JP5928043B2 - Radiography equipment - Google Patents

Description

  The present invention relates to a radiation imaging apparatus that obtains a radiation image, and more particularly to a technique for removing scattered radiation using a radiation grid.

  A conventional radiation imaging apparatus includes a radiation grid for removing scattered radiation in order to prevent scattered radiation from a subject from entering a flat panel radiation detector (radiation detection means). The radiation grid is configured by alternately arranging grid foils that absorb scattered radiation and intermediate layers that transmit radiation. The grid foil is formed of a material that absorbs radiation represented by X-rays such as lead, and the intermediate layer is formed of an intermediate material that transmits radiation represented by X-rays such as aluminum and organic materials. Has been. However, when the radiation passes through the intermediate layer, radiation other than scattered radiation (direct radiation) is also absorbed by the intermediate substance. Thus, an air grid that reliably transmits radiation other than scattered radiation (direct radiation) by using an intermediate layer as a gap has recently been used as a radiation grid.

  By the way, in the part where the radiation is directly blocked by the grid foil, the foil shadow by the grid foil is reflected in the radiation image. Therefore, the present applicant has proposed a false image removal processing method for removing a false image caused by a foil shadow (see, for example, Patent Documents 1 and 2).

International Publication No. WO2010-064287 JP 2011-167334 A

  However, in the air grid, the flat layer radiation detector (FPD) when the air grid is attached to and detached from the flat panel detector (FPD) because the above-described intermediate layer is a gap.・ The false image caused by the displacement between the air grids is large. As shown in FIG. 15A, the displacement includes a lateral displacement of the air grid with respect to the FPD, and as shown in FIG. 15B, there is a rotational displacement of the air grid with respect to the FPD.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiation imaging apparatus capable of removing a foil shadow in consideration of a grid shift.

In order to achieve such an object, the present invention has the following configuration.
That is, the radiation imaging apparatus of the present invention (the former invention) is a radiation imaging apparatus that obtains a radiation image, a radiation source that irradiates radiation, a radiation detection means that detects the irradiated radiation, and the radiation detection means. The grid marker is provided with a radiation grid arranged on the detection side of the grid and configured to arrange grid foils that absorb scattered radiation, and has a thickness in the direction in which the grid foils are juxtaposed and has a groove. The radiation imaging apparatus further includes an initial setting before remounting the radiation grid, where DXg is an observation amount due to a grid shift and DXf is an observation amount due to the shift of the radiation source. Of the radiation detection signal obtained in step 1 and radiation detection obtained when the radiation grid is remounted without the subject. Based on the profile of No., the observables DXg as the shift amount of the profiles relating to the difference between the values of two radiation detection signals at the remounting before and during the re-mounting respectively detected at points spaced apart by the width of the groove And a location separated by the width of the groove based on the profile related to the radiation detection signal obtained when the radiation grid is remounted in the absence of the subject and the profile related to the radiation detection signal obtained in actual imaging An observation amount calculation means for obtaining the observation amount DXf as a shift amount of a profile related to a difference between two radiation detection signal values at the time of the re-mounting and the actual imaging detected in the detection, and detection in a state where the subject exists A captured image collecting means for collecting an actual captured image based on the received radiation detection signal, A radiation image by removing foil shadows by the grid foil based on a survey calculation means and the pickup image acquisition unit is characterized in that the obtained finally.

[Operation / Effect] According to the radiation imaging apparatus of the present invention (the former invention), in addition to the radiation source, the radiation detection means, and the radiation grid, the grid foil has a thickness in the direction in which the grid foils are juxtaposed, A grid marker having a groove is provided on the radiation grid. By providing such a grid marker, it becomes easy to detect the shift characteristic of the entire foil shadow. In addition, since the grid marker is thicker than the grid foil in the direction in which the grid foils are arranged side by side, even if the foil shadow is blurred and reflected in the radiation image, the shadow by the grid marker is clearly detected can do. In the case where such a grid marker is provided, the radiation detection signal obtained by the initial setting before reattaching the radiation grid when the observation amount due to the grid shift is DXg and the observation amount due to the shift of the radiation source is DXf And the profile of the radiation detection signal obtained when the radiation grid is remounted in the absence of the subject, and before remounting detected at locations separated by the groove width (of the grid marker) and The observation amount DXg is obtained as a shift amount of the profile regarding the difference between the values of the two radiation detection signals at the time of remounting , and the profile regarding the radiation detection signal obtained at the time of remounting the radiation grid in the absence of the subject and the actual Based on the profile of the radiation detection signal obtained by Observation amount calculation for obtaining an observation amount DXf as a shift amount of a profile related to a difference between two radiation detection signal values at the time of remounting detected at a position separated by the width of the groove (of the head marker) and actual imaging Means. And a radiographic image collecting means for collecting an actual radiographic image based on a radiation detection signal detected in a state of the subject, and a grid foil based on the observation amount calculating means and the radiographic image collecting means described above. The foil shadow is removed to finally obtain a radiographic image. By obtaining the difference between the values of two radiation detection signals detected at locations separated by the width of the grid marker groove, even if information on the subject is included in the radiation detection signal, the difference is eliminated. Thus, the difference profile is information that reflects the overall deviation characteristics of the foil shadow and the relative deviation characteristics of the radiation source with respect to the radiation detection means. Therefore, as the shift amount of the profile, the observation amount DXg due to grid shift and the observation amount DXf due to shift of the radiation source are respectively obtained. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the observation amounts DXg and DXf.

A radiation imaging apparatus (the latter invention) different from the former invention is a radiation imaging apparatus for obtaining a radiation image, a radiation source for irradiating radiation, a radiation detecting means for detecting the irradiated radiation, and A radiation grid provided on the detection side of the radiation detection means and configured by arranging grid foils that absorb scattered radiation, and the radiation imaging apparatus further includes: (a) radiation detection detected in the absence of a subject Reference calibration data based on the signal, (b) Shift by the amount of grid shift from the actual imaging focus based on grid shift information which is information regarding grid shift with respect to the radiation detection means with reference to the time of collection of the reference calibration data Corresponding calibration image calculation means for obtaining a corresponding calibration image corresponding to the ray as a ray from the calculated focal point, and radiation detected in a state of the subject A captured image collecting unit that collects an actual captured image based on the detection signal, and removing a foil shadow by the grid foil based on the corresponding calibration image calculating unit and the captured image collecting unit to obtain a final radiation image It is characteristically obtained.

[Operation / Effect] According to the radiation imaging apparatus of the present invention (the latter invention), in addition to the radiation source, the radiation detection means and the radiation grid, (a) based on a radiation detection signal detected in the absence of the subject. Reference calibration data, (b) Calculation focus shifted from the actual imaging focus by the amount of grid shift based on grid shift information that is information regarding grid shift with respect to the radiation detection means with reference to the time of collection of the reference calibration data Corresponding calibration image calculating means for obtaining a corresponding calibration image corresponding to the ray as a ray from And a radiographic image collecting means for collecting an actual radiographic image based on a radiation detection signal detected in a state of the subject, and a grid based on the corresponding calibration image calculating means and the radiographic image collecting means described above. The foil shadow by the foil is removed to finally obtain a radiation image. Using the reference calibration data collected in the absence of grid shift, a corresponding calibration image corresponding to the ray is obtained as a ray from the calculation focus shifted from the actual imaging focus by the grid shift amount. The calibration image also corresponds to the shooting focus. Therefore, by matching the corresponding calibration image corresponding to the actual imaging focus with the actual imaging image, a radiographic image considering the grid shift is finally obtained. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the grid shift information.

