JP2014175896A - Two-dimensional image detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-dimensional image detector capable of obtaining a transmission image that has a wide range of grayscale levels and in which image distortion due to leakage current does not occur.SOLUTION: In a two-dimensional image detector, only when leakage current is read out, a proper positive signal is added to the leakage current in advance. This enables the leakage current, which is a negative signal, to be converted into a positive value while setting output of an amplifier to 0 in a basis state. Setting output of the amplifier to 0 in the basis state increases the range of X-ray detection signals capable of being identified by an AD conversion section 9a, thereby increasing the range of grayscale levels of an obtained transmission image. The transmission image is corrected using the leakage current subjected to digital conversion so that the occurrence of image distortion due to leakage current can be prevented in the obtained transmission image. Consequently, the two-dimensional image detector can obtain a transmission image that has a wide range of grayscale levels and in which image distortion due to leakage current does not occur.

Description

  The present invention relates to a two-dimensional image detector that acquires an image based on electromagnetic wave information such as X-rays, visible light, and infrared light.

  2. Description of the Related Art Conventionally, a two-dimensional image photographing device is used as a medical X-ray image photographing device. As a two-dimensional image detector used in the two-dimensional image photographing apparatus, for example, a flat panel X-ray detector (hereinafter abbreviated as FPD) is known.

  First, a specific configuration of the FPD 51 will be described with reference to FIG. The FPD 51 includes a common electrode 52, a conversion layer 53, a support layer 54, and an active matrix substrate 55. The common electrode 52, the conversion layer 53, the support layer 54, and the active matrix substrate 55 are stacked in the order described above. A bias voltage is applied to the common electrode 52. The conversion layer 53 is composed of, for example, an a-Se (amorphous selenium) layer. The support layer 54 is provided with a plurality of pixel electrodes 56, and the active matrix substrate 55 is provided with a plurality of capacitors 57, switching elements 58, and output electrodes 59. The pixel electrode 56 is in contact with the conversion layer 53 and is electrically connected to the capacitor 57. The capacitor 57 is electrically connected to the output electrode 59 through the switching element 58, and accumulates the charge converted by the conversion layer 53. For example, a thin film transistor (TFT) is used as the switching element 58, and the charge accumulated in the capacitor 57 is output from the output electrode 59. The pixel electrode 56, the capacitor 57, the switching element 58, and the output electrode 59 are two-dimensionally arranged.

  Next, the operation of the FPD 51 will be described. When, for example, X-rays are irradiated on the subject as electromagnetic waves, an X-ray image transmitted through the subject is projected onto the conversion layer 53, and charges are generated in proportion to the density of the X-ray image. That is, in the conversion layer 53, X-rays that are electromagnetic wave information are converted into charges that are electrical signals. Since a bias voltage is applied to the common electrode 52, the charges converted in the conversion layer 53 are induced by the generated electric field and collected by the pixel electrode 56. The collected charge is stored in the capacitor 57. Hereinafter, the charge accumulated in the capacitor 57 is referred to as accumulated charge. The accumulated charge is output as an X-ray detection signal from the output electrode 59 when the switching element 58 is turned on. Hereinafter, the flow of charges output from the output electrode 59 at this time is referred to as a signal current. The output signal current is converted into a digital signal by an AD converter and then subjected to image processing and the like, and is displayed on the monitor as a fluoroscopic image of the subject. A symbol x indicates an X-ray irradiation direction.

  In the FPD 51 having the above-described configuration, when the switching element 58 is in an OFF state, it is ideal that the switching element 58 is insulated, so that no current should flow from the capacitor 57 to the output electrode 59. However, a small amount of current passes through the switching element 58 regardless of whether the switching element 58 is turned on or off, and is always output as a leak current from the output electrode 59. Therefore, when the switching element 58 is turned on, the signal current output from the output electrode 59 includes accumulated charge and leakage current. Therefore, when an image is created, a signal based on a leak current as well as a signal based on accumulated charge is converted into information. As a result, in the photographed fluoroscopic image, unnecessary information due to leakage current appears as disturbance of the image, apart from necessary image information due to accumulated charges.

  Therefore, according to the conventional configuration, in order to prevent the image from being disturbed, a device for removing the component related to the leakage current is devised. That is, after irradiating the X-ray, the switching element 58 is turned on and the signal current is read out, and the switching element 58 is turned off and the leakage current is read out. Then, by performing correction for subtracting the leakage current component from the signal current, it is possible to acquire only necessary image information resulting from accumulated charges. Since the above-described device can eliminate unnecessary information due to the leakage current, it is possible to suppress the occurrence of image disturbance in a fluoroscopic image (see, for example, Patent Document 1).

Japanese Patent No. 3979165

However, the conventional apparatus having such a configuration has the following problems.
That is, as shown in FIG. 9A, in the conventional apparatus, the output value of the amplifier (see the symbol “◯”) in the ground state, that is, the state where the stored charge is not read and the leakage current is not output is set to 0. When set, the leakage current has a negative value (see the symbol x). Since the AD converter cannot digitally convert a signal indicating a negative value, the leak current cannot be read out. As a result, the correction for subtracting the component related to the leakage current cannot be performed, so that the obtained perspective image is disturbed.

As the reason for the negative polarity of the leakage current, for example, the following possibilities are conceivable.
First, as shown in FIG. 10, the switching element 58 is provided with three terminals of a gate 60, a source 61, and a drain 62, and charges move from the source 61 to the drain 62 by opening and closing the gate 60. Parasitic capacitances 63 exist between the gate 60 and the source 61 and between the gate 60 and the drain 62, respectively.

  As shown in FIG. 10A, when the switching element 58 is in an OFF state, a very small part of the accumulated charge accumulated in the capacitor 57 passes through the switching element 58 and becomes the charge L from the output electrode 59. Leakage output. Since the accumulated charge has a positive polarity, the charge L has a positive polarity.

  However, as shown in FIG. 10B, the potential at the gate 60 changes from a high voltage to a low voltage (for example, from 25 V to −10 V) at the moment when the switching element 58 is turned off. As a result, the charge M having a negative polarity moves through the parasitic capacitance 63 in the direction indicated by the arrow. That is, the negative charge M is output from the output electrode 59 even though the switching element 58 is off.

