JP2021049204A - Radiation imaging device and radiation imaging system - Google Patents

Abstract

To provide a technology for improving an S/N ratio in general imaging in a radiation imaging device capable of performing energy subtraction imaging and the general imaging.SOLUTION: A radiation imaging device includes: a flexible board including a first pixel array 200 and a second pixel array 300 composed of a plurality of pixels 210 for outputting electric signals according to incident radiation, the pixels arranged in matrix shapes, and a signal line Sig to which first pixels included in the first pixel array 200 and second pixels included in the second pixel array 300 are connected in common, the first pixels and the second pixels arranged so as to face each other; and a control circuit 112 for controlling a first drive circuit 210 for driving the first pixel array 200 and a second drive circuit 310 for driving the second pixel array 300 so that electric signals from the first pixels and electric signals from the second pixels are output to the signal line in the same period.SELECTED DRAWING: Figure 4

Description

The present invention relates to a radiation imaging device and a radiation imaging system. In particular, the present invention relates to a radiation imaging apparatus capable of performing energy subtraction imaging and general imaging using a common radiation detection panel, and a radiation imaging system to which the radiation imaging apparatus is applied.

With the progress of digital technology, a device that obtains a high-quality radiation image by converting the intensity distribution of radiation transmitted through the subject into an electric signal and detecting it, processing this electric signal and reproducing it as a visible image on a monitor or the like. Widely used in industrial non-destructive inspection and medical diagnosis. Further, with the recent progress of semiconductor process technology, a device for taking a radiographic image using a semiconductor sensor has been developed. These systems have a very wide dynamic range compared to conventional radiographic imaging systems that use photosensitive film, and can obtain radiographic images without being affected by fluctuations in the amount of radiation exposure. It has the practical advantage of being able to do it. Further, unlike the conventional photosensitive film method, there is an advantage that an image can be obtained immediately without requiring chemical treatment.

As an application of such medical diagnosis using radiographic images, there is radiographic image diagnosis using the energy subtraction method. Radiation includes low-frequency low-energy components (soft radiation) and high-frequency high-energy components (hard radiation). Radiation with a low energy component is difficult to penetrate the subject, and radiation with a high energy component is easy to pass through the subject. Utilizing the above-mentioned characteristics, a plurality of radiation images having different energy components of the radiation applied to the radiation detection panel are acquired, and image processing is performed to acquire an image in which bone tissue and soft tissue are separated or emphasized. can do. Furthermore, during the IVR (Interventional Radiology) procedure, it is possible to obtain an image in which the catheter inserted in the subject is separated or emphasized. This method is called an energy-subtraction method or an energy difference method.

As a method for realizing the energy subtraction method, there is a method in which a low energy cut filter that absorbs a predetermined energy component is superposed between two radiation detection panels and each radiation detection panel inside the housing of one radiation imaging device. is there. In the configuration described in Patent Document 1, one flexible radiation detection panel is used, and by bending and laminating, energy subtraction imaging and general imaging can be performed, and cost and weight are suppressed. ..

Japanese Unexamined Patent Publication No. 2013-2538887

In the technique of Patent Document 1, the signal line for transmitting an electric signal from the conversion element that receives light and converts it into an electric signal to the readout circuit becomes long. Therefore, the capacitance parasitic on the signal line is about doubled. Since the noise of the readout circuit of the radiation detection panel increases depending on the signal line capacitance, the S / N ratio of the captured image deteriorates. Therefore, in the technique of Patent Document 1, there is a problem in the S / N ratio of the photographed image in general photography. Therefore, an object of the present invention is to provide a technique for improving the S / N ratio in general radiography in a radiation imaging apparatus capable of energy subtraction radiography and general radiography.

In view of the above problems, the radiation imaging apparatus of the present invention includes a first pixel array and a second pixel array in which a plurality of pixels for outputting an electric signal corresponding to the incident radiation are arranged in a matrix, and the above. It has a signal line in which a first pixel included in the first pixel array and a second pixel included in the second pixel array are commonly connected, and the first pixel and the second pixel are included. The flexible substrate arranged so as to face each other, and the electric signal from the first pixel and the electric signal from the second pixel are output to the signal line in the same period. It has a first drive circuit that drives the first pixel array and a control circuit that controls a second drive circuit that drives the second pixel array.

