JP2016054795A - Radiographic imaging apparatus and calibration method of radiographic imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiographic imaging apparatus and a calibration method of a radiographic imaging apparatus capable of acquiring accurate correction data even when calibration accompanied by radiation irradiation is performed when there is a marker arranged in an irradiation path from a radiation source to a conversion panel.SOLUTION: A calibration image 77A is acquired by X-ray irradiation. In addition to a defect 81, a marker area MA is present in the calibration image 77A. The marker area MA is detected from the calibration image 77A, and excluding the detected marker area, a defect search area 82 is set in the calibration image 77A. The defect 81 is detected from the defect search area 82, and defect position information 83 is created.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a radiographic image capturing apparatus that captures a radiographic image using radiation and a calibration method for the radiographic image capturing apparatus.

  In the medical field, an X-ray imaging apparatus that captures an X-ray image of a subject by imaging the subject using radiation, for example, X-rays, is known. Some X-ray imaging apparatuses have special imaging functions such as tomosynthesis imaging and stereo imaging that reconstruct a plurality of X-ray images with different X-ray irradiation directions on a subject to obtain a reconstructed image. (Japanese Patent Laid-Open No. 2012-115380). Japanese Patent Application Laid-Open No. 2012-115380 describes a mammography apparatus as an X-ray imaging apparatus, and the mammography apparatus has a stereo imaging function as a special imaging function.

  The mammography apparatus includes an imaging table on which a subject breast is disposed, a compression plate that compresses the breast above the imaging table, and an X-ray source that is disposed above the compression plate and emits X-rays. Yes. The X-ray source is attached to a rotatable arm so that the irradiation direction of the X-ray source with respect to the imaging table is variable. When performing stereo imaging or tomosynthesis imaging, X-ray images are obtained in a plurality of irradiation directions while changing the irradiation direction of the X-ray source with respect to the breast on the imaging table. An image reconstruction process is performed based on a plurality of X-ray images and the irradiation direction of each X-ray image, and a reconstructed image such as a stereo image or a tomographic image is obtained.

  The imaging table includes a conversion panel for detecting an X-ray image. The conversion panel has a two-dimensional imaging region and converts incident X-rays into electrical signals. An image signal and further an X-ray image are generated based on the electrical signal. The imaging table is made of a material such as carbon having permeability to X-rays, and a marker made of a material having high X-ray absorption characteristics such as gold is provided in a part of the imaging table.

  The marker is provided on the imaging surface on which the breast is arranged on the imaging table, and is arranged in the X-ray irradiation path from the X-ray source to the conversion panel. The marker is used to accurately measure the irradiation direction of the X-ray source with respect to the imaging surface. The irradiation direction of the X-ray source can be measured based on, for example, the output of a potentiometer that measures the rotation angle of the arm. However, compared with the measurement accuracy in the irradiation direction of the X-ray source that is required in stereo imaging and tomosynthesis imaging, the output value of the potentiometer is low in accuracy and has a large variation due to disturbance or the like. Therefore, a marker is used to measure the irradiation direction of the X-ray source with higher accuracy.

  Since there is a gap between the imaging surface of the imaging table where the marker is arranged and the imaging area of the conversion panel, if the irradiation direction of the X-ray source with respect to the imaging table changes, X-rays that have passed through the marker in the imaging area Since the incident position where the light enters is changed, the marker region in which the marker is reflected changes in the imaging region. Since the distance from the X-ray source to the imaging region (SID: Source Image Distance) is determined by the positioning at the time of imaging, if a marker region in the X-ray image is detected by image analysis, an X-ray image is obtained by a technique such as triangulation. The irradiation direction of the X-ray source can be measured based on the marker region detected from the inside.

  In addition to special imaging such as stereo imaging and tomosynthesis imaging functions, the marker is used as a configuration to accurately measure the irradiation direction of an X-ray source in an X-ray imaging apparatus with a biopsy function. Is done. As described above, the marker performs an important function in the measurement of the X-ray irradiation direction.

JP 2012-115380 A

  One of the functions of the X-ray imaging apparatus is calibration with X-ray irradiation performed for maintenance of the conversion panel. As calibration accompanied by X-ray irradiation, for example, gain calibration and defect calibration are known.

  As is well known, gain calibration is processing for creating gain correction data for performing gain correction on an X-ray image photographed by a conversion panel. In the imaging region, a plurality of pixels having sensitivity to X-rays are two-dimensionally arranged. An accurate X-ray image cannot be obtained if there is a variation in the output value of each pixel according to the X-ray incident dose, that is, if the sensitivity of each pixel varies. Therefore, gain correction is performed on the captured X-ray image based on the gain correction data in order to correct the sensitivity variation of each pixel.

  In gain calibration, first, X-rays are uniformly irradiated to the imaging region in a state where the subject does not exist in the X-ray irradiation path, and in this case, calibration is performed based on the image signal output from the conversion panel. An image is generated. Since the sensitivity variation of each pixel is reflected in the calibration image, gain correction data for correcting the sensitivity variation is created based on the calibration image.

  On the other hand, defect calibration is a process for obtaining defect correction data for correcting a defect in an X-ray image caused by a defective pixel in an imaging region. The defect correction data is, for example, defect position information indicating the positions of all defective pixels in the imaging region. In the defect calibration, similarly to the gain calibration, first, an X-ray is uniformly irradiated to the imaging region in a state where the subject does not exist in the X-ray irradiation path, and in this case, an image output from the conversion panel A calibration image is generated based on the signal. Since the calibration image reflects defects caused by defective pixels in the imaging region, defect position information is created based on the calibration image. Using the defect position information as defect correction data, defect correction is performed on the photographed X-ray image.

  However, when a marker is provided, a marker region appears in which the marker is reflected in the calibration image. Therefore, for example, in gain calibration, the sensitivity of the pixels in the marker region cannot be detected accurately, and accurate gain correction data cannot be obtained. On the other hand, in the case of defect calibration, the marker region may be erroneously detected as a point defect, and accurate defect correction data cannot be obtained.

  The present invention relates to a radiographic imaging apparatus and a radiation that can obtain accurate correction data even when calibration is performed with radiation irradiation when there is a marker arranged in an irradiation path from the radiation source to the conversion panel. An object of the present invention is to provide a calibration method for an image capturing apparatus.