It is also possible to combine both the former invention and the latter invention.
That is, in the former invention, (a) reference calibration data based on a radiation detection signal detected in the absence of a subject, (b) the grid for the radiation detection means based on the collection time of the reference calibration data Based on grid shift information, which is information related to shift, the image processing apparatus includes a corresponding calibration image calculation unit that obtains a corresponding calibration image corresponding to the ray as a ray from the calculation focus shifted from the actual imaging focus by the grid shift amount, Based on the calculation means, the corresponding calibration image calculation means, and the photographed image collection means, the shadow of the grid foil is removed to finally obtain a radiation image.

  According to the invention combining both the former invention and the latter invention, in addition to the observation amounts DXg, DXf in the former invention, the grid shadow is further considered based on the grid deviation information in the latter invention. Can be removed.

  In the latter invention, when the observation amount due to the grid shift is DXg, based on the observation amount DXg, the photographed image is a photographed image in which foil shadows are aligned by sliding the photographed image in the direction in which the grid foils are arranged in parallel. It is preferable to provide a foil shadow alignment image generating means for generating a certain foil shadow alignment image. When radiation grid misalignment (for example, lateral misalignment, rotational misalignment) occurs, a method of rotating a captured image to eliminate the rotational misalignment is also conceivable. However, in this case, the amount of calculation becomes enormous. Therefore, the foil shadow alignment image can be easily generated by sliding the photographed image in the direction in which the grid foils are arranged side by side based on the observation amount DXg, and the amount of calculation is reduced even when the photographed image is rotated. Can be made. In addition, although the shift amount (shift amount) with respect to the extending direction of the grid foil remains, the shift amount is small and can be ignored.

  In the case of including such a foil shadow alignment image generation means, a foil shadow enhancement image generation means for generating a foil shadow enhancement image obtained by enhancing the foil shadow from the foil shadow alignment image and removing the subject information, and the foil Fake image removal processing foil shadow image for generating a false image removal processing foil shadow image for removing a false image caused by the foil shadow based on the foil shadow enhancement image generated by the shadow enhancement image generation means and the corresponding calibration image More preferably, the generating means is provided. Since the foil shadow emphasis image generated from the foil shadow alignment image and the corresponding calibration image correspond to each other in position, it becomes easy to generate a false image removal processing foil shadow image based on both images.

  An example of the above-described foil shadow enhanced image generation means is a low-pass filter (LPF) that passes a low-pass region in the extending direction of the grid foil. The information of the subject is in the high range with respect to the extending direction of the grid foil, while the grid foil is in the low range with little change in the extending direction. Therefore, it is possible to easily generate a foil shadow enhanced image from which information on the subject is removed by a low-pass filter (LPF). Of course, the foil shadow enhanced image generating means is not limited to the low-pass filter (LPF). For example, the foil shadow enhanced image generating means is composed of a high-pass filter (HPF) and a subtractor, and the foil shadow is removed by the high-pass filter (HPF) to obtain subject information. A foil obtained by generating an enhanced image and removing the subject information by subtracting the subject information from the original image before passing through a high-pass filter (HPF) with a subtractor. A shadow-enhanced image can be generated.

  The false image removal processing foil image generation means described above obtains integrated values for a plurality of pixels for the foil shadow enhanced image and the corresponding calibration image, and generates a false image removal processing foil image based on each integrated value. . Depending on the width of the foil shadow by the grid foil, it may straddle a plurality of pixels. In that case, the integrated value at the location where the foil shadow straddles a plurality of pixels is used as the foil shadow emphasis image and the corresponding calibration image. The false image removal processing foil image can be precisely generated by obtaining each of the above and generating the false image removal processing foil shadow image based on each integrated value. Note that the foil shadow does not always straddle the plurality of pixels due to the deflection of the individual grid foils. The pixel at the place where the foil shadow is supposed to straddle is recognized from the foil shadow emphasis image and the corresponding calibration image, and the integrated value of the plurality of pixels is uniformly obtained regardless of the state of the foil shadow straddling. Note that the foil shadow enhancement image and the corresponding calibration image are obtained respectively.

  Specifically, based on such a foil image for false image removal processing, it is provided with a false image removal processed image generating means for generating a false image removal processed image from which the foil shadow by the grid foil is removed, and the false image removal processing The false image removal processed image generated by the completed image generating means is finally obtained as a radiation image. Thereby, the foil shadow can be removed in consideration of the grid shift.

According to the radiation imaging apparatus according to the present invention (the former invention), a grid marker having a groove and having a thickness larger than that of the grid foil in the direction in which the grid foils are arranged side by side is provided. By providing such a grid marker, it becomes easy to detect the shift characteristic of the entire foil shadow. In addition, since the grid marker is thicker than the grid foil in the direction in which the grid foils are arranged side by side, even if the foil shadow is blurred and reflected in the radiation image, the shadow by the grid marker is clearly detected can do. In the case where such a grid marker is provided, the radiation detection signal obtained by the initial setting before reattaching the radiation grid when the observation amount due to the grid shift is DXg and the observation amount due to the shift of the radiation source is DXf On the basis of the profile relating to the radiation detection signal obtained when the radiation grid is remounted in the absence of the subject, and before remounting detected at locations separated by the width of the groove (of the grid marker) and The observation amount DXg is obtained as a shift amount of the profile regarding the difference between the values of the two radiation detection signals at the time of remounting, and the profile regarding the radiation detection signal obtained at the time of remounting the radiation grid in the absence of the subject and the actual Based on the profile of the radiation detection signal obtained by Observation amount calculating means for obtaining an observation amount DXf as a shift amount of a profile relating to a difference between two radiation detection signal values at the time of remounting detected at a position separated by the width of the groove) It has. By obtaining the difference between the values of two radiation detection signals detected at locations separated by the width of the grid marker groove, even if information on the subject is included in the radiation detection signal, the difference is eliminated. Thus, the difference profile is information that reflects the overall deviation characteristics of the foil shadow and the relative deviation characteristics of the radiation source with respect to the radiation detection means. Therefore, as the shift amount of the profile, the observation amount DXg due to grid shift and the observation amount DXf due to shift of the radiation source are respectively obtained. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the observation amounts DXg and DXf.
According to the radiation imaging apparatus (the latter invention) according to the present invention, (a) reference calibration data based on a radiation detection signal detected in the absence of a subject, and (b) when the reference calibration data is collected. Correspondence for obtaining a corresponding calibration image corresponding to the ray as a ray from the calculation focus shifted from the actual imaging focus by the amount of the grid deviation based on the grid deviation information which is information on the grid deviation with respect to the radiation detection unit as a reference Calibration image calculation means is provided. Using the reference calibration data collected in the absence of grid shift, a corresponding calibration image corresponding to the ray is obtained as a ray from the calculation focus shifted from the actual imaging focus by the grid shift amount. The calibration image also corresponds to the shooting focus. Therefore, by matching the corresponding calibration image corresponding to the actual imaging focus with the actual imaging image, a radiographic image considering the grid shift is finally obtained. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the grid shift information.

1 is a schematic configuration diagram and a block diagram of an X-ray imaging apparatus according to an embodiment. It is a schematic diagram of the detection surface of a flat panel X-ray detector (FPD). It is the schematic of an X-ray grid. It is each schematic diagram which shows the arrangement | positioning location of the marker for grids. It is an enlarged view of the marker for grids. It is a block diagram of a specific image processing unit according to an embodiment. It is the schematic diagram which illustrated the flow of a series of image processing together with each image. It is a list of marker shadow collection modes by a grid marker in the CVS device. It is the schematic which shows the positional relationship of each shift | offset | difference. It is an example of a profile creation process. It is the schematic which showed the collection of the reference | standard calibration data typically. It is the schematic which shows the positional relationship when calculating | requiring a corresponding | compatible calibration image. It is a graph of each reference | standard calibration data weight function for corresponding | compatible calibration image calculation. It is the schematic which showed typically the production | generation of a foil shadow alignment image. It is the schematic which showed typically the gap | deviation of the air grid with respect to a flat panel type radiation detector (FPD).

