JP5019879B2 - X-ray CT apparatus, image processing program, and image processing method - Google Patents

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to a technique effective for reconstructing a three-dimensional X-ray CT image from rotational imaging data obtained by a two-dimensional X-ray detector. This application is a patent application claiming priority based on Japanese Patent Application No. 2004-262671 based on the Japanese Patent Law, and is incorporated by reference in order to enjoy the benefits of Japanese Patent Application No. 2004-262671. It is an application.

A conventional cone beam X-ray CT apparatus includes an X-ray source that irradiates a subject with X-radiating X-rays and an imaging unit that is disposed opposite to the X-ray source and that captures a transmitted X-ray intensity image that has passed through the subject. A rotation unit for rotating the imaging system around the subject, a reconstruction unit for reconstructing a reconstructed image of the subject from the transmission X-ray intensity image, and a rotation center axis of the imaging system on the transmission X-ray intensity image A rotation center axis projection position setting unit that changes a rotation center axis projection position that is a position projected onto the image, and a reconstructed image reconstructed using the rotation center axis projection position set by the rotation center axis projection position setting unit The rotation center axis projection position of the imaging system is estimated based on the contrast of the X-ray image, and the X-ray tomographic image and / or the X-ray three-dimensional image of the subject from the reconstructed image reconstructed at the estimated rotation center axis projection position. X-ray tomogram or / And displaying the X-ray three-dimensional image. (For example, Patent Document 1)
In Patent Document 1, the rotation center axis projection position of the imaging system is estimated on the assumption that the spatial position of the X-ray source-2D X-ray detector is not displaced.
JP 2000-201918 A.

  However, in Patent Document 1, an X-ray CT apparatus (for example, an X-ray CT apparatus of a C-arm) in which the spatial position of an X-ray source-2D X-ray detector is displaced by the influence of gravity or centrifugal force during rotational imaging. However, no consideration is given to a method for accurately forming a three-dimensional X-ray CT image.

  An object of the present invention is an X-ray CT apparatus capable of forming a three-dimensional X-ray CT image even in an X-ray CT apparatus in which the spatial position of an X-ray source-2D X-ray detector is displaced by rotation. Is to provide.

  An X-ray CT apparatus of the present invention is arranged to face an X-ray source that irradiates a subject with X-rays, and to detect the X-ray transmitted through the subject to detect the subject. An X-ray detector for outputting X-ray image data; a rotating means for rotating the X-ray source and the X-ray detector by a predetermined angle; and the X-ray source and the X-ray source for each predetermined angle. Spatial displacement correction information generating means for calculating a displacement of the spatial position of the X-ray detector and generating spatial displacement correction information for correcting the position of the X-ray image data based on the displacement; The position of the X-ray image data is corrected based on the spatial displacement correction information, and an image reconstruction calculation is performed based on the position-corrected X-ray image data to generate an X-ray CT image of the subject. Image reconstructing means.

  The image processing program according to the present invention includes the X-ray source and the X-ray detector that are generated when the X-ray source and the X-ray detector provided in the X-ray CT apparatus are rotated at predetermined angles. A spatial displacement correction for generating a spatial displacement correction information for correcting a position based on the displacement for the X-ray image data acquired from the X-ray CT apparatus An information generation step, a reading step for reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus, and a position correction of the X-ray image data based on the spatial displacement correction information. An image reconstruction calculation is performed based on line image data, and an image reconstruction step for generating an X-ray CT image of the subject and a display step for displaying the X-ray CT image are executed by a computer. And

  The image processing method according to the present invention includes the X-ray source and the X-ray detector that are generated when the X-ray source and the X-ray detector provided in the X-ray CT apparatus are rotated at predetermined angles. A spatial displacement correction for generating a spatial displacement correction information for correcting a position based on the displacement for the X-ray image data acquired from the X-ray CT apparatus An information generation step, a reading step for reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus, and a position correction of the X-ray image data based on the spatial displacement correction information. An image reconstruction operation is performed based on line image data to generate an X-ray CT image of the subject, and a display step to display the X-ray CT image.

