JP2011212434A - Method and device for photographing radiographic image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a residual image amount generated in a direct exposure region and perform suitable residual image correction based on the residual image amount.SOLUTION: A dose of radiation which has reached a radiographic image detector without passing through an object is estimated based on the preacquired radiation intensity distribution in the radiographic image detector, the residual image charge amount is acquired based on the estimated dose of the radiation and preset attenuation characteristics of the residual image in the radiographic image detector, and interval of photographing of radiographic images on and after the next photographing so as not to saturate the output of the radiographic image detector, based on the sum of the acquired residual image charge amount and the maximum value of the radiographic image signals detected by the radiographic image detector.

Description

  The present invention relates to a radiographic image capturing method and apparatus for performing afterimage correction on a radiographic image signal read from a radiographic image detector repeatedly used for radiographic image capturing.

  Conventionally, a radiation source and a radiation image detector are arranged facing each other around the subject, and these sets are rotated around the subject to radiate radiation from various angles to capture radiation images. A radiation CT image capturing system that reconstructs a tomographic image using an angle radiation image and displays an arbitrary cross section is widely used in clinical practice.

  Here, in the radiation CT image capturing system as described above, it is desirable to increase the angular resolution in order to obtain a radiation CT image with better image quality. However, increasing the angular resolution leads to an increase in the number of images to be captured. In order to capture images within an imaging time that is realistically restricted by the patient's restraint time, breath holding time, and the like, it is necessary to continuously capture images with a short imaging interval.

  However, generally, in the radiographic image detector, information on a radiographic image taken immediately before or immediately before is left, and this becomes an afterimage and is superimposed on a true radiographic image. This afterimage becomes an artifact when reconstructing and creating a tomographic image, and is a problem.

  Therefore, in order to avoid such an afterimage effect, the afterimage decays exponentially with time. Therefore, there is a method of simply setting an appropriate shooting interval so that the next image is taken after the afterimage is sufficiently attenuated. Conceivable.

  However, such a method of simply increasing the shooting interval is not appropriate because of the limitation of the shooting time as described above.

  Therefore, a method for correcting an afterimage included in a radiographic image based on the radiographic image taken immediately before and the elapsed time since the radiographing has been proposed. In addition, in continuous radiographing of a large number of radiographic images, the afterimages of the previous time, the last time, and so on are mixed together as different levels of afterimages due to the difference in the time elapsed since each radiographing. Various methods for correcting afterimages in consideration of attenuation with respect to the passage of time from the past have been proposed.

JP 2006-334154 A Japanese Patent Laid-Open No. 10-192267

  Here, as in the radiation CT image capturing system described above, when the set of the radiation source and the radiation image detector circulates around the subject, the body thickness of the subject to be imaged is, for example, when the subject's abdomen is imaged. When changing depending on the shooting direction, there are cases where an area that is a missing part in shooting in a predetermined shooting direction becomes an image area to be shot in another shooting direction. Specifically, as shown in FIG. 14, when the radiation source 1 and the radiation image detector 2 are disposed to face each other in the horizontal direction, the blank portion is the radiation source 1 and the radiation image detector 2. Is an image area of the photographing target P when they are arranged to face each other in the vertical direction. Note that the blank portion refers to a region where the radiation image detector is directly irradiated with radiation without passing through the imaging target.

  In addition, since the afterimage increases as the radiation exposure amount increases, the radiation dose irradiated to the background portion is particularly large when the region of the radiation image detector that has become the background portion is used as an image region. It is necessary to perform afterimage correction according to the above.

  However, when a radiation image detector called a so-called FPD using a semiconductor material is used, generally, the amount of charge generated at a dose reaching the unexposed portion is compared with the charge storage capacity prepared for each individual pixel. In addition, it is structurally difficult to increase the amount of charge accumulated in individual pixels. For this reason, the circuit is configured so as to prevent the circuit from being destroyed by the excessively generated charge, and the charge generated more than the charge storage capacity cannot be taken out as an image signal.

  Similarly, in the subsequent charge voltage conversion circuit and AD conversion circuit, the entire range of the amount of charge generated by radiation is not normally assigned to the image signal due to the restrictions on the circuit design. The signal recording range is assigned so that sufficient resolution can be obtained. The amount of radiation in the subject portion is generally one to three orders of magnitude lower than that of the blank portion.

  Therefore, it is difficult to directly determine the radiation exposure amount and the afterimage amount of the unexposed portion serving as a reference for the afterimage correction from the pixel signal read from the unexposed portion of the radiation image detector.

  In other words, in an image area that exceeds the recording range of the image signal, such as a missing part, if the radiation exposure amount in that area is not known, a sufficient afterimage correction amount cannot be obtained, resulting in insufficient correction and artifacts. Resulting in.

  Further, when the afterimage correction target pixel is saturated by the accumulated afterimage, even if the amount of afterimage can be estimated from the radiographic image captured in the past, as shown in FIG. In addition, since the output of the radiation image detector is the sum of the signal portion representing the true radiation image and the afterimage component, and exceeds the recording range of the image signal, the signal portion representing the true radiation image is The signal portion representing the true radiation image cannot be extracted by correction.

  Further, for example, Patent Document 1 and Patent Document 2 propose to determine the dose at the time of imaging based on the pixel value of the radiographic image immediately before imaging in order to prevent saturation of the captured image signal. No proposal has been made for a method for determining the dose in consideration of such afterimage correction.

  In view of the above circumstances, the present invention provides a radiographic image capturing method and apparatus that can acquire an afterimage amount generated in a missing portion and can perform appropriate afterimage correction based on the afterimage amount. For the purpose.

  The radiographic imaging method of the present invention is a radiographic image detector that generates a charge upon receiving radiation irradiated from a radiation source and transmitted through a subject, and outputs a radiographic image signal representing the radiographic image of the subject, A radiographic image in a radiographic imaging apparatus comprising a radiographic image detector repeatedly used for radiographic imaging and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector. In the imaging method, the radiation dose reaching the radiation image detector without passing through the subject is estimated based on the radiation intensity distribution obtained in advance in the radiation image detector, and the estimated radiation dose is set in advance. An afterimage charge amount is acquired based on the afterimage attenuation characteristics of the radiation image detector, and the acquired afterimage charge amount and the radiation image detector are used. Based on the sum of the maximum value of the radiation image signal detected, the output of the radiation image detector and obtaining a recording interval of the radiographic image after next so as not to saturate.

  The radiographic imaging method of the present invention is a radiographic image detector that generates a charge upon receiving radiation irradiated from a radiation source and transmitted through a subject, and outputs a radiographic image signal representing the radiographic image of the subject, A radiographic image in a radiographic imaging apparatus comprising a radiographic image detector repeatedly used for radiographic imaging and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector. In the imaging method, the radiation dose reaching the radiation image detector without passing through the subject is estimated based on the radiation intensity distribution obtained in advance in the radiation image detector, and the estimated radiation dose is set in advance. An afterimage charge amount is acquired based on the afterimage attenuation characteristics of the radiation image detector, and the acquired afterimage charge amount and the radiation image detector are used. Based on the sum of the maximum value of the radiation image signal detected, the output of the radiation image detector and acquires the irradiation condition of radiation used in the imaging of the radiation image next time so as not to saturate.

