JP4447943B2 - Radiation imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to a radiation imaging apparatus suitable for an X-ray imaging apparatus and a control method thereof.

  Conventionally, an X-ray imaging system installed in a hospital or the like has a film imaging system in which a patient is irradiated with X-rays and X-rays transmitted through the patient are exposed on a film, and X-rays transmitted through the patient are converted into electrical signals. There is an image processing system that performs digital image processing after conversion.

  One of the image processing methods is a radiation imaging apparatus including a phosphor that converts X-rays into visible light and a photoelectric conversion device that converts visible light into electric signals. X-rays transmitted through the patient are irradiated onto the phosphor, and the in-vivo information of the patient converted into visible light there is output as an electrical signal by the photoelectric conversion device. If converted into an electric signal, it is converted into an digital signal by an AD converter, and X-ray image information for recording, display, printing, diagnosis, etc. can be handled as a digital value.

  Recently, a radiation imaging apparatus using an amorphous silicon semiconductor thin film for a photoelectric conversion device has been put into practical use.

  FIG. 12 is a top view of a conventional photoelectric conversion substrate configured by using an amorphous silicon semiconductor thin film as a material for the MIS type photoelectric conversion element and the switch element, and also includes wirings for connecting them. 13 is a cross-sectional view taken along the line II in FIG. In the following description, for the sake of simplicity, the MIS photoelectric conversion element is simply referred to as a photoelectric conversion element.

  The photoelectric conversion element 101 and the switch element 102 (amorphous silicon TFT, hereinafter simply referred to as TFT) are formed on the same substrate 103, and the lower electrode of the photoelectric conversion element is the same as the lower electrode (gate electrode) of the TFT. The upper electrode of the photoelectric conversion element is shared by the same second metal thin film layer 105 as the upper electrode (source electrode, drain electrode) of the TFT. The first and second metal thin film layers also share the gate driving wiring 106 and the matrix signal wiring 107 in the photoelectric conversion circuit section. In FIG. 12, a total of 4 pixels of 2 × 2 is described as the number of pixels. The hatched portion in FIG. 12 is a light receiving surface of the photoelectric conversion element. Reference numeral 109 denotes a power supply line for applying a bias to the photoelectric conversion element. Reference numeral 110 denotes a contact hole for connecting the photoelectric conversion element and the TFT.

  If the structure as shown in FIG. 12 using an amorphous silicon semiconductor as a main material is used, a photoelectric conversion element, a switch element, a gate driving wiring, and a matrix signal wiring can be simultaneously manufactured on the same substrate, and a large area This photoelectric conversion circuit portion can be provided easily and inexpensively.

  Next, device operation of a single photoelectric conversion element will be described. 14A to 14C are energy band diagrams for explaining the device operation of the photoelectric conversion element shown in FIGS. 12 and 13. This photoelectric conversion element has two types of operation modes, a refresh mode and a photoelectric conversion mode, depending on how the voltage is applied to the first and second metal thin film layers 104 and 105.

FIGS. 14A and 14B show the operation in the refresh mode and the photoelectric conversion mode, respectively, and show the state in the film thickness direction of each layer shown in FIG. M1 is a lower electrode (G electrode) formed of the first metal thin film layer 104 (for example, Cr). The amorphous silicon nitride (a-SiNx) layer 111 is an insulating layer that blocks the passage of both electrons and holes. The amorphous silicon nitride (a-SiNx) layer 111 needs to have a thickness that does not cause a tunnel effect, and is usually set to 500 angstroms or more. The hydrogenated amorphous silicon (a-Si: H) layer 112 is a photoelectric conversion semiconductor layer formed of an intrinsic semiconductor layer (i layer) that is not intentionally doped with a dopant. The N ⁺ layer 113 prevents injection of a single conductivity type carrier made of a non-single-crystal semiconductor such as an N-type a-Si: H layer formed to prevent injection of holes into the a-Si: H layer 112. Is a layer. M2 is an upper electrode (D electrode) formed of the second metal thin film layer 105 (for example, Al).

In Figure 12, the D electrode is not completely cover the N ⁺ layer, the D electrode and the N ⁺ layer for between the the electron transfer is freely performed between the D electrode and the N ⁺ layer is always at the same potential The following explanation assumes that.

In FIG. 14A showing the refresh mode, the D electrode is given a negative potential with respect to the G electrode, and the hole indicated by the black circle (●) in the i layer (a-Si: H) is an electric field. To the D electrode. At the same time, electrons indicated by white circles (◯) are injected into the i layer. At this time, some holes and electrons recombine with each other in the N ⁺ layer or i layer and disappear. If this state continues for a sufficiently long time, the holes in the i layer are swept out of the i layer.

In FIG. 14B showing the photoelectric conversion mode from this state, a positive potential is applied to the D electrode with respect to the G electrode. Then, the electrons in the i layer are instantaneously guided to the D electrode. However, since the N ⁺ layer functions as an injection blocking layer, holes are not guided to the i layer. When light enters the i layer in this state, the light is absorbed in the i layer and electron-hole pairs are generated. Electrons are guided to the D electrode by an electric field, while holes move in the i layer and reach the interface between the i layer and the a-SiNx insulating layer. At this time, since the hole cannot move into the a-SiNx insulating layer, it remains in the i layer. Thus, electrons move to the D electrode and holes move to the interface with the insulating layer in the i layer, so that a current flows from the G electrode in order to maintain electrical neutrality in the photoelectric conversion element. Since the magnitude of this current corresponds to the electron-hole pair generated by the incidence of light, it is proportional to the amount of incident light.

  Then, after the state of FIG. 14B in the photoelectric conversion mode is maintained for a certain period and then in the state of FIG. 14A in the refresh mode again, the holes remaining in the i layer are D as described above. At the same time, a current corresponding to this hole flows. The amount of holes corresponds to the total amount of light incident during the photoelectric conversion mode. At this time, a current corresponding to the amount of electrons injected into the i layer also flows, but since this amount is approximately constant, it may be detected by subtracting. That is, this photoelectric conversion element outputs the amount of light incident in real time, and at the same time can detect the total amount of light incident during a certain period.