  According to the present invention, a three-dimensional X-ray CT image can be formed even in an X-ray CT apparatus in which the spatial position of the X-ray source-2D X-ray detector is displaced.

1 is a block diagram showing a schematic configuration of a C-arm type cone beam X-ray CT apparatus 1 to which the present invention is applied. FIG. It is a conceptual diagram which shows the hole chart 18 used for the production | generation of an image distortion correction table. It is a conceptual diagram for demonstrating the state by which the wire-like phantom 50 is mounted on the bed 17 using the phantom holding body 50a, and is rotationally imaged. It is a conceptual diagram which shows the state which mounted the phantom of FIG. 3 on the bed. 3 is a schematic diagram showing a phantom projection image 35 of a wire phantom 50 collected by a two-dimensional X-ray detector 12. FIG. It is a flowchart which shows the procedure in which the geometric parameter calculation means 300 in embodiment of this invention performs a geometric parameter calculation process. It is the figure shown about the wire reconstruction cross-sectional image when the projection of a rotation center axis | shaft has an error in + u direction. It is the figure shown about the wire reconstruction cross-sectional image in case the projection of a rotation center axis | shaft has an error in -u direction. It is a flowchart which shows the procedure in which the rotation center axis projection position determination means 350 determines a rotation center axis projection position. It is a schematic diagram which shows a wire reconstruction cross-sectional image in case the spatial displacement of an X-ray source-two-dimensional X-ray detector remains. It is a flowchart which shows the procedure in which the space displacement amount correction information generation means 380 generates space displacement amount correction information. It is a conceptual diagram for demonstrating the geometric calculation for producing | generating spatial displacement amount correction information. It is a schematic diagram showing a state in which the correction of the rotation center axis projection position and the spatial displacement amount of the X-ray source-two-dimensional X-ray detector is completed, and the wire reconstruction cross-sectional image is formed at one point. It is a block diagram for demonstrating 2nd embodiment of this invention. It is a conceptual diagram for demonstrating 2nd embodiment of this invention, Comprising: The state with which the wire wire 70 with high contrast is being fixed to the back surface of the bed 17 is shown. It is a flowchart which shows the procedure in which the alignment reconstruction means 400 in 2nd embodiment of this invention performs an alignment reconstruction process. It is a flowchart which shows the detailed procedure of the wire extraction process which is one process shown by FIG. FIG. 2 is a block diagram showing a schematic configuration of a C-arm type cone beam X-ray CT apparatus 1b to which the present invention is applied, which is applied to DSA. It is a 1st flowchart which shows the procedure in which the alignment DSA reconstruction means 500 in 3rd embodiment of this invention performs an alignment DSA reconstruction process. It is a 2nd flowchart which shows the procedure in which the alignment DSA reconstruction means 500 in 3rd embodiment of this invention performs an alignment DSA reconstruction process. 1 is a block diagram showing a schematic configuration of a cone-beam X-ray CT apparatus 1c that is a C-arm type cone-beam X-ray CT apparatus 1c to which the present invention is applied and that includes a two-dimensional X-ray detector using an FPD. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cone beam X-ray CT apparatus, 10 ... Imaging | photography part, 11 ... X-ray source, 11t ... X-ray tube, 11c ... Collimator, 12 ... Two-dimensional X-ray detector, 12i ... X-ray image intensifier, 12c ... TV camera, 12f ... Flat panel detector (FPD), 13 ... C-type arm, 14 ... C-type arm holder, 15 ... Ceiling support, 16 ... Ceiling rail, 17 ... Sleeper, 18 ... Hall chart, 18h ... Hall, DESCRIPTION OF SYMBOLS 20 ... Control calculating part, 30 ... Rotation track surface (midplane), 31 ... Rotation center axis, 32 ... Rotation center, 33 ... Projection of rotation center axis to X-ray entrance plane, 35 ... Phantom projection image, 40 ... Cover Specimen 50 ... Wire phantom 50a ... Phantom holder 51 ... Geometrically correct wire projection position 52 ... Shifted wire projection position 53 ... Wire reconstruction 54 ... Wire reconstruction sectional image when projection of rotation center axis has error in + u direction, 55 ... Wire reconstruction sectional image when projection of rotation center axis has error in -u direction, 56 ... X-ray Wire reconstruction cross-sectional image when spatial displacement of the source 11-2D X-ray detector 12 remains, 56a ... reference wire reconstruction image, 57 ... reconstruction cross-sectional image after fixing the wire reconstruction point, 65 ... displacement 70: High contrast wire arranged on the back side of the patient bed, 80 ... Display device, 90 ... Input device, 100 ... Imaging unit control means, 101 ... Imaging system rotation control means, 102 ... Imaging system position control means, DESCRIPTION OF SYMBOLS 103 ... X-ray irradiation control means 104 ... Bed control means 105 ... Detection system control means 110 ... Image collection means 200 ... Reconstruction means 201 ... Pre-processing means 202 ... Image distortion correction means 203 ... F Filtering means, 204 ... back projection means, 210 ... image display means, 300 ... geometric parameter calculation means, 320 ... image distortion correction table generation means, 330 ... image distortion correction table storage means, 350 ... rotation center axis projection position determination means 380: Spatial displacement correction information generating means, 390: Spatial displacement correction information storing means, 400: Position reconstruction means, 410: Wire extraction means, 500 ... Position DSA reconstruction means, 540: Difference means

