JP6934763B2 - Radiation imaging device and radiation imaging system - Google Patents

Description

The present invention relates to a radiation imaging device and a radiation imaging system.

As an imaging device used for medical image diagnosis and non-destructive inspection, a radiation imaging device including an imaging panel in which pixels combining a conversion element that converts radiation into electric charge and a switch element such as a thin film transistor (TFT) are arranged in an array. Widely used. A method of acquiring a plurality of radiation images using radiation having different energy components using such a radiation imaging device, and acquiring an energy subtraction image in which a specific subject portion is separated or emphasized from the difference between the acquired radiation images. It has been known. In Patent Document 1, scintillators are arranged on both sides of a light-transmitting substrate, and a photodiode that detects light emitted by a scintillator on one side and a photodiode that detects light emitted by a scintillator on the other side are arranged. It is shown to do. A photodiode that detects light emitted by different scintillators can acquire signals of two different energy components with a single irradiation of radiation, and can generate an energy subtraction image.

Japanese Unexamined Patent Publication No. 2010-56396

In Patent Document 1, since two photodiodes are used to generate one pixel data of a radiographic image, the element structure becomes complicated and the manufacturing cost may increase. Also, despite the arrangement of two scintillators, each photodiode detects only light from one scintillator. Therefore, when each photodiode is arranged in a plane as in the second embodiment of Patent Document 1, the detection quantum efficiency (DQE) is lowered and the S / N ratio of the obtained image is lowered. There is a possibility that it will end up.

An object of the present invention is to provide a technique capable of acquiring an energy subtraction image and suppressing deterioration of image quality.

In view of the above problems, in the radiation imaging apparatus according to the embodiment of the present invention, a plurality of conversion elements are arranged in a two-dimensional array on a substrate that transmits light, and the radiation imaging apparatus is arranged on the side of the first surface of the substrate. A radiation imaging device including a first scintillator and a second scintillator arranged on the side of the second surface of the substrate opposite to the first surface, wherein a plurality of conversion elements are present. A first conversion element and a plurality of second conversion elements are included, and the plurality of first conversion elements are arranged so as to receive light from the first scintillator and the second scintillator, and the plurality of second conversion elements are arranged so as to receive light. A light-shielding layer is arranged between the first scintillator and each of the plurality of second conversion elements so that the amount of light that can be received from the first scintillator is smaller than that of the first conversion element. The scintillator is arranged so as to receive the light from the second scintillator.

By the above means, a technique advantageous for improving the resolution of the scintillator and improving the luminance characteristics is provided.

The figure which shows the structural example of the radiation imaging system using the radiation imaging apparatus which concerns on embodiment of this invention. The figure which shows the structural example of the imaging panel of the radiation imaging apparatus of FIG. The figure which shows the structural example of the cross section of the pixel of the radiation imaging apparatus of FIG. The figure which shows the arrangement example of the pixel of the radiation imaging apparatus of FIG. The timing chart which shows the operation of the radiation imaging apparatus of FIG. The timing chart which shows the operation of the radiation imaging apparatus of FIG. The figure which shows the operation flow of the radiation imaging apparatus of FIG. The figure which shows the example of the pixel interpolation of the radiation image pickup apparatus of FIG.

Hereinafter, specific embodiments of the radiation imaging apparatus according to the present invention will be described with reference to the accompanying drawings. In the following description and drawings, common reference numerals are given to common configurations across a plurality of drawings. Therefore, a common configuration will be described with reference to each other of the plurality of drawings, and the description of the configuration with a common reference numeral will be omitted as appropriate. The radiation in the present invention includes beams having the same or higher energy, for example, X, in addition to α-rays, β-rays, γ-rays, etc., which are beams produced by particles (including photons) emitted by radiation decay. It can also include lines, particle rays, cosmic rays, etc.

The configuration and operation of the radiation imaging apparatus according to the embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIG. 1 is a diagram showing a configuration example of a radiation imaging system 200 using the radiation imaging device 210 according to the embodiment of the present invention. The radiation imaging system 200 is configured to electrically image an optical image converted from radiation and obtain an electrical signal (radiation image data) for generating a radiation image. The radiation imaging system 200 includes, for example, a radiation imaging device 210, a radiation source 230, an exposure control unit 220, and a computer 240.

The radiation source 230 starts emitting radiation in accordance with an exposure command (radiation command) from the exposure control unit 220. The radiation emitted from the radiation source 230 is applied to the radiation imaging device 210 through a rugged body (not shown). The radiation source 230 also stops the radiation of radiation in accordance with a stop command from the exposure control unit 220.

The radiation imaging device 210 includes an imaging panel 212 and a control unit 214 that controls the imaging panel 212. The control unit 214 generates a stop signal for stopping the radiation from the radiation source 230 based on the signal obtained from the image pickup panel 212. The stop signal is supplied to the exposure control unit 220, and the exposure control unit 220 sends a stop command to the radiation source 230 in response to the stop signal. The control unit 214 is, for example, a PLD (abbreviation for Programmable Logic Device) such as FPGA (abbreviation for Field Programmable Gate Array), or an ASIC (application specific specialized integrated circuit) or an abbreviation for an ASIC (application specific integrated circuit) integrated circuit. It may consist of a computer or a combination of all or part of these.