  Therefore, when the leakage current is read after the switching element 58 is turned off from on, both the positive charge L and the negative charge M are read. At this time, since the absolute value of the charge M exceeds the absolute value of the charge L, the sum of the charge L and the charge M has a negative polarity, and as a result, the leak current to be read has a negative value.

  In order to solve this problem, as a conventional example, there is a method of setting the output value of the amplifier in the ground state to a predetermined positive value instead of 0 as shown in FIG. 9B. In this case, since the leak current input to the AD converter is raised from a negative value to a positive value, the leak current can be converted into a digital signal by the AD converter. As a result, it is possible to perform correction by subtracting the charge amount related to the leakage current, so that it is possible to remove the image disturbance that occurs in the fluoroscopic image.

  However, when the output value of the amplifier in the ground state is increased, a new problem occurs. That is, as shown in FIG. 9B, when the output value of the amplifier in the ground state is increased, the range of the output value of the amplifier that can be identified by the AD converter becomes narrower than that in FIG. 9A. For this reason, the dynamic range of the FPD 51 is reduced, so that the gradation of the captured fluoroscopic image is reduced.

  Therefore, in the conventional apparatus, if the output value of the amplifier in the ground state is set to a predetermined positive value with an emphasis on removing the image disturbance generated in the fluoroscopic image, the gradation of the fluoroscopic image to be photographed is set. The problem of decreasing is inevitable. On the other hand, when the output value of the amplifier in the ground state is brought close to 0 with an emphasis on diversifying the gradation of the fluoroscopic image, the leakage current takes a negative value, so that the image disturbance generated in the fluoroscopic image can be removed. Disappear. In other words, an apparatus having a conventional configuration cannot simultaneously satisfy both the diversification of gradations and the removal of image disturbance caused by leakage current in the acquired fluoroscopic image.

  The present invention has been made in view of such circumstances, and is a two-dimensional image having various gradations and capable of acquiring a fluoroscopic image that does not cause image disturbance due to leakage current. An object is to provide a detector.

In order to achieve such an object, the present invention has the following configuration.
That is, the two-dimensional image detector according to the present invention includes a charge conversion unit that converts an incident electromagnetic wave into a charge, a conversion charge storage unit that stores the charge converted by the charge conversion unit, and the conversion charge storage unit. A pixel matrix in which pixels composed of an output electrode provided on the switching electrode and switching means for outputting the charge accumulated in the converted charge accumulation means to each of the output electrodes are two-dimensionally arranged, and the output electrode Amplifying means for amplifying the charge information output from, a digital conversion means for converting the charge information amplified by the amplifying means into a digital signal, a switching control means for controlling each of the switching means, and the digital signal An image acquisition means for converting and acquiring an image, and outputting a negative signal output from each of the pixels constituting the pixel matrix. By adding a positive signal to the leakage current has become, it is characterized in that an addition means for converting the leakage current input to the digital conversion means to a positive value.

  [Operation / Effect] According to the two-dimensional image detector according to the present invention, when the leak current is read, an addition means for adding an appropriate positive signal to the leak current in advance is provided, so that there are various gradations. In addition, it is possible to obtain a fluoroscopic image in which image distortion due to leakage current does not occur.

  In order to solve the problem that the leakage current that is a negative signal cannot be read in a device having a conventional configuration, the output value of the amplifier in the ground state is set to take a predetermined positive value instead of 0, The leakage current was raised from a negative value to a positive value. However, in this case, since the range of the X-ray detection signal that can be identified by the digital conversion means is narrowed, the gradation of the fluoroscopic image to be taken is reduced.

  On the other hand, the two-dimensional image detector according to the present invention uses the adding means to add a positive signal only when reading a leak current. As a result, the leak current, which is a negative signal, can be converted to a positive value while setting the output value of the amplifier in the ground state to 0. When the output value of the amplifier in the ground state is set to 0, the range of the X-ray detection signal that can be identified by the digital conversion means is widened, so that the gradation of the obtained fluoroscopic image is varied. Then, by correcting the fluoroscopic image using the digitally converted leak current, it is possible to prevent image disturbance due to the leak current in the acquired fluoroscopic image. Therefore, it is possible to acquire a fluoroscopic image that has not only a variety of gradations but also does not cause image distortion due to leakage current.

In the above-described invention, the adding means includes a switching switch electrically connected to a connection wiring electrically connecting the switching means and the digital conversion means, and the switch and the connection wiring. An additional charge accumulating means for accumulating charges provided therebetween, a low voltage terminal connected to the connection wiring via the switch, and a voltage higher than the voltage of the low voltage terminal and via the switch A high-voltage terminal connected to the connection wiring, the switch is switched to the low-voltage terminal, the charge stored in the converted charge storage means is read, and the switch is By switching from the voltage terminal to the high voltage terminal and increasing the charge input to the amplifying means via the added charge storage means, a negative It is preferable to convert the leakage current has a No. positive.

  [Operation / Effect] According to the above-described configuration, the switch is switched from the low voltage terminal to the high voltage terminal to increase the charge input to the amplifying means via the addition charge accumulating means. In this case, an appropriate amount of charge is amplified to convert the leakage current to a positive value by setting the capacity of the additional charge storage means, the voltage at the low voltage terminal, and the voltage at the high voltage terminal to appropriate values. Means can be input. As a result, it is possible to more reliably convert the leak current, which is a negative signal, to a positive value while setting the output value of the amplifier in the ground state to 0.

  Further, in the above-described invention, the addition unit includes the switching unit and the digital conversion unit in place of the configuration including the switch, the addition charge storage unit, the low voltage terminal, and the high voltage terminal. A current supply means that is electrically connected to a connection wiring that is electrically connected and supplies a current to the connection wiring; and provided between the current supply means and the connection wiring; and the current supply means and the connection wiring; Current supply control means for controlling the electrical connection of the electric charge, and the current supply control means is a charge stored in the converted charge storage means in a state where the current supply means is not electrically connected to the connection wiring. And the current supply means is connected to the connection wiring for a predetermined period via the current supply control means to increase the charge input to the amplification means. , It may be possible to convert the leakage current is a negative signal to a positive value.