Hereinafter, preferred embodiments of an X-ray CT apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
<First embodiment>
FIG. 1 is a C-arm type cone beam X-ray CT apparatus 1 to which the present invention is applied, which is an X-ray image intensifier 12i and a television camera for taking a visible light image by the X-ray image intensifier 12i. It is a block diagram which shows schematic structure of the X-ray CT apparatus provided with the X-ray detector which consists of 12c. FIG. 2 is a conceptual diagram showing a hall chart 18 used for generating an image distortion correction table.

  The cone beam X-ray CT apparatus 1 shown in FIGS. 1 and 1a is configured to irradiate a subject 40 with X-rays, capture an X-ray transmission image of the subject 40, and obtain X-ray image data. And a control arithmetic unit 20 that controls each component of the imaging unit 10 and reconstructs a three-dimensional X-ray CT image of the subject 40 based on X-ray image data. In addition, the display device 80 includes an image display device 80 and an input device 90 including a trackball and a mouse for inputting an instruction for moving the position of the image displayed on the display device 80.

(Shooting unit 10)
The imaging unit 10 is installed on a bed 17 on which the subject 40 is placed, an X-ray source 11 that irradiates the subject 40 placed on the bed 17 with X-rays, and a position facing the X-ray source 11. A two-dimensional X-ray detector 12 that outputs X-ray image data by detecting X-rays transmitted through the X-ray, and a C-type arm 13 that mechanically connects the X-ray source 11 and the two-dimensional X-ray detector 12. Prepare. In addition, the photographing unit 10 includes a C-type arm holding body 14 for holding the C-type arm 13, a ceiling support 15 for attaching the C-type arm holding body 14 to the ceiling, and the ceiling support 15 in the state of FIG. And a ceiling rail 16 that is movably supported in the two-dimensional direction.

  The X-ray source 11 includes an X-ray tube 11t that generates X-rays, and a collimator 11c that controls the direction of X-ray irradiation from the X-ray tube 11t in a cone or quadrangular pyramid shape.

  The two-dimensional X-ray detector 12 includes an X-ray image intensifier 12i that converts an X-ray transmission image into a visible light image, and a television camera 12c that captures a visible light image by the X-ray image intensifier 12i. The X-ray CT apparatus of FIG. 1 and the two-dimensional X-ray detector 12 include an X-ray image intensifier 12i and a television camera 12c. As described in the fourth embodiment, the two-dimensional X-ray detector 12 is provided. May be replaced with a flat panel detector (FPD) or the like using a TFT element.

  The C-arm 13 rotates around the rotation center axis 31 at every predetermined projection angle when the subject 40 is imaged. Thereby, the X-ray source 11 and the two-dimensional X-ray detector 12 perform X-ray imaging while rotating and moving on substantially the same circular orbit. For this rotational movement, there are geometric parameters used for the image reconstruction operation. That is, as the C-arm 13 rotates, a rotation orbit plane (midplane) 30 that includes a circular orbit drawn by the X-ray source 11 and the two-dimensional X-ray detector 12, a rotation center axis 31, And a rotation center 32 that is an intersection of the rotation center axis 31 and the rotation track surface 30.