  However, when the period of the photoelectric conversion mode becomes longer for some reason or when the illuminance of incident light is strong, current may not flow even though light is incident. This is because, as shown in FIG. 14C, a large number of holes remain in the i layer during the photoelectric conversion mode, and the electric field in the i layer decreases due to the holes, and the generated electrons are not guided to the D electrode. This is because they recombine with holes in the i layer. This state is called a saturated state of the photoelectric conversion element. If the light incident state changes in this state, the current may flow in an unstable manner. However, if the refresh mode is set again, the holes in the i layer are swept away and the current proportional to the light is again used in the next photoelectric conversion mode. Flows.

  In X-ray imaging using such a conventional radiation imaging apparatus, first, the photoelectric conversion element is set to the refresh mode to perform a refresh operation, and then the photoelectric conversion element is set to the photoelectric conversion mode and X-rays are irradiated. Then, a single still image is acquired by performing a read operation. In order to acquire continuous moving images, these series of processes may be repeated for the number of moving images to be acquired.

  Here, a method for capturing a moving image will be described. FIG. 15 is a time chart showing the operation during moving image shooting.

  First, a refresh operation R1 is performed before photographing to sweep out hole carriers in the i layer so that photoelectric conversion can be performed. Next, X-rays are irradiated in pulses. Here, as an example, the pulse is irradiated four times. X1 indicates the first pulse irradiation, X2 indicates the second time, X3 indicates the third time, and X4 indicates the fourth time. Further, after the X-ray irradiation, a reading operation and A / D conversion are performed. Here, the read operation indicates a read operation by resetting a photoelectric conversion element, turning on a switch element, sample-holding image data, and transferring image data. F1 indicates readout and A / D conversion after the first X-ray irradiation X1, F2 indicates readout readout and A / D conversion after the second X-ray irradiation X2, and F3 indicates the third X-ray irradiation. Corresponding to the irradiation X3, F4 corresponds to the fourth X-ray irradiation X4. That is, in the example shown in FIG. 15, a total of four cycles of X-ray irradiation, readout, and A / D conversion are repeated.

  After the read operation and A / D conversion, image data write operation to the memory and image processing operations F1 'to F4' such as offset correction are performed, and then the image is displayed on the display (displays D1 to D4).

  With regard to such a series of operations, in a moving image shooting using a conventional MIS type photoelectric conversion element, a refresh operation is always performed once every several to several tens of frames. For example, in the conventional example shown in FIG. 15, a refresh operation is performed once every four frames. That is, first, a refresh operation (R1) is performed, X-ray irradiation (X1 to X4) is performed four times, and a refresh operation (R2) is performed once again. The refresh operation is performed in this way because the i-layer of the photoelectric conversion element is filled with the X-ray irradiation four times and the photoelectric conversion cannot be performed. By performing the refresh operation, the photoelectric conversion is performed. The carriers in the i layer of the element are swept out.

  However, when the refresh operation is performed, X-ray irradiation cannot be performed during that period, and thus display cannot be performed for this period. For example, in the conventional example shown in FIG. 15, the image is interrupted between the display D4 and the display D5. As a result, when a conventional radiation imaging apparatus including a MIS type photoelectric conversion element is used, continuous moving image shooting cannot be performed all the time, and flickering does not occur on the screen when a moving image is displayed on the display. May be difficult to diagnose.

JP 2002-305687 A

  An object of the present invention is to provide a radiation imaging apparatus capable of reducing flicker when displaying a moving image on a display device, and a control method thereof.

  As a result of intensive studies to solve the above problems, the present inventor has come up with various aspects of the invention described below.

The radiation imaging apparatus according to the present invention includes a photoelectric conversion element array in which a plurality of pixels including photoelectric conversion elements and switch elements are arranged in an array on a substrate, and detection for detecting a signal output from the photoelectric conversion element array Means and an output means for outputting the signal output from the detection means to a display device, the output means outputs the signal continuously, and the carrier remaining in the photoelectric conversion element As a result of performing a refresh operation for sweeping out, in a period in which no signal is output from the detection means, an interpolation signal is output, and when the interpolation signal is output to the display device, the display The apparatus is characterized in that marking is performed .

  A radiation imaging system according to the present invention includes a radiation source that irradiates a subject with radiation, the radiation imaging device that detects radiation transmitted through the subject, and an image with respect to a signal output from the radiation imaging device. The image processing means for performing processing, and display means for displaying the image data processed by the image processing means.

The radiation imaging apparatus control method according to the present invention includes a photoelectric conversion element array in which a plurality of pixels including a photoelectric conversion element and a switch element are arranged in an array on a substrate, and a signal output from the photoelectric conversion element array. And detecting means for detecting the radiation imaging apparatus, wherein the signal output from the detection means is continuously output to the display device, and the carrier remaining on the photoelectric conversion element is swept out. As a result of performing a refresh operation for this purpose, during a period when no signal is output from the detection means, an interpolation signal is output, and the interpolation signal is output to the display device. It is characterized in that the marking is performed .

A program according to the present invention includes a photoelectric conversion element array in which a plurality of pixels including a photoelectric conversion element and a switch element are arranged in an array on a substrate, and a detection unit that detects a signal output from the photoelectric conversion element array. , A program for causing a computer to control the radiation imaging apparatus, which continuously outputs a signal output from the detection means to the display device to the computer and remains on the photoelectric conversion element As a result of performing a refresh operation for sweeping out the signal, a process for outputting an interpolation signal is performed in a period in which no signal is output from the detection means, and the interpolation signal is output to the display device. Upon that, it characterized Rukoto to perform the marking on the display device.

  According to the present invention, since an interpolation signal is output even during a period when image data cannot be obtained by refresh, flicker in the display device can be suppressed and a smooth moving image can be displayed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

(First embodiment)
First, a first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing a configuration of a radiation imaging system according to an embodiment of the present invention. In FIG. 1, 201 denotes an X-ray room, 202 denotes an X-ray control room, and 203 denotes a diagnostic room. The overall operation of the present X-ray imaging system is governed by a system control unit 210 provided in the X-ray control room 202.

