image generation circuit 113 may correct the radiation image signal X using the imaging offset image signal U, the correction value stored in the memory, and the coefficient k. By storing the correction value instead of the long-term offset image signal S and the short-term offset image signal T in this way, the memory consumption of the image generation circuit 113 can be reduced.

[0097] Next, the technical significance of alternately acquiring the long-time offset image signal S and the short-time offset image signal T will be described. The driving lines Vg1 to Vgm have various capacitive couplings within the pixel array 200. For example, the driving line Vg2 intersects with the signal lines Sig1 to Sign at multiple points in the pixel array 200, and has capacitive couplings at these intersections. The driving line Vg2 extends parallel to the driving line Vg3, and therefore has capacitive coupling with the driving line Vg3. The driving line Vg2 extends parallel to a portion of the bias line Bs, and therefore has capacitive coupling with the bias line Bs. Furthermore, the driving line Vg2 has capacitive coupling with a node at the connection between the switch element 203 and the conversion element 202.

[0098] Due to this type of capacitive coupling, the potentials of the signal line Sig, bias line Bs, other drive lines Vg, and the node at the connection between the switch element S and the conversion element C also fluctuate in response to changes in the level of the drive signal supplied to the drive line Vg. The signal line Sig, bias line Bs, drive line Vg, and the node at the connection between the switch element 203 and the conversion element 202, whose potentials have fluctuated, return to their original potentials over time. However, the amount of return varies depending on the length of the accumulation period.

[0099] Furthermore, even when the switch element 203 is in the off state, a leakage current can flow. When the switch element 203 is turned off, the node between the conversion element 202 and the switch element 203 changes to the low level due to charge injection from the control terminal (gate). Therefore, immediately after the switch element 203 is turned off, a potential difference occurs between the main terminals (source, drain), causing a leakage current to flow. The leakage current depends on the potential difference between the two main terminals (source, drain) of the switch element. If a leakage current flows during the accumulation period, this potential difference becomes smaller, and therefore the leakage current varies depending on the length of the accumulation period. Furthermore, if a leakage current flows in the switch element 203, a current also flows in the signal line Sig and the bias line Bs.

[0100] For the above reasons, the offset image signals acquired may differ between the case where the long-term offset image signal S and the short-term offset image signal T are each acquired multiple times in succession and the case where the long-term offset image signal S and the short-term offset image signal T are acquired alternately. In the operation of the radiation imaging device 110 described above, the long-term offset image signal S and the short-term offset image signal T are acquired alternately during preparation for imaging, and after preparation for imaging is completed, the radiation image signal X and the imaging-time offset image signal U are acquired alternately. This allows the state of capacitive coupling within the pixel array 200 during preparation for imaging to approach the state of capacitive coupling within the pixel array 200 during imaging of a radiation image, thereby enabling noise included in the radiation image signal X to be reduced with high accuracy.

[0101] 9, the image generating circuit 113 corrects the radiation signal using an imaging offset signal acquired after the radiation signal. Alternatively, the image generating circuit 113 may correct the radiation signal using an imaging offset signal acquired before the radiation signal. For example, the radiation image signal X of the second frame in moving image capture may be corrected using the imaging offset image signal U of the first frame.

[0102] In the above example, the time length 401 is equal to the time length 403. Alternatively, these time lengths may be different from each other. In such a case where the time lengths are different, the image generation circuit 113 may multiply each element of the long-term offset image signal S by the ratio of the time length 403 to the time length 401, and then subtract the result from the radiation image signal X. In the above example, the time length 402 is equal to the time length 404. Alternatively, these time lengths may be different from each other. In such a case where the time lengths are different, the image generation circuit 113 may multiply each element of the short-term offset image signal T by the ratio of the time length 404 to the time length 402, and then subtract the result from the imaging offset image signal U.

[0103] When performing the offset correction shown in FIG. 9, there are long gaps between calculating the difference between the radiation image X and the long-term offset image S, and between the offset image U at the time of imaging and the short-term offset image T. Therefore, although similar to the fixed offset correction mode, the subsequent XSk(UT) is an intermittent offset correction mode, which reduces the impact of temperature fluctuations. This allows the readout time Z for one row to be shorter than in fixed offset correction. The readout times for all of the long-term offset image signal S, short-term offset image signal T, radiation image signal X, and offset image signal U at the time of imaging are shortened. In this example, the readout time Z for one row is set to a short readout time of 30 μsec, as described above. As a result, it is possible to improve stability against temperature changes while also increasing the frame rate.

[0104] Note that the time Z for reading out one row described above is an example and is not limited to this. By optimizing the combination of the time Z for reading out one row in the fixed offset correction mode and the time Z for reading out one row in the intermittent offset correction mode, it is also possible to equalize the frame rates in both modes. Similarly, by optimizing the time Z for reading out one row and the accumulation time (accumulation times 413, 423) in the fixed offset correction mode and the intermittent hybrid offset correction mode, it is also possible to equalize the frame rates in both modes.