  A radiographic imaging device of the present invention is a radiographic image detector that generates a charge upon receiving radiation irradiated from a radiation source and transmitted through a subject, and outputs a radiographic image signal representing the radiographic image of the subject, In a radiographic imaging apparatus comprising a radiographic image detector repeatedly used for radiographic imaging and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector. A radiation dose estimation unit that estimates a dose of radiation that has reached the radiation image detector without passing through the subject based on the radiation intensity distribution in the radiation image detector, and a radiation dose estimated by the radiation dose estimation unit An afterimage charge amount acquisition unit that acquires an afterimage charge amount based on a predetermined afterimage attenuation characteristic of the radiation image detector, and an afterimage charge amount acquisition unit Therefore, based on the sum of the acquired afterimage charge amount and the maximum value of the radiographic image signal detected by the radiographic image detector, the radiographic image capturing interval from the next time is set so as not to saturate the output of the radiographic image detector. An imaging interval acquisition unit for acquiring is provided.

  A radiographic imaging device of the present invention is a radiographic image detector that generates a charge upon receiving radiation irradiated from a radiation source and transmitted through a subject, and outputs a radiographic image signal representing the radiographic image of the subject, In a radiographic imaging apparatus comprising a radiographic image detector repeatedly used for radiographic imaging and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector. A radiation dose estimation unit that estimates a dose of radiation that has reached the radiation image detector without passing through the subject based on the radiation intensity distribution in the radiation image detector, and a radiation dose estimated by the radiation dose estimation unit An afterimage charge amount acquisition unit that acquires an afterimage charge amount based on a predetermined afterimage attenuation characteristic of the radiation image detector, and an afterimage charge amount acquisition unit Therefore, radiation used for radiographic image capture from the next time onward based on the sum of the amount of afterimage charge acquired and the maximum value of the radiographic image signal detected by the radiographic image detector so that the output of the radiographic image detector is not saturated. The radiation dose acquisition part which acquires the irradiation conditions of this is provided.

  In the radiographic imaging device of the present invention, the radiation intensity distribution can be acquired based on the radiographic image signal detected by the radiographic image detector.

  Further, a radiation absorbing member is provided in a region other than the image region in the radiation image detector, and the radiation intensity distribution is based on the radiation image signal output from the radiation image detector in response to the irradiation of the radiation transmitted through the radiation absorbing member. Can be obtained.

  In addition, the radiation image detector shall sequentially detect the radiation irradiated to the subject from different directions, and the radiation dose estimation unit has the maximum radiation irradiation range reaching the radiation image detector without passing through the subject. The radiation dose can be estimated by using the radiation intensity distribution corresponding to the radiation irradiation from the following direction.

  In addition, the radiation image detector shall sequentially detect the radiation applied to the subject from different directions, and the radiation dose estimation unit shall detect the radiation intensity corresponding to the irradiation of the radiation from the direction in which the body thickness of the subject is the thickest. The distribution can be used to estimate the radiation dose.

  Further, the radiation intensity distribution may be acquired based on at least one of the conditions of the tube current of the radiation source, the tube voltage, the irradiation time of the radiation, and the type of the additional filter.

  Further, the afterimage charge amount acquisition unit can acquire an afterimage attenuation characteristic corresponding to at least one of the conditions of the tube voltage of the radiation source, the tube current, the irradiation time of the radiation, and the type of the additional filter. .

  In addition, the imaging interval acquisition unit may acquire the imaging interval based on the maximum afterimage charge amount among the afterimage charge amounts acquired for each pixel constituting the radiation image detector.

  Moreover, a radiation dose acquisition part shall acquire the radiation dose based on the largest afterimage charge amount of the afterimage charge amount acquired about each pixel which comprises a radiographic image detector.

  Further, an afterimage correction unit that performs afterimage correction on the radiation image signal output from the radiation image detector based on the afterimage charge amount acquired by the afterimage charge amount acquisition unit can be further provided.

  In addition, the radiation image detector sequentially detects the radiation applied to the subject from different directions, and the afterimage correction unit includes the afterimage attenuation characteristics of the radiation image detector set in advance and the radiation to be subjected to afterimage correction. It is possible to acquire an afterimage correction amount based on the shooting time until the image signal is shot and to perform afterimage correction based on the afterimage correction amount.

  The radiographic imaging apparatus of the present invention includes a radiographic CT imaging apparatus that reconstructs a tomographic image based on a plurality of image signals detected by a radiographic image detector by irradiating a subject from different directions. can do.

  The radiographic imaging apparatus of the present invention includes a radiographic tomosynthesis imaging apparatus that reconstructs a tomographic image based on a plurality of image signals detected by a radiographic image detector by irradiating a subject from different directions. can do.

  In addition, in the process of repeatedly taking a radiographic image, the radiation dose estimation unit performs an area where the radiation reaches the radiographic image detector without passing through the subject and an area where the radiation passes through the subject and reaches the radiographic image detector. Can be obtained, and the dose of radiation reaching the radiation image detector without passing through the subject can be estimated based on the obtained region and the radiation intensity distribution.

  According to the radiographic imaging method and apparatus of the present invention, the radiation dose reaching the radiographic image detector without passing through the subject is estimated based on the radiation intensity distribution in the radiographic image detector acquired in advance, and the estimation Afterimage charge amount is acquired based on the radiation dose and the afterimage attenuation characteristics of the radiation image detector set in advance, and the acquired afterimage charge amount and the maximum value of the radiation image signal detected by the radiation image detector Based on the sum, the interval between subsequent radiographic images or the radiation dose is acquired so that the output of the radiological image detector does not saturate. The amount of afterimage of the area irradiated with radiation exceeding the range can be acquired, and the radiation to be corrected without saturating the output of the radiation image detector Can obtain an image signal, it is possible to perform appropriate residual image correction.

1 is a schematic configuration diagram of a radiation CT image capturing system using an embodiment of a radiation image capturing apparatus of the present invention. The block diagram which shows the internal structure of a radiation detection part and a computer in the radiation CT imaging system using 1st Embodiment of the radiographic imaging apparatus of this invention. The figure which shows an example of the relative intensity distribution of the radiation according to predetermined mAs value The figure which shows the relative intensity distribution of the radiation set for every tube voltage and mAs value The figure for demonstrating the effect | action which acquires the imaging | photography space | interval of a radiographic image based on the time change of the afterimage charge amount, and the maximum charge amount which generate | occur | produces in each pixel of a radiographic image detector. The flowchart for demonstrating the effect | action of the radiation CT imaging system using 1st Embodiment of the radiographic imaging apparatus of this invention. The figure which shows an example of the afterimage characteristic of the radiographic image signal image | photographed at each imaging angle Diagram for explaining the effect of afterimage correction The perspective view which shows the radiographic image detector in which the radiation absorption member was installed The figure which shows an example of the radiographic image signal for a measurement image | photographed in the state which the test subject P installed The block diagram which shows the internal structure of a radiation detection part and a computer in the radiation CT image imaging system using 2nd Embodiment of the radiographic imaging apparatus of this invention. The flowchart for demonstrating the effect | action of the radiation CT image imaging system using 2nd Embodiment of the radiographic imaging apparatus of this invention. The figure for demonstrating the effect | action which acquires the imaging dose of a radiographic image based on the afterimage charge amount corresponding to each imaging dose, and the maximum charge amount which generate | occur | produces in each pixel of a radiographic image detector The figure for demonstrating that the blank part in a predetermined imaging | photography direction becomes an image area | region in another imaging | photography direction. Diagram for explaining that a radiographic image signal to be corrected is saturated by an afterimage caused by radiation irradiation exceeding the recording range of the image signal Schematic configuration diagram of a radiation tomosynthesis imaging apparatus using an embodiment of a radiographic imaging apparatus of the present invention Schematic configuration diagram of a radiation tomosynthesis imaging apparatus using an embodiment of a radiographic imaging apparatus of the present invention The schematic diagram which shows the omission part and subject area | region in the some radiographic image acquired by the radiation tomosynthesis imaging device

  Hereinafter, a radiation CT image capturing system using the first embodiment of the radiation image capturing apparatus of the present invention will be described with reference to the drawings. First, a schematic configuration of the entire radiation CT image capturing system will be described. FIG. 1 is a diagram showing a schematic configuration of the present radiation CT image capturing system.