  Examples of the operator interface 211 in the X-ray control room 202 include a touch panel on a display, a mouse, a keyboard, a joystick, and a foot switch. From the operator interface 211, settings such as imaging conditions (still image, moving image, tube voltage, tube current, irradiation time, etc.), imaging timing, image processing conditions, subject ID, and captured image processing method can be set. However, most of these pieces of information are transferred from a radiation information system (not shown) and need not be input individually. An important operation of the operator is a confirmation operation of the captured image. That is, it is determined whether the angle is correct, the patient is not moving, and the image processing is appropriate.

  The system control unit 210 instructs an imaging condition based on an instruction from the operator 205 or a radiation information system (not shown) to the imaging control unit 214 that manages the X-ray imaging sequence, and starts a data capturing operation. Based on the instruction, the imaging control unit 214 drives the X-ray generation device 120, the imaging bed 130, and the radiation imaging device 140, which are radiation sources, captures image data, and transfers the image data to the image processing unit 10. Thereafter, the system control unit 210 performs image processing designated by the operator 205 and displays it on the display 160, and saves raw data subjected to basic image processing such as offset correction and white correction in the external storage device 161. To do. The system control unit 210 further performs re-image processing, reproduction display, transfer / storage of image data to a device on the network, display display, printing on a film, and the like based on an instruction from the operator 205.

  Next, a description will be sequentially added following the flow of signals.

  The X-ray generator 120 includes an X-ray tube 121 and an X-ray diaphragm 123. The X-ray tube 121 is driven by a high voltage generation power source 124 controlled by the imaging control unit 214 and emits an X-ray beam 125. The X-ray diaphragm 123 is driven by the imaging control unit 214, and shapes the X-ray beam 125 so that unnecessary X-ray irradiation is not performed in accordance with the change of the imaging region. The X-ray beam 125 is directed to a subject 126 lying on an X-ray transmissive imaging bed 130. The imaging bed 130 is driven based on an instruction from the imaging control unit 214. The X-ray beam 125 is applied to the radiation imaging apparatus 140 after passing through the subject 126 and the imaging bed 130.

  The radiation imaging apparatus 140 is provided with a grid 141, a fluorescent plate 142, a photoelectric conversion circuit unit 8, an X-ray exposure monitor 144, and a drive circuit 145. The grid 141 reduces the influence of X-ray scattering caused by passing through the subject 126. The grid 141 is composed of, for example, an X-ray low absorption member and a high absorption member, and has, for example, a stripe structure of Al and Pb. Then, the grid 141 vibrates based on an instruction from the imaging control unit 214 at the time of X-ray irradiation so that moire does not occur due to a lattice ratio relationship between the photoelectric conversion circuit unit 8 and the grid 141.

The fluorescent plate 142, the photoelectric conversion element array (photoelectric conversion circuit unit) 8, and the drive circuit 145 are provided as components of the digital X-ray imaging apparatus. In the fluorescent plate 142, the host material of the phosphor is excited by high-energy X-rays, and fluorescence in the visible region is obtained by the recombination energy when recombining. The fluorescence may be due to the host itself such as CaWo ₄ or CdWO _4, or due to the emission center substance activated in the host body such as CsI: Tl or Zns: Ag. A photoelectric conversion circuit unit 8 is disposed adjacent to the fluorescent plate 142. The photoelectric conversion circuit unit 8 converts photons into electrical signals. The X-ray exposure monitor 144 monitors the X-ray transmission amount. The X-ray exposure monitor 144 may be one that directly detects X-rays using a crystalline silicon light receiving element or the like, or may be one that detects light from the fluorescent plate 142. In the present embodiment, visible light (proportional to the X-ray dose) transmitted through the photoelectric conversion circuit unit 8 is detected by an amorphous silicon light receiving element formed on the back surface of the substrate of the photoelectric conversion circuit unit 8, and the imaging control unit 214 detects the detected light. Information is sent, and the imaging controller 214 drives the high-voltage generating power source 124 based on the information to block or adjust the X-rays. The drive circuit 145 includes a readout circuit unit and an A / D converter. The drive circuit 145 drives the photoelectric conversion circuit unit 8 under the control of the imaging control unit 214, reads out the analog signal from each pixel, and then outputs the analog signal. Convert to digital signal.

  An image signal from the radiation imaging apparatus 140 is transferred from the X-ray room 201 to the image processing unit 10 in the X-ray control room 202. During this transfer, noise accompanying the generation of X-rays may be increased in the X-ray room 201. Therefore, since it may be assumed that the image data is not accurately transferred due to noise, it is desirable to increase the noise resistance of the transfer path. For example, it is desirable to use a transmission system having an error correction function, or to use a shielded twisted pair wire or a transfer path using an optical fiber. The image processing unit 10 switches display data based on an instruction from the imaging control unit 214. The image processing unit 10 can also perform correction of image data (offset correction, white correction), spatial filtering, recursive processing, and the like in real time, and can perform gradation processing, scattered radiation correction, various spatial frequency processing, and the like. is there.

  The image processed by the image processing unit 10 is displayed on the display 160 via the display adapter 151. In addition, the basic image on which only the data correction is performed simultaneously with the real-time image processing is stored in the external storage device 161. As the external storage device 161, a data storage device satisfying a large capacity, high speed and high reliability is desirable. For example, it is desirable to use a hard disk array such as RAID. Further, the image data stored in the external storage device 161 is stored in the external storage device 162 based on an instruction from the operator 205. At that time, the image data is reconstructed so as to satisfy a predetermined standard (for example, IS & C) and then stored in the external storage device 162. The external storage device 162 is, for example, a magneto-optical disk. Further, instead of the external storage device 162, it may be stored in a hard disk or the like provided in the file server 170 in the diagnosis room 203 connected via the LAN board 163. Various processes can be performed on the image data by the image processing terminal 173 in the diagnosis room 203 and displayed on the monitor 174.

