Imaging apparatus and imaging system

An imaging apparatus has an AEC function that can prevent irregularities in photographed images, without being increased in size. The imaging apparatus comprises a plurality of pixels arranged in a matrix shape, each of the plurality of pixels including a conversion element for converting radiation or light into an electric charge, a plurality of lines that are connected to the plurality of pixel units and that extend in different directions to each other, a current monitor circuit that monitors currents flowing in the plurality of lines, and an arithmetic unit that calculates a two-dimensional distribution by performing back-projection processing with respect to the currents flowing in the plurality of lines monitored by the current monitor circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging apparatus and an imaging system.

2. Description of the Related Art

In recent years, radiation imaging apparatuses including a flat panel detector (hereinafter abbreviated as “FPD”) formed of a semiconductor material have started to be put to practical use as photographing apparatuses that are used for medical diagnostic imaging or nondestructive inspection using X-rays. The radiation imaging apparatuses that use an FPD are capable of digital photographing in which radiation such as X-rays that were transmitted through a subject such as a patient are converted into analog electrical signals at the FPD, and the analog electrical signals are subjected to analog-to-digital conversion to acquire digital image signals. The FPDs that are used in such radiation imaging apparatuses are broadly divided into direct-conversion type FPDs and indirect-conversion type FPDs. A direct-conversion type radiation imaging apparatus includes an FPD in which a plurality of pixels that include a conversion element made using a semiconductor material, such as a-Se, that is capable of converting radiation directly into an electric charge are arranged in a two-dimensional shape. An indirect-conversion type radiation imaging apparatus includes an FPD in which a plurality of pixels that include a conversion element having a wavelength converter such as a phosphor that can convert radiation into light and a photoelectric conversion element made using a semiconductor material such as a-Si that can convert light into an electric charge are arranged in a two-dimensional shape. Such radiation imaging apparatuses that include an FPD are used, for example, in medical diagnostic imaging as digital imaging apparatuses for still image photographing like general photographing or moving image photographing such as fluoroscopy. In X-ray photographing, AEC (automatic exposure control) is used so that the amount of X-rays transmitted through a subject is within a photographing range that can be detected by a radiation imaging apparatus and also to suppress to the minimum the amount of X-ray exposure of a subject.

SUMMARY OF THE INVENTION

In Japanese Patent Application Laid-Open No. H11-188021, an AEC sensor is provided separately to a detector for imaging a subject, and is disposed on the rear face of the radiation imaging apparatus and controls an X-ray generating apparatus. Consequently, in the case of a portable radiation imaging apparatus, there is the problem that the radiation imaging apparatus becomes thicker and is difficult to carry. Further, in Japanese Patent Application Laid-Open No. 2004-73256, AEC sensors are formed between pixels for imaging a subject. When the AEC sensors are disposed between pixels, there is the problem that irregularities arise in photographed images because the pixel layout is uneven in regions where the AEC sensors are disposed.

An object of the present invention is to provide an imaging apparatus and an imaging system that, without being increased in size, have an AEC function that can prevent irregularities in photographed images.

In order to achieve the object, the present invention provides an imaging apparatus comprising a plurality of pixels arranged in a matrix shape, each of the plurality of pixels including a conversion element for converting radiation or light into an electric charge, a plurality of lines that are connected to the plurality of pixels and that extend in different directions to each other, a current monitor circuit that monitors currents flowing in the plurality of lines, and an arithmetic unit that calculates a two-dimensional distribution by performing back-projection processing with respect to the currents flowing in the plurality of lines monitored by the current monitor circuit.

According to the present invention, an imaging apparatus can be provided that, without being increased in size, has an AEC function that can prevent irregularities in photographed images.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1is a block diagram of an imaging system including an imaging apparatus and an X-ray generating apparatus according to a first embodiment of the present invention. The imaging system can be used for diagnosis for medical treatment or for nondestructive inspections for industrial use. An imaging apparatus100includes a detection unit101that includes a plurality of pixels for converting radiation or light into an analog electrical signal that are arranged in a matrix shape, and a drive circuit102that drives the detection unit101to output an analog electrical signal from the detection unit101. The term “radiation” includes electromagnetic waves such as X-rays and γ-rays, and α-rays and β-rays. According to the present embodiment, to simplify the description it is assumed that the detection unit101includes pixels arranged to form 8 rows and 8 columns and is divided into is a first pixel group101aand a second pixel group101bthat each includes four pixel columns. An analog electrical signal112that is output from the first pixel group101ais read by a corresponding first read circuit103a. An analog electrical signal113from the first read circuit103ais converted to a digital signal114by a corresponding first A/D converter104a. Similarly, the analog electrical signal112from the second pixel group101bis read by a corresponding second read circuit103b. An analog electrical signal from the second read circuit103bis converted to a digital signal by a corresponding second A/D converter104b. The digital signals from the first and second A/D converters104aand104bare subjected to simple digital signal processing, such as digital multiplex processing or offset correction, by a digital signal processing unit105, and a resulting digital image signal115is output.