  [Operation / Effect] According to the above-described configuration, the current supply means is connected to the connection wiring via the current supply control means for a predetermined period to increase the charge input to the amplification means. In this case, by setting the amount of current output from the current supply means and the length of the predetermined period to an appropriate value, an appropriate amount of charge is supplied to the amplification means in order to convert the leakage current to a positive value. Can be entered. As a result, it is possible to more reliably convert the leak current, which is a negative signal, to a positive value while setting the output value of the amplifier in the ground state to 0.

  In the above-described invention, the adding means includes the switch, the added charge storage means, the low voltage terminal, and the high voltage terminal, or the current supply means and the current supply control means. In place of the above-described configuration, an adder for adding a voltage to the output from the amplifying means and an adder control means for controlling the adder, wherein the adder control means outputs the output from the amplifying means. In the state in which the voltage is not increased by the adder, the charge accumulated in the converted charge accumulation means is read, and the voltage is output to the output from the amplification means by the adder via the adder control means. The leakage current, which is a negative signal, may be converted to a positive value by increasing.

  [Operation / Effect] According to the above-described configuration, the voltage is increased to the output from the amplification means by the adder via the adder control means. By setting the voltage increased by the adder to an appropriate value, an appropriate amount of charge can be input to the amplifying means in order to convert the leakage current to a positive value. As a result, it is possible to more reliably convert the leak current, which is a negative signal, to a positive value while setting the output value of the amplifier in the ground state to 0.

  In the above-described invention, the adding means is preferably provided between the switching means and the amplifying means.

  [Operation / Effect] According to the above-described configuration, the leakage current converted from the negative value to the positive value by the adding means is amplified by the amplifying means. Thereby, the fluoroscopic image can be corrected using the amplified leakage current.

  In the above-described invention, the adding means may be provided between the amplifying means and the digital converting means in place of the configuration provided between the switching means and the amplifying means. Good.

  [Operation / Effect] According to the above-described configuration, the leakage current is amplified by the amplifying means and then converted to a positive value by the adding means. That is, noise caused by the adding means is not amplified by the amplifying means. Therefore, the noise superimposed on the leakage current can be further reduced.

  In the above-described invention, it is preferable that the timing for converting the leakage current from the negative value to the positive value by the adding means is set before the timing for reading the leakage current.

  [Operation / Effect] According to the above-described configuration, after the leakage current is converted from the negative value to the positive value by the adding means, the leakage current converted to the positive value is read. That is, since operations from conversion to reading are quickly performed, noise generated in the leak current converted from a negative value to a positive value is reduced. Thereby, the leak current converted from the negative value to the positive value can be read more accurately.

  In the above-described invention, the negative value taken by the leakage current is read in advance using digital conversion means that can identify a negative signal experimentally, and the lowest one of the measured leakage currents is selected. Calculating a current value large enough to convert the selected minimum leakage current to a positive value, and calculating the calculated current value by the adding means. It is preferable to set the size.

  [Operation / Effect] According to the above-described configuration, the leak current is read in advance using the digital conversion means that can identify a negative signal experimentally. Therefore, a leak current that takes a negative value can also be read. Then, the lowest one of the measured leakage currents is selected, and a current value large enough to convert the selected lowest leakage current into a positive value is calculated. Since the calculated current value is set as the magnitude of the signal to be added by the adding means, the leak current read when actually obtaining the fluoroscopic image is more reliably converted from a negative value to a positive value. The Thereby, the correction | amendment with respect to a fluoroscopic image can be performed more reliably.

  In the above-described invention, the pixel matrix has two divided regions, and the switching control unit determines whether the pixel constituting one of the divided regions is to be read out. It is preferable to operate so as to simultaneously read out the pixels in the other corresponding divided region.

  [Operation / Effect] According to the above-described configuration, when the pixels constituting one divided region are read out in each of the two divided regions, the other corresponding to the pixel to be read out The pixels in the divided areas are simultaneously read out. As a result, the time required to read out the charge information can be greatly shortened. Further, by dividing the pixels constituting the pixel matrix into two regions, the length of each signal line is shortened for the signal lines necessary for reading out the pixels. When the signal line is shortened, noise included in the read information is reduced, so that more accurate image information can be acquired.

  According to the two-dimensional image detector according to the present invention, when the leakage current is read out, the addition means for adding an appropriate positive signal to the leakage current in advance is provided. Then, using the adding means, an appropriate positive signal is added only when the leakage current is read out. As a result, the leak current, which is a negative signal, can be converted to a positive value while setting the output value of the amplifier in the ground state to 0. When the output value of the amplifier in the ground state is set to 0, the range of the output value of the amplifier that can be identified by the digital conversion means is widened, so that the gradation of the obtained fluoroscopic image is diversified. Then, by correcting the fluoroscopic image using the digitally converted leak current, it is possible to prevent image disturbance due to the leak current in the acquired fluoroscopic image. Therefore, it is possible to acquire a fluoroscopic image that has not only a variety of gradations but also does not cause image distortion due to leakage current.

1 is a plan view illustrating a schematic configuration of a two-dimensional image detector according to Embodiment 1. FIG. 3 is a longitudinal sectional view illustrating a schematic configuration of one of the radiation detection pixels constituting the two-dimensional image detector according to Embodiment 1. FIG. FIG. 3 is a plan view illustrating the configuration of an adding unit according to the first embodiment. 3 is a time chart for explaining an operation according to the first embodiment. FIG. 4 is a graph showing the output value of an amplifier for the two-dimensional image detector according to Example 1. FIG. 10 is a plan view illustrating a configuration of an adding unit according to a second embodiment. FIG. 10 is a plan view illustrating a configuration of an adding unit according to a third embodiment. It is a longitudinal cross-sectional view explaining schematic structure about FPD which concerns on a prior art example. It is a graph which shows the output value of amplifier about FPD which concerns on a prior art example. In a prior art example, it is a figure explaining the reason for which the polarity of leak current takes a negative value.

  Embodiments of the present invention will be described below with reference to the drawings. The X-rays described below are an example of electromagnetic waves in the present invention.