[0105] In so-called video imaging, in which multiple images are continuously acquired as shown in FIGS. 5, 6, and 9, it is possible to consider a case in which a radiation irradiation permission signal is transmitted for each radiation pulse (a case in which a permission signal is transmitted multiple times during video imaging). In this case, it is preferable to determine the timing before and after the transmission of the permission signal based on the timing of the first permission signal transmission in video (continuous) imaging. For example, consider the imaging sequence of FIG. 9. In a configuration in which a series of video images are captured by transmitting permission signals at the start of accumulation period 421 and accumulation period 425, the permission signal transmitted at the start of accumulation period 421 is used as the reference, and the timing before and after the transmission of the permission signal is used as the reference. In other words, in this imaging configuration, the time before period 421 (periods 411 to 420) is before the transmission of the permission signal, and the time after period 421 (periods 421 to 428) is after the transmission of the permission signal. The same applies to the configurations of FIGS. 5 and 6 (based on the permission signal in capturing the first frame of the video).

[0106] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention.

[0107] The disclosure of the present specification includes the following radiation imaging apparatus and radiation imaging system.

[0108] (Item 1) a communication means for transmitting an authorization signal to an external device to authorize radiation irradiation; a readout means for reading out the charges accumulated in the conversion elements to generate a signal; and an image generating means for generating radiation image data from the signal generated by the readout means, wherein the readout means is capable of reading out the charges accumulated in the conversion elements at a first readout time before transmitting the authorization signal to generate a first correction signal, reading out the charges accumulated in the conversion elements based on radiation irradiation after transmitting the authorization signal to generate a radiation signal, and reading out the charges accumulated in the conversion elements based on radiation irradiation after transmitting the authorization signal to generate a second correction signal, wherein the image generating means corrects the radiation signal using the first correction signal or the second correction signal to generate radiation image data, and the second readout time is shorter than the first readout time.

[0109] (Item 2) 2. The radiation imaging device according to item 1, further comprising: a switch element having one terminal connected to the conversion element and the other terminal connected to the readout means; and a drive means for supplying a drive signal to the switch element that switches the switch element between on and off, wherein the readout means has an integral amplifier circuit that converts the charge accumulated in the conversion element into a voltage signal, and a sample and hold circuit that holds the voltage signal, wherein the first correction signal and the second correction signal are generated by holding the voltage signal with the sample and hold circuit, and the time from when the switch element is switched from an off state to an on state by the supply of the drive signal to when the voltage signal is held by the sample and hold circuit is shorter for the generation of the second correction signal than for the generation of the first correction signal.

[0110] (Item 3) 2. The radiation imaging device according to item 1, further comprising: a switch element having one terminal connected to the conversion element and the other terminal connected to the readout means; and a drive means for supplying a drive signal to the switch element that switches the switch element between on and off, wherein the readout means has an integral amplifier circuit that converts the charge accumulated in the conversion element into a voltage signal, and a sample and hold circuit that holds the voltage signal, wherein the first correction signal and the second correction signal are generated by holding the voltage signal with the sample and hold circuit, and the time from when the switch element is switched from an on state to an off state by the supply of the drive signal to when the voltage signal is held by the sample and hold circuit is shorter for the generation of the second correction signal than for the generation of the first correction signal.

[0111] (Item 4) 4. The radiation imaging device according to any one of items 1 to 3, wherein the readout means is capable of, after transmitting the enable signal, reading out the charges accumulated in the conversion elements based on the irradiation of radiation at the first readout time to generate a first radiation signal or reading out the charges at the second readout time to generate a second radiation signal, and the image generation means is capable of operating in a first offset imaging mode to generate radiation image data using the first radiation signal and the first correction signal, and a second offset imaging mode to generate radiation image data using the second radiation signal and the second correction signal.

[0112] (Item 5) 5. The radiation imaging device according to item 4, wherein the readout means controls the first readout time and the second readout time so that the time from when the communication means transmits the enable signal to when the image generation means generates the radiation image data is the same in the first offset radiography mode and the second offset radiography mode.

[0113] (Item 6) 5. The radiation imaging device according to item 4, wherein the readout means is capable of reading out the charges accumulated in the conversion elements in a second readout time before transmitting the enable signal to generate a third correction signal, and the image generation means is capable of operating in a third offset imaging mode to generate radiation image data using the second radiation signal, the second correction signal, and the third correction signal.

[0114] (Item 7) 7. The radiation imaging device according to item 6, wherein the readout means reads out the accumulated charges in the conversion elements so that the charges are accumulated for a first accumulation time or a second accumulation time shorter than the first accumulation time.

