JP2015216441A - X-ray image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray image pickup device that can more properly suppress occurrence of an artifact caused by leak current in an X-ray image.SOLUTION: A gate driver 5 switches each of switching elements 29 connected to predetermined selected gate wires in the order of OFF→ON→OFF before each of plural read out operations of leak signals. Each of leak signals is read out after substantially the same time elapses after each of the switching element is switched. Therefore, the variation of the leak signals is reduced. An image generator 13 performs correction of subtracting the average value of leak signals read out plural times from a normal signal. Since the variation of each leak signal is small, the subtraction correction can be more accurately performed while suppressing the effect of noise caused by the circuit. As a result, high quality can be maintained particularly for X-ray images which have been subjected to reconstruction processing such as tomosynthesis, etc.

Description

  The present invention relates to an X-ray imaging apparatus including an X-ray image detector that acquires an image based on information obtained by X-ray irradiation.

  Conventionally, an X-ray image capturing apparatus is used as a medical X-ray image capturing apparatus. As an X-ray image detector used in the X-ray imaging apparatus, for example, a flat panel X-ray detector (hereinafter abbreviated as FPD) is known.

  As shown in FIG. 10, a conventional FPD 101 has a configuration in which a common electrode 103, a conversion layer 105, a pixel electrode 107, and an active matrix substrate 109 are stacked in the order described above. A bias voltage is applied to the common electrode 103. The conversion layer 105 is made of, for example, a-Se (amorphous selenium) or the like, and converts incident X-rays into electric charges that are electric signals. The active matrix substrate 109 is provided with a plurality of capacitors 111 and a plurality of switching elements 113. The pixel electrode 107, the capacitor 111, and the switching element 113 are each two-dimensionally arranged.

  The capacitor 111 is electrically connected to the signal line 115 via the switching element 113 and accumulates the charge converted by the conversion layer 105. For example, a thin film transistor (TFT) is used as the switching element 113. The electric charge accumulated in the capacitor 111 is read by the switching element 113 via the signal line 115 and transmitted as an electric signal to an image processing unit (not shown). The image processing unit generates an X-ray image based on the transmitted electrical signal.

  Here, when the switching element 113 is in an OFF state, it is ideal that the switching element 113 is insulated, so that no charge should be read from the capacitor 111. However, a small amount of current passes through the switching element 113 and is always output as a leak current regardless of whether the switching element 113 is actually turned on or off. For this reason, the current (signal current) output when the switching element 113 is turned on is a leakage current superimposed on the original electrical signal component. As a result, in the generated X-ray image, unnecessary information due to the leakage current appears as artifacts in addition to the necessary image information due to the original electrical signal component.

  In general, when the signal line 115 for reading an electric signal becomes longer, noise caused by the signal line 115 becomes larger and the time required for reading the electric signal becomes longer. Therefore, in the conventional FPD 101, the signal line 115 may be shortened by dividing the signal line 115 into two at the center and arranging the array amplifier circuits on both sides. The magnitude of the leakage current superimposed on the original signal component is the sum of the leakage currents output from all the switching elements 113 connected to the signal line 115. That is, since the magnitude of the leakage current differs for each divided signal line 115, a luminance difference is likely to occur in the divided portion of the signal line 115. Therefore, when the signal line 115 is divided, an artifact caused by a leak current is particularly noticeable in an area corresponding to the divided part of the signal line 115 in the X-ray image.

  Therefore, according to the conventional configuration, in order to prevent the occurrence of the artifact, a device for removing the component related to the leakage current is devised. That is, after irradiating X-rays, the switching element is turned on and the signal current is read out, and the switching element is turned off and the leakage current is read out. Then, by performing correction for subtracting the leakage current component from the signal current component, it is possible to acquire only necessary image information resulting from the original electrical signal component. With the above-described device, unnecessary information due to the leakage current can be removed, so that it is possible to suppress the occurrence of artifacts in the X-ray image even when the signal line is divided. For example, see Patent Document 1 and FIG.

  Further, this document discloses a configuration in which leakage current is read out a plurality of times in order to suppress the influence of noise components caused by circuits such as amplifiers included in the value of the leakage current to be read out. That is, the leakage current is read out a plurality of times after the switching element 113 is turned off. Then, the original electric signal component is calculated by subtracting the value obtained by averaging the read data of the plurality of leakage currents from the value of the signal current. By having such a configuration, it is possible to suppress the influence of the noise component caused by the circuit on the original electric signal component. As a result, it has been considered that the signal current value can be corrected more appropriately and the original electric signal component can be calculated more accurately.

Japanese Patent No. 3979165

However, the conventional apparatus having such a configuration has the following problems.
That is, when processing for reconstructing an X-ray image, such as tomosynthesis, is performed in a conventional apparatus, the occurrence of artifacts is suppressed in the X-ray image before the reconstruction processing as shown in FIG. On the other hand, in the X-ray image after the reconstruction process, as indicated by a symbol A in FIG. 11B, an artifact may occur in a region corresponding to a signal line dividing unit.

  For example, the following possibilities can be considered as the reason why the artifacts are generated in the X-ray image after the reconstruction processing. First, reconstruction processing such as tomosynthesis has the same effect as the processing of adding and averaging a plurality of images. Therefore, in the X-ray image after the reconstruction process, the random noise included in each X-ray image is smaller than that in the X-ray image before the reconstruction process, so that the S / N ratio is increased. As a result, it is considered that a luminance difference that is not visually recognized as an artifact in the X-ray image before the reconstruction process is visually recognized as an artifact in the X-ray image after the reconstruction process.

  As a result of the investigation conducted by the inventor, as shown by a triangular symbol in FIG. 12, when the leak current is read a plurality of times in the conventional X-ray imaging apparatus, the value of each read leak current fluctuates. did. That is, it has been found that there is a difference between the average value of the leak current read a plurality of times and the value of the leak current read first.

  The most accurate reflection of the leakage current component contained in the signal current component is the value of the leakage current read out first. Therefore, when calculating the original electric signal component, it is desirable to subtract the leak current value read out first from the signal current. However, since the leakage current includes a noise component due to a circuit such as an amplifier, when the value of the leakage current read first is subtracted from the signal current, a correction error due to the noise component occurs.

  In the conventional FPD, as described above, in order to suppress the occurrence of the correction error, a value obtained by averaging the leak current read out a plurality of times is used for the subtraction process. However, since there is a difference between the average value of the leak current read a plurality of times and the value of the leak current read first, a luminance difference is generated in the divided portion of the signal line 115 in the conventional subtraction process. Even if this luminance difference is a difference that cannot be seen with an X-ray image without reconstruction processing, it is visually recognized as an artifact in the image after reconstruction processing because the influence of random noise is reduced by the reconstruction processing. It is thought that it is done.

  Next, in the conventional FPD, the following possibilities can be considered for the reason that the value of each read leakage current fluctuates. FIG. 13A is a circuit diagram more specifically showing the configuration of one pixel of the FPD, and FIG. 13B explains the correlation between the gate potential and the capacitor potential when X-rays are not irradiated. It is a figure to do.

  In the conventional FPD 101, the switching element 113 is provided with three terminals of a gate 117, a source 119, and a drain 121, as shown in FIG. Charges move from the source 119 to the drain 121 by opening and closing the gate 117. A parasitic capacitance 123 exists between the gate 117 and the source 119.