  These geometric parameters are determined in principle from the design data of the imaging unit 10, but actually, due to production errors of the imaging unit 10 and deformation of members, individual cone beam X-ray CT apparatuses 1 are used. It is a value specific to.

(Control operation unit 20)
The control calculation unit 20 is based on the imaging unit control unit 100 that controls the imaging unit 10, the image collection unit 110 that collects and stores the X-ray image data output by the imaging unit 10, and the collected X-ray image data. The reconstructing means 200 for reconstructing a three-dimensional X-ray CT image and an error in mechanical production of the imaging unit 10 are numerically expressed and used as correction data when the reconstructing means 200 performs three-dimensional reconstruction. Geometric parameter calculation means 300 for obtaining geometric parameters. Furthermore, an image display unit 210 that displays a three-dimensional X-ray CT image generated by the reconstruction unit 200 is provided.

  The imaging unit control unit 100 includes an imaging system rotation control unit 101 that controls the rotational movement of the C-arm 13 around the rotation center axis 31 (hereinafter referred to as “propeller rotation”), and the ceiling support 15. An imaging system position control means 102 is provided for controlling the position of the C-arm 13 relative to the subject 40 in a two-dimensional manner by controlling the position on the ceiling rail 16. Further, the imaging unit control means 100 adjusts the position of the subject 40 by controlling the position of the bed 17 and the X-ray irradiation control means 103 that controls ON / OFF of the tube current flowing through the X-ray tube 11t. A couch control unit 104 and a detection system control unit 105 that controls imaging of an X-ray transmission image by the two-dimensional X-ray detector 12 are provided.

(Reconstruction means 200)
The reconstruction unit 200 includes a preprocessing unit 201, an image distortion correction unit 202, a filtering unit 203, and a back projection unit 204.

  The preprocessing means 201 is means for converting the X-ray image data collected by the image collection means 110 into an X-ray absorption coefficient distribution image. In the present embodiment, first, a natural logarithmic conversion operation is performed on each pixel data of an X-ray transmission image of air that has been captured in advance without the subject 40 and the bed 17 being placed in the field of view. Next, a natural logarithmic conversion operation is performed on each pixel data of an X-ray transmission image taken with the subject 40 placed on the bed 17. By taking the difference between the two X-ray transmission images, an X-ray absorption coefficient distribution image of the subject 40 and the bed 17 is obtained.

  The image distortion correction unit 202 corrects the image distortion of the X-ray absorption coefficient distribution image generated by the preprocessing unit 201. This image distortion is an image distortion generated when an X-ray transmission image is converted into a visible light image by the X-ray image intensifier 12i, and is stored in an image distortion correction table storage unit 330 described later. Is used to correct the image distortion of the X-ray absorption coefficient distribution image obtained by the pre-processing means 201.

  The filtering unit 203 performs a filtering process in X-ray CT image reconstruction.

  The back projection means 204 performs a back projection operation based on the X-ray image data after the filtering process, and generates a three-dimensional X-ray CT image. The back projection means 204 applies the space between the X-ray source and the X-ray detector based on the spatial displacement correction information for each X-ray image data after filtering processing (X-ray image data taken from each projection angle). Correct the displacement. Next, the back projection unit 204 generates a projection image based on each X-ray image data. Then, the back projection unit 204 performs a back projection operation on the projection image to generate an X-ray CT image.

  Further, the back projection unit 204 generates a projection image from each X-ray image data after the filtering process. Next, the back projection unit 204 corrects the spatial displacement amount between the X-ray source and the X-ray detector based on the spatial displacement amount correction information for the projection image. Then, the back projection unit 204 may generate an X-ray CT image by performing a back projection operation on the corrected projection image.