  As shown in FIG. 1, the present radiation CT image imaging system is connected to an imaging apparatus 1 that captures a radiographic image of a subject P, a bed 22 that is a support base for supporting the subject P, and the imaging apparatus 1. The computer 30 controls the imaging apparatus 1 and processes a radiation image signal obtained by imaging, and a monitor 31 connected to the computer 30.

  The imaging apparatus 1 includes a radiation source 10 that emits conical radiation, a radiation detection unit 11 that detects radiation emitted from the radiation source 10, a radiation source 10, and a radiation detection unit 11 that face each end. A C-arm 12 that holds them, a drive unit 15 that rotates the C-arm 12, and an arm 20 that holds the drive unit 15 are provided.

  The C arm 12 is attached to the drive unit 15 so as to be able to rotate 360 ° around the rotation axis C. The arm 20 includes a movable portion 20a and is held by a base portion 21 that is movably installed with respect to the ceiling. The C-arm 12 can be moved to a wide range of positions in the photographing room by moving the base 21, and the rotation direction (rotation axis angle) can be changed by moving the movable part 20a of the arm 20. Has been.

  The radiation source 10 and the radiation detection unit 11 are disposed to face each other with the rotation axis C interposed therebetween. When performing radiation CT image capturing, the positional relationship between the rotation axis C, the radiation source 10 and the radiation detection unit 11 is as follows. In a fixed state, the C-arm 12 is rotated 360 ° by the drive unit 15.

  FIG. 2 is a block diagram illustrating a schematic configuration inside the radiation detection unit 11 and the computer 30.

  As illustrated in FIG. 2, the radiation detection unit 11 generates a charge upon receiving radiation transmitted through the subject P, and outputs a radiation image signal representing a radiation image of the subject P. And a signal processing unit 11b that performs predetermined signal processing on the radiation image signal output from the image detector 11a.

  The radiological image detector 11a can repeatedly perform recording and reading of radiographic images, and a so-called direct type radiographic image detector that directly receives radiation and generates charges may be used. Alternatively, a so-called indirect radiation image detector that converts radiation once into visible light and converts the visible light into a charge signal may be used. As a radiation image signal readout method, it is preferable to use a so-called TFT readout method in which a radiation image signal is read out by turning on and off a TFT (thin film transistor) switch. Not exclusively.

  As the indirect radiation image detector, for example, a CMOS (Complementary Metal Oxide Semiconductor) sensor or a CCD (Charge Coupled Device Image Sensor) may be used. As a device using a CMOS sensor, for example, it is desirable to use a material using an organic photoelectric conversion material (OPC (Organic Photoconductor)) as described in JP-A-2009-212377. Further, as a scintillator for converting radiation into visible light, it is preferable to use a scintillator composed of a columnar crystal such as CsI as described in Japanese Patent Application Laid-Open No. 2011-17683. By using such a scintillator, a radiographic image with higher sharpness can be obtained, and the effect is particularly remarkable when a plurality of radiographic images are taken continuously.

  The signal processing unit 11b includes an amplifier unit including a charge amplifier that converts the charge signal read from the radiation image detector 11a into a voltage signal, and an AD conversion unit that converts the voltage signal output from the amplifier unit into a digital signal. Etc.

  The computer 30 includes a central processing unit (CPU), a storage device such as an HDD or an SSD, and the like. By these hardware, an afterimage correction unit 30a, a reconstruction unit 30b, a display signal generation unit 30c, a radiation dose estimation A unit 30d, an afterimage charge amount acquisition unit 30e, an imaging interval acquisition unit 30f, an imaging control unit 30g, and an imaging condition input unit 30h are configured.

  The afterimage correction unit 30a performs afterimage correction on the radiation image signal representing the radiation image of the subject P output from the signal processing unit 11b. The afterimage correction method will be described in detail later. Here, only the afterimage correction unit 30a is shown as the one that performs the correction process, but actually, a known correction process such as sensitivity correction or defect correction is performed before and after the afterimage correction.

  The reconstruction unit 30b reconstructs the radiation CT image signal based on the radiation image signal at each imaging angle that has been subjected to afterimage correction in the afterimage correction unit 30a.

  The display signal generation unit 30c generates a display control signal based on the radiation CT image signal output from the reconstruction unit 30b, and outputs the display control signal to the monitor 31.

  The radiation dose estimation unit 30d receives information on irradiation conditions such as the tube current of the radiation source 10 and the irradiation time of radiation of one imaging input by the photographer using the imaging condition input unit 30h, and based on this information Then, the radiation intensity distribution of the radiation that directly reaches the radiation image detector 11a without passing through the subject P is acquired, and the dose of the radiation irradiated to the so-called blank portion is calculated based on the acquired radiation intensity distribution. To be estimated.

  More specifically, a radiation intensity distribution corresponding to a mAs value obtained by multiplying the tube current of the radiation source 10 and the radiation irradiation time is preset in the radiation dose estimation unit 30d. FIG. 3 shows an example of the radiation intensity distribution. The vertical axis of the radiation intensity distribution shown in FIG. 3 indicates the radiation intensity, the horizontal axis indicates the position of the pixels constituting the radiation image detector 11a, and the radiation intensity distribution is generally represented by a radiation image detector. The distribution is such that the radiation intensity gradually decreases from the substantially central portion of 11a toward the periphery. Although FIG. 3 shows the relative intensity distribution of the radiation in the one-dimensional direction, the relative intensity distribution of the radiation in the two-dimensional direction may be set in advance.

  Further, the radiation intensity distribution is set for each of a plurality of mAs values. However, since the radiation intensity distribution increases in proportion to the mAs value, for example, the mAs value input by the imaging condition input unit 30h is set in advance. If it is not a mAs value, it may be obtained by interpolation using a radiation intensity distribution of a preset mAs value close to the inputted mAs value.

In addition, the radiation intensity distribution corresponding to the predetermined mAs value also changes depending on the tube voltage of the radiation source 10. Therefore, when the tube voltage of the radiation source 10 also has a structure that can be changed, as shown in FIG. 3, radiation intensity distribution _{D 1} corresponding to each mAs value _I 1 ~I _n for each tube voltage _V 1 ~V _{m −1 to} D _m−n may be set in advance.

  The radiation intensity distribution also changes depending on the material and thickness of the additional filter provided in the radiation source 20. Therefore, when it is set as the structure which can change the kind of additional filter, you may make it acquire and set the radiation intensity distribution for every kind of the filter beforehand.

  Further, the radiation dose estimation unit 30d acquires a radiation intensity distribution corresponding to the range of the unexposed portion using the radiation intensity distribution acquired as described above. As another method, for example, an imaging target ( A range of a blank portion corresponding to information on information on a thick person, thin person, etc.) and information on an imaging region (chest, abdomen, head, neck, lower limbs, etc.) is set in advance, and an imaging condition input unit 30h By accepting input of information on the imaging object and imaging region, the range of the blank portion may be acquired, or pre-imaging is performed in a state where the subject is set in advance, and the value of the radiographic image signal of the pre-imaging A range that is larger than a predetermined threshold value may be acquired in advance as a missing part.