  Next, the photoelectric conversion circuit unit 8 and the readout circuit unit 9 in the drive circuit 145 will be described. FIG. 2 is a circuit diagram showing a two-dimensional configuration of the photoelectric conversion circuit unit 8 and the readout circuit unit. However, for simplification of description, 3 × 3 = 9 pixels are shown.

In FIG. 2, S1-1 to S3-3 are photoelectric conversion elements, T1-1 to T3-3 are switch elements (TFT: Thin Film Transistor), G1 to G3 are gate wirings for turning on / off the TFT, M1 ˜M3 are signal wirings, and the Vs line is a wiring for applying a storage bias to the photoelectric conversion element. The electrodes on the sides of the photoelectric conversion elements S1-1 to S3-3 that are painted black are G electrodes, and the opposite side is a D electrode. The D electrode is connected to a part of the Vs line, but for convenience of entering light, for example, a thin N ⁺ layer is used as the D electrode. In the present embodiment, photoelectric conversion elements S1-1 to S3-3, switch elements T1-1 to T3-3, gate lines G1 to G3, signal lines M1 to M3, and Vs lines are included in the photoelectric conversion circuit unit 8. Yes. The Vs line is biased by the power supply Vs. SR1 is a shift register for applying a driving pulse voltage to the gate wirings G1 to G3, and a voltage for turning on the TFT is supplied from the outside. The control signal VSC is for applying two types of bias to the Vs line of the photoelectric conversion element, that is, the D electrode of the photoelectric conversion element. The D electrode becomes Vref (V) when the control signal VSC is “Hi”, and becomes Vs (V) when it is “Lo”. The reading power source Vs (V) and the refreshing power source Vref (V) are DC power sources, respectively. For example, Vs is 9 V and Vref is 3 V.

  The reading circuit unit 9 amplifies the parallel signal outputs of the signal wirings M1 to M3 in the photoelectric conversion circuit unit, converts the signals in series, and outputs them. RES1 to RES3 are switches that reset the signal wirings M1 to M3, A1 to A3 are amplifiers that amplify the signals of the signal wirings M1 to M3, and CL1 to CL3 are samples that temporarily store the signals amplified by the amplifiers A1 to A3. Hold capacitor, Sn1 to Sn3 are switches for sample and hold, B1 to B3 are buffer amplifiers, Sr1 to Sr3 are switches for serial conversion of parallel signals, and SR2 is a pulse for serial conversion to switches Sr1 to Sr3 A shift register Ab is a buffer amplifier that outputs a serially converted signal.

FIG. 3 is an equivalent circuit diagram showing a configuration of one pixel of the X-ray imaging apparatus according to the first embodiment of the present invention. One pixel includes one photoelectric conversion element and one switch element (TFT). The planar structure and cross-sectional structure of the photoelectric conversion element are the same as those shown in FIGS. In FIG. 3, the photoelectric conversion element includes a capacitance component Ci composed of an i layer made of hydrogenated amorphous silicon or the like as a semiconductor photoelectric conversion layer, and an insulating layer such as amorphous silicon nitride (a carrier injection blocking layer of both conductivity types). ) To indicate that there is a capacitive component C _SiN .

Further, when the photoelectric conversion element is in a saturated state, that is, a state where there is no electric field between the D electrode and the node N (i layer) or a state where the electric field is small even when there is an electric field, electrons and holes generated by light Since they recombine with each other, the junction between the i layer and the insulating layer (node N in FIG. 3) cannot store hole carriers. That is, the potential of the node N does not become higher than the potential of the D electrode. In order to embody the operation in the saturated state, in FIG. 3, it is indicated that the diode (D1) is connected in parallel to the capacitive component Ci. That is, in FIG. 3, the photoelectric conversion element is represented by three components of Ci, C _SiN and D1, and this photoelectric conversion element is shown in each of the photoelectric conversion elements S1-1 to S3-3 in FIG. Equivalent to.

In FIG. 3, TFT is a thin film transistor and is a switch element, and corresponds to each of the switch elements T1-1 to T3-3 in FIG. C2 is a read capacitor added to the signal wiring, but is omitted in FIG. Fl is a wavelength converting phosphor for converting an X-ray wavelength into a visible region wavelength, and is disposed at a position in close contact with the TFT directly or indirectly. For example, Gd ₂ O ₂ S or Gd ₂ O ₃ is used as the base material of the phosphor, and a material containing rare earth element ions such as Tb ³⁺ or Eu ³⁺ is used as the emission center. Alternatively, a phosphor using CsI such as CsI: Tl or CsI: Na as a base material may be used.

  The switch SW-B is a switch for switching a voltage applied to the TFT via the gate wirings G1 to G3, and is provided in the shift register SR1 shown in FIG. The switch SW-C is a switch for resetting the read capacitor C2 to the GND potential, and is controlled by an RC (CRES) signal. The switch SW-C corresponds to each of the switches RES1 to RES3 in FIG. Vg (on) (= Vcom) is a power source for turning on the TFT and transferring the signal charge to the read capacitor C2, and Vg (off) is a power source for turning off the TFT.

  Next, the circuit operation for one pixel shown in FIG. 3 will be described with reference to FIGS. FIG. 4 is a time chart showing the circuit operation for one pixel. This circuit operation includes a refresh operation, an X-ray irradiation operation, a transfer operation, and a reset operation, and a refresh period, an X-ray irradiation period, a transfer period, and a reset period are provided correspondingly.

  First, the refresh period will be described. In the refresh operation, first, the switch SW-A is turned on on the Vref side, the switch SW-B is turned on on the Vg (on) side, and the switch SW-C is turned on. In this state, the D electrode is biased to Vref of 3 V, the G electrode is biased to GND potential, and the node N is biased to Vref (3 V) at the maximum. Here, the maximum means the following situation. If the potential of the node N has already reached a potential equal to or higher than Vref by the photoelectric conversion operation prior to the refresh operation, the node N is biased to Vref via the diode D1. On the other hand, when the potential of the node N is equal to or lower than Vref due to the photoelectric conversion operation before the refresh operation, the node N is not biased to the potential of Vref by the refresh operation. In actual use, if a plurality of photoelectric conversion operations have been repeated in the past, the node N can be said to be effectively biased to Vref (3 V) by this refresh operation.