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram and a block diagram of an X-ray imaging apparatus according to an embodiment, FIG. 2 is a schematic diagram of a detection surface of a flat panel X-ray detector (FPD), and FIG. FIG. 4 is a schematic diagram of a line grid, FIG. 4 is a schematic diagram showing arrangement positions of grid markers, and FIG. 5 is an enlarged view of the grid markers. In this embodiment, X-rays will be described as an example of radiation, and X-rays having a C-arm for carrying out, for example, a device (CVS: cardiovascular systems) used for cardiovascular diagnosis as a radiographic apparatus. A description will be given by taking a photographing apparatus as an example. The radiation grid will be described by taking as an example an air grid with a grid layer arranged along a ray connecting the focal point of the X-ray tube and an intermediate layer as a gap.

  As shown in FIG. 1, the X-ray imaging apparatus according to this embodiment includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates X-rays, and a flat that detects the irradiated X-rays. A panel type X-ray detector (hereinafter abbreviated as “FPD”) 3 and a grid foil 4a (see FIG. 3 etc.) arranged on the detection side of the FPD 3 and absorbing scattered X-rays. Line grid 4 is provided. The X-ray tube 2 corresponds to the radiation source in the present invention, the flat panel X-ray detector (FPD) 3 corresponds to the radiation detection means in the present invention, and the X-ray grid 4 corresponds to the radiation grid in the present invention. Equivalent to.

  In addition, the X-ray imaging apparatus includes a C-arm 5 that holds the X-ray tube 2 at one end and holds the FPD 3 together with the X-ray grid 4 at the other end. In FIG. 1, the C arm 5 is formed in a curved shape in the body axis direction of the subject M. The C arm 5 rotates around the axis of the rotation center axis orthogonal to the body axis of the subject M along the C arm 5 itself, so that the X-ray tube 2, the FPD 3 and the X-ray held by the C arm 5 are rotated. The grid 4 can also rotate in the same direction. Further, the C-arm 5 rotates about the axis of the rotation center axis orthogonal to the body axis, so that the X-ray tube 2, the FPD 3 and the X-ray grid 4 can also rotate in the same direction.

  Specifically, the C arm 5 is held on a base 6 fixedly arranged on the floor surface via a support column 7 and an arm holding unit 8. The support column 7 can rotate around the axis of the vertical axis with respect to the base 6, and by this rotation, the X-ray tube 2, the FPD 3 and the X-ray grid 4 rotate in the same direction together with the C arm 5 held by the support column 7. Is possible. Further, by holding the arm holding unit 8 with respect to the column 7 so as to be rotatable around the axis of the body axis of the subject M, the C-arm 5 held by the arm holding unit 8 together with the X-ray tube 2, the FPD 3 and The X-ray grid 4 can also rotate in the same direction. Further, by holding the C arm 5 so as to be rotatable about the axis of the rotation center axis with respect to the arm holding portion 8, the X-ray tube 2, the FPD 3 and the X-ray grid 4 are also rotated in the same direction together with the C arm. Can do.

  Further, the FPD 3 may be configured to approach / separate along the X-ray irradiation axis connecting the X-ray tube 2 and the FPD 3 or to approach / separate in the focusing line direction orthogonal to the irradiation axis. Even under the condition that the positional relationship between the X-ray tube 2, the FPD 3 and the X-ray grid 4 is constant, the positional relationship between the X-ray tube 2, the FPD 3 and the X-ray grid 4 is shifted due to the rotation of the C arm 5. It may occur (the amount of lateral focus deviation described later = Xf).

  Furthermore, the X-ray imaging apparatus includes an image processing unit 11 that performs various image processing based on the X-ray detection signal detected by the FPD 3, reference calibration data obtained prior to X-ray imaging, and an image processing unit 11. A memory unit 12 for writing and storing data such as obtained images, an input unit 13 for inputting data and commands, a display unit 14 for displaying images obtained by the image processing unit 11, and overall control thereof The controller 15 is provided. In addition, a high voltage generating unit for generating a high voltage and supplying a tube current and a tube voltage to the X-ray tube 2 is provided. However, since it is not a feature portion or a configuration related to the feature portion of the present invention, Omitted.

  The memory unit 12 writes and stores reference calibration data and data such as each image obtained by the image processing unit 11 via the controller 15, reads them out as needed, and reads out these data via the controller 15. Is sent to the display unit 14 for display. The memory unit 12 includes a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), a hard disk, and the like.

  The input unit 13 sends data and commands input by the operator to the controller 15. The input unit 13 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The display unit 14 includes a monitor.

  The image processing unit 11 and the controller 15 described above are configured by a central processing unit (CPU) or the like. Data such as each image obtained by the image processing unit 11 is written and stored in the memory unit 12 via the controller 15 or sent to the display unit 14 for display. A specific configuration of the image processing unit 11 will be described in detail later.

  As shown in FIG. 2, the FPD 3 has a detection surface in which a plurality of detection elements d sensitive to X-rays are arranged in a two-dimensional matrix. The detection element d detects X-rays by converting the X-rays transmitted through the subject M into X-ray detection signals (electrical signals), temporarily storing them, and reading the stored X-ray detection signals. An X-ray detection signal detected by each detection element d is converted into a pixel value corresponding to the X-ray detection signal, and the pixel value is assigned to each pixel corresponding to the position of the detection element d, thereby obtaining an X-ray. An image is output and an X-ray image is sent to the image processing unit 11.

  As shown in FIG. 3, the X-ray grid 4 is configured by alternately arranging grid foils 4 a that absorb scattered X-rays and intermediate layers 4 b that transmit X-rays. A grid cover 4c covering the grid foil 4a and the intermediate layer 4b sandwiches the grid foil 4a and the intermediate layer 4b from the X-ray incident surface and the opposite surface. In order to clarify the illustration of the grid foil 4a, the grid cover 4c is illustrated by a two-dot chain line, and the other configurations of the X-ray grid 4 (such as a mechanism for supporting the grid foil 4a) are omitted. The grid foil 4a corresponds to the grid foil in the present invention.

  Further, as shown in FIG. 3, the X-ray grid 4 is arranged by arranging the respective grid foils 4a in parallel with the detection surface of the FPD 3. In this embodiment, the intermediate layer 4b is a gap, and the X-ray grid 4 is also an air grid. The grid foil 4a is not particularly limited as long as it is a substance that absorbs radiation represented by X-rays such as lead. In the present embodiment, the grid foil 4a is arranged along a ray connecting the focal point of the X-ray tube 2 (see FIG. 1). However, in FIG. Parallel arrangement.

  As shown in FIG. 3, when each pixel size is ΔX, in this embodiment, the grid foil 4a is arranged in synchronization with each pixel for easy understanding. That is, the grid foil 4a is disposed in synchronization with every four pixels. Therefore, when the grid foil 4a absorbs X-rays, a foil shadow is generated in the FPD 3 and the foil shadow is reflected in the X-ray image. However, the grid foil 4a is reflected so that the foil shadow is reflected in synchronization with each pixel. Be placed.