By the above means, it is possible to improve the S / N ratio in general radiography in a radiation imaging apparatus capable of energy subtraction radiography and general radiography.

The figure explaining the configuration example of the radiation imaging system. The figure explaining the configuration example of the radiation imaging apparatus. The figure explaining the example of the cross-sectional structure of a pixel. The figure explaining the laminated structure example of the radiation imaging apparatus. The figure explaining the characteristic of a radiation imaging apparatus. The figure explaining the operation example of the radiation imaging system. The figure explaining the operation example of the radiation imaging system. The figure explaining the operation example of the radiation imaging system. The figure explaining the operation example of the radiation imaging system. The figure explaining the modification of the laminated structure of a radiation imaging apparatus.

Embodiments of the present invention will be described below with reference to the accompanying drawings. Similar elements are designated by the same reference numerals throughout the various embodiments, and duplicate description is omitted. Moreover, each embodiment can be changed and combined as appropriate.

<First Embodiment>
FIG. 1 shows a configuration example of the radiation imaging system 100 of the first embodiment of the present invention. The radiation imaging system 100 is configured to electrically image an optical image formed by radiation and obtain an electrical radiation image. The radiation is typically X-rays, but may be α-rays, β-rays, γ-rays, and the like. The radiation imaging system 100 includes, for example, a radiation imaging device 110, a computer 120, an exposure control device 130, and a radiation source 140.

The radiation source 140 starts irradiation of radiation in accordance with an exposure command (radiation command) from the exposure control device 130. The radiation emitted from the radiation source 140 passes through the subject 150 and enters the radiation imaging device 110. The radiation source 140 also stops the irradiation of radiation according to a stop command from the exposure control device 130.

The radiation imaging device 110 includes a radiation detection panel 111 and a control circuit 112. The radiation detection panel 111 generates radiation image data corresponding to the radiation incident on the radiation imaging device 110 and transmits the radiation image data to the computer 120. The radiographic image data is data representing a radiological image. 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 irradiation of radiation from the radiation source 140 based on the signal obtained from the radiation detection panel 111. The stop signal is supplied to the exposure control device 130. The exposure control device 130 sends a stop command to the radiation source 140 in response to the stop signal. The control circuit 112 may be configured by 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). Instead, the control circuit 112 may be configured by a combination of a general-purpose processing circuit such as a processor and a storage circuit such as a memory. In this case, the function of the control circuit 112 may be realized by the general-purpose processing circuit executing the program stored in the storage circuit.

The computer 120 includes a control unit that controls the radiation imaging device 110 and the exposure control device 130, a receiving unit that receives radiation image data from the radiation imaging device 110, and a signal (radiation image data) obtained by the radiation imaging device 110. It has a signal processing unit for processing the above. The control unit, the reception unit, and the signal processing unit may each be configured by a dedicated circuit or a combination of a general-purpose processing circuit and a storage circuit, as in the control circuit 112. In one example, the exposure control device 130 has an exposure switch, and when the exposure switch is turned on by the user, the exposure command is sent to the radiation source 140 and a start notification indicating the start of radiation irradiation is sent to the computer 120. Send to. Upon receiving the start notification, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the start of radiation irradiation in response to the start notification.