  As shown in FIG. 13B, when the switching element 113 is turned from OFF to ON at time t1, the potential at the gate 117 changes from the low voltage Voff to the high voltage Von (the uppermost stage). As a result, the charge M moves in the direction indicated by the arrow via the parasitic capacitance 123 and is injected into the capacitor 111 (second stage from the top, time t1 to t2). The electric charge injected into the capacitor 111 is output as an output current Ion through the switching element 113 (third stage from the top, time t1 to t2, and see FIG. 13A). Therefore, when the switching element 113 is switched from OFF to ON, the potential of the capacitor 111 becomes 0 (bottom stage, time t1 to t2).

  On the other hand, when switching the switching element 113 from ON to OFF at time t3, the charge is discharged from the capacitor 111 via the parasitic capacitance 123 (second stage from the top, times t3 to t5). However, the switching element 113 changes from the ON state to the OFF state while discharging the electric charge from the capacitor 111.

  That is, before the potential of the gate 117 changes from Von to Voff, the switching element 113 is turned off and the output current Ion does not flow (third stage from the top, time t4). Therefore, a part of the electric charge remains in the capacitor 111 without being discharged. As a result, the potential of the capacitor 111 takes a certain negative value in accordance with the magnitude of the charge N remaining in the capacitor 111 (bottom stage, time t4).

  Thereafter, the electric charge remaining in the capacitor 111 gradually passes through the switching element 113 and is output as a leakage current via the signal line 115. Therefore, the potential of the capacitor 111 gradually approaches 0 with the passage of time according to the output of the leakage current (bottom stage, after t6). That is, the leakage current output gradually increases with time. Therefore, in the conventional X-ray imaging apparatus, when the leak current is read out a plurality of times, it is considered that the value of each read out leak current fluctuates.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an X-ray imaging apparatus that can more appropriately suppress the occurrence of artifacts due to leakage current in an X-ray image.

In order to achieve such an object, the present invention has the following configuration.
That is, the X-ray imaging apparatus according to the present invention includes a conversion unit that converts incident X-rays into charges, a charge storage unit that stores charges converted by the conversion unit, and an output electrode provided in the charge storage unit. And an X-ray image detector in which pixels having switching means for outputting charges accumulated in the charge accumulation means to each of the output electrodes are arranged in a two-dimensional matrix, and charge information output from the output electrodes Provided in each of the pixels extending in the first direction and arranged in the first direction, an amplifying means for amplifying the signal, a digital conversion means for converting the charge information amplified by the amplifying means into a digital signal, and the like. A plurality of gate wirings connected to the switching means, extending in a second direction intersecting the first direction, and arranged in the second direction A plurality of signal lines connected to the output electrode provided in each of the pixels; a leakage current reading unit that reads a value of a leakage current output from the switching unit a plurality of times for each signal line; and a plurality of signal lines Correction means for correcting the digital signal using each value of the leak current read out once, Image generation means for generating an X-ray image based on the digital signal corrected by the correction means, and the switching means Switching control means for switching ON / OFF for each gate wiring, and the switching control means is selected in advance prior to each reading of the value of the leakage current that the leakage current reading means performs a plurality of times. Each of the switching means connected to the gate wiring is switched from an OFF state to an ON state, and Is characterized in that for controlling each of said switching means is switched to the ON state to switch the state of OFF.

  [Operation / Effect] According to the X-ray imaging apparatus of the present invention, the leakage current reading unit reads the value of the leakage current output from the switching unit a plurality of times for each signal line. The switching control means switches each of the switching means connected to the gate wiring selected in advance in the order of OFF → ON → OFF before each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. To control.

  In the case where the leakage current value is read a plurality of times, the step of the leakage current reading means reading the leakage current value is repeated a plurality of times after the predetermined switching means is switched. Therefore, each of the leakage current values is read after substantially the same time has elapsed after each of the switching means is switched in the order of OFF → ON → OFF. As a result, fluctuations in the values of the plurality of leak currents to be read are reduced.

  Since the fluctuation of the leakage current value is reduced, the digital signal converted by the digital conversion means is corrected more accurately using a plurality of leakage current values. Therefore, it is possible to avoid the occurrence of artifacts in the X-ray image even when the reconstruction process is performed. Further, since the digital signal is corrected based on a plurality of leak current values, it is possible to avoid the noise caused by the circuit from adversely affecting the correction. Therefore, it is possible to generate a high-quality X-ray image that is more accurately corrected while suppressing the influence of noise caused by the circuit. In particular, it is possible to maintain high quality for an X-ray image subjected to reconstruction processing such as tomosynthesis.

  Further, in the above-described invention, the switching control means may be configured such that the switching means is switched ON / OFF immediately before each reading of the value of the leakage current that the leakage current reading means performs a plurality of times. Preferably, each of the switching means connected to the switch is switched from an OFF state to an ON state, and the switching means switched to the ON state is controlled to be further switched to an OFF state.

  [Operation / Effect] According to the X-ray imaging apparatus of the present invention, the switching control means is configured to turn on or off the switching means immediately before each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. Control is performed so that each of the switching means connected to the gate wiring that has been switched off is switched in the order of OFF → ON → OFF. That is, the switching control unit switches each of the switching units that have been switched ON / OFF most recently in the order of OFF → ON → OFF.

  Then, after switching the switching means in the order of OFF → ON → OFF, the value of the leakage current is read out. In this case, since the switching control means continuously switches the same switching means, the mechanism for the switching control means to control the switching means can be further simplified. Therefore, the X-ray imaging apparatus according to the present invention can be manufactured more easily.

  In the above-described invention, a plurality of dummy pixels that are provided separately from the plurality of pixels and configured not to accumulate charges converted from X-rays, and a plurality of dummy pixels including the switching unit, A dummy wiring extending in one direction and connected to each of the switching means provided in each of the plurality of dummy pixels arranged in the first direction, and the switching control means includes: Prior to each reading of the value of the leakage current that is performed a plurality of times by the leakage current reading means, each of the switching means connected to the dummy wiring is switched from the OFF state to the ON state, and can be switched to the ON state. It is preferable to control the switching means to be switched to an OFF state.

  [Operation / Effect] According to the X-ray imaging apparatus of the present invention, a plurality of dummy pixels are provided in addition to the plurality of pixels. In the dummy pixel, the charge storage means is configured not to store the charge converted from the X-rays. Therefore, the digital signal used for generating the X-ray image is not read from the dummy pixel.

  The switching means of the dummy pixels are connected by dummy wiring. Then, the switching control means controls the switching means connected to the dummy wiring to be switched in the order of OFF → ON → OFF prior to each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. . That is, when reading the leak current, the switching means for the dummy pixel provided separately from the pixel is switched. As a result, the number of times the switching means is used can be reduced in the pixel from which the digital signal used for generating the X-ray image is read out.

  Since the number of times the switching unit is used is reduced, it is possible to avoid fluctuations in the characteristics of the switching unit in the pixel from which the digital signal is read. For this reason, even when the X-ray imaging apparatus is used for a long period of time, the value of the digital signal is read accurately. As a result, it is possible to preferably avoid deterioration of the quality of the generated X-ray image, so that the service life of the X-ray imaging apparatus according to the present invention can be further extended.

  In the above-described invention, the dummy pixel includes an X-ray non-transparent blocking layer on a surface on which X-rays are irradiated so that the charge storage means does not store charges converted from X-rays. It is preferable to configure.

  [Operation / Effect] According to the X-ray imaging apparatus of the present invention, the dummy pixel includes an X-ray non-transmissive blocking layer on the surface irradiated with X-rays. X-rays irradiated to the dummy pixels are blocked by the blocking layer. Therefore, the conversion from X-rays to electric charges is hindered, so that the charge accumulating means does not accumulate electric charges converted from X-rays. In this case, by covering each of the dummy pixels with a blocking layer, the charge storage means can be configured not to store charges converted from X-rays. Therefore, the manufacturing process of the X-ray imaging apparatus according to the present invention can be simplified and the manufacturing cost can be suppressed.