  In order to solve the above-described problems, a radiographic imaging apparatus of the present invention includes a conversion panel, an imaging table, a marker, a calibration image acquisition unit, and a correction data creation unit. The conversion panel has a two-dimensional imaging region, and converts the radiation irradiated from the radiation source and transmitted through the subject into an electrical signal. The photographing stand includes a conversion panel and a subject is arranged. The marker is provided on the imaging stand and is disposed in the irradiation path from the radiation source to the conversion panel. The calibration image acquisition unit acquires a calibration image based on an electrical signal output from the conversion panel when the imaging region is irradiated with radiation in a state where the subject does not exist in the irradiation path. The correction data creation unit creates correction data from which the influence of the marker reflected in the calibration image is removed.

  It is preferable to have a tomosynthesis imaging function that changes the irradiation direction of the radiation source, captures a radiation image of the subject in each irradiation direction, and generates a tomographic image of the subject based on the captured radiation image.

  The correction data creation unit preferably creates defect position information indicating the position of the defective pixel in the imaging region based on the calibration image.

  The correction data creation unit detects a marker area in which the marker appears from the calibration image, and creates defect position information indicating the position of the defective pixel from the defect search area excluding the marker area in the calibration image.

  The correction data creation unit may create defect position information indicating the position of the defective pixel from the calibration image, and exclude the position information of the marker area where the marker appears from the created defect position information.

  The correction data creation unit preferably detects the marker region from the calibration image by image analysis.

  The correction data creation unit may determine whether or not the conversion panel can be used based on the defect position information.

  It is preferable that the correction data generation unit detects the marker region from the calibration image and generates the gain correction data based on the calibration image from which the detected marker region is removed. The correction data creation unit preferably detects the marker region from the calibration image by image analysis.

  The subject is preferably a breast.

  A calibration method for a radiographic imaging apparatus according to the present invention is a calibration method for a radiographic imaging apparatus including a conversion panel, an imaging platform, and a marker, and includes a calibration image acquisition step and a correction data creation step. Yes. The conversion panel has a two-dimensional imaging region, and converts the radiation irradiated from the radiation source and transmitted through the subject into an electrical signal. The photographing stand includes a conversion panel and a subject is arranged. The marker is provided on the imaging stand and is disposed in the irradiation path from the radiation source to the conversion panel. The calibration image acquisition step acquires a calibration image based on an electrical signal output from the conversion panel when the imaging region is irradiated with radiation in a state where the subject does not exist in the irradiation path. In the correction data creation step, correction data from which the influence of the marker reflected in the calibration image is removed is created.

  According to the present invention, when there is a marker arranged in the irradiation path from the radiation source to the conversion panel, the influence of the marker reflected in the calibration image is eliminated even if calibration with radiation irradiation is performed. Since the correction data is created, it is possible to provide a radiation imaging apparatus and a radiation imaging apparatus calibration method capable of obtaining accurate correction data.

It is a schematic block diagram which shows an X-ray image imaging device. It is explanatory drawing of the rotation state of an arm part. It is a schematic block diagram of an image detector. It is explanatory drawing of the marker provided in the imaging stand. It is explanatory drawing of the position of a marker. It is explanatory drawing of the change of the position of the marker area | region according to the irradiation direction of X-ray | X_line. It is a schematic block diagram of a console. It is a functional block diagram of a console. It is explanatory drawing of a calibration image. It is explanatory drawing which shows the distribution state of the pixel value of a calibration image. It is a flowchart which shows the process sequence of defect calibration. It is a flowchart which shows the process sequence of gain calibration. It is a flowchart which shows an imaging | photography procedure. It is explanatory drawing of the defect calibration of 2nd Embodiment.

“First Embodiment”
In FIG. 1, an X-ray imaging apparatus 10 that is an example of a radiographic imaging apparatus is a mammography apparatus that images a breast as a subject H. The X-ray imaging apparatus 10 includes a main unit 11 and a console 12. The main unit 11 has a photographing function for photographing an X-ray image of the subject H. The console 12 includes a display 12A and an input device 12B such as a keyboard and a mouse. The console 12 operates an operation device for operating the main unit 11, a display device that displays an X-ray image captured by the main unit 11, and an X It functions as an image processing apparatus that performs image processing on a line image. The X-ray imaging apparatus 10 has a tomosynthesis imaging function for obtaining a tomographic image of the subject H in addition to a normal imaging function for obtaining a simple projection image of the subject H.

  The main body unit 11 includes a base 13 with a support column extending in the Z direction and a substantially C-shaped arm portion 14 supported by the base 13. The arm unit 14 is attached to the rotating shaft 15, rotates around the Y axis of the rotating shaft 15, and moves up and down by movement of the rotating shaft 15 in the Z direction. The arm unit 14 includes an X-ray source storage unit 18, an imaging table 19, and a connecting unit 20 that connects the X-ray source storage unit 18 and the imaging table 19. The X-ray source accommodating unit 18 accommodates an X-ray source 16 that irradiates X-rays, a radiation source control unit 17 that controls the X-ray source 16, and the like.

  The radiation source control unit 17 is a tube voltage (unit: kV) that determines the energy spectrum of X-rays irradiated by the X-ray source 16, a tube current (unit: mA) that determines the amount of irradiation per unit time, and X-ray irradiation. Is controlled to control the irradiation time (unit: s). The accumulated dose of X-rays to be irradiated is determined by a tube current time product (referred to as mAs value) that is a product of tube current (unit: mA) and irradiation time (unit: s). Irradiation conditions such as tube voltage, tube current, and irradiation time are manually set by an operator such as a radiographer through an operation panel (not shown) of the main unit 11 and set through the console 12. When an irradiation switch (not shown) is operated by the operator, the radiation source control unit 17 controls the X-ray source 16 according to the irradiation conditions.

  The imaging table 19 has an imaging surface 19A on which the subject H is arranged, and includes an image detector 21 that detects an X-ray image. The image detector 21 includes a conversion panel 22 that converts X-rays into electrical signals, and a circuit unit 23. The imaging table 19 is made of a material having X-ray transparency such as carbon, and X-rays are incident on the internal conversion panel 22.