<Description of overall configuration>
As shown in FIG. 1, the two-dimensional image detector 1 according to the first embodiment includes a radiation detection matrix 3, a gate driver 5, amplifier arrays 7 and 8, AD conversion units 9 and 10, and a control unit 11. The image processing device 13 and the image display device 15 are provided. The radiation detection matrix 3 is connected to the gate driver 5 and the amplifier arrays 7 and 8. The radiation detection matrix 3 has a plurality of radiation 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 converters 9 and 10 convert the input electrical signal from an analog signal to a digital signal and output the digital signal to the image processing device 13. The image processing device 13 performs image processing based on signals input from the AD conversion units 9 and 10. The image display device 15 displays the image information input from the image processing device 13 as an image. Operations of the gate driver 5, the amplifiers 7 and 8, the AD conversion units 9 and 10, the image processing device 13, and the image display device 15 are comprehensively controlled by the control unit 11.

  The radiation detection matrix 3 corresponds to the pixel matrix in the present invention, and 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 processing device 13 and the image display device 15 correspond to image acquisition means in the present invention, and the radiation detection pixel 17 corresponds to a pixel in the present invention.

  The radiation detection matrix 3 will be specifically described. In the first embodiment, the radiation detection pixels 17 are arranged in a two-dimensional matrix of about 4,096 × 4,096. However, FIG. 1 shows a simplified arrangement in which the radiation detection pixels 17a to 17p are arranged in a two-dimensional matrix of 4 × 4. The radiation detection matrix 3 has a first region r1 in which radiation detection pixels 17a to 17h are arranged and a second region r2 in which radiation detection pixels 17i to 17p are arranged.

  In the first region r1, the uppermost column of the radiation detection matrix 3, that is, the radiation detection pixels 17a to 17d arranged in the horizontal direction of the line H1, is connected to the gate driver 5 through the gate wiring G1. . Similarly, the radiation detection pixels 17e to 17h arranged in the second column from the top, that is, the line H2, are connected to the gate driver 5 through the gate wiring G2. The amplifier array 7 includes amplifiers 7a to 7d arranged in a horizontal row, and the amplifiers 7a to 7d are connected to the radiation detection pixels 17 at the same position in the vertical direction via signal lines Q1 to Q4. Has been. For example, the amplifier 7a is connected to the radiation detection pixel 17a and the radiation detection pixel 17e via the signal line Q1, and the amplifier 7b is connected to the radiation detection pixel 17b and the radiation detection pixel 17f via the signal line Q2. Yes. 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 Q1, and the AD converter 9b is connected to the amplifier 7b via the signal line Q2.

  The second region r2 has substantially the same configuration as the first region. In other words, the radiation detection pixels 17i to 17l arranged in the third column from the top of the radiation detection matrix 3, that is, the line H3, are connected to the gate driver 5 through the gate wiring G3. Further, the radiation detection pixels 17m to 17p arranged in the fourth column from the top, that is, the line H4, are connected to the gate drive 5 through the gate wiring G4. The amplifier array 8 includes amplifiers 8a to 8d arranged in a horizontal row. The amplifiers 8a to 8d are connected to the radiation detection pixels 17 at the same position in the vertical direction via signal lines R1 to R4. It is connected. For example, the amplifier 8a is connected to the radiation detection pixel 17i and the radiation detection pixel 17m via the signal line R1. 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 R1.

  Thus, by dividing the radiation detection matrix 3 into two regions, the lengths of the signal lines Q1 to Q4 and the signal lines R1 to R4 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, a more accurate fluoroscopic image can be acquired by dividing the radiation detection matrix 3 into two regions.

  Next, the configuration of the radiation detection pixel 17 will be specifically described with reference to FIG. Since each of the radiation detection pixels 17a to 17p shown in FIG. 1 has the same configuration, description will be made using the radiation detection pixel 17a as an example.

  The radiation 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 that are electromagnetic information into electric charges that are electrical information, and is made of, for example, 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, an output electrode 31, and a control electrode 33. The conversion layer 21 corresponds to the charge 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 control electrode 33 and controls the connection between the capacitor 27 and the output electrode 31. For example, a thin film transistor (TFT) is used as the switching element 29. The output electrode 31 is electrically connected to the amplifier 7a via the signal line Q1, and inputs the charge output from the switching element 29 to the amplifier 7a. The control electrode 33 is electrically connected to the gate driver 5 through the gate wiring G1, and controls the operation of the switching element 29. The operation of the control electrode 33 is controlled by the gate driver 5. The capacitor 27 corresponds to the converted charge storage means in the present invention, and the switching element 29 corresponds to the switching means in the present invention.

<Description of operation>
Next, the operation of the two-dimensional image detector 1 will be described with reference to FIG. 1 and FIG. First, X-rays that have passed through the subject are emitted to the two-dimensional image detector 1 from the direction indicated by symbol y in FIG. In the conversion layer 21, X-rays that are electromagnetic wave information are converted into electric charges. Since a bias voltage is applied to the common electrode layer 19, the charges converted in the conversion layer 21 are induced by the generated electric field and collected by the pixel electrode 23, and capacitors included in the radiation detection pixels 17a to 17p. 27 is accumulated. At this time, the charge accumulated in each capacitor 27 is defined as accumulated charge.

<Reading signal signal>
In FIG. 1, a gate operation signal is output from the 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. The Based on the gate operation signal, the gate driver 5 first turns on the control electrode 33 of the line H1 in the first region r1 and the control electrode 33 of the line H4 in the second region r2 through the gate wirings G1 and G4. The control electrode 33 in the on state turns on the switching element 29. 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 Q1 to Q4 and the signal lines R1 to R4. As a result, signal current is read from the radiation detection pixels 17a to 17d and the radiation detection pixels 17m to 17p.

  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, a signal current after digital conversion obtained in a state where the switching element 29 is on is referred to as a signal signal. The signal signals obtained for the radiation detection pixels on the line H1 and the line H4 are input to the image processing device 13. The signal signals on the line H1 are collectively referred to as a signal signal S1, and the signal signals on the line H4 are collectively referred to as a signal signal S4.

  Further, the control unit 11 outputs a gate operation signal to the gate driver 5, an amplifier operation signal to the amplifier arrays 7 and 8, and an AD conversion signal to the AD conversion units 9 and 10. Based on the gate operation signal, the gate driver 5 then simultaneously turns on the control electrode 33 of the line H2 in the first region r1 and the line H3 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 radiation detection pixels 17e to 17h and 17i to 17l are amplified and then converted into digital signals. Then, signal signals obtained for the radiation detection pixels 17e to 17h and 17i to 17l of the line H2 and the line H3 are input to the image processing device 13. The signal signals on the line H2 are collectively referred to as a signal signal S2, and the signal signals on the line H3 are collectively referred to as a signal signal S3.