  In the above-described invention, the X-ray image detector is divided into a plurality of regions, and the switching control means prior to each reading of the value of the leakage current that the leakage current reading means performs a plurality of times. And switching each of the predetermined switching means selected for each divided area from an OFF state to an ON state, and controlling the switching means switched to an ON state to be further switched to an OFF state. Is preferred.

  [Operation and Effect] According to the X-ray imaging apparatus of the present invention, each signal line is divided into a plurality of regions. In this case, since the length of the signal line for outputting the charge signal is shortened, noise caused by the signal line can be reduced and the time required for reading out the electric signal can be shortened.

  Then, the switching control means switches each of the predetermined switching means selected for each divided area in order of OFF → ON → OFF prior to each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. To control. Since the signal line is also divided by dividing the region, the value of the leakage current is different for each divided region. However, for each of the divided areas, switching means for switching in the order of OFF → ON → OFF is selected prior to reading of the leak current value. Therefore, the fluctuations of the leak current values read from each of the regions are all small.

  Since the fluctuation of the leakage current value is reduced, the digital signal converted by the digital conversion means is corrected more accurately using a plurality of leakage current values. For this reason, the luminance difference generated in the region corresponding to the signal line dividing portion in the X-ray image can be further reduced. As a result, it is possible to avoid the occurrence of artifacts in the X-ray image even when the reconstruction process is performed. In particular, the occurrence of artifacts in a region corresponding to the signal line dividing portion can be suitably avoided. Therefore, it is possible to generate a higher quality X-ray image while shortening the readout time of the electric signal.

  Further, since the digital signal is corrected based on a plurality of leak current values, it is possible to avoid the noise caused by the circuit from adversely affecting the correction. Therefore, it is possible to generate a high-quality X-ray image that is more accurately corrected while suppressing the influence of noise caused by the circuit.

  According to the X-ray imaging apparatus of the present invention, the leakage current reading unit reads the value of the leakage current output from the switching unit a plurality of times for each signal line. The switching control means switches each of the switching means connected to the gate wiring selected in advance in the order of OFF → ON → OFF before each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. To control.

  In the case where the leakage current value is read a plurality of times, the step of the leakage current reading means reading the leakage current value is repeated a plurality of times after the predetermined switching means is switched. Therefore, each of the leakage current values is read after substantially the same time has elapsed after each of the switching means is switched in the order of OFF → ON → OFF. As a result, fluctuations in the values of the plurality of leak currents to be read are reduced.

  Since the fluctuation of the leakage current value is reduced, the digital signal converted by the digital conversion means is corrected more accurately using a plurality of leakage current values. Therefore, it is possible to avoid the occurrence of artifacts in the X-ray image even when the reconstruction process is performed. Further, since the digital signal is corrected based on a plurality of leak current values, it is possible to avoid the noise caused by the circuit from adversely affecting the correction. Therefore, it is possible to generate a high-quality X-ray image that is more accurately corrected while suppressing the influence of noise caused by the circuit. In particular, it is possible to maintain high quality for an X-ray image subjected to reconstruction processing such as tomosynthesis.

1 is a plan view illustrating a schematic configuration of an X-ray imaging apparatus according to Embodiment 1. FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of one of X-ray detection pixels constituting an X-ray imaging apparatus according to Embodiment 1. FIG. 3 is a flowchart for explaining an operation process of the X-ray imaging apparatus according to Embodiment 1; It is a time chart which shows the sequence which reads a leak signal in the X-ray imaging device which concerns on a prior art example. 6 is a time chart showing a sequence for reading out a leak signal in the X-ray imaging apparatus according to Embodiment 1; 6 is a plan view illustrating a schematic configuration of an X-ray imaging apparatus according to Embodiment 2. FIG. FIG. 10 is a longitudinal sectional view illustrating a schematic configuration of one dummy pixel according to Example 2. 6 is a time chart showing a sequence for reading out a leak signal in the X-ray imaging apparatus according to Embodiment 2. FIG. 10 is a longitudinal sectional view for explaining a modified example of the schematic configuration of one dummy pixel according to Example 2. It is a longitudinal cross-sectional view explaining schematic structure about FPD which concerns on a prior art example. The X-ray image produced | generated in the X-ray imaging device which concerns on a prior art example is shown. (A) is an X-ray image before reconstruction processing, and (b) shows an X-ray image after reconstruction processing. In a prior art example and Example 1, it is a graph which shows the correlation with the frequency | count of reading leak current, and the value of each read leak current. It is a figure explaining the cause which the value of leak current fluctuates in a conventional example. (A) is a longitudinal sectional view showing the configuration of the FPD more specifically, and (b) is a diagram for explaining the correlation between the gate potential and the capacitor potential when X-rays are not irradiated.

  Embodiment 1 of the present invention will be described below with reference to the drawings.

<Description of overall configuration>
As shown in FIG. 1, the X-ray imaging apparatus 1 according to the first embodiment includes an X-ray image detector 3, a gate driver 5, amplifier arrays 7 and 8, AD converters 9 and 10, and main control. Unit 11, image generation unit 13, and monitor 15. The X-ray image detector 3 is connected to the gate driver 5 and the amplifier arrays 7 and 8. The X-ray image detector 3 has a plurality of X-ray detection pixels 17 arranged in a two-dimensional matrix.

  The gate driver 5 controls ON / OFF of a switching element to be described later via the gate wirings G1 to G4. The amplifier array 7 is connected to the AD conversion unit 9, and the amplifier array 8 is connected to the AD conversion unit 10. The amplifier arrays 7 and 8 amplify the input electric signals and output them to the AD conversion units 9 and 10. The AD conversion units 9 and 10 convert the input electric signal from an analog signal to a digital signal and output the converted signal to the image generation unit 13.

  The image generation unit 13 corrects the digital signals output from the AD conversion units 9 and 10 and generates an X-ray image based on the corrected digital signals. In addition, the image generation unit 13 can appropriately perform reconstruction processing such as tomosynthesis on the generated X-ray image. The monitor 15 displays the X-ray image generated by the image generation unit 13. Operations of the gate driver 5, the amplifier arrays 7 and 8, the AD conversion units 9 and 10, the image generation unit 13, and the monitor 15 are comprehensively controlled by the main control unit 11.

  The gate driver 5 corresponds to the switching control means in the present invention. The amplifier arrays 7 and 8 correspond to amplification means in the present invention, and the AD conversion units 9 and 10 correspond to digital conversion means in the present invention. The image generation unit 13 corresponds to an image generation unit and a correction unit in the present invention, and the X-ray detection pixel 17 corresponds to a pixel in the present invention.

  The X-ray image detector 3 will be specifically described. In the first embodiment, X-ray detection pixels 17 are arranged in a two-dimensional matrix of about 4,096 × 4,096. However, FIG. 1 shows a simplified arrangement of X-ray detection pixels 17a to 17p arranged in a two-dimensional matrix of 4 × 4. The X-ray image detector 3 is divided into a first region R1 in which X-ray detection pixels 17a to 17h are arranged and a second region R2 in which X-ray detection pixels 17i to 17p are arranged.

  In the first region R1, the X-ray detection pixels 17a to 17d arranged in the upper column, that is, in the horizontal direction of the line L1, are connected to the gate driver 5 through the gate wiring G1. Similarly, the X-ray detection pixels 17e to 17h arranged in the column below the first region R1, that is, the line L2, are connected to the gate driver 5 via the gate wiring G2.