  In the present embodiment, as shown in FIG. 4, the grid foil 4a (see the enlarged view of FIG. 5A) is juxtaposed in the direction in which the grid foil 4a is juxtaposed, and the enlarged view of FIG. 5B. As shown in FIG. 6, the grid marker 21 having the groove 21 a is provided on the X-ray grid 4. The grid marker 21 may be provided by being adhered to the X-ray incident surface of the X-ray grid 4, or may be provided by being adhered to a surface opposite to the X-ray incident surface. It may be provided by adhering to both the incident surface and the opposite surface. The material forming the grid marker 21 is, for example, tungsten, but may be the same material as the grid foil 4a or a material different from the grid foil 4a. The grid marker 21 corresponds to the grid marker in the present invention.

  The arrangement location of the grid marker 21 is not particularly limited. For example, an upper marker 21A and a lower marker 21B may be arranged near the center of the X-ray grid 4 as shown in FIG. 4A, or four corners of the X-ray grid 4 as shown in FIG. In addition, an upper right corner marker 21C, an upper left corner marker 21D, a lower right corner marker 21E, and a lower left corner marker 21F may be arranged, respectively. In consideration of the fact that it does not obstruct the imaging region of the subject (that is, a failure in diagnosis), the arrangement location shown in FIG.

  As shown in FIG. 5B, the grid marker 21 has a plurality of grooves 21a. In FIG. 5 (b), for example, there are a total of twelve grooves 21a that are symmetric, and each groove 21a, when arranged on the X-ray grid 4, has one line as shown in FIG. 5 (a). It is arranged to straddle the grid foil 4a. In addition, all cases of the pixels and the X-ray grid 4 are assumed, and grooves 21a that are shifted by half a pixel alternately are formed in order to cope with this in image processing.

  At this time, on the left side of the center line of the grid marker 21 (for example, a marking line), it is shifted slightly to the right side (inside when viewed from the center line) and slightly to the left side (outside when viewed from the center line). The outer misalignment grooves are alternately formed, and on the right side of the center line, the inner misalignment groove is shifted slightly to the left (inward as viewed from the center line) and the outer shift groove is shifted slightly to the right (outward as viewed from the center line). Displacement grooves are formed alternately. The length of the groove 21a is not particularly limited, but is preferably a length that includes at least a plurality of pixel rows (for example, 20 pixel rows) in order to create an average profile described later. The width of the groove 21a is not particularly limited, but a width corresponding to 4 to 6 pixel columns is preferable. From the point of foil shadow interference, it was confirmed from the evaluation profile that when the width of the groove 21 is set to 5 pixel rows or 6 pixel rows, the margin of foil shadow interference is widened and there are few defects.

  Next, an image processing unit and a series of image processing flows will be described with reference to FIGS. FIG. 6 is a block diagram of a specific image processing unit according to the embodiment, FIG. 7 is a schematic diagram illustrating a flow of a series of image processing together with each image, and FIG. 8 is a CVS device. 9 is a list of marker shadow collection modes by grid markers, FIG. 9 is a schematic diagram showing the positional relationship of each shift, FIG. 10 is an example of profile creation processing, and FIG. FIG. 12 is a schematic diagram schematically showing collection of calibration data, FIG. 12 is a schematic diagram showing a positional relationship when a corresponding calibration image is obtained, and FIG. 13 is a reference calibration data weight for calculating the corresponding calibration image. FIG. 14 is a schematic diagram schematically showing generation of a foil shadow alignment image, and FIG. 15 schematically shows a deviation of an air grid with respect to a flat panel radiation detector (FPD). FIG.

  As shown in FIG. 6, the image processing unit 4 includes an observation amount calculation unit 31, a captured image collection unit 32, a corresponding calibration image calculation unit 33, a foil shadow alignment image generation unit 34, and a low-pass filter (hereinafter “LPF”). ”35, a false image removal foil image generation unit 36, and a false image removal processed image generation unit 37. The observation amount calculation unit 31 corresponds to the observation amount calculation unit in the present invention, the captured image collection unit 32 corresponds to the captured image collection unit in the present invention, and the corresponding calibration image calculation unit 33 corresponds to the corresponding calibration image in the present invention. The foil shadow alignment image generation unit 34 corresponds to the calculation means, the foil shadow alignment image generation means 34 in the present invention, and the low-pass filter (LPF) 35 corresponds to the foil shadow enhancement image generation means in the present invention. The false image removal processing foil image generation unit 36 corresponds to the false image removal processing foil image generation unit in the present invention, and the false image removal processed image generation unit 37 in the present invention. Corresponds to generating means.

  As shown in FIGS. 6 and 7, the observation amount calculation unit 31 uses Pro as the profile, DXg as the observation amount due to the grid shift, and DXf as the observation amount due to the lateral focal shift of the X-ray tube 2 (see FIG. 1). Sometimes, the observation amounts DXg and DXf are respectively obtained as shift amounts of the profile Pro relating to the difference between the values of the two X-ray detection signals detected at the positions separated by the width of the groove 21a (see FIG. 5B). . In the CVS apparatus, when marker shadows are collected by the grid markers 21 (see FIGS. 4 and 5), the observation amounts DXg and DXf have a relationship as shown in FIG.

The reference calibration data obtained prior to X-ray imaging is collected before shipment of the X-ray grid 4 (see FIGS. 1 and 3 to 5), and X-ray imaging apparatus is used as a CVS apparatus at customers who use the X-ray imaging apparatus. It is assumed that the focal position of the tube 2 (see FIG. 1) does not cause a focus shift at a home position (HP) until actual photographing. Here, the “home position” is an ideal focusing position where there is no deflection or twist in the grid foil 4a, and is located on the center line of the FPD 3 or the X-ray grid 4 as shown in FIG. It indicates the focal position HP located at a distance of SID ₀ from the FPD 3. The SID is a distance (SID: Source Image Distance) from the focal position in the perpendicular direction to the FPD 3 when a perpendicular is drawn from the focal position of the X-ray tube 2 to the FPD 3. In this embodiment, SID ₀ is set to 1010 mm.

  As shown in FIG. 9, when the coordinates of the home position HP are (0, 0), the amount of focal lateral deviation from the home position HP along the installation surface direction of the FPD 3 or the X-ray grid 4 orthogonal to the perpendicular direction. Is Xf, and when the focal length shift amount from the home position HP along the perpendicular direction is dr, the actual coordinates of the photographing focus are (Xf, dr). Further, when the grid foil 4a serving as a reference is located at the center line of the FPD 3 or the X-ray grid 4, when the grid foil 4a is displaced due to the attachment / detachment of the grid or the like, the amount of deviation is Xg.

  As described above, the focus position of the X-ray tube 2 (see FIG. 1) does not cause a focus shift at the home position HP (0, 0) until actual imaging. Therefore, as shown in FIG. 8, since the initial setting is the same as that at the time of calibration, the marker observation amounts DXg and DXf are both “0” and “0”. When the X-ray grid 4 (see FIG. 9) is remounted (indicated as “Grid remounted” in FIG. 8), a deviation occurs as shown in FIG. 15, so the marker observation amount DXf remains “0”. However, the marker observation amount DXg is DXg (≠ 0). Therefore, if the marker observation amount DXg is obtained, the grid shift amount Xg can be obtained based on the geometrical positional relationship of the following equation (1).

Xg = DXg · (SID ₀ −MG) / SID ₀ (1)
Here, MG is the distance between the detection surfaces of the FPD 3 and the arrangement surface of the grid markers 21 (see FIGS. 4 and 5) as shown in FIG. If the marker observation amount DXg is obtained, the grid shift amount Xg can be obtained because the right side of the equation (1) including MG is known.

  In addition, when photographing is performed at the home position HP (0, 0) (indicated as “after photographing” in FIG. 8), the X-ray grid 4 (see FIG. 9) is mounted again to further drift (see FIG. 9). 8, the marker observation amount DXg becomes DXg ′ (≠ DXg), but in this case as well, if the marker observation amount DXg ′ is obtained, the grid observation amount DXg ′ is calculated based on the above equation (1). A deviation amount Xg ′ (see FIG. 9) can be obtained.