(Geometric parameter calculation means 300)
The geometric parameter calculation unit 300 is a unit that calculates a geometric parameter required when the reconstruction unit 200 performs image reconstruction. The geometric parameters handled by the geometric parameter calculation means 300 are image distortions caused by the rotation orbital plane 30, the rotation center axis 31, and the X-ray image intensifier 12i. In order to calculate these geometric parameters, the geometric parameter calculation means 300 includes an image distortion correction table generation means 320, an image distortion correction table storage means 330, a rotation center axis projection position determination means 350, a spatial displacement amount. Correction information generation means 380 and spatial displacement correction information storage means 390 are provided. Each component of the geometric parameter calculation means 300 will be described later.

  The image distortion correction table generation means 320 generates an image distortion correction table used by the above-described image distortion correction means 202 using the hall chart 18 shown in FIG. The hole chart 18 of FIG. 2 is formed by drilling a number of small holes 18h in a lattice arrangement on a plate material formed of a material that easily absorbs X-rays. In order to generate the image distortion correction table, first, the hole chart 18 is fixed to the X-ray incident surface of the X-ray image intensifier 12i, and an X-ray transmission image of the hole chart 18 (hereinafter referred to as “hole chart distortion projection image”). Shoot.) Next, preprocessing means 201 preprocesses the whole chart distortion projection image. Then, the projection position of each hole 18h in the hall chart distortion projection image is detected. Next, the virtual projection position of each hole 18h is calculated assuming that the hole chart 18 is projected onto the X-ray incident surface without distortion. Then, a calculation for converting the detected projection position of each hole 18h so as to coincide with the virtual projection position is performed for each hole 18h, and an image distortion correction table is generated. In the case of FPD, the detector mounting angle is corrected by image rotation.

  The image distortion correction table storage unit 330 stores the image distortion correction table generated by the image distortion correction table generation unit 320 on a magnetic disk or the like. When the image distortion correction unit 202 corrects the distortion of the X-ray transmission image, the stored image distortion correction table is read out. In the case of FPD, the detector mounting correction angle is stored. In the case of FPD, this correction angle is read when correcting the rotation of the X-ray transmission image.

  As shown in FIGS. 3 and 4, the cone beam X-ray CT apparatus 1 takes an X-ray transmission image (hereinafter referred to as “phantom projection image”) 35 of an index body, for example, a wire phantom 50, and phantom X-rays. Output image data.

  The rotation center axis projection position determining means 350 determines a rotation center axis projection parameter which is a reference for forming a three-dimensional X-ray CT image of the phantom projection image 35 based on the phantom X-ray image data. A method by which the rotation center axis projection position determination unit 350 determines the rotation center axis projection parameter will be described later.

  The spatial displacement correction information generating unit 380 calculates the spatial displacement amount of the X-ray source 11-2D X-ray detector 12 generated for each projection angle. Then, the image reconstruction calculation is performed on the phantom X-ray image data using the rotation center axis projection parameter determined by the rotation center axis projection position determining unit 350, and the reconstructed cross section of the wire phantom 50 obtained as a result is obtained. Spatial displacement correction information for forming an image (hereinafter referred to as “wire reconstructed cross-sectional image”) at one point is generated.

  The spatial displacement correction information storage unit 390 stores the spatial displacement correction information generated by the spatial displacement correction information generation unit 380 on a magnetic disk or the like. When the back projection unit 204 adjusts the spatial displacement amount of the X-ray source 11-2D X-ray detector 12 to correct the X-ray image data, the stored spatial displacement amount correction information is read.

  A specification example of the C-arm type cone beam X-ray CT apparatus 1 is as follows. The distance between the X-ray tube 11t and the rotation center axis 31 is 800 mm, and the distance between the rotation center axis 31 and the X-ray incident surface of the two-dimensional X-ray detector 12, that is, the X-ray incident surface of the X-ray image intensifier 12i is The size of the X-ray incident surface of the 400 mm X-ray image intensifier 12i is a circle of 400 mm, and the image size is 1024 × 1024 (the number of scanning lines). The pitch of the two-dimensional X-ray detector 12 is 0.4 mm. The imaging system rotation control means 101 passes through the two-dimensional X-ray detector 12 from the left hand direction (−100 °) of the subject 40 to the ceiling direction (0 °), and the right hand direction (+ 100 °) of the subject 40. That is, by moving the X-ray tube 11t from the right hand direction (+ 100 °) of the subject 40 through the ceiling direction (0 °) to the left hand direction (−100 °) of the subject 40, 200 A two-dimensional X-ray transmission image of the subject 40 is taken over a projection angle of degrees. A typical example of the rotational speed of the C-arm 13 is 40 degrees per second, and the scan time is 5 seconds.