  The amplifier array 7 is composed of amplifiers 7a to 7d arranged in a horizontal row. The amplifiers 7a to 7d are connected to the X-ray detection pixels 17 at the same position in the vertical direction via signal lines P1 to P4. It is connected. For example, the amplifier 7a is connected to the X-ray detection pixel 17a and the X-ray detection pixel 17e via the signal line P1, and the amplifier 7b is connected to the X-ray detection pixel 17b and the X-ray detection pixel 17f via the signal line P2. It is connected to the.

  The AD conversion unit 9 is composed of AD converters 9a to 9d arranged in a horizontal row, and the AD converters 9a to 9d are connected to amplifiers at the same position in the vertical direction. Yes. For example, the AD converter 9a is connected to the amplifier 7a via the signal line P1, and the AD converter 9b is connected to the amplifier 7b via the signal line P2.

  The second region R2 has substantially the same configuration as the first region R1. That is, the X-ray detection pixels 17i to 17l arranged in the column above the second region R2, that is, the line L3, are connected to the gate driver 5 through the gate wiring G3. The X-ray detection pixels 17m to 17p arranged in the column below the second region R2, that is, the line L4, are connected to the gate drive 5 through the gate wiring G4.

  The amplifier array 8 is configured by amplifiers 8a to 8d arranged in a horizontal row. The amplifiers 8a to 8d are connected to the X-ray detection pixels 17 at the same position in the vertical direction via signal lines Q1 to Q4. Connected. For example, the amplifier 8a is connected to the X-ray detection pixel 17i and the X-ray detection pixel 17m via the signal line Q1. The AD conversion unit 10 is composed of AD converters 10a to 10d arranged in a horizontal row, and the AD converters 10a to 10d are connected to amplifiers that are at the same position in the vertical direction. . For example, the AD converter 10a is connected to the amplifier 8a via the signal line Q1.

  Thus, by dividing the X-ray detection pixels 17a to 17p into two regions, the lengths of the signal lines P1 to P4 and the signal lines Q1 to Q4 are each halved. When the signal line is shortened, noise included in the read signal is reduced, and unnecessary information included in the acquired image is reduced. Therefore, by taking a configuration in which the X-ray detection pixels 17a to 17p are divided into two regions, a more accurate fluoroscopic image can be acquired. The amplifier arrays 7 and 8, the AD conversion units 9 and 10, the signal lines P1 to P4, and the signal lines Q1 to Q4 correspond to leakage current reading means in the present invention.

  Next, the configuration of the X-ray detection pixel 17 will be specifically described with reference to FIG. Since all the X-ray detection pixels 17a to 17p shown in FIG. 1 have the same configuration, description will be made using the X-ray detection pixel 17a as an example.

  The X-ray detection pixel 17a has a structure in which the common electrode 19, the conversion layer 21, the pixel electrode 23, and the active matrix substrate 25 are stacked in the order described above. A high bias voltage is applied to the common electrode 19. The conversion layer 21 converts X-rays, which are electromagnetic information, into charges, which are electrical information, and is made of a photoelectric conversion element such as a-Se or cadmium telluride (CdTe). The pixel electrode 23 is in contact with the conversion layer 21 and collects charges converted by the conversion layer 21. The active matrix substrate 25 is provided with a capacitor 27, a switching element 29, and an output electrode 31. The conversion layer 21 corresponds to the conversion means in the present invention.

  The capacitor 27 is electrically connected to the pixel electrode 23 and accumulates charges collected by the pixel electrode 23. The capacitor 27 is electrically connected to the output electrode 31 via the switching element 29. The switching element 29 is electrically connected to the gate driver 5 through the gate wiring G1 and controls the connection between the capacitor 27 and the output electrode 31. As an example, the switching element 29 is a thin film transistor (TFT).

  The output electrode 31 is electrically connected to the amplifier 7a via the signal line P1, and inputs the charge output from the switching element 29 to the amplifier 7a. The operation of the switching element 29 is controlled by the gate driver 5. The capacitor 27 corresponds to charge storage means in the present invention, and the switching element 29 corresponds to switching means in the present invention.

<Description of Operation According to Example 1>
Next, the operation of the X-ray imaging apparatus 1 according to the first embodiment will be described. FIG. 3 is a flowchart for explaining an operation process of the X-ray imaging apparatus according to the first embodiment.

Step S1 (X-ray irradiation)
First, X-rays that have passed through the subject are irradiated on the X-ray detection pixel 17a from the direction indicated by the symbol IR in FIG. Then, X-rays are converted into electric charges in the conversion layer 21. Since a bias voltage is applied to the common electrode 19, the charges converted in the conversion layer 21 are induced by the generated electric field and collected by the pixel electrode 23. The capacitors included in the respective X-ray detection pixels 17a to 17p 27 is accumulated. The charge accumulated in each of the capacitors 27 by the conversion of the X-rays incident on the conversion layer 21 is hereinafter referred to as “accumulated charge”.

Step S2 (reading signal signals of lines L1 and L4)
In FIG. 1, a gate operation signal is sent from the main control unit 11 to the gate driver 5, an amplifier operation signal is sent to the amplifier arrays 7 and 8, and an AD conversion signal is sent to the AD conversion units 9 and 10. Each is output. Based on the gate operation signal, the gate driver 5 first turns on the switching elements 29 of the line L1 in the first region R1 and the line L4 in the second region R2 via the gate wirings G1 and G4.

  The switching element 29 in the ON state outputs the accumulated charge from the output electrode 31. At this time, the flow of charges output from the output electrode 31 is defined as a signal current. The output signal current is input to the amplifier arrays 7 and 8 via the signal lines P1 to P4 and the signal lines Q1 to Q4. Thereby, the signal current is read from the X-ray detection pixels 17a to 17d and the X-ray detection pixels 17m to 17p.

  After the signal current is read from the X-ray detection pixels 17 a to 17 d and the X-ray detection pixels 17 m to 17 p, the main control unit 11 outputs a gate operation signal to the gate driver 5. Based on the gate operation signal, the gate driver 5 turns off the switching elements 29 of the line L1 and the line L4 via the gate line G1 and the gate line G4.

  The amplifier arrays 7 and 8 amplify the input signal current based on the amplifier operation signal, and the amplified signal current is input to the AD conversion units 9 and 10. The AD converters 9 and 10 convert the input signal current into a digital signal based on the AD conversion signal. Hereinafter, the signal current after digital conversion is referred to as a “signal signal”. Then, the signal signal read for each of the X-ray detection pixels of the line L1 and the line L4 is transmitted to the image generation unit 13. The signal signals on the line L1 are collectively referred to as a signal signal S1, and the signal signals on the line L4 are collectively referred to as a signal signal S4.

Step S3 (reading signal signals of lines L2 and L3)
After the signal signals of the lines L1 and L4 are read, the signal signals of the lines L2 and L3 are read. That is, a gate operation signal is output from the main control unit 11 to the gate driver 5, an amplifier operation signal is output to the amplifier arrays 7 and 8, and an AD conversion signal is output to the AD conversion units 9 and 10, respectively. The Based on the gate operation signal, the gate driver 5 then simultaneously turns on the switching elements 29 of the line L2 in the first region R1 and the line L3 in the second region R2 via the gate wirings G2 and G3, Thereafter, the above-described operation is performed.

  That is, the signal currents of the X-ray detection pixels 17e to 17h and 17i to 17l are read out through the signal lines P1 to P4 and the signal lines Q1 to Q4. After reading the signal currents of the X-ray detection pixels 17e to 17h and 17i to 17l, the gate driver 5 turns off the switching elements 29 of the lines L2 and L3 via the gate wiring G2 and the gate wiring G3.