  When actual imaging is performed using the subject M, the positional relationship between the X-ray tube 2, the FPD 3, and the X-ray grid 4 (both see FIG. 1) is shifted due to rotation of the C arm 5 (see FIG. 1). Occurs. In particular, the X-ray tube 2 is heavier than other devices and is likely to be displaced due to deflection of the C-arm 5 or the like. It should be noted that the positional relationship between the X-ray grid 4 and the FPD 3 is unlikely to shift, and is positioned at the same position unless the X-ray grid 4 is remounted. If only the X-ray tube 2 is displaced in FIGS. 8 and 9, the coordinates of the actual imaging focus are (Xf, dr) as described above.

  During actual imaging (indicated by “imaging focus (Xf, dr)” in FIG. 8), the X-ray grid 4 (see FIG. 9) is in the same positional relationship with the FPD 3 unless reattached. It is assumed that the marker observation amount DXg is constant. On the other hand, since the focus shift occurs during actual photographing, the marker observation amount DXf is DXf (≠ 0). Therefore, if the marker observation amount DXf is obtained, the focal lateral deviation amount Xf can be obtained based on the geometric positional relationship of the following equation (2).

Xf = {Xg- (DXg-DXf)}. {SID ₀ + dr} / MG
+ DXg-DXf (2)
Here, the focal length deviation amount dr from the home position HP along the perpendicular direction is set as the use state of the X-ray imaging apparatus, and is an amount that can be read from the apparatus and is known. The marker observation amount DXg has already been obtained by the above equation (1). Therefore, if the marker observation amount DXf is obtained, the right side of the above equation (2) is known, and therefore the focal lateral deviation amount Xf can be obtained. If the focal point shifted from the actual photographing focal point (Xf, dr) by the amount of grid shift Xg is the calculated focal point, the coordinate of the calculated focal point is (Xf−Xg, dr) as shown in FIG.

  Next, a specific method for calculating the observation amounts DXg and DXf will be described. A profile based on reference calibration data before shipment, a profile based on an X-ray image obtained when the X-ray grid 4 is remounted in the absence of the subject, and a subject M obtained by actual imaging (see FIG. 1) Profiles based on X-ray images (captured images) including the information on () are also created. The same calculation is used for each profile creation method. Therefore, in FIG. 10, the following will be described on behalf of a case where a profile is created based on the reference calibration data when the focus is placed at the home position HP (see FIGS. 8 and 9).

  When collecting the reference calibration data, the focus is moved at a predetermined interval (for example, about 1 mm) from the home position HP along the focusing line Lc as shown in FIG. X-ray images for each focal position are collected as reference calibration data. At this time, the reference calibration data is collected by using a calibration data collection device that is different from the X-ray imaging device used in actual imaging and hardly causes positional deviation. Of course, in the case of using an X-ray imaging apparatus of a type that hardly causes a focus shift for each imaging, the reference calibration data may be collected using the same X-ray imaging apparatus.

  A profile of the X-ray detection signal near the grid marker 21 (see FIGS. 4 and 5) is created from the reference calibration data. FIG. 10 is a profile relating to the vicinity of the upper marker 21A (see FIG. 4A). First, an average profile is obtained by obtaining an average value of X-ray detection signal values in a plurality of pixel rows (for example, 20 pixel rows) located in the groove 21a of the upper marker 21A (see FIG. 5B). Create (see FIG. 10A). Since the foil shadow extends between two pixels, a two-pixel bundling profile for adding the values of the X-ray detection signals of two adjacent pixel rows is created from the average profile (see FIG. 10B). .

  Further, a profile relating to the difference between the values of the two X-ray detection signals respectively detected at locations separated by the width of the groove 21a (see FIG. 5B) is created from the two-pixel bundle profile (FIG. 10C). )). Assuming that the width of the groove 21 is 5 pixel columns, in FIG. 10C, a difference value of each signal at a location separated by 5 pixel columns is obtained to create a 5 pixel column difference difference profile.

  A 5-pixel column difference difference profile obtained when the X-ray grid 4 is remounted in the absence of the subject and a 5-pixel column difference difference profile obtained by actual imaging in the same creation method as in FIG. create. In addition, the vertical axis | shaft of the 5 pixel row difference difference profile of FIG.10 (c) is a difference value, and becomes a positive value or a negative value by the magnitude relationship of a value. Therefore, if the point at which the difference value is “0” is defined as “0 cross point” and the 0 cross point is used as a reference, the shift amount from the 0 cross point in each profile can be obtained as the observation amounts DXg and DXf. it can.

  That is, the X-ray grid 4 in the absence of the subject and the 0 cross point in the 5 pixel column difference difference profile obtained from the reference calibration data when the focus is placed at the home position HP (see FIGS. 8 and 9). Is compared with the 0 cross point in the difference profile of 5 pixel column difference obtained at the time of remounting, the shift amount can be known, and the observation amount DXg can be obtained from the shift amount. In addition, a 0 cross point in the 5 pixel column difference difference profile obtained when the X-ray grid 4 is remounted in the absence of the subject, and a 0 cross point in the 5 pixel column difference difference profile obtained by actual imaging. , The shift amount can be known, and the observation amount DXf can be obtained from the shift amount.

  In this way, the observation amount calculation unit 31 obtains the observation amounts DXg and DXf, respectively, as shown in FIG. 6, and further calculates the grid shift amount Xg and the lateral shift amount Xf by the above equations (1) and (2), respectively. Ask. Those amounts obtained by the observation amount calculation unit 31 are sent to the corresponding calibration image calculation unit 33 and the foil shadow alignment image generation unit 34.

  As shown in FIGS. 6 and 7, the captured image collection unit 32 is based on an X-ray detection signal detected in a state where the subject M (see FIG. 1) exists when the actual captured image is I. To collect an actual photographed image I. FIG. 7 shows a photographed image I in which marker shadows are reflected when the upper marker 21A and the lower marker 21B are arranged as shown in FIG. 4 (a). The actual captured image I collected by the captured image collection unit 32 is sent to the foil shadow alignment image generation unit 34.

  As shown in FIGS. 6 and 7, the corresponding calibration image calculation unit 33 uses the reference calibration data based on the X-ray detection signal detected in the absence of the subject when the reference calibration data is D and the corresponding calibration image is C. Based on the calibration data D and grid shift information, which is information relating to grid shift, a corresponding calibration image C corresponding to the ray is obtained as a ray from the calculation focus shifted from the actual imaging focus by the grid shift amount Xg. When obtaining the corresponding calibration image C, the positional relationship shown in FIG. 12 and the weight function shown in FIG. 13 are used.

As described above, the reference calibration data is an X-ray image obtained by moving the focus from the home position HP along the focusing line Lc at a predetermined interval, as shown in FIGS. As described in FIG. 9, the coordinates of the calculated focal point shifted by the grid shift amount Xg from the actual photographing focal point (Xf, dr) are (Xf−Xg, dr). The pixel _{n 0} in FIG. 12 is a perpendicular intersection corresponding pixel to FPD3 from the home position HP.

  At this time, when the target pixel is n, the ray connecting the pixel n among the rays from the calculation focus (Xf−Xg, dr) is Lf. By using the reference calibration data at the focal point where the ray Lf and the converging line Lc intersect (in FIG. 12, a white square: indicated by “□”), a corresponding calibration image at that time can be obtained. If the distance between the focal point where the ray Lf and the focusing line Lc intersect and the center line is Ln, the distance Ln can be obtained based on the geometric positional relationship of the following equation (3).

