JP2014168602A - Radial ray image detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray image detection apparatus improved in offset correction.SOLUTION: The radial ray image detection apparatus includes: a radial ray detection unit 10 converting incident radial rays x to electric charge to read them out and making image signals by pixels 11 arranged on a substrate 12; and offset correction processing circuits 40, 45 correcting the image signals on the basis of offset data obtained from the pixels 11 when the radial rays x are not incident. In the radial ray image detection apparatus, a period for obtaining the offset data is set just before the radial rays are incident, and the length of the period for obtaining the offset data is set to be shorter than a period for reading out the data as the image signals from the pixels by the radial ray incidence.

Description

  Embodiments described herein relate generally to a radiation image detection apparatus that converts a radiation image such as an X-ray into an electrical signal.

  A radiation image detection device is a detector that converts a radiation image into an electrical signal to enable visual display, and is used for medical diagnosis, non-destructive inspection, and the like.

  Radiation image detection devices, such as X-ray image detection devices, use a direct conversion system that uses an element that converts X-rays electrically, and indirectly convert X-rays into light using a fluorescence conversion film and then convert the light into electrical signals using a photodiode. There is a conversion method. In either method, pixels are arranged in a matrix on a substrate, and each pixel has a detector that converts an X-ray image into an electric charge.

  The indirect conversion method will be described as an example. Each pixel is provided with a photodiode as a light detector, a capacitor for accumulating electric charge, and a switching element for taking out electric charge as a signal. The photodiode and the switching element are formed of an amorphous silicon thin film, a polycrystalline silicon thin film or a semiconductor metal oxide deposited on a glass substrate, the photodiode is a pin diode, and the switching element is a MOS type TFT transistor. Each pixel is controlled by a scanning line arranged in the row direction of the substrate and a signal line arranged in the column direction, and the accumulated charge is input to an integrating amplifier connected to each signal line through the signal line.

  The charge information input to the integrating amplifier is amplified, converted into a potential signal, and output. The potential signal output from the integrating amplifier is converted into a digital value by an analog / digital converter, and finally edited as an image signal and output to the outside of the X-ray image detection apparatus.

  Image information stored in the X-ray image detection apparatus is output to the outside through a LAN line or the like, and transferred to the inside of the information processing apparatus such as a personal computer connected to the outside.

  In the above operation, the potential of only one of the row selection lines is sequentially changed, and the signal from the pixel connected to the row selection line whose potential has changed is output to the outside, so that the signal from one pixel is an output image. An image corresponding to one pixel constituting the image is created. In addition, there is an operation in which the potentials of adjacent row selection lines are simultaneously changed to drive or turn on the switching element, and the signals from a plurality of obtained pixels are integrated into one pixel of the output image. This is known as an operation called “binning mode”.

  The image information output from the X-ray image detection device includes a dark current component generated from each pixel and an offset component peculiar to the integrating amplifier connected to the signal line. The component is included in the captured image. Since it is mixed, the behavior as image noise is shown.

  As shown in FIG. 4, in order to correct the image noise caused by the dark current component and the offset component, an offset acquisition period 201 for acquiring offset data is provided before a series of X-ray imaging operation periods 200, and thereafter By subtracting the offset data from the image data obtained by X-ray imaging performed in the above, it is possible to remove image noise caused by the dark current component. Image data is obtained by an X-ray irradiation period 203 and an image readout period 204 at the start of imaging.

  The offset data acquisition performed prior to the X-ray imaging is generally performed by operating the X-ray image detection apparatus in a state where no X-ray is incident and using uncorrected image data output at the time of reading. is there.

  The above-mentioned offset data includes the dark current component of the photodiode of each pixel, the effect of transistor characteristic drift, the offset component of the integrating amplifier connected to the signal line, and the induced noise from the row selection line. These values vary depending on the exposure time and the driving conditions of the row selection lines that differ between normal shooting and binning mode shooting. Therefore, in general, the same exposure time and row selection line driving conditions are used for X-ray imaging and offset data acquisition, so that the same offset data as the offset component included in the image at the time of imaging can be obtained. .