  In the refresh operation, the switch SW-A is switched to the Vs side after the node N is biased to Vref. As a result, the D electrode is biased to Vs (9 V). By this refresh operation, the hole carriers stored in the node N of the photoelectric conversion element are wiped out to the D electrode side.

  Next, the X-ray irradiation period will be described. In the X-ray irradiation operation, the switch SW-A is set to the Vs side, the switch SW-B is set to the Vg (off) side, and the switch SW-C is turned off. Further, as shown in FIG. 4, X-rays are irradiated in a pulse shape. X-rays that have passed through the subject are irradiated onto the phosphor Fl and converted into visible light. Visible light from the phosphor is irradiated to the semiconductor layer (i layer) and subjected to photoelectric conversion. The hole carriers generated by the photoelectric conversion are stored at the interface between the i layer and the insulating layer (injection blocking layer) and raise the potential of the node N. Since the TFT is in an off state, the potential on the G electrode side also rises by the same amount.

Next, the transfer period will be described. In the transfer operation, the switch SW-A is set to the Vs side, the switch SW-B is set to the Vg (on) side, and the switch SW-C is turned off. As a result, the TFT is turned on. As a result, an amount of electron carriers corresponding to the amount of hole carriers stored by X-ray irradiation flows from the readout capacitor C2 side to the G electrode side via the TFT, and the potential of the readout capacitor C2 increases accordingly. To do. At this time, the relationship Se = Sh × C _SiN / (C _SiN + Ci) is established between the amount of hole carriers (Sh) and the amount of electron carriers (Se). The potential of the read capacitor C2 is simultaneously amplified through an amplifier and output. The TFT is turned on for a time sufficient to sufficiently transfer the signal charge, and then turned off.

  Next, the reset operation will be described. In the reset operation, the switch SW-A is set to the Vs side, the switch SW-B is set to the Vg (off) side, and the switch SW-C is turned on. As a result, the read capacitor C2 is reset to the GND potential and prepared for the next X-ray irradiation.

  In this way, one image is acquired. Then, the cycle of the X-ray irradiation operation, the transfer operation, and the reset operation is continuously performed four times in total including the cycle for acquiring the first image, and then the refresh operation is performed again. Initialize the saturation amount of the photoelectric conversion element. As described above, flickering may occur on the screen when the refresh operation is performed as described above. In this embodiment, flickering can be suppressed by the configuration and method described later.

  Next, operation of the photoelectric conversion device illustrated in FIG. 2 will be described with reference to FIGS. FIG. 5 is a time chart illustrating the operation of the photoelectric conversion apparatus.

  First, the operation during the refresh period will be described. During the refresh period, all the signals of the shift register SR1 are set to the “Hi” state, and the CRES signal of the reading circuit unit 9 is set to the “Hi” state. This is equivalent to switching the switch SW-B to the Vg (off) side and turning on the switch SW-C in the circuit for one pixel shown in FIG. As a result, all the switching TFTs (T1-1 to T3-3) are turned on, and the switch elements RES1 to RES3 in the readout circuit section 9 are also turned on, and all the photoelectric conversion elements S1-1 to S3-3 are turned on. The G electrode becomes the GND potential. When the control signal VSC is “Hi”, the D electrodes of all the photoelectric conversion elements are biased to the refresh power source Vref (negative potential). As a result, all the photoelectric conversion elements S1-1 to S3-3 are in the refresh mode, and refresh is performed.

  Next, the photoelectric conversion period will be described. During the photoelectric conversion period, the control signal VSC is switched to the “Lo” state. This is equivalent to setting the switch SW-A to the Vs side in the circuit for one pixel shown in FIG. As a result, the D electrodes of all the photoelectric conversion elements S1-1 to S3-3 are biased by the reading power source Vs (positive potential), and the photoelectric conversion elements are in the photoelectric conversion mode.

  Next, all the signals of the shift register SR1 are set to “Lo”, and the CRES signal of the reading circuit unit 9 is set to the “Lo” state. As a result, all the switching TFTs (T1-1 to T3-3) are turned off, and the switch elements RES1 to RES3 in the readout circuit section 9 are also turned off, and all the photoelectric conversion elements S1-1 to S3-3 are turned off. Although the G electrode is open in terms of direct current, the photoelectric conversion element is also a capacitor, so that the potential is maintained. However, at this time, since no light (X-rays) is incident on the photoelectric conversion element, no charge is generated. That is, no current flows.

Thereafter, when the light source is turned on in a pulsed manner, light is irradiated to the D electrode (N ⁺ electrode) of each photoelectric conversion element, and so-called photocurrent flows. In addition, the photocurrent that flows by light is accumulated in each photoelectric conversion element as an electric charge, and is retained even after the light source is turned off. Although the light source is not particularly shown in FIG. 2, for example, an X-ray imaging apparatus is literally an X-ray source. In this case, a scintillator for X-ray visible conversion may be used. The present invention can also be applied to an imaging apparatus other than an X-ray imaging apparatus. As a light source when applied to a copying machine, for example, a fluorescent lamp, an LED, a halogen lamp, or the like is used.

  Next, the reading period will be described. The readout period here includes the reset period shown in FIG. In the readout period, first, the photoelectric conversion elements S1-1 to S1-3 in the first row, the photoelectric conversion elements S2-1 to S2-3 in the second row, and finally the third row. Reading is performed in the order of the photoelectric conversion elements S3-1 to S3-3. That is, first, in order to read from the photoelectric conversion elements S1-1 to S1-3 in the first row, the gate pulse from the shift register SR1 to the gate wiring G1 of the switch elements (TFT) T1-1 to T1-3. give. The high level of the gate pulse is the voltage Vcom supplied from the outside as described above. As a result, the switch elements T1-1 to T1-3 are turned on, and the signal charges accumulated in the photoelectric conversion elements S1-1 to S1-3 are transferred to the signal wirings M1 to M3. The signal charges transferred to the signal wirings M1 to M3 are amplified by the amplifiers A1 to A3. Although not shown in FIG. 2, a read capacitor is added to the signal wirings M1 to M3, and the signal charge is transferred to the read capacitor through the TFT. For example, the readout capacitance added to the signal wiring M1 is the sum of the inter-electrode capacitance (Cgs) between the gates / sources of the TFTs constituting the switch elements T1-1 to T3-1 connected to the signal wiring M1 ( 3), and this sum corresponds to the read capacitor C2 in FIG.