  The X-ray source 16 and the imaging table 19 are disposed to face each other, and a compression plate 26 for compressing the subject H (breast) is disposed therebetween. The compression plate 26 is attached to a support portion 27 whose lower end is fixed to the photographing table 19 so as to be movable up and down in the vertical direction (Z direction).

  An arm control unit 28 that controls the rotation and elevation of the arm unit 14 is provided in the base 13. The arm controller 28 controls a motor (not shown) that rotates and lifts the rotary shaft 15 to control the rotation and lift of the arm unit 14. The potentiometer 29 is for measuring the rotation angle (swing angle) of the arm unit 14 with respect to the reference position, and outputs the measurement value to the arm control unit 28. The arm control unit 28 controls the rotation angle of the arm unit 14 based on the measurement value of the potentiometer 29.

  The mode in which the arm unit 14 is rotated includes a first mode in which the connecting unit 20, the X-ray source housing unit 18, and the imaging table 19 are integrally rotated around the rotation axis 15, and the imaging table 19 is fixed at a reference position. In this state, there are two types of modes of the second mode in which only the connecting portion 20 and the X-ray source accommodating portion 18 are rotated.

  The first mode is a mode selected during normal shooting. In the first mode, X-ray imaging (generally referred to as CC (CranioCauda) imaging) in which X-rays are applied to the breast in the head-to-tail direction to obtain a projection image in the head-to-tail direction, or X Inner / outer oblique direction imaging (generally referred to as MLO (MedioLateral Oblique) imaging) is performed in which a line is irradiated to obtain a projected image in the oblique direction. In the first mode, since the X-ray source 16 and the imaging table 19 rotate together, the arm unit 14 only rotates as a whole, and the X-ray irradiation direction on the imaging surface 19A does not change.

  On the other hand, the second mode is a mode selected when performing tomosynthesis imaging. As shown in FIG. 2, in the second mode, only the connecting portion 20 and the X-ray source accommodating portion 18 rotate around the rotation shaft 15. Since the imaging table 19 is fixed at the reference position, the irradiation direction of the X-ray source 16 with respect to the imaging surface 19A changes. For example, the reference angle of the X-ray source 16 is set to 0 °, and the irradiation direction of the X-ray source 16 is perpendicular to the imaging surface 19A at the reference angle. In tomosynthesis imaging, the projection image of the subject H from a plurality of different irradiation directions is captured by changing the angle of the X-ray source 16 within a range of ± 15 ° with respect to the reference angle, for example. By reconstructing each projection image on the console 12, a tomographic image having a desired depth is obtained.

  In FIG. 3, the image detector 21 includes a conversion panel 22, a circuit unit 23 (see FIG. 1), a gate driver 31, a readout circuit 32, a control circuit unit 33, an A / D (Analog / Digital) converter 34, A memory 35 and a communication unit 36 are provided. The conversion panel 22 has an imaging region 38 in which a plurality of pixels 37 that accumulate signal charges corresponding to the incident dose of X-rays are two-dimensionally arranged. The plurality of pixels 37 are arranged in a matrix of G1 to Gn rows (X direction) × D1 to Dm columns (Y direction) at a predetermined pitch, for example. The two-dimensional array of pixels may be a square array as in the present embodiment or a honeycomb array.

  The conversion panel 22 is, for example, a direct conversion type that converts X-rays directly into electric charges and accumulates signal electric charges (an example of an electric signal). In the conversion panel 22, for example, amorphous selenium is used as the X-ray conversion film. In the conversion panel 22, a thin film transistor (TFT) 41, a capacitor (not shown) that accumulates signal charges, and a pixel electrode 42 that defines a pixel 37 are formed on an insulating substrate such as a glass substrate. An X-ray conversion film is formed on the entire surface of the imaging region 38 on the TFT 41 and the pixel electrode 42, and a common electrode is formed on the X-ray conversion film. When X-rays enter the imaging region 38, the X-rays are converted into charges by the X-ray conversion film, and signal charges are accumulated for each pixel 37 through the pixel electrode 42.

  The signal charge accumulated in the pixel 37 is read out by the TFT 41. The TFT 41 has a gate electrode connected to the scanning line 47, a source electrode connected to the signal line 48, and a drain electrode connected to the capacitor of the pixel 37. The scanning lines 47 and the signal lines 48 are wired in a grid pattern. The scanning lines 47 are the number of rows of the pixels 37 in the imaging region 38 (n rows), and the signal lines 48 are the number of columns of the pixels 37 (m. Each column is wired. The scanning line 47 is connected to the gate driver 31, and the signal line 48 is connected to the readout circuit 32.

  The readout circuit 32 includes an integration amplifier that converts the signal charge read from the conversion panel 22 into a voltage signal, and a multiplexer that sequentially switches the columns of the pixels 37 in the imaging region 38 and sequentially outputs the voltage signals column by column. Become.

  The read circuit 32 outputs the read voltage signal to the A / D converter 34 as an image signal. The A / D converter 34 converts the image signal into digital data and writes it in the memory 35 in association with the coordinates representing the position of the pixel 37 in the imaging region 38. The control circuit unit 33 performs predetermined processing on the digital data in the memory 35 to generate an X-ray image that can be displayed on the display 12A.

  The control circuit unit 33 performs offset correction, gain correction, and defect correction on the X-ray image based on preset offset correction data, gain correction data, and defect correction data (see reference numerals 78A to 78C in FIG. 8). Do. The offset correction data 78B is data for correcting density unevenness that occurs in the X-ray image due to variations in offset of each pixel 37 of the conversion panel 22. By performing offset correction, the offset correction data 78B is offset data. An X-ray image in which the variation is corrected is obtained. The gain correction data 78A is data for correcting density unevenness that occurs in the X-ray image due to variations in sensitivity of the pixels 37 of the conversion panel 22. By performing gain correction, the sensitivity of each pixel 37 is corrected. An X-ray image in which the variation is corrected is obtained.