JP 2003-244540 A

  For example, an amorphous silicon photodiode used in an X-ray image detection apparatus is known to take a long time to obtain a stable output. In particular, a large current flows immediately after the bias voltage is applied to the photodiode, and the stabilization period t (FIG. 4) may take several tens of seconds or more.

  In X-ray imaging, X-rays that have passed through a subject and X-rays that have passed outside the subject are simultaneously irradiated onto the X-ray image detection apparatus, and the difference in intensity is often several tens to several hundreds of times. For this reason, in the pixels in the area irradiated with X-rays other than the subject, a large amount of visible light is incident on the photodiode, so that all the charge held by the capacitor is consumed and the reverse bias electric field inside the photodiode disappears. Resulting in.

  In the photodiode in which the reverse bias electric field disappears, photoelectrons generated by external visible light cannot move to the electrodes at both ends of the photodiode, and the generated photoelectrons remain in the amorphous silicon inside the photodiode for a long time. become.

  There are a large number of lattice defects in the amorphous silicon constituting the photodiode. In the photodiode having no reverse bias electric field, a large amount of photoelectrons generated by incident light stay in the amorphous silicon for a long time, and the probability of being trapped by lattice defects inside the amorphous silicon becomes very high.

  It is known that photoelectrons captured by lattice defects are released from the capture by the probability depending on the depth and temperature of the lattice defects. As described above, the time until the release depends on the conditions, but it is known that it takes several seconds to several tens of seconds.

  As described above, in a pixel to which a large amount of X-rays are incident, a large amount of photoelectrons are captured by lattice defects in amorphous silicon inside the photodiode, and the captured photoelectrons continue to be emitted during the next imaging. . In this phenomenon, a past photographed image is added to the current photographed image as an afterimage.

  The afterimage phenomenon often becomes a major obstacle to diagnosis using an X-ray image. This is because when an afterimage is generated, it is mixed with a weak X-ray image signal that has passed through the subject and attenuated.

  In general, as a method of improving the afterimage phenomenon, offset data is acquired before X-ray imaging is started, and a captured image obtained immediately after that is corrected using the offset data.

  In the above method, it is effective to shorten the time from when the offset data is acquired until the photographing operation is performed. This is because the afterimage phenomenon is a phenomenon in which photoelectrons trapped in amorphous silicon are released by probability and mixed into an image, so that the strength of the afterimage changes with time. However, if the period during which the X-ray imaging operation is performed after acquiring the offset data is long due to this property, the offset state changes during that period, and even if the obtained offset data is used, the captured image cannot be completely corrected. Become.

  Although the afterimage correction can be performed by performing the offset data immediately before the X-ray imaging, if the operation of acquiring the offset data is performed immediately before the X-ray imaging, the timing of the X-ray imaging is shifted. This is because a doctor or the like decides to start X-ray imaging and acquires offset data, so a period for acquiring offset data is necessary, and X-ray imaging is performed thereafter. . The offset data acquisition and the X-ray imaging are the same drive conditions. In normal X-ray imaging, an exposure period of 500 milliseconds or more is required. Therefore, when combined with subsequent data read and transfer, the operation takes 1 second or more, so the same amount of time is required to acquire offset data. .

  If effective afterimage correction is performed in consideration of the above phenomenon, the timing of the X-ray imaging operation is delayed. This delay has a very bad influence when imaging a moving part such as the heart, which greatly impedes diagnosis by X-ray imaging.

  According to one embodiment, a pixel disposed on a substrate converts incident radiation into electric charges and reads out the image signal as an image signal, and the image is obtained by offset data acquired from the pixel when the radiation is not incident. In the radiological image detection apparatus including an offset correction processing circuit that corrects a signal, the offset data acquisition period is set immediately before the radiation is incident, and the length of the offset data acquisition period is determined by the radiation incidence as the pixel. The radiation image detecting apparatus is characterized in that it is set to be shorter than the period for reading out as the image signal.