  The amplifier arrays 7 and 8 amplify the signal currents of the X-ray detection pixels 17e to 17h and 17i to 17l. The AD converters 9 and 10 convert the amplified signal current into a digital signal. Then, the signal signals obtained for the X-ray detection pixels 17e to 17h and 17i to 17l of the line L2 and the line L3 are transmitted to the image generation unit 13. The signal signals on the line L2 are collectively referred to as a signal signal S2, and the signal signals on the line L3 are collectively referred to as a signal signal S3. As described above, the signal signals are read from each of the lines L1 to L4 in the conventional manner by the processes according to Step S2 and Step S3.

  Since the leakage current is always output from the output electrode 31, when the switching element 29 is turned on, the output electrode 31 outputs a signal in which the leakage current is superimposed on the accumulated charge. That is, the signal signal is a signal in which a leak current (hereinafter referred to as a leak signal) converted into a digital signal is superimposed. The charge signal converted based on the irradiated X-ray is a charge signal stored in the capacitor 27, that is, a stored charge. Therefore, in order to acquire more accurate image information, it is necessary to read out the leak signal and correct the signal signal using the leak signal.

Step S4 (switching of switching elements)
Here, as a feature of the present invention, after the signal signal is read from each line, the switching element is switched before reading the leak signal. That is, the main control unit 11 outputs a gate operation signal to the gate driver 5. Based on the gate operation signal, the gate driver 5 switches the line L2 and the switching element 29 of the line L3 from the OFF state to the ON state via the gate wirings G2 and G3. Further, the gate driver 5 switches the switching elements 29 of the line L2 and the line L3 from the ON state to the OFF state.

  By switching the switching element 29 from the OFF state to the ON state, charges are injected into the capacitor 27 via the parasitic capacitance. Then, by switching the switching element 29 from the ON state to the OFF state, charges are discharged from the capacitor 27 via the parasitic capacitance. However, since the switching element 29 is turned off when the charge is discharged, some of the charge cannot be discharged from the capacitor 27. As a result, a part of the electric charge that has not been discharged remains in the capacitor 27, so that the potential of the capacitor 27 has a constant negative value. By switching the switching element 29 in the order of OFF → ON → OFF, the process according to step S4 ends.

  Note that the switching element 29 that is switched before reading the leak signal is preferably the switching element 29 connected to the gate wiring from which the signal was read most recently. In this embodiment, the gate wirings from which signals have been read most recently are gate wirings G2 and G3 from which signal signals S2 and S3 have been read. Therefore, in step S4, the switching elements 29 of the line L2 and the line L3 are switched in the order of OFF → ON → OFF. In this case, since the same switching element 29 is continuously switched in the order of OFF → ON → OFF, the mechanism for the main control unit 11 to control the gate driver 5 can be simplified.

Step S5 (Leak signal reading)
After switching the switching element 29, the leakage signal is read out. That is, the control unit 11 outputs an amplifier operation signal to the amplifier arrays 7 and 8 and outputs an AD conversion signal to the AD conversion units 9 and 10. In addition, it is preferable to start reading the leak signal according to step S5 promptly after the end of the step S4.

  At this time, since the switching elements 29 of all the X-ray detection pixels 17 are in the OFF state, no current should flow from the output electrode 31. However, as described above, a part of the electric charge accumulated in the capacitor 27 actually passes through the switching element 29 and is always output as a leak current from the output electrode 31 regardless of whether the switching element 29 is ON or OFF. . Therefore, even when the switching element 29 is in the OFF state, the leakage current is input to the amplifier arrays 7 and 8 via the signal lines P1 to P4 and the signal lines Q1 to Q4.

  Here, in the first region R1, the leak currents flowing from the output electrodes 31 of the X-ray detection pixel 17a and the X-ray detection pixel 17e are summed and input to the amplifier 7a and digitized by the AD converter 9a. This is because the output electrodes 31 of the X-ray detection pixel 17a and the X-ray detection pixel 17e are each connected in parallel to the signal line P1. Similarly, the leak currents of the X-ray detection pixel 17b and the X-ray detection pixel 17f are summed via the signal line P2, input to the amplifier 7b, and digitized by the AD converter 9b.

  Similarly, in the second region R2, for example, the leakage currents of the X-ray detection pixel 17i and the X-ray detection pixel 17m are summed via the signal line Q1 and input to the amplifier 8a and digitized by the AD converter 10a. . Therefore, for example, the leak currents of the X-ray detection pixel 17a and the X-ray detection pixel 17e are read together.

  The amplifier arrays 7 and 8 amplify the leak current input based on the amplifier operation signal and output it to the AD conversion units 9 and 10. The AD conversion units 9 and 10 convert the input leak current into a digital signal, that is, a leak signal, based on the AD conversion signal. Then, the leak signal obtained for each signal line is transmitted to the image generation unit 13.

  The leak signals obtained for each of the signal lines P1 to P4 are collectively referred to as a leak signal LP. The leak signals obtained for each of the signal lines Q1 to Q4 are collectively referred to as a leak signal LQ. Further, the leak signals obtained for all the signal lines are collectively referred to as a leak signal LK.

  After completion of step S5, it is determined whether or not the leak signal is read again, and the process branches. In order to read out the leak signal a plurality of times, when the leak signal is further read out, the process returns to step S4 to continue the processing. That is, the process of switching the switching element 29 and the process of reading out the leak signal are repeated according to the number of times of reading out the leak signal. As a result, the leak signal LK in each signal line is read out a plurality of times.

  The leak signal LK read out at the first, second,... N times is hereinafter referred to as leak signals LK1, LK2,. Similarly, leak signals LP and LQ are hereinafter referred to as leak signals LP1, LP2,... LPn and leak signals LQ1, LQ2,. In this way, the leak signal is read a predetermined number of times. In the first embodiment, the specified number of times to read out the leak signal is four.

Step S6 (Signal signal correction)
After reading out the leak signal a specified number of times, the signal signal is corrected. That is, the image generation unit 13 performs correction to subtract the average value of each leak signal read out a plurality of times from the signal signal. Taking the X-ray detection pixel 17a as an example, first, an average value W is calculated for four leak signals obtained by reading four times from the signal line (signal line Q1) connected to the X-ray detection pixel 17a. .

  Then, the calculated average value W is subtracted from the value of the signal signal read from the X-ray detection pixel 17a. By reading the leak signal a plurality of times and performing subtraction correction using the average value of each read leak signal, it is possible to suppress the influence of noise components included in the leak signal on the subtraction correction.

  The value calculated by such subtraction correction becomes the value of the digital signal based on the accumulated charge of the X-ray detection pixel 17a. Hereinafter, a digital signal based on the accumulated charge is referred to as an accumulated signal. The same correction is performed on the X-ray detection pixels 17b to 17p, and an accumulation signal is calculated for each X-ray detection pixel 17.

Step S7 (Generation of X-ray image)
After correcting the signal signal and calculating the accumulated signal, an X-ray image is generated. That is, the image generation unit 13 generates an X-ray image based on each accumulated signal. The image generation unit 13 appropriately performs reconstruction processing such as tomosynthesis on the generated X-ray image. The generated X-ray image or the reconstructed X-ray image is transmitted to the monitor 15. The monitor 15 displays the X-ray image transmitted from the image generation unit 13. When the monitor 15 displays the X-ray image, all the series of steps related to the X-ray image capturing are completed.