  In addition, the range of the blank portion varies depending on the shooting angle of the C arm 12, that is, the shooting direction. In the present embodiment, the blank portion corresponding to the shooting angle when the range of the blank portion is maximized. The range of the part is adopted as the range of the radiation dose estimation target of the unexposed part. Then, the value of the radiation intensity distribution of the pixel that is the maximum value among the values of the radiation intensity distribution of each pixel in the radiation dose estimation target blank portion is acquired, and the value is output to the afterimage charge amount acquisition unit 30e. . Hereinafter, this value is referred to as an estimated radiation dose at the unexposed portion.

  Further, an area that is equal to or larger than the recording range of the image signal at the imaging angle where the body thickness of the subject P is the thickest may be adopted as the range of the radiation dose estimation target of the missing part.

  The afterimage charge amount acquisition unit 30e calculates an output signal of the radiation image detector 11a according to the estimated radiation dose based on the input estimated radiation dose of the element missing portion, and the output signal and the radiation image detector 11a. Based on the afterimage attenuation characteristics set in advance for each of the pixels, the temporal change in the afterimage charge amount is acquired, and the temporal change in the afterimage charge amount is output to the imaging interval acquisition unit 30f.

  Here, the afterimage attenuation characteristics for each pixel of the radiation image detector 11a are acquired in advance, for example, by recording a solid image or the like in the radiation image detector 11a and obtaining a time change for each pixel of the output signal. It shall be. In this embodiment, the afterimage attenuation characteristic for each pixel is set in advance. However, the present invention is not limited to this. For example, the afterimage attenuation characteristic for each predetermined area including a plurality of pixels is acquired, May be set in advance.

Moreover, since the afterimage attenuation characteristic for each pixel of the radiation image detector 11a changes according to the mAs value of the radiation source 10 and the magnitude of the tube voltage, the attenuation characteristic for each mAs value is set in advance.
The attenuation characteristic may be selected based on the information of the mAs value input by the photographer using the imaging condition input unit 30h. Further, when the tube voltage of the radiation source 10 can be changed, the attenuation characteristic for each tube voltage is set in advance, and information on the tube voltage input by the photographer using the imaging condition input unit 30h. The attenuation characteristic may be selected based on the above. In addition, when the type of the additional filter of the radiation source 10 can be changed, attenuation characteristics for each type of additional filter are set in advance and input by the photographer using the imaging condition input unit 30h. The attenuation characteristic may be selected based on information on the type of additional filter.

  The imaging interval acquisition unit 30f prevents the output of the radiation image detector 11a from being saturated based on the time change of the input afterimage charge amount and the maximum charge amount generated in each pixel of the radiation image detector 11a by radiation irradiation. In addition, the radiographing interval is acquired. Note that the output of the radiation image detector 11a does not saturate means that the charge accumulation amount of each pixel in the radiation image detector 11a does not saturate, and a signal processing circuit connected to the subsequent stage of the radiation image detector 11a, etc. This also means that the dynamic range is not saturated.

  Specifically, as shown in FIG. 5, the imaging interval acquisition unit 30f determines that the sum of the input afterimage charge Qres and the accumulated charge amount Qsub necessary for image formation on the subject portion is saturated by the radiation image detector 11a. An allowable photographing interval Δt that does not exceed the output Qsat is acquired and output to the photographing control unit 30g. Actually, an allowable photographing interval that satisfies the following expression is acquired.

Qsub (c) + Qres (c) <Qsat (c)
The imaging control unit 30g sets the imaging interval from the allowable imaging interval output from the imaging interval acquisition unit 30f, and sets the radiation interval emitted from the radiation source 10 based on the mAs value input in the imaging condition input unit 30h. The dose and the irradiation timing and the rotation speed of the C arm 12 by the drive unit 15 are controlled. The imaging interval set at this time is preferably set to the minimum value that allows the radiation CT imaging system to operate among the allowable imaging intervals.

  Next, the operation of this radiation CT image capturing system will be described with reference to the flowchart shown in FIG. The radiation CT imaging system is configured to reconstruct a radiation CT image by irradiating radiation at a predetermined imaging interval at predetermined angles while rotating the C arm 12 by 360 ° or 180 ° with respect to the subject P. However, before the actual radiographing, a radiographing interval is set in advance so that the radiographic image signal of the subject image area is not saturated with the afterimage signal of the unexposed portion. Is set. First, the operation of acquiring the shooting interval will be described.

  First, radiation conditions are input by the photographer in the imaging condition input unit 30h. Specifically, the tube voltage (kV) of the radiation source 10, the tube current (mA), the irradiation time (s) per one imaging, and the condition of the type of additional filter are input. Note that these values may be directly input in the imaging condition input unit 30h. For example, information on an imaging target (thick person, thin person) and imaging part information (chest, abdomen, head, neck, By setting a table associating the lower limbs) and irradiation conditions in advance, accepting input of information on the imaging target and imaging region, and referring to the table to obtain the irradiation conditions, the input of irradiation conditions indirectly May be received (S10).

  Then, the irradiation conditions received by the imaging condition input unit 30h are input to the radiation dose estimation unit 30d, and the radiation dose estimation unit 30d acquires the estimated radiation dose of the above-described missing part based on the irradiation conditions. (S12). Note that the method for obtaining the estimated radiation dose of the missing part is as described above.

  Then, the estimated radiation dose acquired by the radiation dose estimation unit 30d is input to the afterimage charge amount acquisition unit 30e, and the afterimage charge amount acquisition unit 30e estimates the estimated radiation dose based on the input estimated radiation dose of the missing part. The output signal of the radiation image detector 11a corresponding to the radiation dose is calculated, and the temporal change of the afterimage charge amount is based on the output signal and the afterimage attenuation characteristics preset for each pixel of the radiation image detector 11a. Acquired and the temporal change of the afterimage charge amount is output to the imaging interval acquisition unit 30f (S14).

  Then, the imaging interval acquisition unit 30f does not saturate the output of the radiation image detector 11a based on the time change of the input afterimage charge amount and the maximum charge amount generated in each pixel of the radiation image detector 11a. The radiographic image capturing interval is acquired (S16). Note that the specific method for acquiring the shooting interval is as described above.

  The shooting interval acquired by the shooting interval acquisition unit 30f is output to the shooting control unit 30g, and the shooting control unit 30g calculates and sets the rotation speed of the C-arm 12 based on the input shooting interval. Note that the number of radiographic images to be captured while the C-arm 12 rotates 360 ° or 180 ° is preset, and the rotational speed of the C-arm 12 is calculated based on the number and the imaging interval.

  The above is the description of the method for obtaining the photographing interval that can appropriately perform the afterimage correction.

  Next, the operation of reconstructing a radiation CT image after capturing a radiation image in accordance with the imaging interval acquired as described above, performing afterimage correction on the radiation image, will be described.

  First, the subject P is laid on the bed 22, and the radiation source 10 and the radiation detection unit 11 are arranged at symmetrical positions with the rotational axis C being the approximate center of the subject P's body. Thus, positioning of the C arm 12 is performed. The movement of the C-arm 12 is performed based on the operation of the computer 30 by the photographer.