The circuit block diagram of one Embodiment. The exploded perspective view of one embodiment. Operation | movement explanatory drawing of one Embodiment. Operation | movement explanatory drawing of a prior art.

  An embodiment will be described with reference to the drawings. In the present embodiment, reference secondary offset data is acquired in advance before radiographic imaging, and the immediately preceding secondary offset data is acquired immediately before radiation incidence in radiographic imaging, and the reference secondary offset data and the immediately preceding secondary offset data are acquired. Based on the above, an image signal obtained by radiographic imaging is offset-corrected. Further, the immediately prior secondary offset data acquisition period is set to a period shorter than the image signal readout period after radiation incidence at the time of radiographic imaging.

  If the offset correction data acquired by inspection prior to shipment of the image detection device or at the time of equipment installation or after a sufficient amount of time after recent imaging is used as basic primary offset correction data, the reference secondary and immediately preceding secondary offset data Is data for secondary offset correction at the stage of photographing operation.

  That is, as shown in FIG. 3, reference secondary offset data is acquired at the preparation stage of imaging (reference secondary offset data acquisition period 101), and immediately before X-ray irradiation (X-ray irradiation period 103) at the start of imaging. The immediately preceding secondary offset data is acquired (immediately prior secondary offset data acquisition period 102).

  X-ray image detection devices acquire offset data, gain data, and defective pixel data for each device and store them in a memory device at the final stage of production, installation in equipment, maintenance, etc. The obtained image signal is corrected. This offset data is basic characteristic data of the apparatus, and the ON period indicated by reference numeral 105 in FIG. 3 is the primary offset data acquisition period. Since X-ray image detection devices generally have characteristics that may change due to operating conditions such as driving and factors over time, in addition to the basic correction processing described above, offsets that are likely to fluctuate are revisited at the preparation stage of imaging. Secondary, offset data is acquired. The present embodiment relates to the acquisition of the secondary offset data. In addition to the secondary offset data (reference secondary offset data acquisition period 101) in the imaging preparation stage, the immediately preceding secondary offset data (immediately before the X-ray irradiation at the start of imaging). The secondary offset acquisition period 102) is acquired. One (frame) captured image is obtained by X-ray irradiation (X-ray irradiation period 103) and subsequent image reading (image reading period 104).

  By shortening the immediately preceding secondary offset data acquisition period 102, it is possible to perform photographing with a small time lag, and an image with reduced afterimage noise can be obtained even if the photographing interval is shortened.

(Configuration of the embodiment)
FIG. 1 shows a circuit configuration inside the X-ray image detection apparatus 10. The X-ray image detection apparatus 10 converts incident X-rays into electric signals. As shown in FIG. 2, a plurality of pixels 11 are arranged in a matrix on a plane of a glass substrate 12 in a matrix. . These pixels 11 have a photodiode 14 as a detection element and a capacitor 15 (see FIG. 1). The incident X-ray x is converted into light by a fluorescence conversion film 13 and further photoelectrically converted by the photodiode 14 of the pixel. Accumulate the generated charge.

A drain electrode 16d of a thin film transistor 16 serving as a switching element for reading out the accumulated charges is connected to the capacitor 15 of these pixels. A gate driver 31 is connected to the gate electrode 16g of the thin film transistor 16 via each row selection line 30 ₁ , 30 ₂ , 30 ₃ ,... For each thin film transistor 16 in the row direction.

The gate driver 31 is controlled by a row selection circuit 32, and changes the potential of only one selection line among the row selection lines 30 (30 ₁ , 30 ₂ , 30 ₃ ,. Each of the thin film transistors 16 in the direction is driven (ON), and each gate signal for turning off the thin film transistors in other rows is output. As a result, the potential of the row selection line is sequentially selected from one row to an adjacent row, for example, the lower row selection line in FIG. 16 are read out through the source electrode 16s. By referring to the position of the signal line 33 (33 ₁ , 33 ₂ , 33 ₃ ,...) From which charges have been discharged in this way and the position of the row selection line 30 whose potential has changed at that time, X-rays are obtained. The incident position and intensity can be calculated. Each pixel accumulates an amount of charge in proportion to a certain operating range with respect to an increase in incident X-ray dose.