  As described above, the gate driver 5 turns on the control electrodes 33 in two lines, one line at a time for the first region r1 and the second region r2. On the other hand, when the radiation detection matrix 3 is not divided, the gate driver 5 turns on the control electrodes 33 in one line at the same time. Therefore, by dividing the radiation detection matrix 3 into two regions, the time required to read out the signal signals of all the radiation detection pixels 17 is reduced to about half.

  However, the image processing device 13 cannot acquire accurate image information even if the input signal signals S1 to S4 are used as they are for imaging. This is because the leakage current is always output from the output electrode 31 as described above. Therefore, 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) that is actually 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 before performing imaging and correct the signal signal using the leak signal.

<Reading leak signal>
Therefore, in order to read out the leak signal, a gate operation signal from the control unit 11 to the gate driver 5, an amplifier operation signal to the amplifier arrays 7 and 8, and an AD conversion to the AD conversion units 9 and 10. A signal is output. Based on the gate operation signal, the gate driver 5 turns off the control electrodes 33 of all the radiation detection pixels 17 via the gate wirings G1 to G4. Since the control electrode 33 is in an off state, the switching element 29 is also in an off state. At this time, since it is ideal to be insulated at the portion of the switching element 29, no current should flow from the output electrode 31.

  However, as described above, actually, a part of the electric charge accumulated in the capacitor 27 passes through the switching element 29 and always flows from the output electrode 31 as a leakage current regardless of whether the switching element 29 is on or off. Therefore, even when the switching element 29 is in an off state, the leakage current is input to the amplifier arrays 7 and 8 via the signal lines Q1 to Q4 and the signal lines R1 to R4.

  The amplifier arrays 7 and 8 amplify the input leakage current based on the amplifier operation signal and output the amplified leakage current to the AD conversion units 9 and 10. The AD conversion units 9 and 10 convert the input leakage current into a digital signal based on the AD conversion signal. In this way, a signal after digital conversion obtained in a state where the switching element 29 is off is used as a leak signal. The leak signal obtained for each signal line is input to the image processing device 13. Note that the leak signal in each signal line is collectively referred to as a leak signal LK.

  At this time, for example, in the first region r1, leak currents flowing from the output electrodes 31 of the radiation detection pixel 17a and the radiation 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 radiation detection pixel 17a and the radiation detection pixel 17e are respectively connected in parallel to the signal line Q1. Similarly, the leak currents of the radiation detection pixel 17b and the radiation detection pixel 17f are summed via the signal line Q2, input to the amplifier 7b, and digitized by the AD converter 9b. Similarly, in the second region r2, for example, leakage currents of the radiation detection pixels 17i and the radiation detection pixels 17m are summed via the signal line R1 and input to the amplifier 8a, and are digitized by the AD converter 10a. Therefore, for example, the leakage currents of the radiation detection pixel 17a and the radiation detection pixel 17e are read together.

<Signal signal correction>
The image processing device 13 corrects the signal signal for each radiation detection pixel 17 using the collected leak signal before imaging. Specifically, the leak signal is subtracted from the signal signal. Taking the radiation detection pixel 17a as an example, the value of the leak signal read from the signal line Q1 is subtracted from the value of the signal signal read from the radiation detection pixel 17a. The value obtained by the subtraction correction becomes the value of the digital signal based on the accumulated charge of the radiation 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 radiation detection pixels 17b to 17p, and an accumulation signal is calculated for each radiation detection pixel 17. These accumulated signals are collectively referred to as accumulated signal T.

<Acquisition of fluoroscopic image>
The image processing device 13 performs imaging based on the accumulated signal T input from the AD conversion units 9 and 10 and inputs the obtained image information to the image display device 15. The image display device 15 acquires a fluoroscopic image of X-rays that have passed through the subject based on the image information input from the image processing device 13. Since the fluoroscopic image is acquired based on the accumulation signal T, that is, a digital signal that does not include the leak signal, the fluoroscopic image is not disturbed by the leak current.

  Therefore, in order to acquire a fluoroscopic image, it is necessary to read out a leak signal in addition to reading out a signal signal. The configuration of the first embodiment has a unique configuration for reading a leak signal. According to this configuration, a signal is added to a leak current that takes a negative value, and the leak current is converted to a positive value. The leak current that has become a positive analog signal is input to each of the amplifiers 7a to 7d and 8a to 8d constituting the amplifier arrays 7 and 8. The AD converters 9 and 10 perform digital conversion on the positive analog signal and read out the leak signal.

<Characteristic Configuration of Example 1>
A configuration for adding signals in the first embodiment will be described with reference to FIG. Since all of the radiation detection pixels have the following configuration, description will be made using the radiation detection pixel 17a as an example.

  The radiation detection pixel 17 a is provided with a changeover switch 35, a wiring 36, a capacitor 37, a first node 39, and a second node 41. The changeover switch 35 is electrically connected to the wiring 36 and switches a node connected to the wiring 36. The wiring 36 is a part of the signal line Q1, and connects the switching element 29 and the AD converter 9a. The capacitor 37 is provided between the changeover switch 35 and the wiring 36, and accumulates electric charges input to the amplifier 7a. The first node 39 is a terminal having a voltage VQ 1 and is connected to the wiring 36 through the changeover switch 35. The second node 41 is a terminal having a voltage VQ2, and is connected to the wiring 36 through the changeover switch 35. Voltage VQ2 is set to be higher than voltage VQ1.

  The changeover switch 35 corresponds to the switch in the present invention, and the capacitor 37 corresponds to the added charge storage means in the present invention. The first node 39 corresponds to a low voltage terminal in the present invention, and the second node corresponds to a high voltage terminal in the present invention.

  In the first embodiment, the changeover switch 35, the capacitor 37, the first node 39, and the second node 41 correspond to the adding means in the present invention, and the wiring 36 corresponds to the connection wiring in the present invention.