  Next, by turning on the SMPL signal, the SMPL signal is transferred to the sample hold capacitors CL1 to CL3, and the SMPL signal is turned off and held. Subsequently, by applying pulses in the order of the switches Sr1, Sr2, and Sr3 from the shift register SR2, the signals held in the sample hold capacitors CL1 to CL3 are amplified in the order of the sample hold capacitors CL1, CL2, and CL3. Ab is output to the A / D conversion circuit unit 203 as Vout. As a result, photoelectric conversion signals for one row of the photoelectric conversion elements S1-1, S1-2, and S1-3 are sequentially output. Further, simultaneously with applying a pulse from the shift register SR2 to the switch Sr1, the CRES signal is turned on to reset the signal wirings M1 to M3 to the GND potential. This corresponds to turning on the switch SW-C (reset period) in the circuit for one pixel shown in FIG.

  Further, after the signal wirings M1 to M3 are reset to the GND potential, the switching elements (TFT) T2-1 to T2- are used for reading from the photoelectric conversion elements S1-1 to S1-3 in the second row. A gate pulse is applied to the third gate wiring G2 from the shift register SR1. In this way, the readout operation of the photoelectric conversion elements S2-1 to S2-3 in the second row and the readout operation of the photoelectric conversion elements S3-1 to S3-3 in the third row are continuously performed. As described above, the signals of the signal lines M1 to M3 are sampled and held in the sample and hold capacitors CL1 to CL3, thereby performing the serial conversion operation of the signals of the first row and the second row using the shift register SR2. In the meantime, the signal charges of the photoelectric conversion elements S2-1 to S2-3 and S3-1 to S3-3 in the second row and the third row can be transferred simultaneously using the shift register SR1.

  Through the above operation, the signal charges of all the photoelectric conversion elements in the first to third rows can be output, and one still image is acquired. Thereafter, in order to acquire continuous moving images, for example, a photoelectric conversion period and a readout period (including a reset period) are repeated three more times without performing a refresh operation, and a total of four pieces of image data are acquired. To do.

  Here, a timing of performing a refresh operation when capturing a moving image and a method of processing image data accompanying the refresh operation will be described. FIG. 6 is a flowchart showing the operation of the radiation imaging system according to the first embodiment of the present invention, and FIG. 7 is a time chart along the flowchart shown in FIG. However, FIG. 7 shows the operation for one pixel as in FIG.

  In the radiation imaging system according to the present embodiment, when an imaging operation is started, first, a refresh operation is performed (step S1), thereby initializing the photoelectric conversion element and preparing for photoelectric conversion. Next, the “shooting continuation loop (steps S2 to S10)” process is performed until moving image shooting is completed.

  In the “shooting continuation loop”, first, the frame number n is set to 1 (step S2). Next, the “shooting loop (steps S3 to S8)” process is performed.

  In the “imaging loop”, first, X-ray irradiation is performed using the X-ray generator 120 (step S3). Next, image data is read from the photoelectric conversion circuit unit 8 using the reading circuit unit in the drive circuit 145 (step S4). Next, A / D conversion of the image data is performed using the A / D converter in the drive circuit 145 (step S5). Thereafter, image processing is performed using the image processing unit 10 (step S6). And the image of the said frame (nth frame) is displayed on the display 160 via the display adapter 151 (step S7). Subsequently, the frame number n is changed to n + 1 (step S8). As a result, if the frame number is 4 or less, the “shooting loop” process is performed again. On the other hand, when the frame number is not less than 4 (specifically, when the frame number reaches 5), the “shooting loop” process is terminated and a refresh operation is performed (step S9). That is, in the present embodiment, the “shooting loop” process is performed four times continuously, and then the refresh operation is performed.

  After performing the refresh operation in step S9, the (n-1) th frame image is displayed on the display 160 (step S10). That is, the image of the previous frame (fourth frame) is displayed again. When shooting is continued, the “shooting loop” process is performed again.

  However, in the flowchart shown in FIG. 6, X-ray irradiation (step S3), reading (step S4), A / D conversion (step S5), and image processing (step S6) are sequentially performed in order to show the flow simply. However, as shown in FIG. 7, after performing X-ray irradiation and reading, immediately performing X-ray irradiation of the next frame, A / D conversion and image processing and imaging of the next frame are performed in parallel. Preferably it is done.

  In the time chart shown in FIG. 7, R1 to R3 are refresh operations, X1 to X10 are X-ray irradiation, F1 to F10 are signal reading and A / D conversion, F1 ′ to F10 ′ are memory writing and image processing, D1 to D10 respectively indicate display on the display. 4 shows an operation between two refresh operations, while FIG. 7 also shows an operation for a longer period.

  In this embodiment, the refresh operation of the photoelectric conversion element in the radiation imaging apparatus 140 is performed by R1, the hole carriers in the photoelectric conversion element are swept out, and preparation for photoelectric conversion is performed. Next, X-rays are irradiated four times (X1 to X4) to the subject 126 standing in front of the radiation imaging apparatus 140. The irradiated X-ray obtains information on the subject 126 and enters the radiation imaging apparatus 140, and the incident X-ray is wavelength-converted by the fluorescent plate 142 and detected as an electrical signal by the photoelectric conversion circuit unit 8.

  Next, the detected electrical signal (analog signal) is read out by the drive circuit 145 and further subjected to A / D conversion to become a digital signal. Read corresponding to the first X-ray pulse X1 is F1, read corresponding to the second X-ray pulse X2 is F2, read corresponding to the third X-ray pulse X3 is F3, and fourth X-ray pulse X4 is read. The corresponding reading is F4, and reading and A / D conversion for 4 frames in total are sequentially performed.