  One end of the photodiode 16 is connected to a bias line 34 for applying a necessary bias voltage.

The signal lines 33 ₁ , 33 ₂ , 33 ₃ ,... Are connected to the source electrode 16 s of each thin film transistor 16. (35 ₁ , 35 ₂ ,...) Are connected. Further, a multiplexer 36 and an A / D converter 37 are connected to the output terminals of each integrating amplifier.

Therefore, the charges read from each pixel are sampled and held by the integrating amplifiers 35 ₁ , 35 ₂ ,... And amplified to become potential information, and are selected in units of pixels through the multiplexer 36, and then A / D It is converted into a digital value by the converter 37 and output. The obtained digital output is input to the image reconstruction circuit 38 and becomes an image signal.

  In the above operation, the potential of only one row selection line is changed, and the signal from the pixel connected to the row selection line whose potential has changed is output to the outside, so that the signal from one pixel forms the output image. An image corresponding to one pixel is created. In addition, there is an operation of integrating signals from a plurality of pixels into one pixel of an output image, which is generally known as an operation called “binning mode”.

  In the binning mode, the potentials of adjacent row selection lines are changed simultaneously, and the charge information from adjacent rows of pixels connected to these row selection lines flows into the signal lines at the same time in the vertical direction. In this operation, the electrification information from a plurality of pixels is added and output. In this operation, an image with a reduced number of pixels in the vertical direction is output, but a plurality of pixels in the horizontal direction are added to the image data output from the signal line and converted into a digital signal. By collecting the information, image data reduced in the horizontal direction and the vertical direction is output.

  In the binning mode, it is possible to reduce the time for sequentially driving the row selection lines of the entire screen from driving a plurality of row selection lines at a time, and because the number of pixels of the output image data is small, It is possible to reduce the time for transmitting image data from the detection device to the outside through an electric line, an optical line, or the like. For this reason, this is an effective operation method particularly when moving image shooting or high-speed processing is required.

  The secondary offset data of this embodiment is preferably acquired in the binning mode. That is, this offset data acquisition may be performed with a shorter time than the image readout period after the X-ray irradiation, so that the single row selection line drive may be executed in a shorter period than the image readout period.

  The A / D converted image signal is reconstructed by the image reconstruction circuit 38 into pixel rows and columns.

  The reconstructed image signal is subjected to image processing by an offset correction processing circuit 40 for removing dark current components of pixels in the X-ray image detection unit 10 and offset components of the integrating amplifier 35, and further, each pixel sensitivity difference and integration. After passing through the gain correction processing circuit 41 for removing the amplification factor difference of the amplifier 35 and the defect correction processing circuit 42 for removing the pixel data of the defective pixel, it is displayed on the image display device 43.

  In the offset processing circuit 40, the gain correction processing circuit 41, and the defect correction processing circuit 42, an offset correction table (primary offset data) 40a for storing parameters that are basic characteristic data used for calculation, a gain correction table. (Gain data) 41a and a defect correction table (defect data) 42a are prepared in the memory device 44, and each correction process is performed according to the contents of each table.

  In the present embodiment, a secondary offset correction processing circuit 45 is provided between the offset correction processing circuit 40 and the gain correction processing circuit 41. The memory device 44 stores reference secondary offset data 47 acquired at the imaging preparation stage and immediately before secondary offset data 48 acquired immediately before X-ray irradiation, and these data are subtracted by the difference processing circuit 46. The difference data is input to the secondary offset correction processing circuit 45, and the image signal is subjected to secondary offset processing.