A signal processing unit106has a read circuit unit103that includes the first and second read circuits103aand103b, an A/D converter unit104that includes the first and second A/D converters104aand104b, and the digital signal processing unit105. The imaging apparatus100further includes a power supply unit107that applies a bias to the signal processing unit106. The power supply unit107outputs a first reference voltage Vref1and a second reference voltage Vref2to the read circuit unit103, and outputs a third reference voltage Vref3to the A/D converter unit104. The power supply unit107also supplies an on-bias voltage Von for turning on switching elements inside the pixels as well as an off-bias voltage Voff for turning off the switching elements to the drive circuit102. In addition, the power supply unit107supplies a sensor bias Vs that is applied to photoelectric conversion elements of the detection unit101. The power supply unit107includes an AEC monitor unit508that has an AEC function by monitoring a current that flows in the sensor bias Vs and the off-bias voltage Voff. The imaging apparatus100further includes a control unit108for controlling at least one of the signal processing unit106and the power supply unit107. The control unit108supplies a drive control signal119to the drive circuit102. The drive circuit102supplies a drive signal111to the detection unit101based on the drive control signal119. The control unit108supplies an operation control signal118to the power supply unit107, and the power supply unit107controls a bias that is supplied to the detection unit101, the drive circuit102and the read circuit unit103. The control unit108also supplies signals116,117and120for controlling the read circuit unit103.

Reference numeral501denotes an X-ray generating apparatus (radiation generating apparatus), reference numeral502denotes an X-ray control apparatus for controlling the X-ray generating apparatus501, and reference numeral503denotes an exposure button that a user uses to perform X-ray irradiation. Reference numeral552denotes a communication signal for communication between the imaging apparatus100and the X-ray control apparatus502. Reference numeral505denotes X-ray beams. When the user presses the exposure button503, the X-ray control apparatus502outputs a confirmation signal indicating whether or not irradiation of X-rays is possible to the imaging apparatus100through the communication signal552. When an enabling signal is input from the imaging apparatus100, the X-ray generating apparatus501is caused to start irradiation of the X-ray beams505. After X-ray irradiation starts, the AEC monitor unit508monitors the amount of X-ray irradiation, and if the amount of X-ray irradiation becomes equal to or greater than a certain amount the imaging apparatus100outputs a stop signal to the X-ray control apparatus502, and the X-ray control apparatus502stops the irradiation of the X-ray beams505by the X-ray generating apparatus501.

FIG. 2is a view that illustrates a configuration example of the imaging apparatus100. Note that elements inFIG. 2having the same configuration as that described usingFIG. 1are assigned the same reference numerals, and detailed descriptions thereof are omitted. The detection unit101has a plurality of pixels201that are arranged in a matrix shape. InFIG. 2, 8×8 pixels are arranged over 8 rows and 8 columns. Each of the plurality of pixels201includes a conversion element S that converts radiation or light into an electric charge, and a switching element T that outputs an electrical signal that is based on the electric charge of the conversion element S to a signal line Sig. The plurality of pixels201are arranged in a two-dimensional matrix shape. A photoelectric conversion element such as a PIN-type photodiode or an MIS-type photodiode that is provided on an insulating substrate such as a glass substrate and that includes amorphous silicon as the main material can be used as the conversion element S that converts light into an electric charge. An indirect-type conversion element having a wavelength converter that is provided on the side on which radiation is incident of the above-described photoelectric conversion element and that converts radiation into light falling within the band of wavelengths that can be sensed by the photoelectric conversion element, or a direct-type conversion element that directly converts radiation into an electric charge can be used as the conversion element that converts radiation into an electric charge. A transistor having a control terminal and two main terminals can be used as the switching element T, and in the case of a pixel having the photoelectric conversion element S provided on an insulating substrate, a thin film transistor (TFT) can be used. One of the electrodes of the conversion element S is electrically connected to one of the two main terminals of the switching element T, and the other electrode is electrically connected to sensor bias lines VS1to VS8via a common line. A sensor bias Vs is supplied to the sensor bias lines VS1to VS8, and the sensor bias lines VS1to VS8supply the sensor bias Vs to the conversion elements S. Switching elements T of a plurality of pixels in the row direction, for example, switching elements T11to T18, have control terminals that are commonly electrically connected to a drive line G1of the first row. Drive signals for controlling the conductive state of the switching elements T are applied from the drive circuit102via drive lines G on in row units. In the switching elements T of the plurality of pixels in the column direction, for example, switching elements T11to T81, the other main terminals thereof are electrically connected to a signal line Sig1of the first column. Electrical signals corresponding to the electric charge of the conversion elements S are output to the read circuit103via signal lines Sig during a period in which the switching elements T are in a conductive state.