FIG. 2 shows a configuration example of the radiation detection panel 111. The radiation detection panel 111 includes, for example, a first pixel array 200, a second pixel array 300, a first drive circuit 210, a second drive circuit 310, a read circuit 220, a buffer circuit 230, and an A / D converter 240. To be equipped. The first drive circuit 210, the second drive circuit 310, and the read circuit 220 function as peripheral circuits of the first pixel array 200 and the second pixel array 300. The first pixel array 200 and the second pixel array 300 include, for example, a plurality of pixels 201 arranged in a matrix, a plurality of drive lines Vg1 to Vg8, a plurality of signal lines Sig1 to Sig4, and a bias line. It is composed of Bs. In FIG. 2, for the sake of explanation, the incident surface pixel array 200 is composed of 4 rows × 4 columns of pixels 201, and the second pixel array 300 is composed of 4 rows × 4 columns of pixels 201. However, in practice, more pixels 201 may be arranged. In one example, the radiation detection panel 111 has a size of 17 inches and has pixels 201 of about 3000 rows x about 3000 columns. Each pixel 201 is composed of a conversion element and a switch element.

The first pixel array 200 and the second pixel array 300 include a plurality of conversion elements C11 to C84 and a plurality of switch elements S11 to S84. In the following description, the conversion elements C11 to C84 are collectively referred to as the conversion element C. The description of the conversion element C applies to each of the conversion elements C11 to C84. Similarly, the switch elements S11 to S84, the drive lines Vg1 to Vg8, and the signal lines Sig1 to Sig4 are collectively referred to as the switch element S, the drive lines Vg, and the signal line Sig, respectively. The rows of the first pixel array 200 and the second pixel array 300 are referred to as the first to eighth rows in order from the upper side of the drawing, and each column of the pixel array 200 is referred to as the first to fourth columns in order from the left side of the drawing. Called. Each pixel 201 is composed of a combination of one conversion element C and one switch element S. For example, the pixel 201 in the first row and the second column is composed of a combination of the conversion element C12 and the switch element S12.

In each pixel 201, the conversion element C converts the incident radiation into an electric signal (for example, an electric charge), and the switch element S is connected between the conversion element C and the signal line Sigma corresponding to the conversion element C. ing. For example, the switch elements S11 to S81 are connected between the plurality of conversion elements C11 to C81 and the signal line Sigma1. When the switch element S is turned on, the conversion element C and the signal line sig become conductive, and the electric signal obtained by the conversion element C (for example, the electric charge accumulated in the conversion element C) is transferred to the signal line sig. Will be done. The conversion element C may be, for example, a MIS type photodiode which is arranged on an insulating and flexible substrate such as a flexible film or a glass substrate and whose main material is amorphous silicon. Instead of this, the conversion element C may be a PIN type photodiode. The conversion element C may be configured as a direct type that directly converts radiation into electric charges, or may be configured as an indirect type that detects this light after converting radiation into light. In the indirect type, the scintillator may be shared by a plurality of pixels 201. That is, each pixel 201 is a component for outputting an electric signal corresponding to the incident radiation.

The switch element S is composed of, for example, 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 common. It is connected to the bias power supply Vs via the bias wire Bs. The bias power supply Vs produces a bias voltage.

The first drive circuit 210 and the second drive circuit 310 are controlled by the control circuit 112, and according to the control signal supplied from the control circuit 112, the drive signal is sent to the control terminal of the switch element S of each pixel 201 through the drive line Vg. To supply. The control signal includes an on signal for turning on the switch element S (high level voltage in the following description) and an off signal for turning off the switch element S (low level voltage in the following description). Including. The first drive circuit 210 and the second drive circuit 310 include, for example, a shift register, and the shift register performs a shift operation according to a control signal (for example, a clock signal) supplied from the control circuit 112. An operation example of the first drive circuit 210 and the second drive circuit 310 will be described later.

The reading circuit 220 amplifies and reads out the electric signal obtained by the conversion element C and appearing on the signal line Sigma. The read circuit 220 includes one amplifier circuit 221 for each signal line Sigma. In the example of FIG. 2, since the first pixel array 200 and the second pixel array 300 have four signal line sigs, the read circuit 220 includes four amplifier circuits 221. Each column amplification unit CA includes, for example, an integrator amplifier 222, a variable amplifier 223, a switch element 224, a capacitance 225, and a buffer circuit 226. The switch element 224 and the capacitance 225 form a sample hold circuit. The integrating amplifier 222 includes, for example, an operational amplifier and an integrating capacitance 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 from the reference power supply Vref to the non-inverting input terminal of the operational amplifier. When the reset switch is turned on in response to the control signal RC (reset pulse) supplied from the control circuit 112, the integrated capacitance is reset and the potential of the signal line Sigma is reset to the reference potential.