  Then, when an imaging start instruction is input by the photographer in the computer 30, the imaging control unit 30g acquires the radiation exposure dose condition input in the imaging condition input unit 30h, and corresponds to the irradiation dose condition. A control signal is output to the radiation source 10 and a control signal corresponding to the rotational speed of the C arm 12 based on the imaging interval acquired as described above is output to the drive unit 15 that drives the C arm 12. Based on these control signals, the radiation source 10 and the drive unit 15 are driven and controlled to take a radiographic image of the subject P (S18).

  Specifically, the C arm 12 is rotated by the drive unit 15 based on the input control signal, and the radiation source 10 and the radiation detection unit 11 are rotated together around the rotation axis C passing through the subject P. At the same time, radiation is emitted from the radiation source 10 based on the input control signal.

  Then, at every predetermined angle of the C-arm 12, the conical radiation emitted from the radiation source 10 and passed through the subject P is exposed to the radiation image detector 11 a and the charge signal recorded in the radiation image detector 11 a is read. And a plurality of charge signals obtained by photographing the subject P from different angles are sequentially read out.

  The charge signal read out as described above is converted into a radiation image signal that is a voltage signal in the amplifier unit of the signal processing unit 11b, converted into a digital signal in the AD conversion unit, and then the afterimage of the computer 30. It is output to the correction unit 30a.

  The afterimage correction unit 30a temporarily stores the plurality of input radiation image signals, and then performs afterimage correction on these radiation image signals (S20).

  Here, afterimage correction of the Nth radiographic image signal will be described. FIG. 7 shows the afterimage characteristics of radiographic image signals photographed at various angles. As shown in FIG. 7, the Nth radiographic image signal is an accumulation of each radiographic image signal captured from the first to (N−1) th with respect to the true radiographic image signal (indicated by a dotted line in FIG. 7). This is a size obtained by adding the afterimage amount sh. Therefore, afterimage correction is performed by subtracting the afterimage signal of each radiographic image signal captured from the first to (N-1) th.

  Specifically, as shown in FIG. 8, when correcting afterimages in the Nth radiographic image, the Nth radiographic image is obtained for each radiographic image taken from the first to the N−1th radiograph. Are multiplied by weighting factors W (N, 1) to W (N, N-1) according to the respective time lapses until the imaging of the image, and the multiplied values are added to obtain an afterimage of the Nth radiation image. Correction data is generated. Then, the afterimage of the Nth radiation image is corrected by subtracting the generated afterimage correction data from the Nth radiation image. However, the first to (N-1) th radiographic images used for generating the afterimage correction data of the Nth radiographic image are those that have been subjected to the afterimage correction by the same method. In addition, the first radiographic image may have been subjected to afterimage correction by some known methods using a dark frame image acquired immediately before the first radiographic image is captured. The first image can be an image that has not been subjected to afterimage correction.

  In addition, about the weighting coefficient, the value according to each time progress shall be preset. Further, it is assumed that the weighting coefficient is set for each pixel of the radiation image detector 11a according to the afterimage characteristics. Further, the afterimage correction method of the Nth radiographic image is not limited to the method described in the present embodiment, and does not exclude performing by other methods.

  Although the afterimage correction unit 30a performs afterimage correction on the radiation image signal as described above, the pixel whose output is saturated in the signal of each pixel to be corrected should not be subjected to afterimage correction. warn. Then, the afterimage correction unit 30a outputs the radiographic image signal after the afterimage correction to the reconstruction unit 30b.

  The reconstruction unit 30b reconstructs a radiation CT image signal by using a plurality of corrected radiation image signals at each imaging angle that has been input (S22).

  The radiation CT image signal generated in the reconstruction unit 30b is output to the display signal generation unit 30c, and a display control signal is generated based on the radiation CT image signal in the display signal generation unit 30c and output to the monitor 31. The The monitor 31 displays the radiation CT image of the subject P based on the input display control signal.

  Further, in the radiation CT image capturing system of the first embodiment, the estimated radiation dose of the unexposed portion is acquired based on the radiation irradiation condition input in the imaging condition input unit 30h. The method for acquiring the amount is not limited to this. Hereinafter, another method for acquiring the estimated radiation dose will be described.

  In this method, the estimated radiation dose is acquired by detecting the radiation actually emitted from the radiation source 10 by the radiation image detector 11a.

  Specifically, as shown in FIG. 9, a radiation image detector in which a radiation absorbing member 40 that absorbs radiation is installed on the radiation irradiation side surface of the radiation image detector 11a, and the radiation absorbing member 40 is set. For 11a, a radiation image for measurement is acquired to irradiate the radiation based on the radiation dose condition input in the imaging condition input unit 30h to acquire the estimated radiation dose. The radiation absorbing member 40 is installed in a range other than the image area in which a radiographic image of the subject P can actually be recorded. As for the shape of the radiation absorbing member 40, as shown in FIG. 9, an elongated rectangular shape may be provided along two opposing sides of the radiation image detector 11a, or four sides of the radiation image detector 11a. It may be provided in a frame shape along the line.

  Moreover, the radiographic image for measurement may be taken with the subject P installed, or may be taken without the subject P installed.

  However, in this embodiment, in any case, when the subject P is actually installed and the radiographic image is actually captured, the C-arm 12 is set at an imaging angle that maximizes the range of the blank portion. It is assumed that shooting is performed in a state in which is rotated.

  Alternatively, when the subject P is actually installed and the radiographic image is actually taken, the subject P may be taken with the C arm 12 rotated to the photographing angle at which the body thickness of the subject P is the thickest. Good.

  As for the imaging angle at which the range of the unexposed portion is the largest or the imaging angle at which the subject P has the largest body thickness, for example, information on the subject to be photographed (thick person, thin person, etc.) The imaging angle corresponding to information on the chest, abdomen, head, neck, lower limbs, etc.) is set in advance, and the imaging angle input unit 30h accepts input of information on the imaging target and imaging site. Should be obtained.

  In addition, when taking a radiographic image for measurement with the subject P installed, a plurality of radiographic images for measurement are taken at a plurality of pre-set imaging angles, and there is no omission from the plurality of radiographic images for measurement. You may make it select a thing with the wide range of a part.

  Then, the charge signal representing the measurement radiation image recorded and read out in the radiation image detector 11a as described above is converted into a voltage signal by the amplifier unit of the signal processing unit 11b, and is converted into a digital signal by the AD conversion unit. Is converted into the radiation dose estimation unit 30d.

  In FIG. 10, an example of the radiographic image signal for measurement image | photographed in the state which the test subject P was installed is shown as a continuous line. The horizontal axis in FIG. 10 indicates the pixel position in the direction orthogonal to the length direction of the radiation absorbing member 40, and the vertical axis indicates the output of each pixel. Further, the saturation level shown in FIG. 10 is the saturation level of the output of the radiation image detector 11a.

  As shown in FIG. 10, the output signal FS in the range transmitted through the radiation absorbing member 40 in the range DR of the blank portion is detected without being saturated and with a magnitude proportional to the dose of radiation emitted from the radiation source 10. can do.

  Then, the radiation dose estimation unit 30d estimates the radiation intensity distribution XD of the range DR of the blank portion based on the output signal FS in the range transmitted through the radiation absorption member 40 and the radiation absorption characteristics of the radiation absorption member 40. To do. In addition, in FIG. 10, although the radiation intensity distribution of the range other than a blank part is also shown, it is not necessary to estimate this part.

  Then, the radiation dose estimation unit 30d uses the radiation intensity distribution value of the pixel that is the maximum value among the radiation intensity distribution values of each pixel in the radiation intensity distribution XD in the range DR of the missing part as the estimated radiation of the missing part. Get as a quantity.