  Although the above correction processing may have a function inside the X-ray image detection unit, it is executed by a program stored in an information processing apparatus such as a personal computer connected by an attached LAN line or the like. Sometimes it is done.

(Operation of X-ray image detection apparatus)
In the initial state, charges are stored in the capacitor 15 in FIG. 1 through the bias line 34, and a reverse bias voltage is applied to the photodiodes 14 connected in parallel. At this time, the voltage of the line connecting the photodiode 14 and the thin film transistor 16 is the same as the voltage applied to the signal line 33.

  Since the photodiode 14 is a kind of diode, even if a reverse bias voltage is applied, almost no current flows. Therefore, the electric charge stored in the capacitor 15 is held without decreasing.

  When the incident X-ray x shown in FIG. 2 enters the fluorescence conversion film 13 in the above situation, high-energy X-rays are converted into visible light fluorescence inside the fluorescence conversion film 13, and inside the fluorescence conversion film 13. A part of the generated fluorescence reaches the pixel 11 arranged on the surface of the image detection unit 10.

  Fluorescence incident on the pixel 11 is converted into charges composed of electrons and holes inside the photodiode 14 shown in FIG. 1 and reaches both terminals of the photodiode 14 along the direction of the electric field applied to the capacitor 15. Thus, it is observed as a current flowing in the photodiode 14.

  The current flowing in the photodiode 14 generated by the incidence of the fluorescence flows into the capacitor 15 connected in parallel, and acts to cancel the electric charge stored in the capacitor 15. As a result, the electric charge stored in the capacitor 15 decreases, and the potential difference generated between the terminals of the capacitor 15 also decreases compared to the initial state.

  The row selection line 30 is connected to the thin film transistor 16 connected to the gate driver 31 and arranged in parallel to a specific row. The gate driver 31 has a function of changing the potential of many row selection lines in order. At a certain time, the gate driver 31 has only one row selection line 30 whose potential has changed, and the terminals between the source and drain of the thin film transistor 16 connected in parallel to the row selection line whose potential has changed are insulated. Changes from a state to a conductive state.

  A specific voltage is applied to each signal line 33 and is applied to the capacitor 15 connected through the source 16s and drain 16d terminals of the thin film transistor 16 connected to the row selection line 30 whose potential has been converted. Become.

  Since the capacitor 15 is in the same potential state as the signal line 33 in the initial state, if the charge amount of the capacitor 15 is not changed from the initial state, no charge transfer from the signal line 33 occurs in the capacitor 15. However, in the capacitor 15 connected in parallel with the photodiode 14 in the pixel 11 irradiated with the fluorescence generated inside the fluorescence conversion film 13 by the incident X-ray x from the outside, it is stored inside by the photocurrent generated in the photodiode 14. The charged charge is reduced, and the initial potential is changed. For this reason, a movement of electric charge is generated from the signal line 33 through the thin film transistor 16 in the conductive state, and the amount of electric charge stored in the capacitor 15 returns to the initial state. The amount of electric charge that has moved becomes a signal that flows through the signal line 33 and is transmitted to the outside.

  As shown in FIG. 1, the signal line 33 is connected to the integrating amplifier 35. The signal lines 33 are connected to the corresponding integration amplifiers 35 on a one-to-one basis, and the current flowing through the signal lines 33 is input to the corresponding integration amplifiers 35. The integrating amplifier 35 has a function of integrating a current flowing within a predetermined time and outputting a voltage corresponding to the integrated value to the outside. By performing this operation, the amount of charge flowing through the signal line within a certain time can be converted into a voltage value. As a result, the charge signal generated in the photodiode 14 corresponding to the intensity distribution of the fluorescence generated in the fluorescence conversion film 13 by the input X-ray x is converted into a potential signal by the integrating amplifier 35.

  The potential generated from the integrating amplifier 35 is parallel-serial converted by the multiplexer 36 and sequentially converted into a digital signal by the A / D converter 37. The signal that has become a digital value is converted into an image signal that is sequentially arranged in accordance with the row and column of pixels arranged inside the X-ray image detection unit 10 inside the image reconstruction circuit 38.