The computer 240 controls the radiation imaging device 210 and the exposure control unit 220. Further, the computer 240 includes a signal processing unit 241 that receives the radiation image data output from the radiation imaging device 210 and processes the radiation image data. The signal processing unit 241 can generate a radiographic image from the radiographic image data.

The exposure control unit 220 has an exposure switch (not shown) as an example, and when the exposure switch is turned on by the user, it sends an exposure command to the radiation source 230 and starts indicating the start of radiation emission. Send a notification to computer 240. Upon receiving the start notification, the computer 240 notifies the control unit 214 of the radiation imaging apparatus 210 of the start of radiation emission in response to the start notification.

FIG. 2 shows a configuration example of the imaging panel 212. The imaging panel 212 includes a pixel array 112. The pixel array 112 includes a plurality of pixel PIXs including conversion elements S arranged in a two-dimensional array for detecting radiation. Further, the pixel array 112 has a plurality of row signal lines Sign1 to Sigma4 along the row direction (vertical direction in FIG. 2) for outputting the signal generated by the conversion element S. Further, the image pickup panel 212 includes a drive circuit (row selection circuit) 114 for driving the pixel array 112, and a read circuit 113 for detecting a signal appearing in the column signal line Sigma of the pixel array 112. In the configuration shown in FIG. 2, for simplification of description, the pixel array 112 is composed of 4 rows × 4 columns of pixel PIXs, but in reality, more pixel PIXs may be arranged. In one example, the imaging panel 212 may have a size of 17 inches and a pixel PIX of about 3000 rows x about 3000 columns.

Each pixel PIX has a conversion element S for detecting radiation, a switch T for connecting the conversion element S and a column signal line Sigma (a signal line Sigma corresponding to the conversion element C among a plurality of signal line sigs). including. Each conversion element S outputs a signal corresponding to the amount of incident radiation to the column signal line Sigma. The conversion element S may be, for example, a MIS type photodiode which is arranged on an insulating substrate such as a glass substrate and whose main material is amorphous silicon. Further, the conversion element S may be a PIN type photodiode. In the present embodiment, the conversion element S can be configured as an indirect element that detects light after converting radiation into light with a scintillator. In an indirect device, the scintillator can be shared by a plurality of pixel PIXs (plurality of conversion elements S).

The switch T may be 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 S has two main electrodes, one main electrode of the conversion element S is connected to one of the two main terminals of the switch T, and the other main electrode of the conversion element S is common. It is connected to the bias power supply 103 via the bias wire Bs. The bias power supply 103 supplies the bias voltage Vs. The control terminal of the switch T of each pixel PIX arranged in the first row is connected to the gate line Vg1 arranged along the row direction (horizontal direction in FIG. 2). Similarly, the control terminals of the switch SW of each pixel PIX arranged in the second to fourth rows are connected to the gate lines Vg2 to Vg4, respectively. A gate signal is supplied to the gate lines Vg1 to Vg4 by the drive circuit 114.

In each pixel PIX arranged in the first row, the main terminal on the side not connected to the conversion element S of the switch T is connected to the row signal line Sigma1 in the first row. Similarly, in each pixel PIX arranged in the 2nd to 4th rows, the main terminal on the side not connected to the conversion element S of the switch T is connected to the row signal lines Sigma2 to Sigma4 in the 2nd to 4th rows, respectively. ..

The read circuit 113 has a plurality of column amplification units CA so that one column amplification unit CA corresponds to one column signal line Sigma. Each column amplification unit CA may include an integrator amplifier 105, a variable amplifier 104, a sample hold circuit 107, and a buffer circuit 106. The integrator amplifier 105 amplifies the signal appearing on the column signal line Sigma. The integrating amplifier 105 may include an operational amplifier and an integrated capacitance and reset switch connected in parallel between the inverting input and output terminals of the operational amplifier. A reference potential Vref is supplied to the non-inverting input terminal of the operational amplifier. By turning on the reset switch, the integrated capacitance is reset and the potential of the column signal line Sigma is reset to the reference potential Vref. The reset switch can be controlled by the reset pulse RC supplied from the control unit 214.

The variable amplifier 104 amplifies the signal output from the integrating amplifier 105 at a set amplification factor. The sample hold circuit 107 sample holds the signal output from the variable amplifier 104. The sample hold circuit 107 may be composed of a sampling switch and a sampling capacitance. The buffer circuit 106 buffers (impedance conversion) the signal output from the sample hold circuit 107 and outputs the signal. The sampling switch can be controlled by a sampling pulse supplied from the control unit 214.

Further, the read circuit 113 includes a multiplexer 108 that selects and outputs signals from a plurality of column amplification units CA provided so as to correspond to each column signal line Sigma in a predetermined order. The multiplexer 108 includes, for example, a shift register. The shift register performs a shift operation according to the clock signal CLK supplied from the control unit 214, and the shift register selects one signal from the plurality of column amplification units CA. The read circuit 113 further includes a buffer 109 that buffers (imperometrically converts) the signal output from the multiplexer 108, and an AD converter 110 that converts an analog signal, which is a signal output from the buffer 109, into a digital signal. sell. The output of the AD converter 110, that is, the radiographic image data, is transferred to the computer 240.