  Next, an outline of operations in imaging by the C-arm type cone beam X-ray CT apparatus 1 of the present embodiment will be described.

  First, the imaging system rotation control means 101 starts the propeller rotation of the C-arm 13. After the rotation acceleration period, the X-ray irradiation control means 103 irradiates the X-ray tube 11t with X-rays. The detection system control means 105 starts capturing a visible light image by the television camera 12c. The X-ray irradiated from the X-ray tube 11t passes through the subject 40 and then enters the X-ray image intensifier 12i. The X-ray transmission image is converted into a visible light image by the X-ray image intensifier 12i and is taken into the television camera 12c. The television camera 12c converts a visible light image into a video signal. The video signal undergoes A / D conversion, and is then recorded in the image collecting unit 110 as two-dimensional X-ray image data including a digital signal. The standard scanning mode for photographing by the television camera 12c is 30 frames per second and 1024 scanning lines. The rotation angle pitch is 1.33 degrees, and 150 X-ray transmission images are acquired in 5 seconds. When 200-degree rotation imaging is completed, the X-ray irradiation control unit 103 ends X-ray irradiation of the X-ray tube 11t, and the imaging system rotation control unit 101 stops rotating.

  The reconstruction unit 200 reads the two-dimensional X-ray image data from the image collection unit 110 in parallel with the above-described imaging or after the imaging is completed, performs an image reconstruction calculation based on the X-ray image data, Reconstruction calculation of a three-dimensional X-ray CT image of the specimen 40 is performed. The image display unit 210 displays a three-dimensional X-ray CT image on a display device 80 including a CRT device or a liquid crystal display device. Note that the image display unit 210 may display a two-dimensional image based on the two-dimensional X-ray image data recorded in the image collection unit 110.

  Next, the contents of processing in the geometric parameter calculation means 300 will be described with reference to FIGS. FIG. 3 is a conceptual diagram for explaining a state in which the wire phantom 50 is rotated and photographed. FIG. 4 is a conceptual diagram showing the state of FIG. 3 as viewed from the bed 17 toward the C-arm 13. FIG. 5 is a schematic diagram showing a phantom projection image 35 of the wire-like phantom 50 obtained as a result of the rotational shooting shown in FIGS. 3 and 4. FIG. 6 is a flowchart illustrating a procedure in which the geometric parameter calculation unit 300 performs a geometric parameter calculation process. Hereinafter, description will be made in the order of steps in FIG.

(Step S310)
The Hall chart 18 is fixed to the X-ray incident surface of the X-ray image intensifier 12i to perform rotational imaging, and the image collection means 110 collects a Hall chart distortion projection image at each projection angle (S310). In the case of this embodiment, the number of hall chart distortion projection images to be collected is 150 as described above.

(Step S320)
The image distortion correction table generation unit 320 generates an image distortion correction table based on the 150 hole chart distortion projection images obtained in step S310.

(Step S330)
The image distortion correction table storage unit 330 stores the image distortion correction table generated in step S320 (S330).

(Step S340)
The wire phantom 50 is photographed (S340). As shown in FIG. 3, the phantom holder 50 a is placed on the bed 17. And the phantom holding body 50a makes the wire-like phantom 50 project from the bed 17 at a position as close as possible to the rotation center axis 31, as shown in FIGS. Then, the X-ray source 11 and the two-dimensional X-ray detector 12 perform rotational imaging of the wire phantom 50, take an X-ray transmission image of the wire phantom 50, and output phantom X-ray image data. The X-ray transmission image of the wire phantom 50 includes a phantom projection image 35 that is a projection image of the wire phantom 50. The image collecting unit 110 collects phantom X-ray image data (S340). As shown in FIG. 5, the phantom projection image 35 is displayed at a position close to the projection 33 on the X-ray incident surface of the rotation center axis 31 at all projection angles. When shooting of the wire phantom 50 is completed, the wire phantom 50 and the wire phantom holder 50a are removed from the bed 17.