  Normal image signal correction processing passes through an offset correction circuit 40, a gain correction processing circuit 41, and a defect correction processing circuit 42.

  That is, the image signal output from the image reconstruction circuit 38 includes an image noise including an offset component that differs depending on each pixel 11 arranged in the X-ray image detection unit 10 and an individual offset component of the integrating amplifier 35. include. These noise components can be removed by passing the image signal output from the image reconstruction circuit 38 through the offset correction processing circuit 40.

  Similarly, the image signal output from the image reconstruction circuit 38 includes variations in the light detection efficiency, the amplification factor of the integration amplifier 35, and the conversion efficiency of the fluorescence conversion film 13 that vary depending on the individual pixels 11. Sensitivity variations can be removed by passing the gain correction processing circuit 41.

  The image signal output from the gain correction processing circuit 41 is input to the defect correction processing circuit 42. The defect correction processing circuit 42 removes the signal from the defective pixel included in the image based on the defect data recorded in the defect correction table 42a, that is, the defective pixel information, and generates the original signal from the surrounding normal pixels. Has a function of repairing and outputting image information from defective pixels.

  Next, operations unique to this embodiment will be described. In the present embodiment, in addition to the normal primary offset correction process, a secondary offset correction processing circuit 45, reference secondary offset data 47, and immediately preceding secondary offset data 48 are included.

  An offset correction table (primary offset data) 40a used in a normal offset correction processing circuit 40 is driven by the same exposure period and row selection line operation as the X-ray imaging operation, and is an X-ray image during a period when X-rays are not irradiated. It consists of image data obtained from a detection device. The image data stored in the offset correction table 40a is obtained in a situation where there is no influence of the afterimage due to the immediately preceding X-ray irradiation after a sufficient period from the X-ray irradiation.

  On the other hand, the reference secondary offset data 47 is obtained when the X-ray is not irradiated during the exposure period shorter than the X-ray imaging operation or the binning mode driving condition in which the driving of the row selection line is different and the number of output pixels is small. It consists of image data obtained from an image detection device. Similar to the primary offset data 40a, the reference secondary offset data 47 is obtained in a situation where there is no influence of the afterimage due to the immediately preceding X-ray irradiation after a sufficient period from the X-ray irradiation.

  The immediately preceding secondary offset data 48 is obtained with the same exposure time and row selection line driving conditions as the reference secondary offset data 47, but unlike the reference secondary offset data 47, the offset obtained immediately before the X-ray imaging. In some cases, it is data, and an afterimage component generated in the immediately preceding X-ray imaging is included.

  As shown in FIG. 3, in the present embodiment, the primary offset data 40a acquired in advance in the offset data acquisition period 105 is stored in memory, and the secondary offset data acquisition period 101 that is sufficiently long after X-ray imaging is used as a reference. Data of the secondary offset data 47 is acquired. Since this reference secondary offset data is acquired when a sufficient time has been taken since the previous X-ray imaging, an afterimage component derived from the previous X-ray imaging is not included. Further, by performing a plurality of offset photographing and secondary offset photographing, and using the average value of the data as the primary offset data 40a and the reference secondary offset data 47, it is possible to obtain high-quality data with little noise.

  Next, X-ray imaging is performed. When the X-ray image detection apparatus receives imaging start information for performing X-ray imaging by a doctor or the like, the immediately preceding secondary offset data 48 is displayed in the immediately preceding secondary offset data period 102. The acquisition operation of is started. The immediately preceding secondary offset data 48 is performed under the same exposure time and row selection line driving conditions as the reference secondary offset data 47. At this time, by driving in the time shorter than the irradiation time of X-ray imaging or in the binning mode, the immediately preceding secondary offset data acquisition operation can be completed in an operation time shorter than the X-ray imaging operation performed thereafter. It becomes.