In the present embodiment, as will be described later, scintillators that convert radiation into visible light are provided on both the incident surface side for incident radiation on the substrate and the back surface on the side opposite to the incident surface. It is arranged so as to cover the surface of. Further, the conversion element S included in each pixel PIX includes two types of conversion elements S. In the configuration shown in FIG. 2, the conversion elements S12, S14, S21, S23, S32, S34, S41, and S43 are arranged so as to receive light from the two scintillators. Hereinafter, when these conversion elements that receive light from two scintillators of the conversion elements S are specified, they are referred to as the first conversion element 901. Further, in the conversion elements S11, S13, S22, S24, S31, S33, S42, and S44, a light shielding layer 903 is arranged between one scintillator and each of the conversion elements S. As a result, the conversion elements S11, S13, S22, S24, S31, S33, S42, and S44 are arranged so as to block the light from one scintillator and receive the light from the other scintillator. In the following, these conversion elements S will be referred to as a second conversion element 902 when the conversion elements in which the light from one of the scintillators of the conversion elements S is blocked are specified. The light-shielding layer 903 is a layer that blocks the light emitted by the scintillator, and may block light between either one of the scintillators covering the incident surface side or the back surface side of the substrate and the second conversion element 902. At this time, the light from one scintillator may not be completely blocked by the second conversion element 902. The scintillator covering either the incident surface side or the back surface side of the substrate and the second conversion element 902 so that the amount of light that can be received from one scintillator is smaller than that of the first conversion element 901. A light-shielding layer 903 may be arranged between them.

Here, it is assumed that the light-shielding layer 903 is arranged between the scintillator arranged on the incident surface side of the substrate and the second conversion element 902. Of the radiation incident from the incident surface side of the substrate, the low-energy component is absorbed by the scintillator covering the incident surface side of the substrate, converted into visible light, and incident on each pixel PIX. In the second conversion element 902, since the incident surface side of the substrate is shielded from light, the light emitted on the incident surface side of the substrate is not incident. Therefore, the light converted from the low energy component of the radiation does not enter the second conversion element 902. On the other hand, since the light-shielding layer 903 is not arranged in the first conversion element 901, the light converted from the component having low energy of radiation is incident.

Further, of the radiation, the high-energy component that is not absorbed by the scintillator arranged on the incident surface side of the substrate is absorbed by the scintillator covering the back surface side of the substrate and converted into visible light. In the first conversion element 901 and the second conversion element 902, the back surface side of the substrate is not shielded from light, so that the light converted from the high-energy component of the radiation is the first conversion element 901 and the second. It is incident on both of the conversion elements 902 of.

As described above, in the first conversion element 901, the signal caused by the high-energy component and the low-energy component of the radiation, and in the second conversion element 902, the signal caused by the high-energy component of the radiation. You can get each. That is, information on different radiation energies can be held by pixel PIXs adjacent to each other. By holding the information acquired from the radiations of different energy components in the adjacent pixel PIXs in this way, energy subtraction can be performed by using the method described later.

FIG. 3 schematically shows an example of a cross-sectional structure of a pixel PIXA having a first conversion element 901 and a pixel PIXB and a pixel PIXC having a second conversion element 902. Here, it is described that the radiation is incident from the upper side of the drawing, but the radiation may be incident from the lower side of the drawing. In FIG. 3A, the first conversion element 901 and the second conversion element 902 are arranged between the substrate 310 and the scintillator 904 arranged on the incident surface side of the substrate 310. Further, FIG. 3A shows a case where the light-shielding layer 903 is arranged between the second conversion element 902 and the scintillator 904 in the pixel PIXB. Further, in FIG. 3B, it is shown in FIG. 3A that the first conversion element 901 and the second conversion element 902 are arranged between the substrate 310 and the scintillator 904 that covers the incident surface side of the substrate 310. ) Is the same. On the other hand, in the configuration of FIG. 3B, in the pixel PIXC, the light-shielding layer 903 is arranged between the second conversion element 902 and the scintillator 905 arranged on the back surface side opposite to the incident surface of the substrate 310. Indicates the case where it is done.

The conversion element S of each pixel PIX is arranged on an insulating substrate 310 such as a glass substrate that transmits the light emitted by the scintillators 904 and 905. Each pixel PIX includes a conductive layer 311, an insulating layer 312, a semiconductor layer 313, an impurity semiconductor layer 314, and a conductive layer 315 on the substrate 310 in this order. The conductive layer 311 constitutes a gate electrode of a transistor (for example, a TFT) constituting the switch T. The insulating layer 312 is arranged so as to cover the conductive layer 311, and the semiconductor layer 313 is arranged on the portion of the conductive layer 311 constituting the gate electrode via the insulating layer 312. The impurity semiconductor layer 314 is arranged on the semiconductor layer 313 so as to form two main terminals (source and drain) of the transistor constituting the switch T. The conductive layer 315 constitutes a wiring pattern connected to each of the two main terminals (source and drain) of the transistors constituting the switch T. A part of the conductive layer 315 constitutes the column signal line Sigma, and the other part constitutes a wiring pattern for connecting the conversion element S and the switch T.