<Effects of Configuration of Example 1>
In the X-ray imaging apparatus 1 according to the first embodiment, in the configuration in which each of the leak signals read out a plurality of times is used to correct the signal signal, the switching element 29 is turned off in advance before reading out each leak signal → Switch from ON to OFF. With such a configuration, the X-ray imaging apparatus according to the first embodiment reads each value compared with the value of the leak signal (FIG. 12, triangular sign) read out in the X-ray imaging apparatus according to the conventional example. Fluctuation in the value of the leak signal is suppressed (FIG. 12, circle symbols). As a result, it is possible to avoid the occurrence of artifacts in an X-ray image that has been subjected to reconstruction processing such as tomosynthesis. In particular, the occurrence of artifacts in a region corresponding to the signal line dividing portion can be suitably avoided.

  Here, the effect of the configuration of the first embodiment will be described using a time chart while comparing with the conventional example.

  First, FIG. 4 shows a time chart of an operation related to a conventional X-ray imaging apparatus. In this case, the switching elements connected to the gate wiring G1 and the gate wiring G4 are turned on, and a signal current is output for the X-ray detection pixels 17 of the line L1 and the line L4 (time t1, uppermost stage). After outputting the signal current, the switching elements connected to the gate wiring G1 and the gate wiring G4 are turned off (time t2, uppermost stage). The signal current is amplified and then digitally converted, and the signal signals S1 and S4 are read out. Next, the same operation is performed on the gate wiring G2 and the gate wiring G3 (time t3 to t4, the second stage from the top), and the signal signals S2 and S3 are read.

  In the conventional X-ray imaging apparatus, after reading the signal signals S1 to S4, all the switching elements are maintained in the OFF state without switching (second time from the top after time t4). Then, the leakage signal is read out four times in a state where all the switching elements are OFF, and the leakage signals LK1 to LK4 are read out (time t5 to t8, the lowest stage). Correction is performed for each of the signal signals S1 to S4 using the average value of the leak signals LK1 to LK4 read in this way. That is, the signal signals S1 and S2 are corrected using the average value of the leak signals LP1 to LP4, and the signal signals S3 and S4 are corrected using the average value of the leak signals LQ1 to LQ4.

  The value of the leak signal superimposed on each of the signal signals S1 and S2 is the leak signal LP1. The value of the leak signal superimposed on each of the signal signals S3 and S4 is the leak signal LQ1. Therefore, originally, by subtracting the leak signal LP1 from the signal signal S2 and subtracting the leak signal LQ1 from the signal signal S3, there should be no luminance difference between the signal line divisions, that is, the line L2 and the line L3. .

  However, the leak signals LP1 and LQ1 include electrical noise caused by the circuit. Therefore, when the leak signal LP1 is subtracted from the signal signal S2, an error occurs in the subtraction correction. Therefore, in the conventional example, the average value of the leak signals LP1 to LP4 is subtracted from the signal signals S1 and S2, and the average value of the leak signals LQ1 to LQ4 is subtracted from the signal signals S3 and S4. Thus, the influence of electrical noise is suppressed by performing subtraction correction using the average value of leak signals read out a plurality of times.

  As a result of repeated studies by the inventor, it has been found that the difference in fluctuation is large for each of the leak signals read in the configuration according to the conventional example, as indicated by a triangular symbol in FIG. That is, there is a large difference between the average value of the leak signals LK1 to LK4 and the value of the leak signal LK1. As a result, even if the signal signal is corrected using the average value of the leak signals LK1 to LK4, a luminance difference still remains between the accumulated signal on the line L2 and the accumulated signal on the line L3. As a result, artifacts due to the remaining luminance difference are generated by the reconstruction process of the X-ray image.

  As a cause of the large fluctuation of the leak signal in the conventional example, it can be considered that the electric charge accumulated in the capacitor is output as a leak current with time. That is, as shown in FIG. 4, the switching element is turned on and the charge C accumulated in the capacitor is read as a signal current (time t3, third stage from the top). When the switching element is switched from ON to OFF after reading the signal current, a part of the electric charge that has not been discharged via the parasitic capacitance remains in the capacitor as the residual electric charge N (time t4, third stage from the top). . When the residual charge N remains, the capacitor potential takes a certain negative value.

  The electric charge remaining in the capacitor gradually passes through the switching element as time elapses and is output from the output electrode as a leakage current E. Therefore, after switching the switching element from ON to OFF, the potential of the capacitor rises from a certain negative value with the passage of time and gradually approaches 0 (after time t9, the third stage from the top). That is, since the output of the leak current E increases with time, the value of the leak signal read after the second time becomes larger as compared with the leak signal read after the first time. (Time t5 to t8, the third step from the top). As a result, in the conventional configuration, the value of the leak signal is considered to vary greatly every time it is read out.

  Therefore, as shown in FIG. 5, in the X-ray imaging apparatus 1 according to the first embodiment, the switching element 29 that is in the OFF state is switched to the ON state before reading out each leak signal. The switching element 29 is switched again to the OFF state (time t5 to t12, second stage from the top). When switching the switching element 29 from the OFF state to the ON state, the potential of the capacitor 27 becomes 0 (time t5, t7, t9, t11, the third stage from the top). When the switching element 29 is switched again from the ON state to the OFF state, the potential of the capacitor 27 takes a certain negative value (time t6, t8, t10, t12, the third stage from the top).

  That is, in the first embodiment, each leak signal is read after substantially the same time has elapsed after switching the switching element 29 in the order of OFF → ON → OFF. Each time the switching element 29 is switched in the order of OFF → ON → OFF, the charge amount of the capacitor 27 becomes a negative constant value. Therefore, at the time of reading each leak signal, the output of the leak current due to the charge remaining in the capacitor 27 is almost the same (time t13 to t16, the third stage from the top). Therefore, in the X-ray imaging apparatus 1 according to the first embodiment, the fluctuation of each leak signal is smaller than that in the conventional example.

  Since the fluctuation of each leak signal is suppressed, the difference between the average value of the leak signals LK1 to LK4 and the value of the leak signal LK1 becomes small. That is, in the first embodiment, the difference between the average value of the leak signals LP1 to LP4 and the value of the leak signal LP1 becomes small. The difference between the average value of leak signals LQ1 to LQ4 and the value of leak signal LQ1 is similarly reduced.

  In the first embodiment, the accumulation signal of the X-ray detection pixel 17 in the line L2 is calculated by subtracting the average value of the leak signals LP1 to LP4 from the signal signal S2. The accumulated signal of the X-ray detection pixel 17 in the line L3 is calculated by subtracting the average value of the leak signals LQ1 to LQ4 from the signal signal S3. Therefore, it is possible to suppress a luminance difference generated between the line L2 and the line L3, which is a signal line dividing unit. By suppressing the luminance difference generated between the line L2 and the line L3, even when the reconstruction process is performed, an artifact is generated in the region of the X-ray image corresponding to the signal line dividing unit. Can be avoided.

  In addition, when subtraction correction is performed using the average value of the leak signals LK1 to LK4 when calculating the accumulated signal, a correction error caused by circuit noise is smaller than when subtraction correction is performed using the leak signal LK1. Can be suppressed. Therefore, in the X-ray imaging apparatus 1 according to the first embodiment, it is possible to more suitably avoid the occurrence of artifacts in the X-ray image while suppressing correction errors due to circuit noise.

  Next, Embodiment 2 of the present invention will be described with reference to the drawings. Note that the same components as those in the X-ray imaging apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the X-ray imaging apparatus 1 </ b> A according to the second embodiment, the X-ray image detector 3 </ b> A includes a gate wiring dedicated to reading leakage current and an X-ray detection pixel dedicated to reading leakage current. That is, as shown in FIG. 6, the X-ray image detector 3A is provided with a gate wiring Gx, a gate wiring Gy, and dummy pixels 33a to 33h. The gate wiring Gx and the gate wiring Gy correspond to dummy wirings in the present invention.