  Thereafter, the read digital signal is written into a memory in the imaging control unit 214, and image processing (offset correction, gain correction, etc.) is performed by the image processing unit 10. The writing to the memory and the image processing corresponding to the reading process F1 are F1 ′, the reading process F2 corresponds to the image processing F2 ′, the reading process F3 corresponds to the image processing F3 ′, and the reading process F4 corresponds to the image processing F4. 'Corresponds.

  Subsequently, the image data subjected to the image processing is displayed on the display 160 via the display adapter 151. The display on the display corresponding to the image processing F1 'is D1, which is sequentially displayed as D1, D2, D3, and D4. However, since the refresh operation is performed between the X-ray pulse irradiations X4 and X5, there is no image data corresponding to that period. Therefore, in the first embodiment, a signal obtained along with the X-ray pulse irradiation X4 is displayed on the display as an interpolation signal. That is, the display on the display of D4 is continuously performed.

  According to the first embodiment as described above, the frame without image data is interpolated in order to continuously display the previous frame when displaying on the display corresponding to the period when the image data does not exist by the refresh operation. As a result, flickering of the screen can be suppressed.

It is ideal to sweep all holes in the i layer in the refresh mode, but it is ideal to sweep all holes, but there is no particular problem because a sufficient current can be obtained by sweeping only some of the holes. That is, it is not necessary to be in a saturated state as shown in FIG. 14C at the detection opportunity in the next photoelectric conversion mode. Further, the potential of the D electrode with respect to the G electrode in the refresh mode, the period of the refresh mode, and the characteristics of the N ⁺ layer injection blocking layer may be determined so as to satisfy this condition. Furthermore, injection of electrons into the i layer is not a necessary condition in the refresh mode, and the potential of the D electrode with respect to the G electrode is not limited to negative. This is because when a large number of holes remain in the i layer, even if the potential of the D electrode with respect to the G electrode is a positive potential, the electric field in the i layer is applied in the direction leading the holes to the D electrode. Similarly, the characteristics of the N ⁺ layer, which is an injection blocking layer, are not a requirement that electrons can be injected into the i layer.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 8 is a flowchart showing the operation of the radiation imaging system according to the second embodiment of the present invention. In this embodiment, the refresh timing is determined according to the amount of signals output from each pixel, that is, the amount of carriers accumulated in the photoelectric conversion elements constituting each pixel, instead of the number of frames. When refreshing, the voltage applied to the Vs line is changed from Vs (for example, 9 V) to the refresh voltage Vref (for example, 3 V).

  First, after refreshing initialization (step S21), the “shooting continuation loop (steps S22 to S29)” is entered, and the shooting continuation loop process is continued until shooting is completed. In the imaging continuation loop, it is determined whether the voltage of the Vs line is the refresh voltage Vref (step S22).

  If the voltage of the Vs line is not changed to the refresh voltage Vref, the frame number is changed from n to n + 1 (step S24). Then, similarly to the first embodiment, processing from X-ray irradiation (step S25) to image processing (step S28) is performed. Subsequently, an image of a frame corresponding to the changed frame number n is displayed on the display 160 (step S29). When shooting is continued, the “shooting loop” process is performed again.

  On the other hand, when the voltage of the Vs line is changed to the refresh voltage Vref, a refresh operation is performed (step S23), and the image of the frame corresponding to the frame number n is displayed on the display 160 without changing the frame number n. Displayed (step S29). That is, the image of the previous frame is displayed again. When shooting is continued, the “shooting loop” process is performed again.

  According to the second embodiment as described above, the same effect as that of the first embodiment can be obtained. Further, since it is determined whether or not the refresh operation is performed based on the sensor bias Vs instead of the continuous shooting number, there is an advantage that it is not necessary to define the continuous shooting number.

(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 9 is a time chart showing the operation of the radiation imaging system according to the second embodiment of the present invention. However, FIG. 9 shows the operation for one pixel as in FIG.

  In the first and second embodiments, the previous frame is continuously drawn in a period when there is no image data corresponding to the refresh operation period, whereas in the present embodiment, the frame immediately before the refresh operation period is drawn. Then, an intermediate image is generated using the immediately following frame, and the resulting image is rendered as an image corresponding to the refresh operation period. Examples of the intermediate image generation method include morphing. In the third embodiment, in order to perform real-time shooting, the processing time is shortened (previous frame + immediate frame) /2=4.5 frames, and D4.5 is set between D4 and D5. it's shown.

  According to such a 3rd embodiment, compared with the 1st and 2nd embodiment, a movie can be drawn smoothly by generating an intermediate picture.

  In the third embodiment, one frame immediately before and immediately after the refresh operation is used for generating the intermediate image. However, two frames immediately before and after the refresh operation may be used, or more frames may be used. May be.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. 10 and 11 are schematic views showing the operation of the radiation imaging system according to the fourth embodiment of the present invention. 10 and 11 show an example of an image displayed on the display 160. FIG. FIG. 10 is a diagram showing a frame image actually obtained by photographing, and FIG. 11 is a diagram showing an interpolated frame image.

  In the fourth embodiment, the interpolated frame is marked so that the diagnosing engineer can distinguish between the actual frame and the interpolated frame. That is, as shown in FIG. 10, no special display is performed on the actual frame, and marking 200 is added to the interpolated frame as shown in FIG.

  In this way, if an engineer can identify which frame has been interpolated, it is possible to make a diagnosis using the interpolated image data even when performing a diagnosis by selecting a still image from a moving image. The possibility of misdiagnosis caused by using the interpolated image data can be significantly reduced.

  Note that, as shown in FIG. 16, even in the radiation imaging apparatus that performs the refresh operation for each X-ray irradiation, the interpolated frame is displayed on the display 160 while corresponding to the refresh operation as in these embodiments. You may do it.