Each pixel PIX further includes an interlayer insulating film 316 that covers the insulating layer 312 and the conductive layer 315. The interlayer insulating film 316 is provided with a contact plug 317 for connecting to a portion of the conductive layer 315 that constitutes the switch T. Further, each pixel PIX includes a conversion element S arranged on the interlayer insulating film 316. In the example shown in FIG. 3, the conversion element S is configured as an indirect type conversion element that converts light converted from radiation by scintillators 904 and 905 into an electric signal. The conversion element S includes a conductive layer 318, an insulating layer 319, a semiconductor layer 320, an impurity semiconductor layer 321 and a conductive layer 322, and an electrode layer 325 laminated on the interlayer insulating film 316. A protective layer 323 and an adhesive layer 324 are arranged on the conversion element S. The scintillator 904 is arranged on the adhesive layer 324 so as to cover the incident surface side of the substrate 310. Further, the scintillator 905 is arranged so as to cover the back surface side of the substrate 310 opposite to the incident surface.

Each of the conductive layers 318 constitutes a lower electrode of the conversion element S. Further, the conductive layer 322 and the electrode layer 325 form an upper electrode of each conversion element S. The conductive layer 318, the insulating layer 319, the semiconductor layer 320, the impurity semiconductor layer 321 and the conductive layer 322 form a MIS type sensor as the conversion element S. For example, the impurity semiconductor layer 321 is formed of an n-type impurity semiconductor layer.

The scintillators 904 and 905 can be constructed using materials such as GOS (gadolinium acid sulfide) and CsI (cesium iodide). These materials can be formed by laminating, printing, vapor deposition, etc. The scintillator 904 and the scintillator 905 may use the same material, or different materials may be used depending on the energy of the radiation to be acquired.

In the present embodiment, the conversion element S shows an example in which a MIS type sensor is used, but the conversion element S is not limited thereto. The conversion element S may be, for example, a pn type or PIN type photodiode.

Next, the arrangement of the light-shielding layer 903 for blocking the light incident from the scintillator 904 or the scintillator 905, which is arranged on the second conversion element 902, will be described. In the configuration shown in FIG. 3A, the second conversion element 902 of the pixel PIXB comprises a conductive layer 318, a semiconductor layer 320, and an upper electrode forming a lower electrode from the incident surface side of the substrate 310 toward the scintillator 904. The constituent conductive layer 322 is included in this order. The conductive layer 322 constituting the upper electrode functions as a light-shielding layer 903. Specifically, the conductive layer 322 functions as a light-shielding layer 903 by forming the conductive layer 322 with a material such as Al, Mo, Cr, or Cu that is opaque to the light emitted by the scintillator 904. That is, the second conversion element 902 of the pixel PIXB has a light-shielding layer between the scintillator 904 and the second conversion element 902 so that the amount of light that can be received from the scintillator 904 is smaller than that of the first conversion element 901. 903 is arranged. Further, the second conversion element 902 of the pixel PIXB is arranged so as to receive the light from the scintillator 905, similarly to the first conversion element 901 of the pixel PIXA. Further, in the configuration shown in FIG. 3B, the second conversion element 902 of the pixel PIXC includes the conductive layer 318, the semiconductor layer 320, and the upper portion forming the lower electrode from the incident surface side of the substrate 310 toward the scintillator 904. The conductive layer 322 and the electrode layer 325 constituting the electrode are included in this order. The conductive layer 318 constituting the lower electrode functions as a light-shielding layer 903. Specifically, by forming the conductive layer 318 with a material that is opaque to the light emitted by the scintillator 905, such as Al, Mo, Cr, and Cu, the conductive layer 322 functions as the light-shielding layer 903. That is, the second conversion element 902 of the pixel PIXC has a light-shielding layer between the scintillator 905 and the second conversion element 902 so that the amount of light that can be received from the scintillator 905 is smaller than that of the first conversion element 901. 903 is arranged. Further, the second conversion element 902 of the pixel PIXC is arranged so as to receive the light from the scintillator 904, similarly to the first conversion element 901 of the pixel PIXA.

On the other hand, in the first conversion element 901 of the pixel PIXA, a material transparent to the light emitted by the scintillator 904, such as ITO (indium tin oxide), is used for the conductive layer 318 and the electrode layer 325. Thereby, signals having different energy components can be acquired between the adjacent pixel PIXA and the pixel PIXB or the pixel PIXC.

Further, in the present embodiment, an example in which the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC have a single-layer structure is shown, but the present invention is not limited to this. For example, in the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC, a transparent material and an opaque material may be laminated, and in that case, the amount of light shielding is determined by the area of the opaque material. Further, in the present embodiment, the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC are made to function as the light-shielding layer 903, but the arrangement of the light-shielding layer 903 is not limited to this. For example, in the pixel PIXB, a dedicated light-shielding layer 903 using Al, Mo, Cr, Cu, or the like may be arranged in the protective layer 323 with respect to the light incident from the scintillator 904. In this case, the potential of the light-shielding layer 903 may be fixed at a constant potential for use.