  The defect correction data 78C is data for correcting abnormal data generated in an X-ray image due to defective pixels of each pixel 37 of the conversion panel 22 and foreign matter on the imaging surface 19, and the like by performing defect correction. An X-ray image in which abnormal data is corrected is obtained. Specifically, the defect correction is corrected by interpolation based on data of normal pixels around the defect. More specifically, the defective pixel is a pixel that is not sensitive to incident X-rays and does not generate charges, or the amount of generated charges does not reach the reference range, or is larger than the reference range. In the X-ray image, the defect appears as a black spot or a white spot. A plurality of defective pixels may occur in adjacent regions, and the size of the defect varies depending on the number of defective pixels.

  The control circuit unit 33 transmits the corrected X-ray image to the console 12 through the wireless or wired communication unit 36. The control circuit unit 33 is provided with an AEC unit 51 that performs automatic exposure control (AEC) of the X-ray image. Since the X-ray transmittance varies depending on individual differences such as the thickness of the subject H, AEC is performed to obtain a more appropriate image quality according to the subject H.

  In this example, AEC performs pre-imaging under low irradiation conditions (X-ray irradiation time and tube current time product) prior to main imaging, and determines irradiation conditions for main imaging based on the results of pre-imaging. Is done in a way that The AEC unit 51 is provided with an AEC region setting unit 51A. In order to perform AEC, the AEC region setting unit 51A sets a region (hereinafter referred to as an AEC region) in which the incident dose is measured in the imaging region 38.

  The thicker the subject H is, the higher the X-ray absorption is, so the dose is lower. The thinner the subject H is, the lower the X-ray absorption is, so the dose is higher. Since the low-dose region with a low dose has a low density in the X-ray image, AEC is executed so that the dose in the low-dose region becomes the target dose.

  For example, the AEC region setting unit 51A selects a low-dose region from a plurality of candidate regions set in advance in the imaging region 38, and sets the selected low-dose region as an AEC region. The control circuit unit 33 reads out digital data obtained by pre-imaging from the memory 35 and applies a predetermined process to generate a pre-image (X-ray image). The pre-image is input to the AEC unit 51. The pre-image reflects the incident dose in the imaging region 38. The AEC area setting unit 51A specifies a preset candidate area in the pre-image, and sets, for example, a low-dose area where the dose is lowest among the specified candidate areas as the AEC area.

  The AEC unit 51 performs calculation based on the set incident dose in the AEC region, and determines the irradiation conditions for the main imaging. The AEC unit 51 grasps the incident dose from the pixel value of the AEC area, and determines the irradiation condition of the main imaging by proportional calculation so that the incident dose of the AEC area becomes the target dose based on the irradiation condition of the pre-imaging. To do. The control circuit unit 33 transmits the irradiation conditions determined by the AEC unit 51 to the console 12. The console 12 sets the irradiation condition received from the control circuit unit 33 in the radiation source control unit 17. Real shooting is performed under the set irradiation conditions.

  As shown in FIG. 4, a marker 56 is provided on the imaging surface 19 </ b> A of the imaging table 19. The marker 56 is disposed in the X-ray irradiation path from the X-ray source 16 to the conversion panel 22. The marker 56 is used to accurately measure the irradiation direction of the X-ray source 16 in tomosynthesis imaging. The marker 56 is formed of a material having high X-ray absorption characteristics such as gold. When X-rays are irradiated toward the imaging surface 19A, the X-rays are absorbed by the marker 56, so that the marker 56 is also reflected in the imaging region 38 and the X-ray image captured in the imaging region 38.

  Since the marker 56 is used for measuring the irradiation direction of the X-ray source 16, the marker area MA in the X-ray image is preferably a position that does not overlap the subject H. In the case of the X-ray imaging apparatus 10 that captures the breast as in this example, as shown in FIG. 5, in the Y-axis direction of the imaging surface 19A, the subject H (breast) is supported by the support portion 27 (FIG. The chest wall is located on the opposite side of the nipple, and the nipple is located on the support 27 side. Since the subject H (breast) has a convex mountain shape from the chest wall side toward the nipple, the region where the subject H does not exist in the imaging region 38 is increased on the nipple side. Therefore, as a position that does not overlap with the subject H (breast), the Y axis direction is closer to the support 27 than the center of the imaging surface 19A, and the X axis direction is a position that avoids the nipple, that is, the X axis. It is preferable that the markers 56 are arranged at two locations that are respectively shifted from the center of the direction to the left and right.

  Further, as shown in FIG. 6, since there is a gap between the imaging surface 19 </ b> A on which the marker 56 is provided and the imaging region 38 of the conversion panel 22, imaging is performed when the irradiation direction of the X-ray source 16 changes. In the area 38, the position of the marker area MA where the marker 56 is reflected changes. For example, the positions of the marker areas MA1 and MA2 when the rotation angle is ± 15 ° with respect to the position of the marker area MA0 at the reference position (rotation angle = 0 °) of the X-ray source 16 are shifted to the left and right, respectively. Therefore, the direction of irradiation of the X-ray source 16 can be measured by analyzing the captured X-ray image and detecting the position of the marker area MA.

  The irradiation direction of the X-ray source 16 can also be measured by the output of the potentiometer 29. However, the output value of the potentiometer 29 has low accuracy and varies due to disturbances and the like. Therefore, the measurement using the marker 56 makes it possible to accurately measure the irradiation direction of the X-ray source 16.

  The shape of the marker 56 is, for example, a cross shape. The cross shape is a shape that takes into account the ease of detection by image analysis. The marker area MA is detected by image analysis. The elongated line shape is easy to detect by image analysis. Furthermore, in order to specify the center position, it is preferable that the line shape is a cross shape.

  As shown in FIG. 7, the console 12 is configured by installing a control program such as an operating system and application programs such as a console program and an image processing program based on a computer such as a personal computer, a server computer, and a workstation. .

  The console 12 includes a CPU (Central Processing Unit) 61, a memory 62, a storage device 63, and a communication I / F 64 in addition to the display 12A and the input device 12B. These are connected via a data bus 66.

  The storage device 63 is, for example, an HDD (Hard Disk Drive), and stores a control program and application program (hereinafter referred to as AP) 68. The storage device 63 stores data used for image processing such as correction data, reference data used for shooting control, and the like.