  The embodiment of the present invention can be realized by, for example, a computer executing a program. Also, means for supplying a program to a computer, for example, a computer-readable recording medium such as a CD-ROM recording such a program, or a transmission medium such as the Internet for transmitting such a program is also applied as an embodiment of the present invention. Can do. The above program can also be applied as an embodiment of the present invention. The above program, recording medium, transmission medium, and program product are included in the scope of the present invention.

It is a schematic diagram which shows the structure of the radiation imaging system which concerns on embodiment of this invention. 3 is a circuit diagram showing a two-dimensional configuration of a photoelectric conversion circuit unit 8 and a readout circuit unit 9. FIG. 1 is an equivalent circuit diagram showing a configuration of one pixel of an X-ray imaging apparatus according to a first embodiment of the present invention. It is a time chart which shows the circuit operation | movement for 1 pixel. It is a time chart which shows operation | movement of a photoelectric conversion apparatus. It is a flowchart which shows operation | movement of the radiation imaging system which concerns on the 1st Embodiment of this invention. It is a time chart along the flowchart shown in FIG. It is a flowchart which shows operation | movement of the radiation imaging system which concerns on the 2nd Embodiment of this invention. It is a time chart which shows operation | movement of the radiation imaging system which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows operation | movement of the radiation imaging system which concerns on the 4th Embodiment of this invention, Comprising: It is a figure which shows the image of the flame | frame actually obtained by imaging | photography. It is a schematic diagram which shows operation | movement of the radiation imaging system which concerns on the 4th Embodiment of this invention, Comprising: It is a figure which shows the image of the interpolated frame. It is a top view of the conventional photoelectric conversion board comprised using the amorphous silicon semiconductor thin film for the material of a MIS type photoelectric conversion element and a switch element. It is sectional drawing along the II line | wire in FIG. FIG. 14 is an energy band diagram showing device operation of the photoelectric conversion element shown in FIGS. 12 and 13. It is a time chart which shows the operation | movement at the time of the conventional moving image imaging | photography. It is a time chart which shows the example which performs refresh operation | movement for every X-ray irradiation.

Explanation of symbols

8: photoelectric conversion circuit unit 9: readout circuit unit 101: photoelectric conversion element 102: switch element 103: substrate 104: first metal thin film layer 105: second metal thin film layer 106: wiring for gate drive 107: matrix signal Wiring 109: Power supply line 110: Contact hole 111: Amorphous silicon nitride (a-SiNx) layer 112: Hydrogenated amorphous silicon (a-Si: H) layer 113: N ⁺ layer 201: X-ray chamber 202: X-ray control chamber 203: Diagnostic room

Claims (12)

A photoelectric conversion element array in which a plurality of pixels including a photoelectric conversion element and a switch element are arranged in an array on a substrate;
Detecting means for detecting a signal output from the photoelectric conversion element array;
Output means for outputting a signal output from the detection means to a display device;
Have
The output means continuously outputs the signal, and as a result of performing a refresh operation for sweeping out the carrier remaining in the photoelectric conversion element, in a period in which no signal is output from the detection means, interpolation is performed. A radiation imaging apparatus characterized by causing the display device to perform marking when outputting a signal and outputting the interpolation signal to the display device.   2. The radiation imaging apparatus according to claim 1, wherein a signal output from the detection unit in a frame immediately before a period in which the signal is not output is used as the interpolation signal.   2. The intermediate image signal using the signal output from the detection unit in a frame immediately before and after a period in which the signal is not output is used as the interpolation signal. The radiation imaging apparatus described. The radiation according to any one of claims 1 to 3 , wherein amorphous silicon is used as a material for the photoelectric conversion element and the switch element, and the photoelectric conversion element is a MIS type photoelectric conversion element. Imaging device. Radiation having a wavelength converter for performing a wavelength conversion on any one of claims 1 to 4 wave output is wavelength converted by the wavelength converter is characterized in that incident on the photoelectric conversion element 1 The radiation imaging apparatus according to Item. A radiation source for irradiating the subject with radiation;
A radiation imaging apparatus according to any one of claims 1 to 5 for detecting the radiation transmitted through the subject,
Image processing means for performing image processing on a signal output from the radiation imaging apparatus;
Display means for displaying the image data after being processed by the image processing means;
A radiation imaging system comprising: A radiation imaging apparatus comprising: a photoelectric conversion element array in which a plurality of pixels including a photoelectric conversion element and a switch element are arranged in an array on a substrate; and a detection unit that detects a signal output from the photoelectric conversion element array. A method of controlling,
The signal output from the detection means is continuously output to the display device, and as a result of performing a refresh operation for sweeping out the carriers remaining in the photoelectric conversion element, no signal is output from the detection means. A control method for a radiation imaging apparatus, characterized in that, during the period, an interpolation signal is output, and the display apparatus performs marking when outputting the interpolation signal to the display apparatus . The method for controlling a radiation imaging apparatus according to claim 7 , wherein a signal output from the detection unit in a frame immediately before a period in which the signal is not output is used as the interpolation signal. As a signal for the interpolation to claim 7 which comprises using a signal of an intermediate image using the frame and signals output from said detecting means in the frame immediately following the immediately preceding period in which the signal is not being output A control method of the radiation imaging apparatus described. A radiation imaging apparatus comprising: a photoelectric conversion element array in which a plurality of pixels including a photoelectric conversion element and a switch element are arranged in an array on a substrate; and a detection unit that detects a signal output from the photoelectric conversion element array. A program for controlling a computer,
A signal output from the detection means is output as a result of performing a refresh operation for continuously outputting the signal output from the detection means to a display device to a computer and sweeping out carriers remaining in the photoelectric conversion element. in the period it does not come is, to perform a process of outputting a signal for interpolation, when a signal for the interpolation on the display device, program characterized Rukoto to perform the marking on the display device . 11. The program according to claim 10 , which causes a computer to perform processing using the signal output from the detection unit in a frame immediately before a period in which the signal is not output as the interpolation signal. Causing the computer to perform processing using the intermediate image signal using the signal output from the detection means in the frame immediately before and after the period in which the signal is not output as the signal for interpolation. The program according to claim 10 , wherein

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