<Addition of signal in embodiment 1>
The changeover switch 35 switches the node connected to the wiring 36 from the first node 39 to the second node 41 when adding a signal to the leakage current. That is, since the voltage applied to the capacitor 37 is increased by (VQ2-VQ1), the electric charge accumulated in the capacitor 37 is output to the amplifier 7a in accordance with the change in the voltage applied to the capacitor 37. Since the charge input to the amplifier 7a, that is, a positive signal increases, the leak current that is a negative signal is converted to a positive value. As a result, the leak current input to the AD converter 9a via the amplifier 7a also has a positive value, so that the leak current can be digitally converted to obtain a leak signal.

  When the electrostatic capacity of the capacitor 37 is C and the charge output from the capacitor 37 is Q, Q = C × (VQ2−VQ1). Therefore, by setting C, VQ1, and VQ2 to appropriate values, it is possible to input an appropriate amount of charge to the amplifier 7a in order to convert the leakage current to a positive value.

<Description of Operation in Embodiment 1>
A shooting sequence according to the first embodiment will be described with reference to FIGS. 1, 3, and 4. FIG.

  First, in the period P1 shown in FIG. 4, the gate driver 5 turns on the switching elements 29 of the line H1 and the line H4. The signal currents on the lines H1 and H4 are amplified by the amplifier arrays 7 and 8, and then converted into digital signals by the AD converters 9 and 10. Then, the read signal signal S1 and signal signal S4 are input to the image processing device 13.

  Next, in the period P2, the gate driver 5 turns on the switching elements 29 of the line H2 and the line H3. The signal currents on the lines H2 and H3 are amplified by the amplifier arrays 7 and 8, and then converted into digital signals by the AD converters 9 and 10. Then, the read signal signal S2 and signal signal S3 are input to the image processing device 13.

  Here, when the signal signal is read in the period P1 and the period P2, switching by the selector switch 35 is not performed. That is, in the period P 1 and the period P 2, the first node 39 is connected to the wiring 36, so that no charge is input from the capacitor 37 to the amplifier arrays 7 and 8. Therefore, no signal is added to the signal current output from the output electrode 31.

  Then, before reading out the leakage current, in the period U, the changeover switch 35 switches the node connected to the wiring 36 from the first node 39 to the second node 41. At this time, the switching element 29 is turned off so that the signal signal is not read out. Since the charge input to the amplifier arrays 7 and 8 is increased by switching by the changeover switch 35, the leak current input to the AD conversion units 9 and 10 is converted from a negative value to a positive value.

  The leak current converted to a positive value is converted into a digital signal by the AD converters 9 and 10 (see the symbol W in FIG. 4). The leak signal LK digitized by the AD converters 9 and 10 is input to the image processing device 13.

  The image processing device 13 calculates the accumulation signal T using the input signal signals S1 to S4 and the leak signal LK, and performs imaging based on the accumulation signal T. The obtained image information is input to the image display device 15, and a fluoroscopic image is acquired based on the input image information.

  In the first embodiment, when reading the leakage current, charges are input from the capacitor 37 to the amplifier arrays 7 and 8, but when reading the signal current, no charges are input. As a result, for the reason described later, correction for subtracting the leak signal from the signal signal can be performed without reducing the gradation of the fluoroscopic image. That is, it is possible to prevent the occurrence of image disturbance due to the leakage current and to obtain a fluoroscopic image having various gradations.

<Determination of current value to be added to leakage current>
In the first embodiment, in order to surely digitally convert the leakage current, it is necessary to know in advance how much a signal is added to the leakage current to reliably convert the leakage signal to a positive value. . Therefore, an AD converter that can identify a negative signal experimentally is used to read in advance a negative value taken by the leakage current. Specifically, first, a negative leak signal output from each amplifier is measured, and the lowest one of the leak signals is selected. Then, a current value large enough to convert the lowest selected leak signal into a positive value is calculated. Based on the calculated current value, appropriate values are set for the capacitance C of the capacitor 37, the voltage VQ1 of the first node 39, and the voltage VQ2 of the second node 39. A fluoroscopic image is acquired.

<Effects of Configuration of Example 1>
Here, the effects described above in the first embodiment will be described with reference to FIG.

  When acquiring a transmission image by irradiating X-rays in a two-dimensional image detector having a conventional configuration, the output value of the amplifier in the ground state in which the stored charge is not read and the leakage current is not output in advance. Set to 0. This is because, as shown in FIG. 5A, the range of the output value of the amplifier that can be identified by the AD converter is widened, so that the gradation of the obtained fluoroscopic image is diversified. In this case, since the accumulated charge is 0, it is ideal that the leakage current is also 0. Since the AD converter can identify a signal having a value of 0 or more, the leak current should be digitally converted by the AD converter, and the leak signal should be read out.

  However, the actual leakage current takes a negative value. Since the AD converter cannot digitally convert a negative signal, the AD converter cannot digitally convert the leak current and read the leak signal. For this reason, since the correction for subtracting the leak signal from the signal signal cannot be performed, the disturbance of the image due to the leak current occurs in the obtained fluoroscopic image.

  In the conventional configuration, in order to make the leakage current input to the AD converter a positive value, as shown in FIG. 5B, the amplifier in the ground state in which the stored charge is not read and the leakage current is not output. Is set to take a predetermined positive value instead of zero. In this case, when the leakage current is read, the leakage current is raised from a negative value to a positive value, so that the AD converter can digitally convert the leakage current and read it as a leakage signal. Therefore, it is possible to perform correction by subtracting the leak signal from the signal signal, and thus it is possible to suppress image disturbance due to the leak current in the obtained fluoroscopic image.

  However, when the amplifier output in the ground state is set to a large value, as shown in FIG. 5B, the range of amplifier output values that can be identified by the AD converter becomes narrower than that in FIG. 5A. . As a result, the dynamic range is reduced, so that the gradation of the captured fluoroscopic image is reduced. That is, in the conventional two-dimensional image detector, in order to perform correction for subtracting the leak current, the dynamic range must be reduced. When the dynamic range is widened, correction for subtracting the leak signal from the signal signal can be performed. Can not.