Ln = Xf−Xg + {(n−n ₀ ) · ΔX−Xf + Xg} · dr /
(SID ₀ + dr) (3)
Here, ΔX is the size of each pixel as described in FIG. 3, and ΔX is known. Since the right side of the expression (3) other than ΔX has already been obtained or is already known, the distance Ln can be obtained.

By obtaining this distance Ln, the focal point where the ray Lf and the converging line Lc intersect is the focal position when the reference calibration data is collected (in FIG. 12,... Xf ₋₂ , Xf ₋₁ , HP, Xf ₁ , Xf ₂ , Xf ₃ , Xf ₄ , Xf ₅ ,... For example, if the focal point where the ray Lf and the focusing line Lc intersect is coincident with the focal position Xf ₄ when the reference calibration data is collected, the reference calibration data (X-ray image) at the focal position Xf ₄ is used as it is. A corresponding calibration image may be used.

However, the focal point where the ray Lf and the converging line Lc intersect does not necessarily coincide with the focal position when the reference calibration data is collected. Taking the case of FIG. 12 as an example, the point closest to the focal point where the ray Lf and the converging line Lc intersect is the focal point position Xf ₃ from the group of focal points when the reference calibration data is collected. , it is a Xf _4. Therefore, weight correction is performed based on the reference calibration data (X-ray image) at the focal position Xf ₃ , the reference calibration data (X-ray image) at the focal position Xf ₄ , and the weight function shown in FIG. For example, an image corresponding to calibration can be obtained. The weighting function has the focal length on the horizontal axis and the weight on the vertical axis.

For example, as shown in FIG. 13, the weighting functions at the focal positions Xf ₁ , Xf ₂ , Xf ₃ , Xf ₄ , Xf ₅ ,... Are Wf ₁ , Wf ₂ , Wf ₃ , Wf ₄ , Wf ₅ ,. In the case of FIG. 12, the product of the reference calibration data at the focal position Xf ₃ and the weight function Wf ₃ at that time, the reference calibration data at the focal position Xf ₄ and the weight function Wf ₄ at that time in the case of FIG. A calibration-corresponding image can be obtained by assigning a pixel value (value of an X-ray detection signal) obtained by summing up the products according to each pixel.

  In this way, the corresponding calibration image calculation unit 33 obtains the corresponding calibration image C as shown in FIG. The corresponding calibration image C obtained by the corresponding calibration image calculation unit 33 is sent to the foil image generation unit 36 for false image removal processing.

  As shown in FIGS. 6 and 7, the foil shadow alignment image generation unit 34 displays the photographed image I in the direction in which the grid foils 4 a are arranged in parallel (the horizontal direction in FIG. 7) when the foil shadow alignment image is G. The foil shadow alignment image G which is a photographed image in which the foil shadows are aligned is generated by sliding. The foil shadow alignment image G is generated as shown in FIG.

  As shown in FIG. 14, the captured image I is slid along with the subject information. When the entire X-ray grid 4 is laterally displaced, the captured image I may be slid by the same shift amount (for example, the grid displacement amount Xg), but the X-ray grid 4 is rotationally displaced. In this case, for example, the sign in the sliding direction is reversed between the shift amount at the upper marker 21A (see FIG. 4A) and the shift amount at the lower marker 21B (see FIG. 4A). . In this case, if the shift amount at the upper marker 21A is Xgu and the shift amount at the lower marker 21B is Xgl, a photographed image I for each piece of subject information is displayed in the vicinity of the upper marker 21A (see FIGS. 7 and 14). In this case, the image is moved by the shift amount Xgu, and in the vicinity of the lower marker 21B, the captured image I is moved by the shift amount Xgl in the vicinity of the subject information (to the left in the case of FIGS. 7 and 14). Then, in the vicinity of the central pixel row, the captured image I may be moved by the average value | Xgu−Xgl | / 2 obtained from the absolute value of the shift amount difference together with the subject information.

  In this manner, the foil shadow alignment image G shown in FIG. 14B can be generated from the photographed image I shown in FIG. When generating a more precise foil shadow alignment image G, the shift amount at the upper marker 21A, the shift amount near the center pixel row, and the shift amount at the lower marker 21B are not divided into three. The shift amount for each divided pixel row may be obtained by linear interpolation.

  For example, as shown in FIG. 14C, when the pixel row is on the horizontal axis and the shift amount is on the vertical axis, the shift amount at the upper marker 21A and the shift amount at the lower marker 21B are known. Therefore, if linear interpolation is performed by connecting the shift amounts, the shift amount for each pixel row can be determined more precisely by linear interpolation, and thus a more accurate foil shadow alignment image G can be generated. As shown in FIG. 14B, the shift amount (deviation amount) with respect to the extending direction of the grid foil 4a (vertical direction in FIGS. 7 and 14) remains, but the shift amount is small and ignored. can do.

  In this way, the foil shadow alignment image generator 34 generates a foil shadow alignment image G as shown in FIG. The foil shadow alignment image G generated by the foil shadow alignment image generation unit 34 is sent to the LPF 35 and the false image removal processed image generation unit 37.

  As shown in FIG. 6 and FIG. 7, the LPF 35 emphasizes the foil shadow with respect to the foil shadow alignment image G and provides information on the subject M (see FIG. 1) when the foil shadow enhanced image is E. In order to generate the removed foil shadow enhanced image E, the low-pass region is passed with respect to the extending direction (vertical direction in FIG. 7) of the grid foil 4a. The foil shadow enhanced image E generated by the LPF 35 is sent to the false image removal processing foil image generator 36.

As shown in FIGS. 6 and 7, the false image removal processing foil image generation unit 36 uses the foil shadow enhancement image E generated by the LPF 35 and the corresponding calibration when the false image removal processing foil image is Cor. Based on the image C, a false image removal processing foil shadow image Cor for removing a false image due to the foil shadow is generated. Since the foil shadow straddles between two pixels, the integrated value at that location is obtained for each row of the foil shadow enhanced image E and the corresponding calibration image C. As shown in FIG. 7, when the integrated value in the foil shadow enhanced image E is E _sum and the integrated value in the corresponding calibration image C is C _sum , the false image removal processing foil shadow image Cor can be generated at the ratio of the integrated values. (Cor = E · C _sum / E _sum )

As described above, the foil shadow does not necessarily straddle the plurality of pixels (two pixels in this embodiment) due to the deflection of the individual grid foils 4a. Depending on the bending state, the foil shadow may cover only one pixel, or the foil shadow may cover another pixel (for example, an adjacent pixel) without covering even one pixel. In that case, the pixel at the place where the foil shadow seems to straddle is recognized from the foil shadow emphasis image E and the corresponding calibration image C, and the plurality of the same are uniformly applied regardless of the situation of the foil shadow straddling. Integrated values C _sum and E _sum are obtained for each pixel (2 pixels here).

  In this way, the false image removal processing foil image generation unit 36 generates the false image removal processing foil image Cor as shown in FIG. The false image removal processing foil image Cor generated by the false image removal processing foil image generation unit 36 is sent to the false image removal processed image generation unit 37.

As shown in FIGS. 6 and 7, the false image removal processed image generation unit 37 uses the false image removal processing foil when the X-ray image finally obtained by removing the foil shadow is I _after. Based on the shadow image Cor, a false image removal processed image from which the foil shadow by the grid foil 4a is removed is generated. Then, the false image removal processed image generated by the false image removal processed image generation unit 37 is finally obtained as an X-ray image I _after . For each pixel, an X-ray image I _after can be obtained by dividing the false image removal processing foil shadow image Cor from the foil shadow alignment image G (I _after = G / Cor).