  The gate line Gx and the dummy pixels 33a to 33d are included in the first region R1. The dummy pixels 33a to 33d are arranged in a column further above the line L1 in the first region, that is, in the horizontal direction of the line Lx. The dummy pixels 33a to 33d are connected to the gate driver 5 through the gate wiring Gx.

  The dummy pixel 33a is connected to the amplifier 7a, the X-ray detection pixel 17a, and the X-ray detection pixel 17e through the signal line P1, and the dummy pixel 33b is connected to the amplifier 7b, the X-ray detection pixel 17b, through the signal line P2. And the X-ray detection pixel 17f. The dummy pixel 33c is connected to the amplifier 7c, the X-ray detection pixel 17c, and the X-ray detection pixel 17g via the signal line P3, and the dummy pixel 33d is connected to the amplifier 7d and the X-ray detection pixel via the signal line P4. 17d and the X-ray detection pixel 17h.

  The gate line Gy and the dummy pixels 33e to 33h are included in the second region R2. The dummy pixels 33e to 33h are arranged in a column further below the line L4 in the second region, that is, in the horizontal direction of the line Ly. The dummy pixels 33e to 33h are connected to the gate driver 5 via the gate wiring Gy.

  The second region R2 has substantially the same configuration as the first region R1. For example, the dummy pixel 33e is connected to the amplifier 8a, the X-ray detection pixel 17i, and the X-ray detection pixel 17m via the signal line Q1, and the dummy pixel 33f is connected to the amplifier 8b and the X-ray detection pixel 17j via the signal line Q2. And the X-ray detection pixel 17n.

  Here, the configuration of the dummy pixels 33a to 33h arranged in the line Lx and the line Ly will be described with reference to the drawings. Since all the dummy pixels 33a to 33h have the same configuration, description will be made using the dummy pixel 33a as an example.

  The configuration of the dummy pixel 33a is substantially the same as the configuration of the X-ray detection pixels 17a to 17p arranged on the lines L1 to L4. However, unlike the X-ray detection pixels 17 a to 17 p, the dummy pixel 33 a is configured not to accumulate accumulated charge in the capacitor 27. That is, the X-ray detection pixels 17a to 17p arranged on the lines L1 to L4 are pixels that actually detect the irradiated X-rays. On the other hand, the dummy pixels 33a to 33h arranged in the line Lx and the line Ly are pixels that do not detect X-rays.

  The following is an example of a configuration in which the accumulated charge is not accumulated in the capacitor 27. That is, as shown in FIG. 7, the structure which coat | covers the surface of the common electrode 19 with the interruption | blocking layer 35 is mentioned. The blocking layer 35 is made of a radiopaque material. Since the X-rays irradiated from the direction indicated by IR in the figure are blocked by the blocking layer 35, the X-rays are not incident on the conversion layer 21. For this reason, no charge is generated in the conversion layer 21, so that no charge is accumulated in the capacitor 27.

  In the case of adopting such a configuration, it is possible to easily store the accumulated charge in the capacitor 27 by covering each of the dummy pixels 33 a to 33 h arranged in the line Lx and the line Ly with the blocking layer 33. Therefore, the manufacturing process of the X-ray imaging apparatus 1A according to the second embodiment can be simplified and the manufacturing cost can be suppressed.

<Description of Operation According to Second Embodiment>
Next, the operation of the X-ray imaging apparatus 1A according to the second embodiment will be described. In addition, since the process except step S4 is common in Example 1 among the processes of operation | movement, detailed description is abbreviate | omitted.

  In step S1, the detection surface of the X-ray image detector 3A is irradiated with X-rays. Accumulated charges are accumulated in the capacitor 27 in each of the X-ray detection pixels 17a to 17p arranged in the lines L1 to L4 by the X-ray irradiation. In step S2, the signal signals S1 and S4 are read, and in step S3, the signal signals S2 and S3 are read.

Step S4 (switching of switching elements)
After the signal signal is read from each of the lines L1 to L4, the switching element is switched. That is, the main control unit 11 outputs a gate operation signal to the gate driver 5. Based on the gate operation signal, the gate driver 5 switches each of the switching elements 29 of the dummy pixels 33a to 33h from the OFF state to the ON state via the gate wirings Gx and Gy. Further, the gate driver 5 switches each of the switching elements 29 of the dummy pixels 33a to 33h from the ON state to the OFF state.

  By switching the switching element 29 from the OFF state to the ON state, charges are injected into the capacitor 27 via the parasitic capacitance in each of the dummy pixels 33a to 33h. Then, by switching the switching element 29 from the ON state to the OFF state again, a part of the electric charge that has not been discharged from the capacitor 27 remains in the capacitor 27. Therefore, the charge amount of the capacitor 27 is negative in each of the dummy pixels 33a to 33h. By switching the switching element 29 in the order of ON → OFF → ON, the process according to step S4 is completed.

  After the switching elements 29 of the dummy pixels 33a to 33h are sequentially switched, the leakage signals LK1 to LK4 are read in step S5. In step S6, the average value of the leak signals LK1 to LK4 is calculated for each signal line. Then, subtraction correction is performed on each of the signal signals S1 to S4 using each of the calculated average values of the leak signals LK1 to LK4. Finally, in step S7, an X-ray image is generated based on the accumulated signal calculated by the subtraction correction, and the generated X-ray image is displayed on the monitor 15.

<Effects of Configuration of Example 2>
In the X-ray imaging apparatus 1A according to the second embodiment, as shown in FIG. 8, before reading each leak signal, each of the switching elements 29 connected to the gate wiring Gx or the gate wiring Gy is turned OFF → ON →. Switching in the order of OFF (time t1 to t2, third stage from the top). Then, subtraction correction is performed on the signal signal using the average value of each read leak signal, and an X-ray image is generated based on the calculated accumulated signal.

  The dummy pixels 33a to 33h connected to the gate line Gx or the gate line Gy are covered with an X-ray non-transmissive blocking layer 35. Since the X-rays irradiated to the dummy pixels 33a to 33h are blocked by the blocking layer 35, the capacitor 27 provided in each of the dummy pixels 33a to 33h does not accumulate charges converted from the X-rays. Therefore, no signal signal is output even if each of the switching elements 29 of the dummy pixels 33a to 33h is switched from OFF to ON. By switching each of the switching elements 29 from ON to OFF, the potential of the capacitor 27 in the dummy pixels 33a to 33h becomes a constant negative value.

  Each time the switching element 29 is switched from the ON state to the OFF state, the potential of the capacitor 27 becomes a constant negative value, so that the fluctuation of each leak signal is smaller than that of the conventional example (from time t3 to t6, To 4th stage). Since subtraction correction is performed using the average value of each read leak signal, it is possible to avoid occurrence of correction errors due to circuit noise when performing subtraction correction.

  Further, the second embodiment includes a switching element 29 exclusively for switching when reading a leak signal, in addition to the switching element 29 for reading the signal current. That is, in addition to the gate lines G1 to G4, the gate line Gx and the gate line Gy are provided. In the dummy pixels 33a to 33d connected to the gate line Gx and the dummy pixels 33e to 33h connected to the gate line Gy, the switching element 29 is switched exclusively when reading the leak signal.

  Therefore, in each of the X-ray detection pixels 17a to 17p irradiated with X-rays, the switching element 29 is switched exclusively when reading the signal current, and is not switched when reading the leak current. Therefore, the number of times the switching element 29 is used in the X-ray detection pixels 17a to 17p can be kept low. That is, the number of times of use of the switching element 29 used for reading out the electric signal used for generating the X-ray image can be kept low. As a result, it is possible to avoid fluctuations in the characteristics of the switching element 29 in the X-ray detection pixels 17a to 17p. An example of the characteristics of the switching element 29 is an ON / OFF duty ratio.