[0115] (Item 8) 8. The radiation imaging device according to item 7, wherein the readout means controls the first accumulation time, the second accumulation time, the first readout time, and the second readout time so that the time from when the communication means transmits the enable signal to when the image generation means generates the radiation image data is the same in the first offset radiography mode and the third offset radiography mode.

[0116] (Item 9) 9. A radiation imaging system comprising: the radiation imaging device according to any one of items 1 to 8; and control means for acquiring radiation image data generated by the image generation means and performing image processing on the radiation image data. [Explanation of symbols]

[0117] 100 Radiation Imaging System 110 Radiation imaging device 113 Image generation circuit 115 Means of communication 120 Computer 130 Exposure control device 202 Conversion element 220 Readout circuit

Claims

1. a conversion element capable of accumulating charges for generating a radiation image; a communication means for transmitting a permission signal to an external device to permit irradiation of radiation; a readout means for reading out the charges accumulated in the conversion element and generating a signal; an image generating means for generating radiation image data from the signal generated by the readout means, the readout means is capable of reading out the charges accumulated in the conversion elements in a first readout time before the transmission of the enable signal to generate a first correction signal, reading out the charges accumulated in the conversion elements based on irradiation of radiation after the transmission of the enable signal to generate a radiation signal, and reading out the charges accumulated in the conversion elements not based on irradiation of radiation after the transmission of the enable signal in a second readout time to generate a second correction signal, the image generating means corrects the radiation signal using the first correction signal or the second correction signal to generate radiation image data; The radiation imaging apparatus is characterized in that the second readout time is shorter than the first readout time.

2. a switch element having one terminal connected to the conversion element and the other terminal connected to the readout means, and a drive means for supplying a drive signal to the switch element to switch the switch element between an on state and an off state, the readout means has an integral amplifier circuit that converts the electric charge accumulated in the conversion element into a voltage signal, and a sample-and-hold circuit that holds the voltage signal; the first correction signal and the second correction signal are generated by holding the voltage signal by the sample-and-hold circuit; 2. The radiation imaging device according to claim 1, wherein the time from when the switch element is switched from an off state to an on state by the supply of the drive signal to when the voltage signal is held by the sample-and-hold circuit is shorter for generating the second correction signal than for generating the first correction signal.

3. a switch element having one terminal connected to the conversion element and the other terminal connected to the readout means, and a drive means for supplying a drive signal to the switch element to switch the switch element between an on state and an off state, the readout means has an integral amplifier circuit that converts the electric charge accumulated in the conversion element into a voltage signal, and a sample-and-hold circuit that holds the voltage signal; the first correction signal and the second correction signal are generated by holding the voltage signal by the sample-and-hold circuit; 2. The radiation imaging device according to claim 1, wherein the time from when the switch element is switched from an on state to an off state by the supply of the drive signal to when the voltage signal is held by the sample-and-hold circuit is shorter for generating the second correction signal than for generating the first correction signal.

4. the readout means is capable of, after transmitting the enable signal, reading out the charges accumulated in the conversion elements based on irradiation with radiation at the first readout time to generate a first radiation signal or reading out the charges at the second readout time to generate a second radiation signal; 2. The radiation imaging apparatus according to claim 1, wherein the image generating means is operable in a first offset imaging mode in which radiation image data is generated using the first radiation signal and the first correction signal, and in a second offset imaging mode in which radiation image data is generated using the second radiation signal and the second correction signal.

5. 5. The radiation imaging device according to claim 4, wherein the readout means controls the first readout time and the second readout time so that the time from when the communication means transmits the permission signal to when the image generation means generates the radiation image data is the same in the first offset imaging mode and the second offset imaging mode.

6. the readout means is capable of reading out the charges accumulated in the conversion elements for a second readout time before transmitting the enable signal to generate a third correction signal; 5. The radiation imaging apparatus according to claim 4, wherein the image generating means is operable in a third offset imaging mode in which radiation image data is generated using the second radiation signal, the second corrected signal, and the third corrected signal.

7. 7. The radiation imaging device according to claim 6, wherein the readout means reads out the accumulated charges so that the charges accumulated in the conversion elements become charges accumulated for a first accumulation time or a second accumulation time shorter than the first accumulation time.

8. 8. The radiation imaging device according to claim 7, wherein the readout means controls the first accumulation time, the second accumulation time, the first readout time, and the second readout time so that the time from when the communication means transmits the enable signal to when the image generation means generates the radiation image data is the same in the first offset imaging mode and the third offset imaging mode.

9. 10. A radiation imaging system comprising: the radiation imaging apparatus according to claim 1; and control means for acquiring radiation image data generated by the image generating means and performing image processing on the radiation image data.

Images