  Thus, as a result of intensive studies, the inventor has come up with a two-dimensional image detector that can perform correction for subtracting the leak signal from the signal signal without reducing the dynamic range. That is, when reading out the leak current, an appropriate positive signal is added to the leak current in advance, and the leak current input to the AD converters 9 and 10 is converted into a positive value. Since the leak current that has been moved to a positive value can be digitally converted by the AD converters 9 and 10, a leak signal can be acquired and correction can be performed to subtract the leak signal from the signal signal.

  Then, when reading the signal signal, the operation for adding the positive signal is not performed, and the operation for adding the positive signal is performed only when the leakage current is read. As a result, as shown in FIG. 5C, the leak current, which is a negative signal, can be raised to a positive value while setting the output value of the amplifier in the ground state to 0.

  When the output value of the amplifier in the ground state is set to 0, the range of the output value of the amplifier that can be identified by the AD conversion units 9 and 10 is widened, so that the gradation of the obtained fluoroscopic image is diversified. Then, by performing correction by subtracting the leak signal from the signal signal, it is possible to prevent image disturbance due to the leak current in the acquired fluoroscopic image. Therefore, in the first embodiment of the present invention, it is possible to obtain a fluoroscopic image having various gradations and free from image disturbance due to leakage current.

  Next, Embodiment 2 of the present invention will be described with reference to FIG. Since all of the radiation detection pixels have the following configuration, description will be made using the radiation detection pixel 17a as an example.

<Characteristic Configuration of Example 2>
The radiation detection pixel 17 a is provided with a current source 43, a wiring 44, a current source connection switch 45, and a connection switch control unit 47. The current source 43 is electrically connected to the wiring 44 and supplies a predetermined current IA to the wiring 44. The wiring 44 is a part of the signal line Q1, and connects the switching element 29 and the AD converter 9a. The current source connection switch 45 is provided between the current source 43 and the wiring 44 and connects the current source 43 to the wiring 44. The connection switch control unit 47 is connected to the current source connection switch 45 and controls the operation of the current source connection switch 45.

  The current source 43 corresponds to current supply means in the present invention, and the current source connection switch 45 corresponds to current supply control means in the present invention.

  In the second embodiment, the current source 43, the current source connection switch 45, and the connection switch control unit 47 correspond to the adding means in the present invention, and the wiring 44 corresponds to the connection wiring in the present invention.

<Addition of signal in embodiment 2>
The connection switch control unit 47 causes the current source connection switch 45 to output a current source connection signal. The current source connection switch 45 connects the current source 43 to the wiring 44 over a predetermined period Z based on the input current source connection signal. That is, electric charge is output from the current source 43 to the amplifier 7a. For this reason, since the charge input to the amplifier 7a, that is, a positive signal increases, the leak current that is a negative signal can be converted to a positive value. As a result, the leak current amplified and input to the AD converter 9a also has a positive value, so that the leak signal can be obtained by digital conversion.

  When the current IA is supplied from the current source 43 to the amplifier 7a over a predetermined period Z, the equation Q = IA × Z is established, where Q is the charge input from the current source 43 to the amplifier 7a. Therefore, by setting IA and Z to appropriate values, it is possible to input an appropriate amount of charge to the amplifier 7a in order to convert the leakage current to a positive value.

  The shooting sequence according to the second embodiment is common to the shooting sequence of the first embodiment shown in FIG. 4 in that a signal is not added in the period P1 or the period P2 and a positive signal is added in the period U. . That is, in Example 2, the signal signal is read without connecting the current source 43 to the wiring 44 in the period P1 or the period P2. In the period U, the current source 43 is connected to the wiring 44 to convert the leak current from a negative value to a positive value. The leak current converted to a positive value is digitized by the AD converters 9 and 10 and read out as a leak signal in the period W.

  In the second embodiment, the magnitude of a signal to be added to the leak current when reading the leak current is calculated in advance by the same method as in the first embodiment. Based on the calculated current value, appropriate values are set for the current IA and the predetermined period Z, and a fluoroscopic image is actually acquired based on the setting.

  In the second embodiment, the same effects as in the first embodiment can be obtained by the above-described configuration and shooting sequence. That is, in the two-dimensional image detector 1 according to the second embodiment, it is possible to acquire a fluoroscopic image having various gradations without any image disturbance due to the leakage current.

  Next, Embodiment 3 of the present invention will be described with reference to FIG. Since all of the radiation detection pixels have the following configuration, description will be made using the radiation detection pixel 17a as an example.

<Characteristic Configuration of Example 3>
The radiation detection pixel 17 a is provided with an adder 49, a wiring 50, and an adder control unit 51. The adder 49 is provided in the wiring 50 and adds a predetermined voltage VA to the wiring 50. The wiring 50 is a part of the signal line Q1, and connects the amplifier 7a and the AD converter 9a. The adder control unit 51 is connected to the adder 49 and controls the operation of the adder 49.

  In the third embodiment, the adder 49 and the adder control unit 51 correspond to the adding means in the present invention.

<Addition of Signal in Example 3>
The adder control unit 51 causes the adder 49 to output a voltage addition signal. The adder 49 adds a predetermined voltage VA to the wiring 50 based on the voltage addition signal. By adding the voltage, the leak current that was a negative signal is converted into a positive signal and input to the AD converter 9a. As a result, the AD converter 9a can digitally convert the leak current, so that a leak signal can be acquired.

  The shooting sequence according to the third embodiment is common to the shooting sequence according to the first embodiment shown in FIG. 4 in that a signal is not added in the period P1 or the period P2 and a positive signal is added in the period U. . That is, in the third embodiment, in the period P1 or the period P2, the signal signal is read without adding the voltage by the adder 49. Then, the voltage is added to the adder 49 in the period U, and the leakage current is converted from a negative value to a positive value. The leak current converted to a positive value is digitized by the AD converters 9 and 10 and read out as a leak signal in the period W.

  In the third embodiment, the magnitude of a signal to be added to the leak current when reading the leak current is calculated in advance by the same method as in the first embodiment. An appropriate value is set for the predetermined voltage VA based on the calculated current value, and a fluoroscopic image is actually acquired based on the setting.

  With the above-described configuration and shooting sequence, the same effects as in the first and second embodiments can be obtained in the third embodiment. In other words, in the two-dimensional image detector 1 according to the third embodiment, it is possible to acquire fluoroscopic images having various gradations without any image disturbance due to the leakage current.