According to the present embodiment, the drive lines G1to G8that extend in the horizontal direction and the sensor bias lines VS1to VS8that extend in the vertical direction are connected to the AEC monitor unit508. The AEC monitor unit508monitors (detects) currents that flow in the drive lines G1to G8and the sensor bias lines VS1to VS8during X-ray irradiation. A plurality of signal lines Sig1to Sig8arranged in the column direction transmit the electrical signals output from the plurality of pixels201of the detection unit101to the read circuit103in parallel. According to the present embodiment, the detection unit101is divided into the first pixel group101aand the second pixel group101bthat each includes four pixel columns. Analog electrical signals that were output from the first pixel group101aare read in parallel by the corresponding first read circuit103ain the read circuit103, and analog electrical signals that output from the second pixel group101bare read in parallel by the second read circuit103b.

FIG. 3is a view that illustrates a configuration example of the first read circuit103a. Although the following description takes the configuration of the first read circuit103aas an example, the configuration of the second read circuit103bis the same as that of the first read circuit103a. The first read circuit103aincludes a first amplification circuit unit202aconfigured to amplify the electrical signals that are output in parallel from the first pixel group101a, and a first sample and hold circuit unit203athat samples and holds electrical signals from the first amplification circuit unit202a. The second read circuit103bsimilarly includes a second amplification circuit unit202band a second sample and hold circuit unit203b. The first and second amplification circuit units202aand202beach includes an operational amplifier A configured to amplify and output the read electrical signal, an integration capacitor group Cf and a reset switch RC configured to reset the integration capacitors Cf, and are provided in correspondence with the respective signal lines Sig. An electrical signal of the signal line Sig is input to an inverting input terminal of the operational amplifier A, and an amplified electrical signal is output from an output terminal of the operational amplifier A. The reference voltage Vref1is input to the non-inverting input terminal of the operational amplifier A. The first and second sample and hold circuit units203aand203binclude sampling switches SHON, SHEN, SHOS and SHES, and sampling capacitors Chon, Chen, Chos and Ches, and are provided in correspondence with the respective amplification circuit units202aand202b. The first read circuit103aincludes a first multiplexer204athat sequentially outputs electrical signals read in parallel from the first sample and hold circuit unit203aand that outputs the electrical signals as serial image signals. Similarly, the second read circuit103bincludes a second multiplexer204bthat sequentially outputs electrical signals read in parallel from the second sample and hold circuit unit203band that outputs the electrical signals as serial image signals. The first multiplexer204aincludes switches MSON, MSEN, MSOS and MSES that correspond to the sampling capacitors Chon, Chen, Chos and Ches, and converts parallel signals to serial signals by sequentially selecting the respective switches. The first read circuit103aalso includes output buffer circuits SFN and SFS that perform impedance conversion on the output signals of the first multiplexer204a, switches SRN and SRS, and a first variable amplifier205a. InFIG. 2, the A/D converter104aconverts the output signals of the first variable amplifier205afrom analog signals to digital signals, and outputs image data to the signal processing circuit105.