The variable amplifier 223 amplifies the signal from the integrating amplifier 222 at a set amplification factor. The sample hold circuit sample holds the signal from the variable amplifier 223. The on / off of the switch element 224 constituting the sample hold circuit is controlled by the control signal SH supplied from the control circuit 112. The buffer circuit 226 buffers (impedance conversion) the signal from the sample hold circuit and outputs it.

The read 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 the shift register performs a shift operation according to a control signal (for example, a clock signal) supplied from the control circuit 112. By this shift operation, one signal from a plurality of amplifier circuits 221 is selected.

The buffer circuit 230 buffers (impedance conversion) the signal output from the multiplexer 227. The A / D converter 240 converts the analog signal output from the buffer circuit 230 into a digital signal. The output of the A / D converter 240, that is, the radiographic image data, is transmitted to the computer 120.

FIG. 3 schematically shows an example of the cross-sectional structure of one pixel 201. Pixels 201 are formed on, for example, an insulating substrate 301 such as a flexible film or 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 constitutes a gate of a transistor (for example, a TFT) constituting the switch element S. The insulating layer 303 is arranged so as to cover the conductive layer 302. The semiconductor layer 304 is arranged on the portion of the conductive layer 302 that constitutes the gate via the insulating layer 303. The impurity semiconductor layer 305 is arranged on the semiconductor layer 304 so as to form two main terminals (source and drain) of the transistor constituting the switch element S. The conductive layer 306 constitutes a wiring pattern connected to each of the two main terminals (source and drain) of the transistors constituting the switch element S. A part of the conductive layer 306 constitutes a signal line Sigma, and another part constitutes a wiring pattern for connecting the conversion element C and the switch element S.

The pixel 201 further has 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 connecting to the conductive layer 306 (switch element S). The pixel 201 further has 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 layer 316 in this order on the interlayer insulating film 307. These layers constitute an indirect conversion element C. The conductive layer 309 and the conductive layer 313 form the lower electrode and the upper electrode of the photoelectric conversion element constituting the conversion element C, respectively. The conductive layer 313 is made of, for example, a transparent material. The conductive layer 309, the insulating layer 310, the semiconductor layer 311 and the impurity semiconductor layer 312 and the conductive layer 313 form a MIS type sensor as a photoelectric conversion element. The impurity semiconductor layer 312 is formed of, for example, an n-type impurity semiconductor layer. The scintillator layer 316 is composed of, for example, a gadolinium-based material or a CsI (cesium iodide) material, and converts radiation into light.

Instead of the above example, the conversion element C may be configured as a direct type conversion element that directly converts the incident radiation into an electric signal (charge). As the direct type conversion element C, for example, there is a conversion element whose main material is amorphous selenium, gallium arsenide, gallium phosphide, lead iodide, mercury iodide, CdTe, CdZnTe and the like. The conversion element C is not limited to the MIS type, and may be, for example, a pn type or PIN type photodiode.

Next, the laminated structure of the radiation detection panel 111 will be described with reference to FIG. The first pixel array 200 and the second pixel array 300 shown in FIG. 2 are formed on a flexible substrate such as a film. The first pixel array 200 is arranged on the incident surface side of the radiation, and the second pixel array 300 is arranged on the surface opposite to the incident surface of the radiation. That is, the first pixel and the second pixel are flexible groups so that the first pixel included in the first pixel array 200 and the second pixel included in the second pixel array face each other. It is placed on the table. Therefore, the first pixel array 200 mainly absorbs low-energy components of radiation and converts them into electrical signals. The second pixel array 300 absorbs high-energy components of radiation and converts them into electrical signals. Further, the first drive circuit 210 drives the first pixel array 200, and the second drive circuit 310 drives the second pixel array 300, each of which can be driven independently. .. Further, the signal lines Sig1 to Sig4 and the read circuit 220 are common to the first pixel array 200 and the second pixel array 300. The pixels 201 of the first pixel array 200 and the second pixel array 300 are configured so that the pixel centers are aligned. In the first embodiment, the pixel centers of the conversion element C11 and the conversion element C81 are aligned, and the other conversion elements are similarly the conversion element C21 and the conversion element C71, the conversion element C31 and the conversion element C61, and the conversion element C41 and the conversion element. The pixel centers are aligned as in C51. Therefore, when the radiation is irradiated and the image is taken, for example, the conversion element C24 and the conversion element C74 can obtain a signal at the same position of the subject. An example of this operation will be described later.