  In the case of an air grid, since the intermediate layer is an air gap, the contrast between the pixels over which the foil shadows straddle and the pixels that do not straddle is strong, and the false image is easily noticeable. The problems of the invention can be solved by applying the above-described image processing unit and a series of image processing flows to an air grid.

  According to the X-ray imaging apparatus according to the present embodiment, in addition to the X-ray tube 2, the FPD 3 and the X-ray grid 4, the X-ray imaging apparatus has a thickness larger than the grid foil 4 a in the direction in which the grid foil 4 a is arranged in parallel. The grid marker 21 is provided on the X-ray grid 4. By providing such a grid marker 21, it is easy to detect the shift characteristic of the entire foil shadow. In addition, since the grid marker 21 has a greater thickness than the grid foil 4a in the direction in which the grid foils 4a are arranged side by side, even if the foil shadow is blurred and reflected in the X-ray image, the grid marker 21 is used. Shadows can be detected clearly. In the case where such a grid marker 21 is provided, when the observation amount due to the grid shift is DXg and the observation amount due to the shift of the X-ray tube 2 is DXf, it is separated by the width of the groove 21a (of the grid marker 21). The observation amount calculation unit 31 that obtains the observation amounts DXg and DXf as the shift amount of the profile relating to the difference between the values of the two X-ray detection signals detected at the respective locations is provided. The image capturing unit 32 includes a captured image collection unit 32 that collects an actual captured image based on an X-ray detection signal detected in a state of the subject M, and includes the observation amount calculation unit 31 and the captured image collection unit 32 described above. Based on the above, the foil shadow by the grid foil 4a is removed to finally obtain an X-ray image. By obtaining the difference between the values of two X-ray detection signals detected at locations separated by the width of the groove 21a of the grid marker 21, even if information on the subject is included in the X-ray detection signal, the difference is obtained. The difference profile is information that reflects the overall deviation characteristic of the foil shadow and the relative deviation characteristic of the X-ray tube 2 with respect to the FPD 3. Therefore, the observation amount DXg due to grid shift and the observation amount DXf due to lateral focus shift of the X-ray tube 2 are respectively obtained as the shift amount of the profile. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the observation amounts DXg and DXf.

  In addition, according to the X-ray imaging apparatus according to the present embodiment, actual imaging is performed based on the reference calibration data based on the X-ray detection signal detected in the absence of the subject and the grid shift information that is information regarding grid shift. A corresponding calibration image calculation unit 33 for obtaining a corresponding calibration image corresponding to the ray as a ray from the calculation focus shifted by the grid shift amount Xg from the focus is provided. Then, based on the above-described corresponding calibration image calculation unit 33 and the above-described captured image collection unit 32, the foil shadows by the grid foil 4a are removed, and an X-ray image is finally obtained. Using the reference calibration data collected in the absence of grid shift, a corresponding calibration image corresponding to the ray is obtained as a ray from the calculation focus shifted from the actual imaging focus by the grid shift amount Xg. The calibration image also corresponds to the shooting focus. Therefore, by matching the corresponding calibration image corresponding to the actual photographing focus with the actual photographed image, an X-ray image in consideration of grid shift can be finally obtained. As a result, it is possible to remove the foil shadow in consideration of the grid shift based on the grid shift information.

  In this embodiment, both the observation amount calculation unit 31 and the corresponding calibration image calculation unit 33 are provided. Therefore, in addition to the observation amounts DXg and DXf, the foil shadow can be removed in consideration of the grid shift based on the grid shift information.

  Further, in this embodiment, when both the observation amount calculation unit 31 and the corresponding calibration image calculation unit 33 are provided, the captured image is slid in the direction in which the grid foils 4a are arranged side by side based on the observation amount DXg. It is preferable to include a foil shadow alignment image generation unit 34 that generates a foil shadow alignment image that is a photographed image in which the foil shadows are aligned. When the X-ray grid 4 is displaced (for example, lateral displacement, rotational displacement), a method of rotating the captured image in order to eliminate the rotational displacement is also conceivable. In this case, however, the calculation amount is enormous. Therefore, based on the observation amount DXg, the foil shadow alignment image can be easily generated by sliding the photographed image in the direction in which the grid foils 4a are arranged side by side. Can be reduced. As described above, the shift amount (shift amount) with respect to the extending direction of the grid foil 4a remains, but the shift amount is small and can be ignored.

  When the foil shadow alignment image generation unit 34 is provided, the LPF 35 serves as a foil shadow enhancement image generation unit that generates a foil shadow enhancement image in which the foil shadow is emphasized with respect to the foil shadow alignment image and information on the subject is removed. And a false image removal foil image generator for generating a false image removal foil image for removing a false image caused by the foil shadow based on the foil shadow enhanced image generated by the LPF 35 and the corresponding calibration image. 36 is more preferable. Since the foil shadow emphasis image generated from the foil shadow alignment image and the corresponding calibration image correspond to each other in position, it becomes easy to generate a false image removal processing foil shadow image based on both images.

  In the present embodiment, the foil shadow enhanced image generating means is a low-pass filter (LPF) 35 that passes a low-pass region with respect to the extending direction of the grid foil 4a. The information of the subject is in the high range with respect to the extending direction of the grid foil 4a, whereas the grid foil 4a has a low change with respect to the extending direction. Therefore, it is possible to easily generate a foil shadow enhanced image from which information on the subject is removed by the low-pass filter (LPF) 35.

  Of course, the foil shadow enhanced image generating means is not limited to the low-pass filter (LPF) as in this embodiment. For example, the foil shadow enhanced image generating means is composed of a high-pass filter (HPF) and a subtractor, and an image in which the information of the subject is enhanced by removing the foil shadow by the high-pass filter (HPF). A foil shadow enhanced image from which the information of the subject is removed by subtracting the image in which the subject information is enhanced from the original image before being generated and passed through the high pass filter (HPF) by a subtractor. Can be generated.

  The false image removal processing foil image generation unit 36 described above obtains integrated values for a plurality of pixels (two pixels in this embodiment) for the foil shadow enhanced image and the corresponding calibration image, and based on each integrated value. A foil image for false image removal processing is generated. The foil shadow by the grid foil 4a may straddle a plurality of pixels (in this case, two pixels) depending on its width. In that case, the integrated value at the location where the foil shadow straddles the plurality of pixels is obtained. By obtaining the foil shadow enhanced image and the corresponding calibration image, and generating the false image removal foil shadow image based on the respective integrated values, the false image removal processing foil shadow image can be accurately generated.

  Specifically, a false image removal processed image generation unit 37 that generates a false image removal processed image obtained by removing the foil shadow from the grid foil 4a based on the foil image for false image removal processing is provided, and the false image The false image removal processed image generated by the removal processed image generation unit 37 is finally obtained as an X-ray image. Thereby, the foil shadow can be removed in consideration of the grid shift.

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

  (1) In the above-described embodiment, the X-ray is taken as an example of the radiation, but the present invention may be applied to radiation other than the X-ray (for example, γ-ray).

  (2) In the above-described embodiment, the X-ray imaging apparatus is an apparatus including a C arm for implementation in a CVS apparatus, but is not limited thereto. For example, it may have a structure in which a subject (in this case, the subject to be examined is a subject) is transported on a belt and photographed, as in a non-destructive inspection apparatus used for industrial use, etc. It may be a structure such as an X-ray CT apparatus used in the present invention.

  (3) In the above-described embodiment, the air grid is adopted as the radiation grid, but the present invention is not limited to this. In addition to the air gap, a grid made of an intermediate material that transmits radiation represented by X-rays such as aluminum or an organic material may be used. A cross grid may also be used. In the case of a cross grid, grid shift is less likely to occur than in the case of an air grid in which a grid foil extends only in one direction, but it can of course be applied. In this case, what is necessary is just to obtain | require by expanding the direction of deviation from one direction to two directions, respectively.