  When the estimated radiation dose is acquired by the above-described method, the estimated radiation dose corresponding to the actual radiation exposure condition of the actual imaging is acquired based on the measurement radiation image captured under the radiation exposure condition of one radiation. However, a plurality of estimated radiation doses may be acquired based on the measurement radiographic images captured with different mAs values. Further, since beam hardening is caused by the radiation absorbing member 40, at least based on the measurement radiation image captured with different tube voltages or types of additional filters, the actual tube voltage or type of additional filters is selected. It is desirable to select and acquire the estimated radiation dose.

  Next, a radiation CT image capturing system using the second embodiment of the radiation image capturing apparatus of the present invention will be described. The schematic configuration of the entire radiation CT image capturing system of the second embodiment is the same as that of the radiation CT image capturing system of the first embodiment shown in FIG.

  In the radiation CT image capturing system of the first embodiment, a radiographic image capturing interval is acquired based on the estimated radiation dose of the unexposed portion, and a radiographic image is captured at the rotational speed of the C-arm 12 according to the capturing interval. However, in the radiation CT image capturing system of the second embodiment, the radiographic image signal of the subject image region is saturated by the afterimage signal of the missing part based on the estimated radiation dose of the missing part. A radiographic image is acquired with a radiographic image obtained with the radiographic dose.

  Accordingly, as shown in FIG. 11, the computer 30 of the radiation CT image capturing system of the second embodiment includes an afterimage charge amount acquisition unit 30e instead of the imaging interval acquisition unit 30f in the computer 30 of the first embodiment. An imaging dose acquisition unit i is provided that acquires the imaging dose of each radiographic image in the main imaging based on the afterimage charge amount acquired by.

  Further, since the operation of other parts in the computer 30 is different from that of the first embodiment, the operation will be described in detail with reference to the flowchart shown in FIG.

  In the radiation CT image capturing system according to the second embodiment, first, the radiation dose estimation unit 30d acquires the estimated radiation dose of the missing part (S30). Specifically, in the radiation dose estimation unit 30d, a radiation intensity distribution as shown in FIG. 3 is set in advance for each imaging dose, and based on each radiation intensity distribution and the information on the range of the missing part. Then, a radiation intensity distribution corresponding to the range of the blank portion for each imaging dose is acquired.

  As for the information on the range of the unplugged part, as in the first embodiment, for example, information on the imaging target (thick person, thin person, etc.) and imaging part (chest, abdomen, head, neck, lower limbs, etc.) ) And the like are set in advance, and the range of the missing part is acquired by accepting input of information on the imaging target and the imaging part by the imaging condition input unit 30h. Alternatively, pre-imaging may be performed in a state where the subject is set in advance, and a range in which the value of the radiographic image signal of the pre-imaging is larger than a predetermined threshold may be acquired in advance as a blank portion.

  In addition, the range of the blank portion varies depending on the shooting angle of the C-arm 12, that is, the shooting direction, but in this embodiment as well, as in the first embodiment, the range of the blank portion is maximized. The range of the missing part corresponding to the imaging angle is adopted as the range of the radiation dose estimation target of the missing part. Then, the value of the radiation intensity distribution of the pixel that is the maximum value among the values of the radiation intensity distribution of each pixel in the blank portion of the radiation dose estimation target is acquired as the estimated radiation dose.

  As described above, the estimated radiation dose of the blank portion corresponding to each imaging dose is acquired. Then, the estimated radiation dose of the blank portion corresponding to each imaging dose acquired by the radiation dose estimation unit 30d is output to the afterimage charge amount acquisition unit 30e.

  Next, the photographing condition is input by the photographer in the photographing condition input unit 30h (S32). As for the imaging interval condition, these values may be directly input in the imaging condition input unit 30h. For example, a table in which imaging site information is associated with imaging interval conditions is set in advance. Alternatively, an input of imaging interval conditions may be received indirectly by receiving input of imaging region information and referring to a table to obtain imaging interval conditions. For example, when the imaging region is the chest, the imaging interval (circulation time) is set short because the motion of the heart becomes an artifact. In addition, a table that associates shooting speed information such as high-speed shooting mode, medium-speed shooting mode, and low-speed shooting mode with shooting interval conditions is set in advance. The condition may be obtained.

  The imaging interval condition received by the imaging condition input unit 30h is input to the afterimage charge amount acquisition unit 30e. In the afterimage charge amount acquisition unit 30e, the input imaging interval condition and the portion where each imaging dose is omitted. The afterimage charge amount of each imaging dose is calculated based on the estimated radiation dose (S34). Specifically, the afterimage charge amount acquisition unit 30e calculates an output signal of the radiation image detector 11a according to the estimated radiation dose, based on the estimated radiation dose of the input portion where each imaging dose is omitted, An afterimage charge amount of each imaging dose is calculated based on the output signal and an afterimage attenuation characteristic preset for each pixel of the radiation image detector 11a, and the afterimage charge amount of each imaging dose is calculated as an imaging dose acquisition unit. Output to 30i. Here, the acquisition method of the afterimage attenuation characteristic for each pixel of the radiation image detector 11a is the same as that in the first embodiment, and also in the second embodiment, a predetermined image including a plurality of pixels is included. An afterimage attenuation characteristic for each area may be acquired and set in advance.

  The imaging dose acquisition unit 30i outputs the output of the radiation image detector 11a based on the afterimage charge amount of each input imaging dose and the maximum charge amount generated in each pixel of the radiation image detector 11a by radiation irradiation. A radiographic imaging dose that does not saturate is acquired (S36).

  Specifically, as shown in FIG. 13, the imaging dose acquisition unit 30i determines that the sum of the afterimage charge Qres of each input imaging dose and the accumulated charge amount Qsub necessary for image formation of the subject portion is a radiation image detector. An allowable imaging dose that does not exceed the saturation output Qsat of 11a is acquired and output to the imaging control unit 30e. In practice, an allowable imaging dose that satisfies the following formula is acquired.

Qsub (c) + Qres (c) <Qsat (c)
Then, the imaging control unit 30g sets the radiation conditions for the radiation source 10 based on the input allowable imaging dose.

  Next, a radiographic image is taken based on the information on the radiation irradiation conditions acquired as described above (S38).

  First, the subject P is laid on the bed 22, and the radiation source 10 and the radiation detection unit 11 are arranged at symmetrical positions with the rotational axis C being the approximate center of the subject P's body. Thus, positioning of the C arm 12 is performed.

  When a shooting start instruction is input by the photographer in the computer 30, the shooting control unit 30g acquires the shooting interval condition input in the shooting condition input unit 30h, and rotates the C-arm 12 based on the shooting interval. A control signal corresponding to the speed is output to the drive unit 15 that drives the C-arm 12, and a control signal based on the tube voltage and tube current set as described above is output to the radiation source 10. Based on the signal, the radiation source 10 and the drive unit 15 are driven and controlled, and a radiation image of the subject P is taken.

  Specifically, the C arm 12 is rotated by the drive unit 15 based on the input control signal, and the radiation source 10 and the radiation detection unit 11 are rotated together around the rotation axis C passing through the subject P. At the same time, radiation is emitted from the radiation source 10 based on the input control signal.

  Then, at every predetermined angle of the C-arm 12, the conical radiation emitted from the radiation source 10 and passed through the subject P is exposed to the radiation image detector 11 a and the charge signal recorded in the radiation image detector 11 a is read. And a plurality of charge signals obtained by photographing the subject P from different angles are sequentially read out.