  The memory 62 is a work memory for the CPU 61 to execute processing, and is configured by a RAM (Random Access Memory). The CPU 61 centrally controls each part of the computer by loading a control program stored in the storage device 63 into the memory 62 and executing processing according to the program. A communication I / F (Inter / face) 64 is a communication interface for communicating with the main unit 11.

  An application for causing the console 12 to function as an operating device of the main unit 11, a display device that displays an X-ray image captured by the main unit 11, and an image processing device that performs image processing on the X-ray image as the AP 68. The program is installed.

  As shown in FIG. 8, when the AP 68 is activated in the console 12, the CPU 61 cooperates with the memory 62 and the like as a GUI (Graphical User Interface) control unit 71, a photographing control unit 72, and an image processing unit 73. Function. The GUI control unit 71 displays an operation screen on the display 12A and receives an operation instruction input from the input device 12B through the operation screen. The GUI control unit 71 inputs the input operation instruction to the imaging control unit 72 and the image processing unit 73, receives the processing results executed by the imaging control unit 72 and the image processing unit 73, and displays them on the display 12A. Control.

  The imaging control unit 72 comprehensively controls the arm control unit 28, the radiation source control unit 17, and the image detector 21 of the main unit 11 based on an operation instruction from the GUI control unit 71. The imaging control unit 72 acquires an X-ray image generated by the main unit 11 in normal imaging or tomosynthesis imaging. The acquired X-ray image is stored in the storage device 63. When tomosynthesis imaging is performed, a plurality of X-ray images with different irradiation directions obtained by one tomosynthesis imaging are stored as one image set 76.

  The image processing unit 73 performs various image processes on the X-ray image. The image processing unit 73 includes a correction data creation unit 73A and a tomographic image generation unit 73B.

  Correction data 78 for performing image correction is stored in the storage device 63. The gain correction data 78A for performing gain correction, the offset correction data 78B for performing offset correction, and the defect correction data 78C for performing defect correction are transmitted to the control circuit unit 33 by the imaging control unit 72 and used. Is done.

  The tomographic image generation unit 73B performs image reconstruction processing based on the image set 76 obtained by tomosynthesis imaging, and generates a tomographic image set 79 including a plurality of tomographic images.

  The correction data 78 is created by executing calibration of the conversion panel 22. The correction data creation unit 73A creates correction data 78 based on the calibration image 77A and the dark image 77B.

  There are roughly two types of calibration: calibration with X-ray irradiation and calibration without X-ray irradiation. Calibration involving X-ray irradiation includes gain calibration for obtaining gain correction data 78A and defect calibration for obtaining defect correction data 78C. Calibration that does not involve X-ray irradiation includes offset calibration for obtaining offset correction data 78B.

  Defect calibration is performed during regular maintenance in addition to product shipment and installation. This is because the number and number of defective pixels change with time. Offset calibration and gain calibration are performed each time the X-ray image capturing apparatus 10 is activated, for example. This is because the dark current characteristic and the sensitivity characteristic of the conversion panel 22 change depending on environmental conditions such as temperature as well as changes depending on the on / off of the power source.

  The dark image 77B is an image acquired at the time of offset calibration. The dark image 77B is generated by the control circuit unit 33 based on an electrical signal output from the conversion panel 22 in a state where X-rays are not irradiated. The imaging control unit 72 acquires the generated dark image 77B by controlling the image detector 21. The dark current characteristic of each pixel 37 is reflected in the dark image 77B. During one calibration, a plurality of dark images 77B are acquired. The correction data creation unit 73A takes an average value of a plurality of dark images 77B and creates offset correction data 78B.

  On the other hand, the calibration image 77A is an image acquired at the time of gain calibration and defect correction calibration accompanied by X-ray irradiation. The calibration image 77A is generated by the control circuit unit 33 based on the electrical signal output from the conversion panel 22 when the imaging region 38 is irradiated with X-rays in a state where the subject H is not present in the irradiation path. The imaging control unit 72 acquires the calibration image 77A by controlling the X-ray source 16 and the image detector 21. The imaging control unit 72 corresponds to a calibration image acquisition unit. Since the subject H does not exist, the entire surface of the imaging region 38 of the conversion panel 22 is uniformly irradiated with X-rays. Therefore, the sensitivity characteristics of each pixel 37 and information on defective pixels are reflected in the calibration image 77A. The

  Furthermore, since the calibration image 77A is an image obtained by irradiating X-rays, as shown in FIG. 9, the calibration image 77A has a defect 81 due to a defective pixel, in addition to the imaging table. A marker area MA in which 19 markers 56 appear is also generated. Here, the reference numerals P1 to P8 in parentheses indicate position information of the defect 81 and the marker area MA in the calibration image 77A. Since the marker 56 absorbs X-rays, in the calibration image 77, like the defect 81, the marker area MA is not incident with X-rays or appears as very few black spots. Therefore, as shown in FIG. 10 showing the distribution state of the pixel value of each pixel of the calibration image 77, the pixel value of the marker area MA and the pixel value of the defect 81 may be substantially equal to each other. The marker area MA and the defect 81 cannot be distinguished based on the value.

  As described above, the calibration image 77A is affected by the marker 56, for example, the marker area MA and the defect 81 are mixed. When the gain correction data 78A and the defect correction data 78C are created from the calibration image 77A, the influence of the marker 56 is reflected in the gain correction data 78A and the defect correction data 78C, and the appropriate gain correction data 78A and the defect correction data. 78C is not obtained.

  Therefore, the correction data creation unit 73A creates gain correction data 78A and defect correction data 78C from which the influence of the marker 56 reflected in the calibration image 77A is removed. Specifically, the correction data creation unit 73A removes the marker area MA from the calibration image 77A by image analysis. Hereinafter, defect calibration and gain calibration will be described with reference to the flowcharts of FIGS. 11 and 12.

  As shown in FIG. 11, when executing defect calibration, a calibration image 77A is acquired by X-ray irradiation (step (S) 100). In step 100, the operator confirms that there is no subject H on the irradiation path, and instructs the execution of defect calibration through the console 12. When execution of calibration is instructed, the imaging control unit 72 sets the arm unit 14 through the arm control unit 28 at, for example, a reference position where the rotation angle of the X-ray source 16 is 0 °.