Further, when the light from the scintillator 905 is blocked as in the pixel PIXC shown in FIG. 3B, the positions of the switch T of the pixel PIXA and the column signal line Sigma that receive the light from the scintillator 905 are set on the side of the pixel PIXC. You may arrange it close to. With such an arrangement, in the pixel PIXA, the opening ratio of the first conversion element 901 to the scintillator 905 can be increased.

Further, the light-shielding layer 903 does not need to completely block the light from the scintillator 904 or the scintillator 905 to the second conversion element 902 as described above. Energy subtraction is possible if the amount of light received from the scintillator 904 or the scintillator 905 on the side where the light-shielding layer 903 is arranged differs between the adjacent pixel PIXA and the pixel PIXB or the pixel PIXC. In such a case, it is investigated in advance what percentage of the light received by the first conversion element 901 of the pixel PIXA is incident on the second conversion element 902 of the pixel PIXB or the pixel PIXC. It can be corrected by performing difference processing with reference to the output of the first conversion element 901.

As shown in FIG. 3, in the orthogonal projection of the substrate 310 on the incident surface, each of the column signal lines Sigma is arranged so as to overlap a part of the pixel PIX. Such a configuration is advantageous in that the area of the conversion element S of each pixel PIX is increased, but is disadvantageous in that the capacitive coupling between the column signal line Sigma and the conversion element S is large. be. When radiation is incident on the conversion element S, electric charges are accumulated in the conversion element S, and the potential of the conductive layer 318, which is the lower electrode, changes, the column signal line Sigma is capacitively coupled between the column signal line Sigma and the conversion element S. Crosstalk occurs in which the potential of the is changed. FIGS. 4A and 4B show a method of dealing with this crosstalk. In the conversion elements S arranged in the row direction intersecting the column direction among the plurality of conversion elements S, the number of pixels PIX having the second conversion element 902 on which the included light-shielding layer 903 is arranged is the same for each row. Arrange as follows. Further, in the conversion elements S arranged in the column direction among the plurality of conversion elements S, the number of pixels PIX having the plurality of second conversion elements 902 included is the same for each row. By arranging in this way, it is possible to suppress the occurrence of artifacts due to crosstalk in row and column units.

Further, the radiation imaging device 210 may have a function of automatically detecting the start of irradiation of radiation. In this case, for example, the gate wire Vg is operated so that the switch T is turned on / off, the signal from the conversion element S is read out, and the presence or absence of radiation irradiation is determined from the output signal. When the number of pixels PIX having the second conversion element 902 including the light-shielding layer 903 is different for each row, the amount of signals output for each row changes, and the detection accuracy varies. Therefore, as shown in FIGS. 4A and 4B, in the conversion elements S arranged in the row direction intersecting the column direction among the plurality of conversion elements S, the included light-shielding layer 903 is arranged in the second conversion element S. The number of pixels PIX having the conversion element 902 is arranged to be the same for each row. With such an arrangement, the detection accuracy of automatically detecting the start of radiation irradiation is stabilized.

Further, in the arrangement example of the pixel PIX of FIG. 4B, the density of the pixel PIX having the second conversion element 902 is reduced as compared with the arrangement example of the pixel PIX of FIG. 4A. Since the light from the scintillator 905 is incident on the conversion element S via the substrate 310, the light is diffused depending on the thickness of the substrate 310, and the MTF (Modulation Transfer Function) is lowered. Therefore, even if the density of the pixel PIX having the second conversion element 902 is reduced, the resolution does not substantially decrease. That is, when the second conversion element 902 receives the light emitted by the scintillators 905 facing each other via the substrate 310 among the two scintillators, the number of pixels PIX including the first conversion element 901 is larger than the number of pixels PIX. The number of pixel PIXs including the conversion element 902 may be smaller.

Further, in order to suppress the diffusion of light from the scintillator 905 through the substrate 310 and reduce the decrease in MTF, the thickness of the substrate 310 may be reduced by mechanical polishing or chemical polishing. Further, in order to reduce the decrease in MTF, as shown in FIG. 3, between the scintillator 905 and the substrate 310, a scattering prevention layer such as a louver layer or a microlens that imparts directivity to the light emitted by the scintillator. 326 may be provided. Further, in order to reduce the decrease in MTF, the resolution may be increased by sharpening processing in the image processing in the signal processing unit 241 of the computer 240. Further, as a method of combining the MTF of the low energy component due to the light from the scintillator 904 and the high energy component due to the light from the scintillator 905, in addition to increasing the resolution, the MTF is decreased by adjusting the higher resolution to the lower resolution. Let me. After that, energy subtraction processing may be performed.

Next, the operation of the radiation imaging device 210 and the radiation imaging system 200 will be described with reference to FIG. Here, the operation of the radiation image pickup apparatus 210 having the image pickup panel 212 including the pixel PIX of 4 rows and 4 columns each including the conversion element S, which is shown in FIG. 2, will be described as an example. The operation of the radiation imaging system 200 is controlled by the computer 240. The operation of the radiation imaging device 210 is controlled by the control unit 214 under the control of the computer 240.