In order to align the pixel centers of gravity of the first pixel array 200 and the second pixel array 300, it is possible to perform alignment with high accuracy by adding a plurality of alignment marks to each pixel array. However, it is difficult to completely match the pixel centers of the first pixel array 200 and the second pixel array 300. FIG. 5 shows the relationship between the amount of deviation with respect to the center of gravity of the pixel and the resolving power (MTF (Modulation Transfer Function)). FIG. 5 shows a pixel array having a pixel pitch of 125 um. If the amount of deviation between the center of gravity of the orthographic projection of the first pixel and the center of gravity of the orthographic projection of the second pixel from the side where the radiation is incident is within 0.5 pixels, the decrease of 1 lp / mm is about 4%. Therefore, it can be said that there is almost no effect.

A modified example of the laminated configuration of the radiation imaging system 100 will be described with reference to FIGS. 10 (a) to 10 (f). The first pixel array 200, the second pixel array 300, the read circuit 220, and the signal lines Sig1 to Sig4 are as described above. The first scintillator 401 and the second scintillator 402 are formed of a gadolinium-based material or a CsI (cesium iodide) material. The first reflective layer 403 and the second reflective layer 404 are made of aluminum, titanium oxide, or the like, and reflect the light emitted by the scintillator. Reference numeral 405 is a low-energy cut filter made of copper or tin and for cutting low-energy radiation so as not to reach the second scintillator 402, and reference numeral 406 is a flexible substrate made of a film material or the like. Further, 407 is a common scintillator common to the incident surface and the back surface, 408 and 409 are bases made of glass or the like, and 414 is flexible wiring such as FPC.

Next, the features of each of the modified examples shown in FIGS. 10 (a) to 10 (f) will be described. In the configuration shown in FIG. 10A, the first scintillator 401 and the second scintillator 402 are arranged between the first pixel array 200 and the second pixel array 300. Therefore, since the curvature when the flexible substrate 406 is bent is loose, the signal lines Sigma 1 to 4 are unlikely to be broken. Further, since the flexible substrate 406 wraps the first scintillator 401 and the second scintillator 402, it also has a moisture-proof effect. Next, in the configuration shown in FIG. 10B, since the distance between the first pixel array 200 and the second pixel array 300 is short, the pixel centers of the first pixel array 200 and the second pixel array 300 are aligned. There is an advantage that it is easy to perform alignment. Next, in the configuration shown in FIG. 10C, since the first pixel array 200 and the second pixel array 300 have a common scintillator 407, the manufacturing cost can be reduced. Next, in the configuration shown in FIG. 10D, the first pixel array 200 and the second pixel array 300 are arranged on the glass bases 408 and 409. Therefore, there is less expansion and contraction and distortion than the resin film, and there is an advantage that alignment when aligning the pixel centers of the first pixel array 200 and the second pixel array 300 is easy. Next, in the configuration shown in FIG. 10E, transparent ITO is used as the wiring material of the conversion element C of the second pixel array 300 so that light can be detected from both sides. Therefore, a third scintillator 410 and a third reflection layer 411 are further arranged on the back side of the second pixel array 300 so that high-energy radiation can be further captured. Further, if the flexible substrate 406 is a thin film, the resolution does not decrease much even if it is incident from the back surface. Next, as shown in FIG. 10 (f), the first pixel array 200 also has a fourth scintillator 412 and a fourth reflection layer 413 on the incident side, so that the scintillators are arranged on both sides.