(Step S350)
The rotation center axis projection position determining means 350 uses the phantom projection image 35 included in the phantom X-ray image data collected in step S340 and rotates it as a reference for forming a three-dimensional X-ray CT image. A central axis projection parameter is determined (S350). Details of specific processing of the calculation will be described later with reference to FIGS. In the following processing, it is sufficient to perform processing using phantom X-ray image data limited to the rotating orbital plane (midplane) 30. By doing so, the amount of calculation can be reduced.

(Step S360)
Using the wire reconstructed image 53 output when obtaining the rotation center axis projection parameter in step S350, the target wire reconstructed point is one point with the highest contrast (hereinafter referred to as “reference wire reconstructed image”). Secure to. Hereinafter, processing related to correcting the spatial displacement amount of the X-ray source 11-2D X-ray detector 12 generated at each projection angle so as to form an image on the reference wire reconstruction image 56a is performed.

(Step S370)
Based on the phantom X-ray image data collected in step S340, the projection position 52 of the wire-like phantom 50 is estimated for each phantom projection image 35, and the coordinate (u) in the left-right direction and the coordinate in the body axis direction are estimated. The u-coordinate of the intersection point of the straight line represented by the value of (v) or the straight line representing the projection position 52 and the rotary orbital plane 30 is obtained (S370). Here, as a method for estimating the projection position 52 in the phantom projection image 35, a projection data profile is taken in the u-axis direction, and adjacent to the u-axis direction in order to prevent errors due to the minimum value or mixing of defective data. There are methods such as obtaining from the second-order differentiation of several image values and assigning the minimum value. Furthermore, the same processing can be performed on a plurality of lines parallel to the u-axis direction, and the estimation accuracy of the projection position 52 in the phantom projection image 35 can be increased. The wire projection position 52 obtained here is used to generate spatial displacement correction information in the next step S380.

(Step S380)
The reconstructed cross section of the wire phantom 50 reconstructed by correcting the spatial displacement amount of the X-ray source 11-2D X-ray detector 12 generated for each projection angle and reconstructing using the rotation center axis projection parameter obtained in step S350. Spatial displacement correction information for forming an image at one point is generated (S380). Details of the specific processing of the calculation will be described later with reference to FIGS.

(Step S390)
The spatial displacement correction information calculated in step S380 is stored in the spatial displacement correction information storage means 390 (S390). The spatial displacement correction information stored in the spatial displacement correction information storage means 390 is obtained by correcting the spatial displacement of the X-ray source 11-2D X-ray detector 12 generated at each projection angle in the back projection means 204. This is used to form a reconstructed cross-sectional image of the wire phantom 50 at one point.

  Next, the details of the rotation center axis projection position determining unit 350 and the spatial displacement correction information generating unit 380 including the features of the present invention will be described with reference to FIGS. 7 and 8 are conceptual diagrams showing how the wire reconstructed image 53 is formed by adjusting the rotation center axis projection parameter, and FIG. 9 is a rotation center axis projection position in the rotation center axis projection position determining means 350. FIG. 10 is a conceptual diagram illustrating a wire reconstructed cross-sectional image obtained as a result of the rotation center axis projection position determination process.

  First, the wire reconstruction image 53 obtained when the initial position of the rotation center shaft 31 is different will be described with reference to FIGS. 7 and 8. 7 and 8 are viewed from the foot direction of the subject 40. For simplicity, only the X-ray image intensifier 12i and the television camera 12c are shown, and the others are omitted. The X-ray image intensifier 12 i and the television camera 12 c move from the direction of the left hand of the subject 40 to the direction of the right hand of the subject 40 through the direction of the ceiling.