FIG. 4is a view that illustrates a configuration example of the imaging apparatus100according to the present invention. Note that elements inFIG. 4having the same configuration as that described usingFIG. 2are assigned the same reference numerals, and detailed descriptions thereof are omitted. The AEC monitor unit508includes sensor bias current monitor circuit units MVS1to MVS8, drive line current monitor circuit units MVG1to MVG8, filter unit560and arithmetic unit561. The sensor bias current monitor circuit units MVS1to MVS8monitor currents flowing in the sensor bias lines VS1to VS8. The drive line current monitor circuit units MVG1to MVG8monitor currents flowing in the drive lines G1to G8. The filter unit560performs filter processing on monitor output results of the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8. The arithmetic unit561performs back-projection processing on output results of the filter unit560, calculates a value of a region of interest, and if the value of the region of interest exceeds a previously set threshold value, outputs the stop signal551to the control unit108to stop X-ray irradiation. Further, region of interest information and threshold value information are output to the AEC monitor unit508from the control unit108by means of a monitor condition signal550.

The sensor bias current monitor circuit units MVS1to MVS8include a transimpedance amplifier mamp1, feedback resistances MRF1and MRF2, a switch MSW, an instrumentation amplifier mamp2and an analog-to-digital converter MADC. Similarly, the drive line current monitor circuit units MVG1to MVG8include the transimpedance amplifier mamp1, the feedback resistances MRF1and MRF2, the switch MSW, the instrumentation amplifier mamp2and the analog-to-digital converter MADC. The transimpedance amplifier mamp1converts a current flowing in the sensor bias lines VS1to VSBor the drive lines G1to G8into a voltage. The feedback resistances MRF1and MRF2set a conversion gain when converting a current into a voltage. The instrumentation amplifier mamp2further multiplies the voltage obtained by conversion at the transimpedance amplifier mamp1by the gain. The analog-to-digital converter MADC converts the voltage value from the instrumentation amplifier mamp2from an analog value to a digital value. Monitoring to realize the AEC function cannot be correctly performed unless a signal is input that is within an input range of the analog-to-digital converter MADC. Therefore, a gain changeover switch MSW for lowering the current-voltage conversion gain when the analog-to-digital converter MADC has overflowed is provided. Thus, AGC (automatic gain control) is realized that changes over the switch MSW by means of an overflow signal OF.

FIG. 5is a flowchart illustrating operations of the imaging apparatus according to the present invention.FIGS. 6A to 6D,FIGS. 7A to 7CandFIG. 8are views that illustrate methods of processing monitor output results. Operations of the first embodiment will now be described referring to the flowchart shown inFIG. 5. In step S301, a monitoring position (region of interest) of the AEC is designated by a technician before photographing. The X-ray control apparatus502performs control of the X-ray generating apparatus501so that the amount of X-rays at the designated monitoring position becomes the optimal amount. Designation of the monitoring position can be performed by a technician, or the monitoring position can be automatically decided by designating a photographing site. Information regarding the designated monitoring position is output to the AEC monitor unit508from the control unit108by means of the monitor condition signal550.

In step S302, photographing is started. In step S303, a voltage is supplied to the sensor bias lines VS1to VS8in the detection unit101, and the imaging apparatus100performs idling (K). In the idling (K), the drive lines G1to G8are actuated in sequential order, the switching elements T are turned on in row units, and resetting of a dark current that flows in the conversion elements S is performed. Next, in step S304, the exposure button503is pushed. Thereafter, in step S305, the reset operation is performed as far as the last drive line G8, and the imaging apparatus100transitions to an accumulation operation (W). Next, in step S306, the AEC monitor unit508starts to monitor the currents flowing in the sensor bias lines VS1to VS8and the drive lines G1to G8. When X-rays (light) are irradiated onto the conversion elements S, electrons and positive holes are generated in the conversion elements S, and because the switching elements T are turned off during the period of the accumulation operation (W), most of the generated electrons and positive holes do not flow to an external circuit and are accumulated in the conversion elements S. A part of a current that depends on a parasitic capacitance of the switching elements T flows to the sensor bias lines VS1to VS8and the drive lines G1to G8, and the amount of X-rays irradiated during the accumulation operation (W) is monitored by measuring the current.

A current of an amount in proportion to the amount of X-rays that were irradiated onto the conversion elements S11to S81connected to the sensor bias line VS1flows in the sensor bias lines VS1, and a current of an amount in proportion to the amount of X-rays irradiated onto the conversion elements S11to S18flows in the drive line G1. The currents that flowed through the aforementioned lines are converted into digital values via the transimpedance amplifier mamp1, the instrumentation amplifier mamp2and the analog-to-digital converter MADC.FIG. 6Ais a view that represents currents that flow in the sensor bias lines VS1to VSB, andFIG. 6Bis a view that represents currents that flow in the drive lines G1to G8. In step S307, the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8output the digital values of the currents that flow in the sensor bias lines VS1to VS8and the drive line G1to G8, respectively.