An operation example of the radiation imaging system 100 in general imaging will be described with reference to FIG. The operation of the radiation imaging system 100 is controlled by the computer 120. The operation of the radiation imaging device 110 is controlled by the control circuit 112 under the control of the computer 120. The operation shown in FIG. 6 is started, for example, by instructing the user of the radiation imaging system 100. “Operation” in FIG. 6 indicates the operation of the radiation imaging system 100. The operation of the radiation imaging system 100 includes a standby sequence, a radiation image acquisition sequence, and an offset image acquisition sequence. The waiting sequence is a series of operations performed while waiting for the start of irradiation of radiation. The radiographic image acquisition sequence is a series of operations for acquiring a radiological image. The offset image acquisition sequence is a series of operations for acquiring an offset image. The offset image is an image formed by signals obtained from each pixel 201 when the radiation imaging device 110 is not irradiated with radiation. “Radiation” in FIG. 6 indicates the presence or absence of radiation. Low levels indicate no radiation and high levels indicate radiation. “Vg1” to “Vg8” in FIG. 6 indicate the levels of drive signals supplied from the first drive circuit 210 and the second drive circuit 310 to the drive lines Vg1 to Vg8. The switch element S connected to the drive line Vg to which the low level (off signal) drive signal is supplied is off, and the switch element connected to the drive line Vg to which the high level (on signal) drive signal is supplied. S is on. “Sig1” to “Sig4” in FIG. 6 indicate whether or not a signal is read through each signal line Sig1 to Sig4, and the conversion element C to be read. A low level indicates that the signal has not been read, and a high level indicates that the signal has been read. Further, in the case of high level, the code of the conversion element C to be read is shown. During the standby sequence, the radiation imaging device 110 repeats the reset operation. The reset operation is an operation of resetting the dark charge stored in the conversion element C of each pixel 201. The dark charge is a charge generated even though no radiation is incident on the conversion element C. Resetting the conversion element C in order from the pixel 201 in the first row to the pixel 201 in the fourth row and from the pixel 201 in the eighth row to the pixel 201 in the fifth row is called a single reset operation. Further, in the reset operation, since the conversion element C may be reset, the drive speed can be increased as compared with the read operation.

The control circuit 112 recognizes that irradiation of radiation from the radiation source 140 is started based on, for example, a start notification supplied from the exposure control device 130 via the computer 120, and acquires a radiation image from the standby sequence. Move to the sequence. Instead of this, the radiation imaging apparatus 110 may have a detection circuit for detecting a current flowing through the bias line Bs or the signal line Sigma of the first pixel array 200, and the radiation is based on the output of the detection circuit. The start of irradiation of radiation from the source 140 may be recognized.

The radiographic image acquisition sequence includes a storage operation and a reading operation. In the storage operation, the first drive circuit 210 and the second drive circuit 310 supply an off signal to each drive line Vg1 to Vg8 for a predetermined time. As a result, the electric charge corresponding to the radiation incident on each conversion element C is accumulated in the conversion element C. Subsequently, in the read operation, the control circuit 112 reads the electric charge (electric signal) accumulated in each conversion element C.

Hereinafter, the reading operation will be described in detail. Hereinafter, the electric charge read through the signal line Sigma 1 will be mainly described, but the same applies to the electric charge read through the signal lines Sigma 2-4. First, the first drive circuit 210 supplies an on signal only to the drive line Vg1. As a result, the switch element S11 is turned on and the conversion element C11 and the signal line Sig1 are in a conductive state, so that the electric charge obtained by the conversion element C11 is read out to the signal line Sig1. On the other hand, since the ON signal is also supplied to the second drive line Vg8 during the same period, the switch element S81 is also turned on, and the conversion element C81 and the signal line Sig1 are also in a conductive state. Therefore, the electric charge obtained by the conversion element C11 and the electric charge obtained by the conversion element C81 are read out to the signal line Sigma1. As can be seen from the structure of FIG. 4, the conversion element C11 and the conversion element C81 have the same pixel centers. Therefore, the signals at the same position of the subject are read out in the same period, and the two signals of the first pixel array 200 and the second pixel array 300 can be added and read out. When the first pixel array 200 and the second pixel array 300 are individually read out and signals are added as a digital image, noise is also added, so that the amount of noise is increased by √2 times. By adding an electric signal to the same signal line as in the present embodiment, the signal can be added with almost no increase in noise, so that the S / N is improved by about √2 times.