  When the irradiation switch is operated by the operator after the arm unit 14 is set, the imaging control unit 72 irradiates the X-ray from the X-ray source 16 under a predetermined irradiation condition. X-rays pass through the imaging surface 19 </ b> A of the imaging table 19 and enter the imaging region 38 of the image detector 21. Since the marker 56 is provided on the imaging surface 19 </ b> A, the marker 56 appears in the imaging region 38. Also, defective pixels in the imaging region 38 are not sensitive to incident X-rays.

  At the timing when the X-ray irradiation is completed, the image detector 21 starts a reading operation. An electrical signal is read from the conversion panel 22 by the reading circuit 32, and a calibration image 77 </ b> A is generated by the control circuit unit 33. The control circuit unit 33 transmits the generated calibration image 77A to the console 12. In the console 12, the imaging control unit 72 acquires the calibration image 77 </ b> A and stores it in the storage device 63. The acquired calibration image 77A includes a marker area MA and a defect 81.

  The correction data creation unit 73A detects the marker area MA from the calibration image 77A by image analysis (S110). The correction data creation unit 73A stores shape information of the marker 56 in advance, and the correction data creation unit 73A detects the marker area MA from the calibration image 77A by a pattern matching technique. Since the marker 56 has a cross shape and high detection accuracy by image analysis, the marker area MA can be detected accurately. The correction data creation unit 73A specifies the position of the detected marker area MA and sets a defect search area 82 (area indicated by hatching in FIG. 11) excluding the marker area MA from the entire calibration image 77A (S120). ).

  The correction data creation unit 73A detects the defect 81 from the defect search area 82, and creates defect position information 83 representing the positions of a plurality of defective pixels in the imaging area 38 (S130). When detecting the defect 81, the correction data creating unit 73A specifies the coordinates of the calibration image 77A of the detected defect 81, and records the specified coordinates. In addition, the size of the area of the defect 81 is measured by, for example, counting the number of pixels, and the measured number is recorded as the size of the defect 81.

  The correction data creation unit 73A records the position and size information for each detected defect 81, and, for example, the positions and sizes of all the detected defects 81, such as the defects 81 P1 to P6 shown in FIG. Defect position information 83 in which information is recorded is created. Since the correction data creation unit 73A detects the defect 81 from the defect search area 82 excluding the marker area MA, the correction data creation unit 73A erroneously detects the marker area MA located at P7 and P8 shown in FIG. There is no. For this reason, the defect position information 83 includes only information on the defect 81 that does not include the marker area MA.

  In the defect calibration, in addition to the creation of the defect correction data 78C, it is determined whether or not the conversion panel 22 can be used. The correction data creation unit 73A determines whether or not the conversion panel 22 can be used based on the created defect position information 83 (S140). There is a limit to defect correction. If the number of defects 81 is too large or the size of one defect 81 is too large, it is not possible to secure an appropriate image quality, so whether or not the conversion panel 22 can be used is determined according to a certain standard. . Specifically, the correction data creation unit 73A determines whether the number and size of the defects 81 are within the allowable range based on the defect position information 83 (S150).

  When the allowable range is exceeded (N in S150), the correction data creation unit 73A determines that the conversion panel 22 is unusable. If it is determined that the correction data creation unit 73A cannot be used, the correction data creation unit 73A issues a warning (S170) through the display 12A. In the warning, for example, the defect position information 83 is presented in addition to a message that the conversion panel 22 cannot be used because the number and size of the defects 81 exceed the allowable range. On the other hand, when the number and size of the defects 81 are within the allowable range (Y in S150), the correction data creation unit 73A determines that the conversion panel 22 is usable. In this case, the correction data creation unit 73A stores the defect position information 83 as defect correction data 78C (S160). Thus, the defect calibration is completed.

  As shown in FIG. 12, when gain calibration is executed, a calibration image 77A is acquired by X-ray irradiation (S200). The calibration image 77A is acquired in the same procedure as in the case of defect calibration. Therefore, the marker area MA and the defect 81 exist in the calibration image 77A. Note that when the gain calibration is executed at the same timing as the defect calibration, the calibration image 77A acquired by the defect calibration may be used.

  Next, offset correction and defect correction are performed on the calibration image 77A (S210). In the offset correction, the pixel value of the dark image 77B acquired in advance is subtracted from the pixel value of the calibration image 77A. In the defect correction, an interpolation process is performed on the defect 81 in the calibration image 77A based on the defect correction data 78C obtained by the defect calibration. Thereby, the defect 81 is removed from the calibration image 77A.

  The correction data creation unit 73A detects the marker area MA from the calibration image 77A by image analysis, similarly to the defect calibration (S230). Then, the correction data creation unit 73A removes the marker area MA from the calibration image 77A by interpolation processing using surrounding normal pixels for the detected marker area MA, as in the defect 81 correction processing ( S240). The correction data creation unit 73A stores the calibration image 77A that has been subjected to processing such as offset correction and removal of the marker area MA as gain correction data 78A. The gain correction data 78A is transmitted to the image detector 21.

  According to the X-ray imaging apparatus 10 of this example, even if calibration with X-ray irradiation is performed when there is a marker 56 arranged in the irradiation path from the X-ray source 16 to the conversion panel 22, the calibration is performed. Correction data (gain correction data 78A and defect correction data 78C) from which the influence of the marker 56 shown in the image 77A is removed can be created. Therefore, it is possible to acquire accurate correction data from which the influence of the marker 56 is eliminated.

  In addition, since the marker area MA in the calibration image 77A is detected by image analysis, accurate position detection is possible. The marker region MA can be detected without using image analysis. For example, since the position where the marker 56 is provided on the imaging surface 19A is determined, the rotation angle of the X-ray source 16 with respect to the imaging surface 19A and the SID that is the distance between the X-ray source 16 and the imaging region 38 of the conversion panel 22 are set. If it is known, the position of the marker area MA in the calibration image 77A can be estimated.

  However, since the rotation angle of the X-ray source 16 is measured by the potentiometer 29, if the accuracy of the potentiometer 29 is low, the accuracy of detecting the position of the marker area MA also decreases. Therefore, as in the present example, accurate position detection can be performed by detecting the marker area MA by image analysis. Accurate position detection of the marker area MA is useful for creating accurate correction data.