Next, in step S308, the filter unit560performs filter processing on the digital values output from the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8. Because the digital values output from the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8includes a large amount of low-frequency noise components, the low-frequency components are removed via a high-pass filter of the filter unit560. Values output from the filter unit560are illustrated inFIGS. 6C and 6D.FIG. 6Cis a view that represents currents of the sensor bias lines VS1to VS8, andFIG. 6Dis a view that represents currents of the drive lines G1to G8.

Next, in step S309, in order to convert the output values of the filter unit560into two-dimensional data, the arithmetic unit561performs back-projection processing with respect to the sensor bias lines VS1to VS8that extend in the vertical direction.FIG. 7Ais a view that illustrates back-projection processing with respect to the sensor bias lines VS1to VS8, in which one-dimensional output results output from the filter unit560are back-projected onto a two-dimensional memory. When performing the back-projection processing, since the digital values output from the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8are values obtained by integrating the values for one column or one row, values obtained by dividing the digital values by the number of rows or the number of columns, respectively, are subjected to the back-projection processing.

Next, in step S310, as shown inFIG. 7B, the arithmetic unit561performs back-projection processing with respect to the drive lines G1to G8that extend in the horizontal direction. Thereafter, in step S311, the arithmetic unit561adds the back-projection results for the drive lines G1to G8that extend in the vertical direction to the results of the back-projection processing (FIG. 7A) for the sensor bias lines VS1to VS8that extend in the vertical direction. The filter processing and back-projection processing are performed by a similar method to reconstruction processing that is performed by a CT apparatus. By performing back-projection processing for the sensor bias lines VS1to VS8that extend in the vertical direction and back-projection processing for the drive lines G1to G8that extend in the horizontal direction, a two-dimensional distribution of X-rays transmitted through the subject can be obtained. That is, the sensor bias current monitor circuit units MVS1to MVS8and the drive line current monitor circuit units MVG1to MVG8monitor currents that flow in the sensor bias lines VS1to VS8and the drive lines G1to G8that extend in two different directions that are connected to the plurality of pixels201. The arithmetic unit561calculates the two-dimensional distribution by performing back-projection processing with respect to the currents flowing in the sensor bias lines VS1to VS8and the drive lines G1to G8that extend in the two different directions. Next, since it is necessary to calculate an integrated value of the X-ray amounts at the monitoring position (region of interest) to realize the AEC function, as shown inFIG. 7C, the arithmetic unit561adds the back-projection processing results shown inFIG. 7Bto the addition memory.

Next, in step S312, as shown inFIG. 8, the arithmetic unit561performs subject correction processing by multiplying the values of the addition memory after the addition processing as shown inFIG. 7Cby subject correction coefficients. Depending on the site that is photographed, a large amount of X-rays is irradiated at a part of the detector101and the output of a corresponding column or row increases, and it is not possible to accurately read the value of a portion at which a small amount of X-rays was irradiated in the same column. Therefore, by calculating subject correction coefficients in advance in accordance with the photographing site and multiplying by the subject correction coefficients, the amount of X-rays of a region of interest can be monitored with a high degree of accuracy.FIG. 8illustrates an example with respect to photographing of the chest. When photographing the chest, the output increases because X-ray absorption does not occur at portions at the sides of the torso (regions of row5to row8of column1and column8inFIG. 8). However, since current that is the total for one row flows in the drive lines G1to G8, it appears as if one row was averaged. Therefore, when back-projection processing is performed, a value for a place at which the output is a large value decreases and a value for a place at which the output is a small value increases. Since the relationship between the sizes of outputs at a region depends on the photographing site, it is possible to calculate subject correction coefficients in advance and perform correction.

Next, in step S313, the arithmetic unit561determines whether or not a value after subject correction at a previously set monitoring position exceeds a threshold value, and if the value does not exceed the threshold value, the arithmetic unit561returns to step S307to continue the monitoring. If the aforementioned value exceeds the threshold value, in step S314, the arithmetic unit561outputs the stop signal551for stopping the X-ray irradiation to the control unit108, and the control unit108stops the X-ray irradiation (radiation irradiation) of the X-ray generating apparatus501through the X-ray control apparatus502. With respect to the determination method, the user may designate a monitoring position in advance, or a monitoring position may be decided according to the photographing site or the like. Further, with respect to the size of the monitoring position, any one of an average value, a maximum value and a minimum value of a single region (for example, row3, column3) or a plurality of regions (for example, rows3to5, columns3to6) may be compared with the threshold value. Further, methods are available which have a single threshold value, or have a plurality of threshold values that differ by region in a matrix shape, and which stop the X-ray irradiation if any one value exceeds a threshold value, or if all values exceed a threshold value, or if half or more of the values exceed a threshold value. After the X-ray irradiation has been stopped, in step S315, the imaging apparatus100starts a read operation for a subject image that is to be used for diagnosis.