First, the control unit 214 causes the drive circuit 114 and the read circuit 113 to perform blank reading until the radiation from the radiation source 230, in other words, the radiation to the radiation imaging device 210 is started. In the blank reading, the drive circuit 114 drives the gate signals supplied to the gate lines Vg1 to Vg4 in each row of the pixel array 112 to the active level in order, and resets the dark charge accumulated in the conversion element S. be. Here, at the time of blank reading, an active level reset pulse is supplied to the reset switch of the integrating amplifier 105, and the column signal line Sigma is reset to the reference potential. The dark charge is a charge generated even though no radiation is incident on the conversion element S.

The control unit 214 can recognize the start of radiation from the radiation source 230, for example, based on the start notification supplied from the exposure control unit 220 via the computer 240. Further, as shown in FIG. 1, the radiation imaging apparatus 210 may be provided with a detection circuit 216 for detecting a current flowing through a bias line Bs or a column signal line Sigma of the pixel array 112. The control unit 214 can recognize the start of irradiation of radiation from the radiation source 230 based on the output of the detection circuit 216.

When the radiation is applied, the control unit 214 controls the switch T in an open state (off state). As a result, the electric charge generated in the conversion element S due to the irradiation of radiation is accumulated. The control unit 214 stands by in this state until the irradiation of radiation is completed.

Next, the control unit 214 causes the drive circuit 114 and the read circuit 113 to execute the main reading. In this reading, the drive circuit 114 drives the gate signals supplied to the gate lines Vg1 to Vg4 in each row of the pixel array 112 to the active level. Then, the reading circuit 113 reads out the electric charge stored in the conversion element S via the column signal line Sigma, and outputs it to the computer 240 as radiographic image data through the multiplexer 108, the buffer 109, and the AD converter 110.

Next, acquisition of offset image data will be described. The conversion element S continues to accumulate dark charges even when it is not irradiated with radiation. Therefore, the control unit 214 acquires the offset image data by performing the same operation as when acquiring the radiation image data without irradiating the radiation. By subtracting the offset image data from the radiation image data, the offset component due to the dark charge can be removed.

Next, the drive for capturing a moving image will be described with reference to FIG. When capturing a moving image, a plurality of gate lines Vg are driven to an active level at the same time in order to read them at high speed. At this time, if the signal of the pixel PIX having the first conversion element 901 and the pixel PIX having the second conversion element 902 is output to one column signal wiring Sigma, the energy component cannot be separated. Therefore, as shown in FIG. 6, by simultaneously setting the gate signals supplied to the gate line Vg1 and the gate line Vg3 to the active level, the signals of the conversion element S12 and the conversion element S32, which are the first conversion elements 901, are set. Is output to the column signal line Sigma2. At the same time, the signals of the conversion element S11 and the conversion element S31, which are the second conversion elements 902, are output to the column signal line Sig1. Energy subtraction processing can be performed by outputting the signals of the first conversion element 901 and the second conversion element 902 to different column signal lines Sigma.

Next, the image processing flow in this embodiment will be described with reference to FIG. 7. First, in step S910, the control unit 214 controls to accumulate the electric charge generated by the conversion element S during irradiation of radiation in order to acquire the radiation image data after performing the above-mentioned blank reading. Next, in step S911, the control unit 214 causes the drive circuit 114 and the read circuit 113 to perform the main reading, and reads out the radiographic image data. In step S911, the radiographic image data is output to the computer 240. Next, the control unit 214 performs a storage operation for acquiring the offset image data in step S912, and in step 913, causes the drive circuit 114 and the read circuit 113 to read the offset image data, and causes the computer 240 to output the offset image data.

Next, the signal processing unit 241 of the computer 240 performs offset correction by subtracting the radiation image data acquired in step S911 with the offset image data acquired in step S913. Next, in step S915, the signal processing unit 241 uses the radiation image data after offset correction as the radiation image data output from the first conversion element 901 and the radiation image data output from the second conversion element 902. Separate into. Here, in the configuration of FIG. 3A, the second conversion element 902 receives radiation from above in the figure, blocks light from the scintillator 904, and emits light generated by high-energy radiation from the scintillator 905. Will be described as receiving light. Further, the radiation image data output from the first conversion element 901 is referred to as double-sided image data, and the radiation image data output from the second conversion element 902 is referred to as single-sided image data.

Next, in step S916, the signal processing unit 241 performs gain correction of the double-sided image data using the gain correction image data taken in the absence of a subject. Further, in step S917, the signal processing unit 241 corrects the gain of the double-sided image data by using the image data for gain correction.

After performing the gain correction, the signal processing unit 241 compensates for the lack of double-sided image data of the pixel PIX not including the first conversion element 901, in other words, the pixel PIX having the second conversion element 902 in step S918. Pixel interpolation of. Similarly, in step S919, the signal processing unit 241 performs pixel interpolation for compensating for the lack of single-sided image data of the pixel PIX that does not include the second conversion element 902, in other words, the pixel PIX that has the first conversion element 901. .. The pixel interpolation in steps S918 and S919 will be described with reference to FIG. Here, an arrangement in which the number of pixel PIXs including the first conversion element 901 shown in FIG. 4B is larger than the number of pixel PIXs including the second conversion element 902 will be described as an example.