  The read charge signal as described above is converted into a radiographic image signal that is a voltage signal in the amplifier unit of the signal processing unit 11b, converted into a digital signal in the AD conversion unit, and then an afterimage of the computer 30. It is output to the correction unit 30a.

  The afterimage correction unit 30a temporarily stores the plurality of input radiation image signals, and then performs afterimage correction on these radiation image signals (S40). Note that the effect of afterimage correction is the same as that in the first embodiment.

  Although the afterimage correction unit 30a performs afterimage correction on the radiation image signal, it should be noted that in the signal of each image to be corrected, a pixel whose output is saturated should not be subjected to afterimage correction. Then, the afterimage correction unit 30a outputs the radiographic image signal after the afterimage correction to the reconstruction unit 30b.

  The reconstruction unit 30b reconstructs a radiation CT image signal by using the plurality of corrected radiation image signals at each imaging angle that has been input (S42).

  The radiation CT image signal generated in the reconstruction unit 30b is output to the display signal generation unit 30c, and a display control signal is generated based on the radiation CT image signal in the display signal generation unit 30c and output to the monitor 31. The The monitor 31 displays the radiation CT image of the subject P based on the input display control signal.

  Also in the second embodiment, similarly to the first embodiment, radiation of each imaging dose actually emitted from the radiation source 10 is emitted by the radiation image detector 11a provided with the radiation absorbing member 40. The estimated radiation dose may be acquired by detection.

  Specifically, a plurality of measurement radiation images are acquired to acquire an estimated radiation dose by irradiating the radiation image detector 11a to which the radiation absorbing member 40 is set with radiation of each imaging dose.

  At this time, also in the present embodiment, when the subject P is actually installed and the radiographic image is actually captured, the C-arm 12 is rotated to an imaging angle that maximizes the range of the blank area. It is assumed that a radiographic image for measurement is taken.

  Then, the charge signal representing the radiation image for measurement of each imaging dose read from the radiation image detector 11a is converted into a voltage signal by the amplifier unit of the signal processing unit 11b, and converted into a digital signal by the AD conversion unit. After that, it is input to the radiation dose estimation unit 30d.

  Then, the radiation dose estimation unit 30d, for the radiographic image signal for measurement of each imaging dose, as shown in FIG. Based on the above, the radiation intensity distribution XD in the range DR of the blank portion is estimated. In addition, in FIG. 10, although the radiation intensity distribution of the range other than a blank part is also shown, it is not necessary to estimate this part.

  Then, the radiation dose estimation unit 30d uses the radiation intensity distribution value of the pixel that is the maximum value among the radiation intensity distribution values of each pixel in the radiation intensity distribution XD in the range DR of the missing part as the estimated radiation of the missing part. Get as a quantity. In this way, the estimated radiation dose for each imaging dose is acquired.

  In the above description, the radiographic image capturing apparatus according to the embodiment of the present invention is used in the radiographic CT image capturing system. However, the present invention is not limited to this, and the radiographic image detector is used repeatedly. As long as the radiographic image capturing apparatus performs after image capturing and performs afterimage correction, the present invention may be applied to other apparatuses.

  For example, the present invention can be applied to a radiation tomosynthesis imaging apparatus capable of imaging a tomographic image. FIG. 16 shows an example of a radiation tomosynthesis imaging apparatus. In this apparatus, the radiation source 10 is moved along an arcuate trajectory M centered on a point Q set in the subject P on the imaging table 23, and every time the movement position changes, that is, the radiation irradiation axis. A radiographic image is taken every time the angle formed between O and the imaging table 23 changes. A tomographic image or a three-dimensional image can be reconstructed by performing a reconstruction operation based on the plurality of radiation images thus obtained.

  FIG. 17 shows another example of the radiation tomosynthesis imaging apparatus. In this apparatus, for example, the radiation source 10 is movably supported by a traveling system installed on a ceiling or the like, and the radiation source 10 is moved in a direction parallel to the imaging table 22, that is, along a linear locus N. . Each time the movement position changes, the tilt angle of the radiation source 10, that is, the angle formed by the radiation irradiation axis O and the imaging table 22 is changed, and a radiographic image is taken each time. Also in this case, a tomographic image or a three-dimensional image can be reconstructed by performing a reconstruction operation based on a plurality of radiographic images obtained by imaging.

  Here, in the radiation CT image capturing systems of the first and second embodiments, the radiation dose estimation unit 30d has a blanking according to the imaging angle of the C arm 12 when the range of the blanking unit is maximized. The radiation intensity distribution of the pixel that is the maximum value among the radiation intensity distribution values of each pixel in the radiation loss estimation target range of the radiation dose estimation target The radiation dose is acquired as the estimated radiation dose of the missing part. However, in the radiation tomosynthesis imaging apparatus shown in FIGS. 16 and 17, the radiation irradiation axis O and the detection surface of the radiation image detector 11a are obtained every time a plurality of radiation images are captured. As a result, the range of the unaccompanied portion changes, and the range of the radiation dose estimation target of the unexposed portion is determined as follows.

More specifically, for example, in the radiation tomosynthesis imaging apparatus shown in FIG. 16 or FIG. 17, the relationship between the subject region and the blank portion when the subject P is photographed from the front is as shown in FIG. FIG. 18B shows the relationship between the subject area and the blank portion when the subject P is photographed from the right oblique direction shown in FIG. 16 (FIG. 17), and the subject P is shown in FIG. FIG. 18C shows the relationship between the subject area and the missing part when the image is taken from the left oblique direction shown in FIG. 18A to 18C schematically show a subject area and a blank portion on a radiographic image, and their sizes and shapes are not accurate.

  Then, what is necessary when acquiring the estimated radiation dose of the missing part is a range in which the missing part and the subject area are interchanged in a series of imaging processes of a plurality of radiation images. Therefore, first, an area obtained by performing OR operation on the blank portion of each radiographic image shown in FIGS. 18A to 18C is acquired, and an area obtained by performing OR operation on the subject area of each radiographic image is acquired. Then, an area obtained by ANDing the OR operation area of the background area and the OR area of the subject area is acquired as an area where the background area and the subject area are interchanged. That is, this AND operation area is acquired as the range of the radiation dose estimation target of the missing part.

  Then, the radiation dose estimation unit 30d calculates the radiation intensity distribution of the pixel that is the maximum value among the radiation intensity distribution values of the pixels in the radiation dose estimation target missing portion acquired as described above. Obtained as estimated radiation dose.

  Note that the method of acquiring the afterimage charge amount after acquiring the estimated radiation dose of the unexposed portion, acquiring the imaging interval and imaging dose, and correcting the afterimage is the same as in the first and second embodiments.

  Also, in the radiation CT image capturing system of the first and second embodiments, the region where the blank portion and the subject region are interchanged as described above is acquired as the range of the radiation dose estimation target of the blank portion, Of the radiation intensity distribution values of each pixel in the radiation dose estimation target, the radiation intensity distribution of the pixel having the maximum value may be acquired as the estimated radiation dose of the radiation missing portion. Thus, by acquiring the estimated radiation dose of the element missing part, it is possible to obtain a more accurate estimated radiation dose of the element missing part.