After the charges obtained by the conversion element C11 and the conversion element C81 are read out, the first drive circuit 210 and the second drive circuit 310 supply an on signal to the drive line Vg2 and the drive line Vg7. As a result, the switch element S21 and the switch element S71 are turned on, and the conversion element C21 and the conversion element C71 and the signal line Sig1 are in a conductive state. Therefore, the electric charge obtained by the conversion element C21 and the conversion element C71 is a signal line. It is added to Sig1 and read out. In this case, the pixel including the switch element S21 is the first pixel included in the first pixel array 200, and the pixel including the switch element S71 is the second pixel included in the second pixel array 300. By repeating such an operation with the drive lines Vg3 / Vg4 and the drive lines Vg6 / Vg5 and reading them out, the entire first pixel array 200 and the second pixel array 300 can be read out.

The radiation imaging device 110 transmits the electric charge of each conversion element C obtained by the radiation image acquisition sequence to the computer 120 as a digital signal through the multiplexer 227, the buffer circuit 230, and the A / D converter 240. A radiographic image can be obtained by synthesizing the data of each pixel 201.

Next, the offset image acquisition sequence will be described. The radiographic image acquisition sequence includes a reset operation, a storage operation, and a read operation. The control circuit 112 first performs the same reset operation as the standby sequence once. As a result, the states of the first pixel array 200 and the second pixel array 300 become the same as before the start of the radiographic image acquisition sequence. After that, the control circuit 112 acquires an offset image by performing the same storage operation and reading operation as the radiation image acquisition sequence. The offset image is also transmitted from the radiation imaging device 110 to the computer 120 in the same manner as the radiation image. By subtracting the offset image from the radiation image, the offset component due to the dark charge generated in the conversion element C during the irradiation of the radiation is removed from the radiation image.

An operation example of energy subtraction imaging of the radiation imaging system 100 will be described with reference to FIG. 7. It should be noted that the description will be omitted with reference to FIG.

Unlike general photography, in energy subtraction photography, the signals of the first pixel array 200 and the second pixel array 300 are acquired individually. In the read-out operation of the radiation imaging sequence of FIG. 7, in order to read out the second pixel array 300 first, the drive lines Vg8, Vg7, Vg6, and Vg5 are turned on in order, and the conversion elements C51 to C84 are read out. After that, the drive lines Vg1, Vg2, Vg3, and Vg4 of the first pixel array 200 are turned on in order, and the conversion elements C11 to the conversion elements C44 are read out.

The second pixel array 300 is read first because the second pixel array 300 reads out the remaining signals that cannot be completely absorbed by the first pixel array 200, so that the amount of signals is larger than that of the first pixel array 200. Is small. Therefore, it is necessary to shorten the accumulation time from the reset operation to the read operation in order to reduce the influence of the dark charge as much as possible.

In energy subtraction imaging, the signals of the first pixel array 200 and the second pixel array 300 are individually read out, and the read images are used to perform image processing of energy subtraction to separate or emphasize bone tissue and soft tissue. You can get the image.

Next, another operation example in the energy subtraction imaging of the radiation imaging system 100 will be described with reference to FIG. In the operation example of FIG. 7, the signal of the second pixel array 300 was read out first, but in FIG. 8, the signal of the second pixel array 300 and the signal of the first pixel array 200 are read out alternately. In the present embodiment, since the pixel centers of the second pixel array 300 and the first pixel array 200 are aligned, for example, the conversion element C14 and the conversion element C84 are spatially located close to each other. Therefore, when external noise is received, the reading operation is performed at a location close to each other in space and time, and the noise is read out as in-phase noise. If it is in-phase noise, it can be reduced by image processing of energy subtraction.