First, pixel interpolation of double-sided image data will be described with reference to FIG. 8A. The double-sided image data of the pixel E having the second conversion element 902 for outputting the single-sided image data is the pixels A, B, C, D having the first conversion element 901 for outputting the double-sided image data adjacent to the pixel E. Interpolation is performed using double-sided image data of F, G, H, and I. For example, the signal processing unit 241 may interpolate the double-sided image data of the pixel E by using the average value of the double-sided image data of eight pixels adjacent to the pixel E. Further, for example, the signal processing unit 241 may interpolate the double-sided image data of the pixel E by using the average value of the double-sided image data of some adjacent pixels, such as the pixels B, D, F, and H. .. By performing pixel interpolation in step S918, radiation image data generated by the high-energy component and the low-energy component of the radiation of each pixel PIX is generated.

Next, pixel interpolation of single-sided image data will be described with reference to FIG. 8B. The single-sided image data of the pixel J having the first conversion element 901 that outputs the double-sided image data is the pixels K, L, M, N having the second conversion element 902 that outputs the single-sided image data adjacent to the pixel J. Interpolate using single-sided image data. For example, the signal processing unit 241 may interpolate the single-sided image data of the pixel J by using the average value of the single-sided image data of four pixels adjacent to the pixel J. In this case, for example, the distance from the position where the pixel J is arranged to the pixel K and the distance to the pixel N are different. Therefore, the single-sided image data output from the pixels K, L, M, and N may be weighted and averaged according to the distance. By performing pixel interpolation in step S919, radiation image data generated by the high energy component of the radiation of each pixel PIX is generated.

Next, in step S920, the signal processing unit 241 generates radiographic image data based on the low energy component of radiation. As described above, when the light-shielding layer 903 is provided on the side where the radiation of the second conversion element 902 is incident, the single-sided image data becomes the radiation image data due to the high energy component. Further, the double-sided image data is radiation image data having both high-energy and low-energy components. Therefore, it is possible to generate low-energy component radiographic image data by subtracting the pixel-stored single-sided image data from the pixel-interpolated double-sided image data.

Further, when the light-shielding layer 903 is provided on the side opposite to the side on which the radiation of the second conversion element 902 is incident, the single-sided image data becomes the radiation image data due to the low energy component. Therefore, it is possible to generate high-energy component radiographic image data by subtracting the pixel-stored single-sided image data from the pixel-interpolated double-sided image data. However, the amount of light from the scintillator 905 is less than the amount of light from the scintillator 904 because the radiation image with the high energy component is a component of radiation that cannot be completely absorbed by the scintillator 904 on the side where the radiation is incident. Therefore, when the single-sided image data is subtracted from the double-sided image data to generate the high-energy component radiation image data, the noise of the low-energy component radiation image data is added to the high-energy component radiation image data. As a result, the S / N ratio of the radiographic image data of the high energy component becomes low. Therefore, as shown in the present embodiment described above, the side where the radiation of the second conversion element 902 is incident is shielded, the double-sided image data is an image of a high energy component + a low energy component, and the single-sided image data is an image of a high energy component. Let it be data. Then, the S / N ratio can be improved by subtracting the single-sided image data from the double-sided image data to generate a low-energy image.

The signal processing unit 241 generates an energy subtraction image in step S922. Specifically, the difference between the signal output from each of the first conversion elements 901 acquired in the signal processing unit 241 step S920 and the signal output from each of the second conversion elements 902, and the second conversion. The difference between the signal output from each of the elements 902 and the signal is taken. As a result, an energy subtraction image, which is the difference between the radiation image data of the high energy component and the radiation image data of the low energy component, is generated.

Further, the signal processing unit 241 may generate a normal radiation image without energy subtraction in step S920 based on the double-sided image data output from the first conversion element 901 in step S918. The first conversion element 901 receives the light from the scintillator 904 on the side where the radiation is incident and the light from the scintillator 905 on the side opposite to the side where the radiation is incident. As a result, a higher S / N ratio can be obtained in a normal radiographic image than in the case of receiving only the light emitted by one scintillator.

Here, in order to generate one pixel data of a radiation image as shown in Patent Document 1, only the light of the scintillator on the side opposite to the conversion element that receives only the light of the scintillator on the side where the radiation is incident is received. Consider a radiation imaging device that arranges two conversion elements with a conversion element. An energy subtraction image can be generated by taking the difference between the two signals output from the two conversion elements, and a normal radiation image can be generated by adding the two signals. However, since two conversion elements are required to generate one pixel data, the structure may become complicated and the manufacturing cost may increase. In addition, the size of each conversion element may become smaller, and the S / N ratio of the obtained signal may decrease. Further, when generating a normal radiographic image, when adding two signals, noise superimposed on each signal is also added, so that the S / N ratio may be lowered. On the other hand, in the present embodiment, the light-shielding layer 903 for blocking the light from the scintillator 904 or the scintillator 905 is arranged only in a part of the pixel PIXs including the second conversion element 902 among the plurality of pixel PIXs. .. That is, since it is only necessary to add the light-shielding layer 903 to a part of the pixel PIX, it is possible to realize a radiation imaging device capable of acquiring an energy subtraction image while suppressing the manufacturing cost without complicating the structure. Further, since the first conversion element 901 receives the light emitted from the scintillator 904 and the scintillator 905, the sensitivity to the incident radiation is improved, and as a result, the image quality of the obtained radiation image can be improved. Further, even when generating a normal radiation image, a radiation image is generated from a signal generated by receiving the light emitted by the two scintillators 904 and 905. Therefore, as compared with the structure as in Patent Document 1, the S / N ratio when a normal radiographic image is taken is improved.