  The imaging procedure of the X-ray imaging apparatus 10 will be described with reference to the flowchart shown in FIG. The operator positions the subject H on the photographing stand 19 and fixes the subject H to the photographing stand 19 with the compression plate 26 (S1010). Next, the X-ray source 16 is set to the initial position (S1020).

  For normal imaging, the first mode in which the X-ray source 16 and imaging table 19 rotate integrally is selected, and the arm unit 14 is set to the initial position according to the direction of head-to-tail imaging or inward / outward imaging. set. In the case of tomosynthesis imaging, the second mode in which the X-ray source 16 rotates with respect to the imaging table 19 whose position is fixed is selected, for example, a position where the rotation angle is plus 15 ° or minus 15 °. The position that is the first shooting position in continuous shooting is set as the initial position.

  With the X-ray source 16 set to the initial position, the irradiation condition of the X-ray source 16 is determined (S1030). The operator operates the console 12 to set the irradiation conditions, or performs pre-imaging and executes AEC. After the irradiation conditions are determined by AEC, X-rays are irradiated under the determined irradiation conditions, and imaging is performed (S1040). After the X-ray irradiation is completed, an electrical signal is read from the conversion panel 22.

  The control circuit unit 33 performs image correction (offset correction, gain correction, and defect correction) on the X-ray image based on the offset correction data 78B, the gain correction data 78A, and the defect correction data 78C (S1050). Since the influence of the marker 56 is removed from the gain correction data 78A and the defect correction data 78C, accurate gain correction and defect correction are possible.

  The image-corrected X-ray image is transmitted from the image detector 21 to the console 12. In the case of normal imaging, the main unit 11 ends imaging when a single X-ray image (projected image) is captured. In the case of tomosynthesis imaging, an X-ray image for each irradiation direction is acquired while changing the irradiation direction of the X-ray source 16. In the case of tomosynthesis imaging, a plurality of X-ray images are stored in the console 12 as an image set 76.

  In the case of normal imaging on the console 12 (N in S1060), the image processing unit 73 removes the marker area MA from the X-ray image after the correction by the control circuit unit 33 is completed (S1080). In normal imaging, since the tomographic image is not generated (S1090), the X-ray image from which the marker area MA has been removed is displayed on the display 12A as a diagnostic X-ray image and transmitted to an image server or the like. To be used for diagnosis.

  In the case of tomosynthesis imaging (Y in S1060), the image set 76 is input to the tomographic image generation unit 73B. The tomographic image generation unit 73B detects the marker area MA by image analysis for each X-ray image included in the image set 76, and based on the position of the detected marker area MA, the X-ray source 16 of each X-ray image. The irradiation direction is calculated (S1070). The irradiation direction is calculated by the principle of triangulation based on the SID up to the X-ray source 16 and the imaging area 38 and the position of the marker area MA.

  The tomographic image generation unit 73B removes the marker area MA from the X-ray image (S1080). Thereafter, a tomographic image is generated based on the image set 76 (S1090). The tomographic image generation unit 73B performs an image reconstruction process based on the irradiation direction of each X-ray image to generate a tomographic image set 79. Since the irradiation direction is calculated by the marker area MA, an accurate image reconstruction process is possible. The generated tomographic image set 79 is transmitted to the image server and used for diagnosis.

  In this example, the marker area MA is removed from the images (X-ray image and tomographic image) used for diagnosis, but the marker area MA may not be removed. As described above, since the marker 56 is projected on the end of the X-ray image so as not to overlap with the subject H as much as possible, there is a case where the diagnosis is not affected even if the marker area MA is not removed. is there.

“Second Embodiment”
In the first embodiment, as shown in FIG. 11, the defect search area 82 excluding the marker area MA is set in the calibration image 77A and the defect position information 83 is created, but the second position shown in FIG. As in the embodiment, after creating the defect position information 83 in which the marker area MA is included as the defect 81, the information on the defect 81 corresponding to the marker area MA may be excluded from the defect position information 83.

  In the second embodiment, the calibration image 77A is acquired (S300), as in the first embodiment. Then, the correction data creation unit 73A detects the defect 81 from the entire calibration image 77A including the marker area MA in addition to the defect 81, and creates defect position information 83 (S310). In this case, the marker area MA existing in P7 and P8 (see FIG. 9) is also detected as the defect 81 and recorded as the defect 81 in the defect position information 83.

  The correction data creation unit 73A detects a cross-shaped marker area MA from the calibration image 77A by image analysis such as pattern matching (S320), and specifies the position of the detected marker area MA. Then, the position information of the marker area MA in P7 and P8 recorded as the defect 81 is excluded from the defect position information 83.

  In this example, in order to exclude the position information of the marker area MA from the defect position information 83, the position of the marker area MA is specified by image analysis from the calibration image 77, but the image analysis may not be performed. Good. For example, if a feature that can identify the marker area MA and the defect 81 can be grasped from the position and size information recorded in the defect position information 83, the position information of the marker area MA is specified from the feature, and the specified position information is obtained. The defect position information 83 may be excluded.

  The correction data creation unit 73A determines whether or not the conversion panel 22 can be used based on the defect position information 83 from which the marker area MA is excluded (S340, S350). If the number and size of the defects are within the allowable range (Y in S350), the defect position information 83 is stored as defect correction data. If it is outside the allowable range (N in S350), a warning (S370) is performed. Each step of S340 to S370 in the second embodiment is the same as S140 to S170 in the first embodiment.

  In each of the above embodiments, the gain correction data 78A and the defect correction data 78C are respectively created based on one calibration image 77A obtained by irradiating X-rays in one irradiation direction. When images from a plurality of irradiation directions are used as in tomosynthesis imaging, gain correction data 78A and defect correction are based on a plurality of calibration images 77A obtained by irradiating X-rays in a plurality of irradiation directions. Data 78C may be created.

  This is because, as shown in FIG. 6, when the irradiation direction changes, the position of the marker area MA in the imaging area 38 changes, so that the position of the marker area MA also changes in the calibration image 77A. As a result, there may be a defect 81 that overlaps the marker area MA in a certain irradiation direction but does not overlap the marker area MA in another irradiation direction. In this case, if the defect correction data 78C is created only from the calibration image 77A obtained in one irradiation direction, there is a possibility that the defect 81 may not be detected. In addition, regarding the gain correction data 78A, accurate information cannot be obtained for pixels that are shadows of the marker area MA.