Next, another operation example in the energy subtraction imaging of the radiation imaging system 100 will be described with reference to FIG. In the operations of FIGS. 7 and 8, both the first pixel array 200 and the second pixel array 300 were turned on line by line from the drive line Vg1 to the drive line Vg8 to read the signal. Since the second pixel array 300 reads out the remaining signals that cannot be completely absorbed by the first pixel array 200, the signal amount is smaller than that of the first pixel array 200. Therefore, only in the second pixel array 300, the drive lines Vg8 / Vg7 and the drive lines Vg6 / Vg5 are turned on at the same time, signals for two lines are output to the signal line, and the signals are added and read out. Thereby, the S / N read from the second pixel array 300 can be improved. Further, the S / N can be increased by increasing the gain of the amplifier of the readout circuit and reading only when the second pixel array 300 is read out.

100 Radiation imaging system 110 Radiation imaging device 112 Control circuit 200 First pixel array 300 Second pixel array 201 Pixel 210 First drive circuit 310 Second drive circuit 220 Read circuit

Claims (9)

A first pixel array and a second pixel array in which a plurality of pixels for outputting an electric signal corresponding to incident radiation are arranged in a matrix, a first pixel included in the first pixel array, and the first pixel array. A flexible substrate having a signal line in which a second pixel included in a two-pixel array is commonly connected, and the first pixel and the second pixel are arranged so as to face each other. When,
The first drive circuit for driving the first pixel array and the first drive circuit so as to output the electric signal from the first pixel and the electric signal from the second pixel to the signal line in the same period. A control circuit that controls a second drive circuit that drives the two pixel arrays, and a control circuit that controls the second drive circuit.
Radiation imaging device with. The first aspect of claim 1 is that the amount of deviation between the center of gravity of the orthographic projection of the first pixel and the center of gravity of the orthographic projection of the second pixel from the side on which radiation is incident is within 0.5 pixels. The radiation imaging device described. The control circuit drives the first pixel array so that the electric signal from the first pixel and the electric signal from the second pixel are output to the signal line in another period. The radiation imaging apparatus according to claim 1 or 2, wherein the drive circuit of the above and the second pixel array can be driven. The first pixel and the second pixel each include a conversion element for converting radiation into an electric signal and a switch element for outputting the electric signal to the signal line.
The first drive circuit and the second drive circuit supply the electric signal from the first pixel and the second pixel by supplying an on signal for turning on the switch element to the switch element. The radiation imaging device according to any one of claims 1 to 3, wherein the first pixel array and the second pixel array are driven so as to output to the signal line. The switch element is a transistor having a control terminal and two main terminals.
One of the two main electrodes of the conversion element is electrically connected to one of the two main terminals, and the signal line is connected to the other of the two main terminals. The radiation imaging device according to claim 4, wherein the radiation imaging device is electrically connected. It further includes a read circuit electrically connected to the signal line.
In general photographing, the reading circuit obtains a signal obtained by adding an electric signal from the first pixel and an electric signal from the second pixel output to the signal line in the same period by the signal line. The radiation imaging apparatus according to any one of claims 1 to 5, characterized in that it is read out. The claim is characterized in that the read circuit is electrically connected to the signal line so that the distance to the second pixel in the signal line is closer than the distance to the first pixel. Item 6. The radiation imaging device according to item 6. The read circuit is characterized in that, in energy subtraction imaging, an electric signal output from the first pixel to the signal line and an electric signal from the second pixel to the signal line are individually read out in different periods. The radiation imaging apparatus according to claim 7. The radiation imaging apparatus according to any one of claims 1 to 8.
A computer that processes radiation image data from the radiation imaging device, and
A radiation imaging system characterized by including.

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