Further, in the present embodiment, one imaging panel 212 can be used to record a radiation image of radiation of two different energy components by irradiating a subject with one radiation (one-shot method). Therefore, as compared with the radiation imaging device that generates an energy subtraction image using two imaging panels, the number of parts of the radiation imaging device is reduced, and the manufacturing cost can be reduced. Further, since the weight of the radiation imaging device 210 can be reduced, it is possible to realize a radiation imaging device that is easy to use for a portable user. Further, since the energy subtraction image is generated by one imaging panel, it is possible to realize a radiation imaging apparatus in which the problem of positional deviation between the conversion elements between the two imaging panels does not occur. Further, it is possible to realize a radiation imaging device capable of generating a radiation image having a high S / N ratio in generating not only an energy subtraction image but also a normal radiation image.

Although the embodiments according to the present invention have been described above, it goes without saying that the present invention is not limited to these embodiments, and the above-described embodiments may be appropriately modified or combined without departing from the gist of the present invention. It is possible.

210: Radiation imaging device, 310: Substrate, 901: First conversion element, 902: Second conversion element, 903: Light-shielding layer, 904,905: Scintillator

Claims (16)

A substrate on which a plurality of conversion elements are arranged in a two-dimensional array for transmitting light, a first scintillator arranged on the side of the first surface of the substrate, and the first surface of the substrate A radiographic imaging device that includes a second scintillator located on the opposite side of the second surface.
The plurality of conversion elements include a plurality of first conversion elements and a plurality of second conversion elements.
The plurality of first conversion elements are arranged so as to receive light from the first scintillator and the second scintillator.
The plurality of second conversion elements include the first scintillator and the plurality of second conversion elements so that the amount of light that can be received from the first scintillator is smaller than that of the first conversion element. A radiation imaging device characterized in that a light-shielding layer is arranged between each of them and is arranged so as to receive light from the second scintillator. The radiation imaging apparatus according to claim 1, wherein the plurality of conversion elements are arranged between the first surface and the first scintillator. The plurality of conversion elements include a first electrode, a semiconductor layer, and a second electrode in this order from the side of the first surface toward the first scintillator.
The radiation imaging apparatus according to claim 2, wherein the second electrode functions as the light-shielding layer in the plurality of second conversion elements. The radiation imaging apparatus according to claim 2 or 3, wherein an anti-scattering layer is arranged between the second scintillator and the second surface. The radiation imaging apparatus according to claim 1, wherein the plurality of conversion elements are arranged between the second surface and the second scintillator. The plurality of conversion elements include a first electrode, a semiconductor layer, and a second electrode in this order from the side of the second surface toward the second scintillator.
The radiation imaging apparatus according to claim 5, wherein the first electrode functions as the light-shielding layer in the plurality of second conversion elements. The radiation imaging apparatus according to any one of claims 1 to 6, wherein radiation is incident from the side of the first surface. The radiation imaging apparatus according to any one of claims 1 to 6, wherein radiation is incident from the side of the second surface. The radiation imaging apparatus further includes a plurality of signal lines along the column direction for outputting signals generated by the plurality of conversion elements.
The first to eighth aspects of the plurality of conversion elements, wherein the number of the plurality of second conversion elements included in the conversion elements arranged in the row direction intersecting the column direction is the same for each row. The radiation imaging device according to any one item. The radiation imaging device according to claim 9, wherein the number of the plurality of second conversion elements included in the conversion elements arranged in the row direction among the plurality of conversion elements is the same for each row. The radiation imaging apparatus further includes a plurality of signal lines along the column direction for outputting signals generated by the plurality of conversion elements.
The method according to any one of claims 1 to 8, wherein the number of the plurality of second conversion elements included in the conversion elements arranged in the column direction among the plurality of conversion elements is the same for each column. The radiation imaging device described. The radiation imaging apparatus according to any one of claims 1 to 11, wherein the number of the plurality of second conversion elements is smaller than the number of the plurality of first conversion elements. The radiation imaging apparatus according to any one of claims 1 to 12.
A radiation imaging system including a signal processing unit that processes a signal from the radiation imaging device. The signal processing unit generates an energy subtraction image based on the signal output from each of the plurality of first conversion elements and the signal output from each of the plurality of second conversion elements. The radiation imaging system according to claim 13. The signal processing unit has a difference between a signal output from each of the plurality of first conversion elements and a signal output from each of the plurality of second conversion elements, and each of the second conversion elements. The radiation imaging system according to claim 13 or 14, wherein an energy subtraction image is generated based on a difference between the signal output from the signal and the signal output from the signal. The radiation imaging system according to claim 13, wherein the signal processing unit generates a normal radiation image based on signals output from each of the plurality of first conversion elements.

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