DESCRIPTION OF SYMBOLS 1 Imaging device 10 Radiation source 11 Radiation detection part 11a Radiation image detector 11b Signal processing part 12 C arm 15 Drive part 30 Computer 30a Afterimage correction part 30b Reconstruction part 30c Display signal generation part 30d Radiation dose estimation part 30e Acquisition of afterimage charge amount Unit 30e imaging control unit 30f imaging interval acquisition unit 30g imaging control unit 30h imaging condition input unit 30i imaging dose acquisition unit 31 monitor 40 radiation absorbing member

Claims (17)

A radiation image detector that emits radiation upon receiving radiation that has been emitted from a radiation source and transmitted through a subject, and that outputs a radiation image signal representing the radiation image of the subject, and is used repeatedly to capture a radiation image In a radiographic image capturing method in a radiographic image capturing apparatus, comprising: a radiographic image detector that is provided; and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector.
Based on the radiation intensity distribution in the radiation image detector acquired in advance, estimate the dose of radiation that has reached the radiation image detector without passing through the subject,
An afterimage charge amount is acquired based on the estimated radiation dose and an afterimage attenuation characteristic of the radiation image detector set in advance,
Based on the sum of the acquired afterimage charge amount and the maximum value of the radiographic image signal detected by the radiographic image detector, the radiographic image capturing interval from the next time onward so that the output of the radiographic image detector is not saturated. A radiographic image capturing method characterized in that A radiation image detector that emits radiation upon receiving radiation that has been emitted from a radiation source and transmitted through a subject, and that outputs a radiation image signal representing the radiation image of the subject, and is used repeatedly to capture a radiation image In a radiographic image capturing method in a radiographic image capturing apparatus, comprising: a radiographic image detector that is provided; and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector.
Based on the radiation intensity distribution in the radiation image detector acquired in advance, estimate the dose of radiation that has reached the radiation image detector without passing through the subject,
An afterimage charge amount is acquired based on the estimated radiation dose and an afterimage attenuation characteristic of the radiation image detector set in advance,
Based on the sum of the acquired afterimage charge amount and the maximum value of the radiographic image signal detected by the radiographic image detector, the radiographic image detector is used for subsequent radiographic imaging so that the output of the radiographic image detector is not saturated. A radiation image capturing method, wherein the radiation irradiation condition is acquired. A radiation image detector that emits radiation upon receiving radiation that has been emitted from a radiation source and transmitted through a subject, and that outputs a radiation image signal representing the radiation image of the subject, and is used repeatedly to capture a radiation image In a radiographic image capturing apparatus comprising: a radiographic image detector to be provided; and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector;
Based on the radiation intensity distribution in the radiation image detector acquired in advance, a radiation dose estimation unit that estimates the dose of radiation that has reached the radiation image detector without passing through the subject;
An afterimage charge amount acquisition unit for acquiring an afterimage charge amount based on a radiation dose estimated by the radiation amount estimation unit and a preset afterimage attenuation characteristic of the radiation image detector;
Based on the sum of the afterimage charge amount acquired by the afterimage charge amount acquisition unit and the maximum value of the radiation image signal detected by the radiation image detector, the output of the radiation image detector is prevented from being saturated next time. A radiographic image capturing apparatus, comprising: an imaging interval acquisition unit that acquires an interval between radiographic image capturing. A radiation image detector that emits radiation upon receiving radiation that has been emitted from a radiation source and transmitted through a subject, and that outputs a radiation image signal representing the radiation image of the subject, and is used repeatedly to capture a radiation image In a radiographic image capturing apparatus comprising: a radiographic image detector to be provided; and a signal processing unit that performs predetermined signal processing on the radiographic image signal output from the radiographic image detector;
Based on the radiation intensity distribution in the radiation image detector acquired in advance, a radiation dose estimation unit that estimates the dose of radiation that has reached the radiation image detector without passing through the subject;
An afterimage charge amount acquisition unit for acquiring an afterimage charge amount based on a radiation dose estimated by the radiation amount estimation unit and a preset afterimage attenuation characteristic of the radiation image detector;
Based on the sum of the afterimage charge amount acquired by the afterimage charge amount acquisition unit and the maximum value of the radiation image signal detected by the radiation image detector, the output of the radiation image detector is prevented from being saturated next time. A radiation image capturing apparatus, comprising: a radiation dose acquiring unit configured to acquire the radiation irradiation condition used for capturing the radiation image.   5. The radiographic image capturing apparatus according to claim 3, wherein the radiation intensity distribution is acquired based on a radiographic image signal detected by the radiographic image detector. A radiation absorbing member provided in a region other than the image region in the radiation image detector,
6. The radiation intensity distribution according to claim 5, wherein the radiation intensity distribution is acquired based on a radiation image signal output from the radiation image detector in response to irradiation of radiation transmitted through the radiation absorbing member. Radiation imaging device. The radiation image detector sequentially detects the radiation applied to the subject from different directions;
The radiation dose estimation unit uses the radiation intensity distribution according to the radiation irradiation from the direction in which the radiation irradiation range reaching the radiation image detector without passing through the subject is maximized, and the radiation dose The radiation image capturing apparatus according to claim 3, wherein the radiation image capturing apparatus is configured to perform estimation. The radiation image detector sequentially detects the radiation applied to the subject from different directions;
The radiation dose estimation unit is configured to estimate the radiation dose using a radiation intensity distribution according to radiation irradiation from a direction in which the body thickness of the subject is maximized. The radiographic imaging apparatus according to any one of 3 to 6.   The radiation intensity distribution is acquired based on at least one of the following conditions: tube current of the radiation source, tube voltage, radiation irradiation time, and type of additional filter. 4. The radiographic imaging apparatus according to 4.   The afterimage charge amount acquisition unit acquires an afterimage attenuation characteristic corresponding to at least one of the tube voltage, tube current, radiation irradiation time, and type of additional filter of the radiation source. The radiographic imaging device according to any one of claims 3 to 8.   The imaging interval acquisition unit acquires the imaging interval based on a maximum afterimage charge amount of the afterimage charge amount acquired for each pixel constituting the radiation image detector. The radiographic imaging apparatus according to claim 3.   The radiation dose acquisition unit acquires the radiation dose based on a maximum afterimage charge amount among the afterimage charge amounts acquired for each pixel constituting the radiation image detector. The radiographic imaging device according to claim 4.   The afterimage correction unit that performs afterimage correction on the radiation image signal output from the radiation image detector based on the afterimage charge amount acquired by the afterimage charge amount acquisition unit. The radiographic imaging apparatus of any one of Claims. The radiation image detector sequentially detects the radiation applied to the subject from different directions;
The afterimage correction unit acquires an afterimage correction amount based on a preset afterimage attenuation characteristic of the radiographic image detector and an imaging time until imaging of the radiographic image signal to be subjected to the afterimage correction, and the afterimage The radiographic image capturing apparatus according to claim 13, wherein the afterimage correction is performed based on a correction amount.   4. A radiation CT imaging apparatus for reconstructing a tomographic image based on a plurality of image signals detected by the radiation image detector by irradiating the subject with radiation from different directions. 14. The radiographic image capturing apparatus according to any one of claims 14.   The radiation tomosynthesis imaging apparatus for reconstructing a tomographic image based on a plurality of image signals detected by the radiation image detector by irradiating the subject with radiation from different directions. 14. The radiographic image capturing apparatus according to any one of claims 14. In the process of repeatedly taking the radiographic image, the radiation dose estimating unit transmits the radiographic image through a region where the radiation reaches the radiographic image detector without passing through the subject and the radiation passes through the subject. Get the area where the area that reached the detector is swapped,
17. The dose of radiation that has reached the radiation image detector without passing through the subject is estimated based on the acquired region and the radiation intensity distribution. The radiographic imaging apparatus according to item 1.