  When the immediately preceding secondary offset data acquisition operation is completed, the X-ray imaging operation is started immediately. The X-ray imaging operation includes an X-ray incident period 103 to the X-ray image detection unit 10 and a pixel charge readout period 104 obtained. The image data obtained by this operation is subjected to the offset correction processing circuit 40 using the primary offset data 40a to remove the leakage current of each pixel, the offset component of the integrating amplifier, the induced noise from the row selection line, and the like.

  Next, image data obtained by subtracting the reference secondary offset data 47 from the immediately preceding secondary offset data 48 by the difference processing circuit 46 is created. Since the subtracted image data is a difference between the immediately preceding secondary offset data 48 having an afterimage component and the reference secondary offset data 47 having no afterimage component, only the afterimage component remains.

  The image signal that has passed through the offset correction processing circuit 40 is subjected to subtraction processing by the secondary offset correction processing circuit 45 to remove the image data component subjected to the above-described subtraction processing. By performing this process, it is possible to remove the afterimage component generated in the previous X-ray imaging operation from the X-ray image.

  The image signal that has been subjected to the secondary offset correction process is output to the outside through the same gain correction process 41 and defect correction process 42 as in the prior art.

  By performing the above operation, it is possible to shorten the time lag that occurs immediately before X-ray imaging and output an X-ray image with little afterimage.

  In addition, even if an afterimage of the previous shooting remains in the second shooting after the first shooting, it can be removed by acquiring the immediately preceding secondary offset data, so the shooting interval can be reduced. .

  It is also effective to perform low-pass filter processing on the reference secondary offset data 47 and the immediately preceding secondary offset data 48 used for the secondary offset correction processing 45 in the above embodiment. By performing this processing, it is possible to reduce the A / D conversion error included in the immediately preceding secondary offset data obtained only for each X-ray irradiation, and to improve the noise component of the final image.

  In the description of the above-described embodiment, an example in which various correction processes are performed inside the X-ray image detection unit has been shown. However, these processes are performed inside the information processing apparatus such as a personal computer connected to the outside of the X-ray image detection unit. It is also effective to be performed by software processing.

  Moreover, although this embodiment demonstrated the indirect conversion system, it can implement also about the direct conversion system which does not use a fluorescence conversion film. In the direct conversion method, a radiation-electric conversion film that directly converts radiation such as X-rays into electric charge is used. A plurality of pixel electrodes are formed on one surface of the film and a common electrode is formed on the other surface, and charges are accumulated in capacitors connected to the individual pixel electrodes. Image signal processing is the same as in the above embodiment.

  The above embodiment has explained that the binning mode is used to acquire the immediately preceding secondary offset data. As a result, the number of row selection lines to be collectively driven can be increased and the data acquisition period can be shortened. On the other hand, since the data becomes the average value of the offset values of the pixels selected simultaneously, the data acquisition period so that the deviation from the offset value of the image signal obtained by the subsequent X-ray irradiation remains within a practical range. Select.

  In the above embodiment, a time difference is not provided between the end of the immediately preceding offset data acquisition period and the start of X-ray irradiation. However, a slight time difference may be provided.

  As described above, in the image detection apparatus for radiation such as X-rays, the time lag immediately before X-ray imaging is small, and an operation with reduced afterimage can be performed.

  In the case of moving image shooting, a plurality of frames are read in, for example, the binning mode while irradiating X-rays, but acquisition of the immediately preceding secondary offset data is acquired once immediately before X-ray irradiation and used for data correction. When the moving image time is long, X-ray irradiation is turned off every predetermined period, and the immediately preceding secondary offset data is acquired and updated during that period. The acquisition period is preferably within one frame readout period.