  By preventing fluctuations in the characteristics of the switching elements 29 connected to the gate wirings G1 to G4, the value of the signal signal can be accurately read even when used for a long time. Therefore, it is possible to preferably avoid deterioration of the quality of the generated X-ray image. As a result, the service life of the X-ray imaging apparatus according to the present invention can be extended.

  The present invention is not limited to the above embodiment, and can be modified as follows.

  (1) In each of the above-described embodiments, the number of times of reading the leak signal is four, but the number of times of reading the leak signal may be any number. When the number of times of reading out the leak signal is increased, the influence of noise caused by a circuit such as an amplifier included in the average value of the leak signal is further reduced. Therefore, it is possible to further reduce the influence of noise on the signal signal subtraction correction.

  (2) In the first embodiment described above, before the leakage signal is read, the switching element 29 connected to the gate wiring from which the signal was read most recently is switched in the order of OFF → ON → OFF. Not limited. That is, at least one gate wiring is selected for each divided region. The switching element 29 connected to the selected gate wiring may be switched in the order of OFF → ON → OFF before reading out the leak signal.

  Specifically, even when the gate wiring from which the signal was read most recently is G2 and the gate wiring G3, the leakage signal may be read after switching the switching element 29 connected to the gate wiring G1 and the gate wiring G4. . Further, the leakage signal may be read after switching the switching element 29 connected to the gate wirings G1 to G4.

  (3) In the above-described second embodiment, in the dummy pixel 33a, the surface of the pixel electrode 19 is covered with the blocking layer 35 as a configuration in which the accumulated charge is not accumulated in the capacitor 27. However, the present invention is not limited to this. That is, as another example of the configuration in which the accumulated charge is not accumulated in the capacitor 27, there is a configuration in which the conversion layer 21 is omitted as shown in FIG. In this case, since the X-rays incident on the dummy pixels 33a are not converted into charges by the photoelectric conversion element, accumulation of accumulated charges in the capacitor 27 can be avoided more reliably. In addition to the configuration in which the conversion layer 21 is omitted, at least one of the common electrode 19 and the pixel electrode 23 may be further omitted.

  (4) In the above-described second embodiment, the line Lx is arranged in the column above the line L1, and the line Ly is arranged in the column below the line L4. Absent. That is, the arrangement of the line Lx having the gate wiring Gx and the line Ly having the gate wiring Gy may be changed as appropriate.

  (5) In each of the embodiments described above, the X-ray image detector 3 is divided into two regions, but the present invention is not limited to this. That is, it may be configured to be divided into three or more regions, or may be configured not to be divided.

  In the modification based on the first embodiment, at least one gate wiring is selected for each divided region. Then, before reading out the leak signal, the switching element 29 connected to the selected gate wiring is switched in the order of OFF → ON → OFF. Specifically, when the X-ray image detector 3 is divided into three regions, at least one gate wiring is selected for each of the three regions. Before reading out the leak signal, the switching elements 29 connected to each of the selected at least three gate wirings are switched in the order of OFF → ON → OFF.

  In the case of the modification based on the second embodiment, a gate wiring dedicated to reading out a leak signal and a dummy pixel dedicated to reading out the leak signal are provided in accordance with the number of divided areas. Before reading out the leak signal, the switching element 29 is switched in the order of OFF → ON → OFF in the dummy pixel connected to the dedicated gate wiring. Specifically, in the case where the X-ray image detector is divided into three regions, at least one or more gate wiring dedicated to reading a leak signal is provided for each of the three regions.

  Thus, when the X-ray image detector 3 is divided into more regions, the length of each signal line becomes shorter. Accordingly, noise caused by the signal line can be further reduced, and the time required for reading out the charge signal can be further shortened.

  (6) In each of the embodiments described above, the signal signals are read simultaneously for the line L1 and the line L4, and then the signal signals are read simultaneously for the line L2 and the line L3. Also good.

DESCRIPTION OF SYMBOLS 1 ... X-ray imaging device 3 ... X-ray image detector 5 ... Gate driver (switching control means)
7, 8 ... Amplifier array (amplification means)
9, 10 ... AD converter (digital conversion means)
11 ... main control unit 13 ... image generation unit (image generation means, correction means)
17a to 17p: X-ray detection pixels (pixels)
21 ... Conversion layer (conversion means)
27. Capacitor (charge storage means)
29 ... Switching element (switching means)
31 ... Output electrodes 33a to 33h ... Dummy pixels 35 ... Shielding layers G1 to G4 ... Gate wiring Gx, Gy ... Gate wiring (dummy wiring)
P1-P4, Q1-Q4 ... signal lines

Claims (5)

Conversion means for converting incident X-rays into charges, charge storage means for storing charges converted by the conversion means, output electrodes provided in the charge storage means, and charges stored in the charge storage means An X-ray image detector in which pixels having switching means for outputting to each of the output electrodes are arranged in a two-dimensional matrix;
Amplifying means for amplifying the charge information output from the output electrode;
Digital conversion means for converting the charge information amplified by the amplification means into a digital signal;
A plurality of gate wirings extending in a first direction and connected to the switching means provided in each of the pixels arranged in the first direction;
A plurality of signal lines extending in a second direction intersecting with the first direction and connected to the output electrode provided in each of the pixels arranged in the second direction;
Leakage current reading means for reading the value of the leakage current output from the switching means a plurality of times for each signal line;
Correction means for correcting the digital signal using each of the leak current values read a plurality of times;
Image generating means for generating an X-ray image based on the digital signal corrected by the correcting means;
Switching control means for switching ON / OFF of the switching means for each gate wiring,
The switching control means sets each of the switching means connected to the gate wiring selected in advance from an OFF state prior to each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. An X-ray imaging apparatus characterized by switching to an ON state and further controlling each of the switching means switched to an ON state to an OFF state. The X-ray imaging apparatus according to claim 1,
The switching control means is connected to the gate wiring that has been turned ON / OFF of the switching means immediately before each reading of the value of the leakage current that the leakage current reading means performs a plurality of times. An X-ray imaging apparatus for controlling each of the means from an OFF state to an ON state and controlling the switching means switched to the ON state to be further turned OFF. The X-ray imaging apparatus according to claim 1 or 2,
A plurality of dummy pixels provided separately from the plurality of pixels and configured to not store charges converted from X-rays, and a plurality of dummy pixels including the switching unit;
A dummy wiring extending in the first direction and connected to each of the switching means provided in each of the plurality of dummy pixels arranged in the first direction;
The switching control means switches each of the switching means connected to the dummy wiring from an OFF state to an ON state prior to each reading of the value of the leakage current performed by the leakage current reading means a plurality of times. An X-ray imaging apparatus for controlling the switching means switched to the ON state to further switch to the OFF state. The X-ray imaging apparatus according to claim 3,
The dummy pixel includes an X-ray non-transparent blocking layer on a surface on which X-rays are irradiated, so that the charge storage means does not store charges converted from X-rays. apparatus. The X-ray imaging apparatus according to any one of claims 1 to 4,
Each of the signal lines is divided into a plurality of regions,
The switching control means turns on each of the predetermined switching means selected for each divided area from an OFF state prior to each reading of the value of the leakage current that the leakage current reading means performs a plurality of times. An X-ray imaging apparatus which controls to switch to the OFF state and further switch the switching means switched to the ON state to the OFF state.