By monitoring currents flowing in the sensor bias lines VS1to VS8and the drive lines G1to G8and performing back-projection processing in this manner, it is possible to determine the amount of X-rays at a region of interest that were transmitted through a subject. The AEC function can be realized by controlling the X-ray generating apparatus501so that the amount of X-rays at the region of interest becomes the optimal amount based on the determined amount of X-rays.

Second Embodiment

FIG. 9is a view that illustrates a configuration example of the imaging apparatus100according to a second embodiment of the present invention. Note that elements inFIG. 9having the same configuration as that described in the first embodiment are assigned the same reference numerals, and detailed descriptions thereof are omitted. In the first embodiment, the sensor bias lines VS1to VS8were wired commonly to a single column and the drive lines G1to G8were wired commonly to a single row. When a large amount of X-rays is irradiated at a part of the detector101and the output of a corresponding column or row increases, and it is not possible to accurately read the value of a portion at which a small amount of X-rays was irradiated in the same column. Therefore, according to the second embodiment, the sensor bias lines VS1to VS8are divided into two groups on the upper and lower sides, namely, sensor bias lines VSU1to VSU8and VSD1to VSD8, and the drive lines G1to G8are divided into two groups on the left and right sides, namely, drive lines GR1to GR8and GL1to GL8. Thus, according to the present embodiment, the detector101is divided into a total of four blocks. Consequently, even if a large amount of X-rays is irradiated at one part of the detector101, it is possible to accurately monitor the X-rays at another block. The drive circuit102supplies a drive signal to the drive lines GR1to GR8and GL1to GL8. The sensor bias current monitor circuit units MVSU1to MVSU8monitor currents flowing in the sensor bias lines VSU1to VSU8and output the monitoring results to the filter unit560. The sensor bias current monitor circuit units MVSD1to MVSD8monitor currents flowing in the sensor bias lines VSD1to VSD8and output the monitoring results to the filter unit560. The drive line current monitor circuit units MVGL1to MVGL8monitor currents flowing in the drive lines GL1to GL8and output the monitoring results to the filter unit560. The drive line current monitor circuit units MVGR1to MVGR8monitor currents flowing in the drive lines GR1to GR8and output the monitoring results to the filter unit560.

As described above, the current monitor circuit units may be configured to monitor currents in each region into which the plurality of pixels201are divided with respect to at least one line among lines that extend in two or more different directions.

Third Embodiment

FIG. 10is a view that illustrates a configuration example of the imaging apparatus100according to a third embodiment of the present invention. Note that elements inFIG. 10that have the same configuration as that described in the first embodiment are assigned the same reference numerals, and detailed descriptions thereof are omitted. In the first embodiment, because the arrangement of the lines is such that the sensor bias lines VS1to VS8and the drive lines G1to G8are orthogonal to each other, back-projection processing is performed from two directions. According to the third embodiment, the sensor bias lines VS1to VS7are wired in a diagonal direction. The sensor bias current monitor circuit units MVS1to MVS7monitor currents that flow in the sensor bias lines VS1to VSD7that extend in the diagonal direction, and output the monitoring results to the filter unit560. The drive line current monitor circuit units MVG1to MVG4monitor currents that flow in the drive lines G1to G4that extend in the horizontal direction, and output the monitoring results to the filter unit560.

In addition, switches R1to R4are connected between a non-inverting input terminal and an output terminal of operational amplifiers A1to A4, respectively. Signal line current monitor circuit units MVi1to MVi4have the same configuration as the above described sensor bias current monitor circuit units MVS1to MVS7, and monitor currents flowing in signal lines Sig1to Sig4that extend in the vertical direction, and output the monitoring results to the filter unit560. Since the sensor bias current monitor circuit units MVS1to MVS7, the drive line current monitor circuit units MVG1to MVG4and the signal line current monitor circuit units MVi1to MVi4monitor currents, the arithmetic unit561performs back-projection processing for lines in three different directions. When performing back-projection processing, the greater the number of directions for which the back-projection processing is performed, the greater the accuracy with which a two-dimensional distribution can be determined. Further, as shown inFIG. 11, although back-projection processing is also performed in the diagonal direction, since the number of pixels for which results are integrated differs depending on the lines, it is necessary to divide the respective results by the number of pixels whose results are integrated for each line.