  (4) In the above-described embodiment, the focusing grid is used, but the present invention can also be applied to grids arranged in parallel.

  (5) In the above-described embodiment, the grid synchronous with the pixel (synchronous grid) is described, but the present invention may be applied to an asynchronous grid. In the case of a grid other than an air grid, the present invention may be applied to a grid having a structure in which a plurality of grid foils are arranged in parallel on one pixel.

  (6) In the embodiment described above, both the observation amount calculation means (observation amount calculation section 31 in the embodiment) and the corresponding calibration image calculation means (corresponding calibration image calculation section 33 in the embodiment) are provided. In view of the problem of removing the foil shadow in consideration, only one of them may be provided. For example, only the observation amount may be obtained without obtaining the corresponding calibration image, or conversely, only the corresponding calibration image may be obtained without obtaining the observation amount. Further, the observation amount (particularly the observation amount Xg) can be obtained by correlation processing using a foil shadow or the like without obtaining from the grid marker 21.

  (7) In the embodiment described above, the foil shadow alignment image generation means (in the embodiment, the foil shadow alignment image generation unit 34) is provided on the assumption that the grid shift is large, but it is not always necessary to generate the foil shadow alignment image. . For example, in the case where the corresponding calibration image calculation means (corresponding calibration image calculation unit 33 in the embodiment) is provided, the object shadow information is emphasized with respect to the captured image (without generating the foil shadow alignment image). Based on the foil shadow enhanced image generating means (LPF 35 in the embodiment) for generating the foil shadow enhanced image from which the image is removed, the foil shadow enhanced image generated by the foil shadow enhanced image generating means (LPF 35), and the corresponding calibration image A false image removal processing foil image generation means (in the embodiment, a false image removal processing foil image generation unit 36) for generating a false image removal processing foil image for removing a false image caused by the foil shadow. Also good. In this case, the image that is the basis of the foil shadow enhancement image is a photographed image, whereas in the case where the foil shadow alignment image generation unit (the foil shadow alignment image generation unit 34) is provided as in the embodiment, the foil shadow Except that the image that is the basis of the enhanced image is a foil shadow aligned image, the subsequent operations and effects are the same. That is, if the grid shift is small, the foil shadow emphasis image generated from the photographed image and the corresponding calibration image correspond to each other in position, so that the false image removal processing foil shadow image can be easily generated based on both images.

2 ... X-ray tube 3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 4 ... X-ray grid 4a ... Grid foil 21 ... Grid marker 21a ... Groove 31 ... Observation amount calculation part 32 ... Photographed image collection part 33 ... Corresponding calibration image calculation part 34 ... Foil shadow alignment image generation part 35 ... Low-pass type Filter (LPF)
36 ... Fake image removal processing foil image generation unit 37 ... False image removal processed image generation unit M ... Subject

Claims (8)

A radiographic apparatus for obtaining radiographic images,
A radiation source that emits radiation;
Radiation detecting means for detecting the irradiated radiation;
A radiation grid provided on the detection side of the radiation detection means and configured by arranging grid foils that absorb scattered radiation; and
In the direction in which the grid foils are arranged side by side, the grid foil has a thickness, and a grid marker having grooves is provided on the radiation grid.
Furthermore, the radiation imaging apparatus includes:
When the observation amount due to the grid shift is DXg and the observation amount due to the shift of the radiation source is DXf, the radiation detection signal profile obtained by the initial setting before reattachment of the radiation grid and the radiation without the subject are present. Based on the profile regarding the radiation detection signal obtained at the time of remounting the grid, the values of the two radiation detection signals before and at the time of remounting, which are respectively detected at locations separated by the width of the groove, The observation amount DXg is obtained as the shift amount of the profile relating to the difference, and the profile relating to the radiation detection signal obtained when the radiation grid is remounted in the absence of the subject and the profile relating to the radiation detection signal obtained in actual imaging. Based on the reattachment detected at each location separated by the width of the groove An observation amount calculating means for calculating the amount of observation DXf as and the shift amount of the profiles relating to the difference between the values of two radiation detection signal in the actual shooting,
A captured image collecting means for collecting an actual captured image based on a radiation detection signal detected in a certain state of the subject,
A radiation imaging apparatus characterized by finally obtaining a radiation image by removing a foil shadow by the grid foil based on the observation amount calculating means and the captured image collecting means. A radiographic apparatus for obtaining radiographic images,
A radiation source that emits radiation;
Radiation detecting means for detecting the irradiated radiation;
A radiation grid provided on the detection side of the radiation detection means and configured by arranging grid foils that absorb scattered radiation; and
Furthermore, the radiation imaging apparatus includes:
(A) Reference calibration data based on a radiation detection signal detected in the absence of the subject, (b) Grid shift information which is information relating to grid shift with respect to the radiation detection means based on the collection time of the reference calibration data. A corresponding calibration image calculation means for obtaining a corresponding calibration image corresponding to the ray as a ray from the calculation focus shifted from the actual photographing focus by the amount of grid shift;
A captured image collecting means for collecting an actual captured image based on a radiation detection signal detected in a certain state of the subject,
A radiation imaging apparatus, wherein a radiation image is finally obtained by removing a foil shadow by the grid foil based on the corresponding calibration image calculating means and the captured image collecting means. The radiographic apparatus according to claim 1,
(A) Reference calibration data based on a radiation detection signal detected in the absence of the subject, (b) Grid deviation which is information regarding the grid deviation with respect to the radiation detection means based on the time of collection of the reference calibration data. Corresponding calibration image calculation means for obtaining a corresponding calibration image corresponding to the ray as a ray from the calculation focus shifted from the actual photographing focus by the amount of grid shift based on the information,
A radiation imaging apparatus, wherein a radiation image is finally obtained by removing a foil shadow by the grid foil based on the observation amount calculating means, the corresponding calibration image calculating means, and the captured image collecting means. In the radiographic apparatus of Claim 2 or Claim 3,
When the observation amount due to grid shift is DXg, based on the observation amount DXg, the foil shadow alignment is a photographed image in which the foil shadows are aligned by sliding the photographed image in the direction in which the grid foils are arranged side by side. A radiation imaging apparatus comprising foil shadow alignment image generation means for generating an image. The radiation imaging apparatus according to claim 4,
A foil shadow enhanced image generating means for generating a foil shadow enhanced image in which the foil shadow is enhanced with respect to the foil shadow aligned image and the information of the subject is removed;
Based on the foil shadow enhanced image generated by the foil shadow enhanced image generating means and the corresponding calibration image, the false image removal for generating a false image removal processing foil shadow image for removing the false image caused by the foil shadow A radiation imaging apparatus comprising: a processing foil image generation means. The radiographic apparatus according to claim 5,
The radiographic apparatus according to claim 1, wherein the foil shadow enhanced image generating means is a low-pass filter that allows a low-pass region to pass in the extending direction of the grid foil. In the radiographic apparatus of Claim 5 or Claim 6,
The false image removal processing foil image generation means obtains an integrated value at a plurality of pixels for the foil shadow enhanced image and the corresponding calibration image, and calculates the false image removal processing foil image based on each integrated value. A radiation imaging apparatus characterized by generating. In the radiography apparatus in any one of Claims 5-7,
Based on the foil image for false image removal processing, comprising a false image removal processed image generating means for generating a false image removal processed image obtained by removing the foil shadow by the grid foil,
A radiographic apparatus characterized by finally obtaining the false image removal processed image generated by the false image removal processed image generating means as the radiation image.

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