  Therefore, if a plurality of calibration images 77A are acquired by irradiating X-rays from a plurality of irradiation directions, the shadow area of the marker area MA can be reduced. It becomes possible. Thereby, the accuracy of the gain correction data 78A and the defect correction data 78C is also improved.

  In each of the above embodiments, offset correction, gain correction, and defect correction have been described as examples of image correction, but other corrections may be performed. As the defect correction, correction of point defects has been mainly described as an example. However, for example, when the signal line 48 is disconnected, a linear defect occurs. Such linear defects may be corrected.

  In each of the above embodiments, an example in which the control circuit unit 33 of the image detection unit 21 performs image generation (including image correction) such as an X-ray image and a calibration image 77A based on the electric signal output from the conversion panel 22 is performed. As described above, in the main unit 11, the image generation may be performed by a processing unit different from the control circuit unit 33 or the image detector 21.

  Further, all or part of image generation and AEC may be performed not by the control circuit unit 33 of the main unit 11 but by the image processing unit 73 of the console 12. When the image processing unit 73 performs all image generation and AEC, the main body unit 11 transmits digital data to the console 12 without performing image generation. In the console 12, the image processing unit 73 performs image generation based on the digital data. When performing AEC, a pre-image is generated and AEC is executed. Further, only the AEC may be performed by the image processing unit 73 of the console 12. In this case, a pre-image is generated by the control circuit unit 33 and the generated pre-image is transmitted to the console 12. The image processing unit 73 executes AEC based on the received pre-image.

  In the present embodiment, the conversion panel 22 that converts the irradiated radiation into an electrical signal has been described as an example of the electrical reading method using the TFT 41. However, as described in, for example, Japanese Patent Application Laid-Open No. 2010-103181. Alternatively, an optical reading type that reads signal charges by irradiating the conversion panel with light may be used. Further, as the conversion panel 22, instead of the direct conversion type, an indirect conversion type in which X-rays are once converted into visible light by a scintillator (phosphor), and the signal charge is accumulated by photoelectric conversion of the visible light may be used. Good. Further, instead of the conversion panel 22 that reads out an electrical signal using the TFT 41, a CCD (Charge Coupled Device) image sensor that reads out signal charges without using the TFT 41, or a CMOS (Complementary Metal oxide) that reads out signal voltage without using the TFT 41. Semiconductor) image sensor or the like may be used.

  In the above embodiment, the X-ray imaging apparatus 10 having a tomosynthesis imaging function has been described as an example. However, instead of or in addition to the tomosynthesis imaging function, an X-ray imaging apparatus having a stereo imaging function and a biopsy (biopsy) function. In addition, the present invention may be applied.

  The present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention. For example, the above-described various embodiments and various modifications can be appropriately combined. In addition, the present invention is not limited to X-rays but can be applied to a radiographic imaging apparatus that uses other radiation such as γ-rays.

DESCRIPTION OF SYMBOLS 10 X-ray imaging device 11 Main body unit 12 Console 16 X-ray source 19 Imaging stand 19A Imaging surface 21 Image detector 22 Conversion panel 33 Control circuit part 56 Marker 72 Imaging control part (calibration image acquisition part)
73A correction data creation unit 77A calibration image 78 correction data 78A gain correction data 78B offset correction data 78C defect correction data 81 defect MA marker area

Claims (11)

A conversion panel that has a two-dimensional imaging region and converts radiation irradiated from a radiation source and transmitted through a subject into an electrical signal;
A photographic stand containing the conversion panel and on which the subject is disposed;
A marker provided on the imaging table and disposed in an irradiation path from the radiation source to the conversion panel;
A calibration image acquisition unit that acquires a calibration image based on the electrical signal output by the conversion panel when the imaging region is irradiated with the radiation in a state where the subject does not exist in the irradiation path;
A radiographic imaging apparatus, comprising: a correction data creating unit that creates correction data from which the influence of the marker reflected in the calibration image is removed.   It has a tomosynthesis imaging function that changes the irradiation direction of the radiation source, captures a radiation image of the subject in each irradiation direction, and generates a tomographic image of the subject based on the captured radiation image. The radiographic imaging apparatus according to claim 1.   The radiographic image capturing apparatus according to claim 1, wherein the correction data creating unit creates defect position information representing a position of a defective pixel in the imaging region based on the calibration image.   The correction data creating unit detects a marker area in which the marker is reflected from the calibration image, and indicates the position of the defect image from a defect search area excluding the marker area in the calibration image. The radiographic image capturing apparatus according to claim 3, wherein position information is created.   The correction data creation unit creates the defect position information representing the position of the defective pixel from the calibration image, and excludes the position information of the marker area in which the marker appears from the created defect position information. The radiographic imaging device according to claim 3, wherein   The radiographic image capturing apparatus according to claim 4, wherein the correction data generation unit detects the marker region from the calibration image by image analysis.   The radiographic image capturing apparatus according to claim 3, wherein the correction data creation unit determines whether or not the conversion panel can be used based on the defect position information.   2. The correction data creation unit detects the marker region from the calibration image and creates gain correction data based on the calibration image from which the detected marker region is removed. The radiographic imaging apparatus of any one of -7.   The radiographic image capturing apparatus according to claim 8, wherein the correction data generation unit detects the marker region from the calibration image by image analysis.   The radiographic image capturing apparatus according to claim 1, wherein the subject is a breast. A conversion panel that has a two-dimensional imaging area, converts radiation irradiated from a radiation source and transmitted through the subject into an electrical signal, an imaging table that includes the conversion panel and on which the subject is disposed, and the imaging table In a calibration method of a radiographic imaging apparatus provided with a marker disposed in an irradiation path from the radiation source to the conversion panel,
A calibration image acquisition step of acquiring a calibration image based on the electrical signal output by the conversion panel when the imaging region is irradiated with the radiation in a state where the subject does not exist in the irradiation path;
A calibration method for a radiographic imaging apparatus, comprising: a correction data creating step for creating correction data from which the influence of the marker reflected in the calibration image is removed.

Images