Note that, the current monitor circuit units may be configured to monitor currents that flow in lines extending in two or more different directions among the signal lines Sig1to Sig4, the sensor bias lines VS1to VS7and the drive lines G1to G8. In such case, the arithmetic unit561calculates the two-dimensional distribution by performing back-projection processing on currents flowing in lines extending in two or more different directions that are monitored by the current monitor circuit units.

Fourth Embodiment

FIG. 12is a view that illustrates a configuration example of a pixel201(FIG. 2) according to a fourth embodiment of the present invention. Note that elements inFIG. 12having the same configuration as that described in the third embodiment are assigned the same reference numerals, and detailed descriptions thereof are omitted. As shown inFIG. 12, a dummy line Vd is connected to an interconnection point between the conversion element S and the switching element T via a capacitor Cd. It is thereby possible to extract a current generated by irradiated X-rays to an external circuit through the dummy line Vd.

FIG. 13is a view that illustrates a configuration example of an imaging apparatus according to the present invention, which illustrates a method of wiring the dummy lines Vd inside the detector101. Dummy lines Vd1to Vd7are arranged so as to be orthogonal to the sensor bias lines VS' to VS7, and are connected in the diagonal direction to the respective capacitors Cd of the pixels201in a matrix shape. The dummy line current monitor circuit units MVD1to MVD7have the same configuration as the above described sensor bias current monitor circuit units MVS1to MVS7and the drive line current monitor circuit units MVG1to MVG4, and monitor currents that flow in the dummy lines VS1to VS7, and output the monitoring results to the filter unit560. The sensor bias current monitor circuit units MVS1to MVS7, the drive line current monitor circuit units MVG1to MVG4, the signal line current monitor circuit units MVi1to MVi4and the dummy line current monitor circuit units MVD1to MVD7monitor currents. Consequently, the arithmetic unit561can perform back-projection processing with respect to lines in four different directions, and it is possible to determine the two-dimensional distribution with greater accuracy. In addition, similarly to the second embodiment, the two-dimensional distribution can be determined with further accuracy by dividing the detector101into blocks and leading out lines from four directions.

Note that the current monitor circuit units may be configured to monitor currents that flow in lines extending in two or more different directions among the signal lines Sig1to Sig4, the sensor bias lines VS1to VS7, the drive lines G1to G8and the dummy lines Vd1to Vd7. In that case, the arithmetic unit561calculates the two-dimensional distribution by performing back-projection processing on currents that flow in lines extending in two or more different directions that are monitored by the current monitor circuit units.

Fifth Embodiment

FIG. 14is a view that illustrates a configuration example of an imaging apparatus according to a fifth embodiment of the present invention. Note that elements inFIG. 14having the same configuration as that described in the first embodiment are assigned the same reference numerals, and detailed descriptions thereof are omitted. Although according to the first embodiment the sensor bias lines VS and the drive lines G over the entire surface of the detector101are monitored, according to the fifth embodiment only a current that flows in the sensor bias lines VS and a current that flows in the drive lines G at a monitoring position are measured. A column selection switch MSW3and a row selection switch MSW4are set to a monitoring position by means of the monitor condition signal550that is output from the control unit108to the AEC monitor unit508, and only the monitoring position is measured. The column selection switch MSW3selectively connects the sensor bias current monitor circuit unit MVS to the sensor bias line VS of the column at the monitoring position, and the row selection switch MSW4selectively connects the drive line current monitor circuit unit MVG to the drive line G of the row at the monitoring position. By adopting this configuration, it is possible to reduce the scale of the circuit, decrease the electrical power consumption, and prevent an increase in the size of the apparatus.

It is to be understood that the foregoing first to fifth embodiments are intended to illustrate specific examples for implementing the present invention, and are not intended to limit the technical scope of the present invention. That is, the present invention can be implemented in various forms without departing from the technical concept or the principal features thereof.

This application claims the benefit of Japanese Patent Application No. 2012-288451, filed Dec. 28, 2012, which is hereby incorporated by reference herein in its entirety.