  Further, in the third embodiment, the leak current is amplified by the amplifier 7a and then converted to a positive value by the adder 49. That is, noise caused by the adder 49 is not amplified by the amplifier 7a. That is, noise superimposed on the leak current can be reduced, and the signal signal can be corrected using a more accurate leak signal.

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

  (1) In each of the above-described embodiments, as shown in FIG. 4, the leak signal is read only once for one fluoroscopic image capturing, and the signal signal is corrected using the leak signal. It is not limited to this. That is, the leak signal may be read out twice or more for one fluoroscopic image capturing. In this case, the value of the leak signal read for the first time and the value of the leak signal read for the second time and thereafter are averaged. Then, the obtained average value is subtracted from the signal signal to calculate the accumulated signal.

  Thus, by calculating the average value of leak signals read twice or more, the leak signals can be read more accurately. Therefore, by correcting the signal signal using the average value of the leak signal, it is possible to acquire a fluoroscopic image with less image disturbance due to fluctuations in the timing of reading the leak signal.

  (2) In each of the above-described embodiments, the radiation detection pixels 17 constituting the radiation detection matrix 3 are divided into two regions. However, the present invention is not limited to this. That is, the radiation detection matrix 3 may be configured not to be divided, or may be configured to be divided into two or more regions.

  (3) In each of the embodiments described above, the leak signal is read after reading the signal signal, but the present invention is not limited to this. That is, the leak signal may be read before reading the signal signal, or the leak signal may be read after reading the signal signals S1 and S4, and finally the signal signals S2 and S3 may be read.

  (4) In each of the embodiments described above, the signal signals S2 and S3 are read after reading the signal signals S1 and S4, but the present invention is not limited to this. That is, after reading out the signal signals S1 and S3, the signal signals S2 and S4 may be read out, or after reading out the signal signals S2 and S3, the signal signals S1 and S4 may be read out.

1 ... Two-dimensional image detector 3 ... Radiation detection matrix (pixel matrix)
5 ... Gate triber (switching control means)
7, 8 ... Amplifier array (amplification means)
9, 10 ... AD converter (digital conversion means)
17a to 17p: Radiation detection pixels (pixels)
21 ... Conversion layer (charge conversion means)
27: Capacitor (conversion charge storage means)
29 ... Switching element (switching means)
31 ... Output electrode 35 ... Changeover switch (switch)
37: Capacitor (additional charge storage means)
39 ... 1st node (low voltage terminal)
41 ... 2nd node (high voltage terminal)
43 ... Current source (current supply means)
45 ... Connection switch (current supply control means)
49 ... Adders G1 to G4 ... Gate wirings H1 to H4 ... Lines Q1 to Q4, R1 to R4 ... Signal lines

Claims (9)

Charge conversion means for converting incident electromagnetic waves into charges, conversion charge storage means for storing charges converted by the charge conversion means, output electrodes provided in the conversion charge storage means, and conversion charge storage means A pixel matrix in which pixels composed of switching means for outputting the charge accumulated in each of the output electrodes to two-dimensionally, and
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;
Switching control means for controlling each of the switching means;
Image acquisition means for converting the digital signal and acquiring an image,
Addition that adds a positive signal to the leak current that is output from each of the pixels constituting the pixel matrix and is a negative signal, and converts the leak current that is input to the digital conversion means to a positive value A two-dimensional image detector comprising means. The two-dimensional image detector according to claim 1, wherein the adding unit includes:
A switch that is electrically connected to a connection wiring that electrically connects the switching means and the digital conversion means;
Added charge storage means for storing charges provided between the switch and the connection wiring;
A low voltage terminal connected to the connection wiring via the switch;
A high voltage terminal having a voltage higher than the voltage of the low voltage terminal and connected to the connection wiring through the switch;
With the switch being switched to the low voltage terminal, the charge accumulated in the converted charge accumulation means is read out,
By switching the switch from the low voltage terminal to the high voltage terminal and increasing the charge input to the amplifying means via the added charge storage means, the leakage current that is a negative signal is reduced. Two-dimensional image detector that converts to positive values. The two-dimensional image detector according to claim 1, wherein the adding unit includes:
A current supply means electrically connected to a connection wiring electrically connecting the switching means and the digital conversion means, and supplying a current to the connection wiring;
A current supply control means provided between the current supply means and the connection wiring, for controlling electrical connection between the current supply means and the connection wiring;
The current supply control means reads the charge accumulated in the converted charge accumulation means in a state where the current supply means is not electrically connected to the connection wiring,
By connecting the current supply means to the connection wiring for a predetermined period via the current supply control means and increasing the charge input to the amplifying means, the leakage current that is a negative signal is corrected positively. A two-dimensional image detector that converts to the value of. The two-dimensional image detector according to claim 1, wherein the adding unit includes:
An adder for adding a voltage to the output from the amplification means;
And an adder control means for controlling the adder,
The adder control means causes the output from the amplifying means to read out the charge accumulated in the converted charge accumulating means in a state where the voltage is not increased by the adder,
A two-dimensional image detector for converting the leak current, which is a negative signal, into a positive value by increasing the voltage to the output from the amplifying means by the adder via the adder control means. The two-dimensional image detector according to claim 2 or 3,
The adding means is a two-dimensional image detector provided between the switching means and the amplifying means. The two-dimensional image detector according to claim 4, wherein
The adding means is a two-dimensional image detector provided between the amplifying means and the digital converting means. The two-dimensional image detector according to any one of claims 1 to 6,
The two-dimensional image detector in which the timing for converting the leakage current from the negative value to the positive value by the adding means is set before the timing for reading the leakage current. The two-dimensional image detector according to any one of claims 1 to 7,
Using a digital conversion means that can identify a negative signal experimentally, the negative value taken by the leakage current is read in advance, the lowest one of the measured leakage currents is selected, and the lowest selected A two-dimensional calculation of a current value large enough to convert the leakage current into a positive value and setting the calculated current value as the magnitude of the signal added by the adding means Image detector. The two-dimensional image detector according to any one of claims 1 to 8,
The pixel matrix has two divided regions,
The switching control unit operates so as to simultaneously read out the pixels in the other divided region corresponding to the pixel to be read when reading out the pixels constituting the one divided region. Image detector.

Images