  Moreover, embodiment described above is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10: X-ray image detection unit 11: pixel 12: substrate 13: fluorescence conversion film 14: photodiode 15: capacitor 16: thin film transistor 30 (301, 302, 303...): Row selection line 31: gate driver 32: row selection circuit 33: (331, 332, 333...): Signal line 34: bias line 35: integrating amplifier 36: multiplexer 37: A / D converter 38: image reconstruction circuit 40: offset correction processing circuit 40a: offset correction table 41 : Gain correction processing circuit 41a: gain correction table 42: defect correction processing circuit 42a: defect correction table 43: image display device 44: memory device 45: secondary offset correction processing circuit 46: difference processing circuit 47: reference secondary Offset data 48: immediately before secondary offset data x: incident X-ray 101: reference secondary offset Set data acquisition period 102: just before the secondary offset data acquisition period 103: X-ray irradiation period 104: image reading period 105: offset data acquisition period

Claims (8)

A radiation detector that converts incident radiation into electric charge and reads it as an image signal by pixels arranged on the substrate, and offset correction processing that corrects the image signal by offset data acquired from the pixel when the radiation is not incident In a radiological image detection apparatus comprising a circuit,
The offset data acquisition period is set immediately before the radiation is incident, and the length of the offset data acquisition period is set to be shorter than the period for reading out the image signal from the pixel by the radiation incidence. Radiation image detection apparatus.   The offset data includes reference offset data acquired in advance before the radiation incidence and immediately preceding offset data acquired immediately before the radiation incidence, and the offset processing is performed by performing a differential process between the reference offset data and the immediately preceding offset data. The radiation image detection apparatus according to claim 1, wherein the radiation image detection apparatus is input to a circuit.   A memory device for storing offset data, gain data, and defect data, wherein the offset correction data includes primary offset data that is basic characteristic data of the radiation detector, the reference secondary offset data, and the immediately preceding secondary data; The offset correction processing using the secondary offset data further corrects the image signal corrected by the primary offset data. 3. The radiological image detection apparatus according to 2. The substrate, a plurality of row selection lines and a plurality of signal lines arranged on the substrate, a plurality of switching elements connected to the row selection lines and the signal lines, and a connection to the switching elements The radiation detection unit comprising a pixel that converts radiation incident from the outside directly or through a fluorescence conversion film into a charge, and obtains an image signal by radiographic imaging,
An integrating amplifier that is connected to each of the signal lines and converts the charge of the pixel read out through the switching element by the control of the row selection line and the signal line into a potential signal;
A memory device for storing offset data of the pixels obtained in a non-incident state by the control of the row selection line and the signal line;
In the radiological image detection apparatus comprising:
Prior to the radiographic image acquisition, reference secondary offset data is acquired in advance and stored in the memory device, the immediately prior secondary offset data is acquired immediately before the radiation incidence of the radiographic image acquisition, and the immediately preceding secondary offset data acquisition period is This is a period shorter than the image signal readout period after the incidence of radiation at the time of radiographic imaging, and offset correction is performed on the image signal obtained from the potential signal of the radiographic imaging from the reference secondary offset data and the immediately preceding offset data. The radiographic image detection apparatus according to claim 1, wherein the radiation image detection apparatus is a radiographic image detection apparatus.   Image signal readout has the operation of sequentially outputting signals from pixels in a single row to the outside by sequentially scanning the row selection lines, and the immediately preceding secondary offset data acquisition is to simultaneously change a plurality of row selection lines. 5. The radiological image detection apparatus according to claim 4, further comprising an operation of combining signals from a plurality of pixels connected to the row selection lines and outputting the signals to the outside through the signal lines.   Both the readout of the image signal and the acquisition of the immediately preceding secondary offset data are performed by synthesizing signals from a plurality of pixels connected to the row selection lines by simultaneously changing the potentials of the row selection lines of the plurality of rows. The radiation image detection apparatus according to claim 4, wherein the radiation image detection apparatus is obtained through the signal line.   The radiological image detection apparatus according to claim 3, wherein the reference secondary offset data and the immediately preceding secondary offset data are acquired under the same conditions.   The radiographic image detection apparatus according to claim 4, wherein the detection element that forms a pixel by converting the electric charge through the fluorescence conversion film is a photodiode, and is formed of amorphous silicon.

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