FIG. 7 shows the result of image reconstruction processing when the projection of the rotation center axis 31 on the two-dimensional X-ray detector 12 has an error in the + u direction with reference to the actual wire projection position 52 (solid line). . In this case, the reconstructed cross-sectional image 54 of the wire phantom 50 does not form an image at one point, but draws a semicircular arc opened on the right side as shown in FIG. On the other hand, FIG. 8 shows that the projection of the rotation center axis 31 on the two-dimensional X-ray detector 12 shows the actual wire projection position 52 (solid line). The result of image reconstruction processing when there is an error in the -u direction as a reference is shown. In this case, the reconstructed cross-sectional image 55 does not form a single point, but draws a semicircular arc opened on the left side, and its radius is the correct position of the projection position (geometrically correct wire projection position 51: dotted line). Is equal to the deviation from

  The reconstructed cross-sectional images 54 and 55 shown in FIGS. 7 and 8 are composed of a plurality of semicircles. In addition to the shift of the rotation center axis projection position, the X-ray source 11 described later is used for each X-ray image data. This is because it is drawn assuming that there is a spatial displacement amount of the two-dimensional X-ray detector 12.

  Next, a procedure in which the rotation center axis projection position determination unit 350 determines the rotation center axis projection position will be described in detail with reference to FIG.

(Step S351)
A rotation center axis projection position (hereinafter referred to as center) is set as an initial position (design position) (S351).

(Step S352)
The preprocessing unit 201 performs preprocessing of the phantom X-ray image data collected in step S340 (S352).

(Step S353)
The image distortion correction unit 202 performs an image distortion correction process on the phantom X-ray image data that has been pre-processed in step S352 (S353).

(Step S354)
The filtering unit 203 performs a filtering process on the phantom X-ray image data that has been subjected to the image distortion correction process in step S353 (S354).

(Step S355)
The back projection unit 204 performs back projection processing on the phantom X-ray image data subjected to the filtering processing in step S354 with the rotation center axis projection position (center) value, and generates a wire reconstructed image 53 (S355). .

(Step S356)
A wire region is extracted from the wire reconstructed image 53 generated in step S355, and the radius of the arc having the highest contrast is calculated (S356). Here, for example, a threshold processing method is used to extract the wire region, and a parameter fitting method to a circular curve equation can be used to calculate the radius of the arc.

(Step S357)
It is determined whether the arc radius calculated in step S356 can be regarded as zero (S357). If it can be regarded as zero, the current center value is output and the process ends. If it cannot be regarded as zero, the process proceeds to step S358.

(Step S358)
When the radius of the arc cannot be regarded as zero in step S357, it is determined whether it is the case of FIG. 7 or FIG. 8, and correction is performed by adding / subtracting so that the center value is correct accordingly. Then, the process from step S355 is performed again.

  FIG. 10 shows the wire reconstruction image 53 after the rotation center axis projection position determination process (step S350). FIG. 10 shows that the wire reconstructed cross-sectional image 56 is formed at three positions because the spatial displacement of the X-ray source 11-2D X-ray detector 12 to be corrected remains. The figure localized at several points like the wire reconstructed cross-sectional image 56 is schematic and actually forms an image roughly, but when the wire reconstructed image 53 is enlarged, a straight line is drawn in the projection angle direction. In many cases, it becomes a figure that is drawn.

  Therefore, in step S360 described above, the wire reconstruction point having the highest contrast among the plurality of wire reconstruction points displayed in FIG. 10 is fixed to the reference wire reconstruction image 56a. Hereinafter, based on FIGS. 11 to 13, a process for obtaining the wire reconstruction image 56a of FIG. 13 by matching the other wire reconstruction points with the reference wire reconstruction image 56a will be described. FIG. 11 is a flowchart showing a procedure by which the spatial displacement correction information generating unit 380 generates the spatial displacement correction information. FIG. 12 is a conceptual diagram for explaining the geometric calculation for generating the spatial displacement correction information. Hereinafter, description will be made in the order of steps in FIG.

(Step S381)
A projection angle β corresponding to the wire projection position 52 calculated in step S370 is set (S381).
(Step S382)
The coordinates (x, y) of the reference wire reconstruction image 56a fixed in step S360 are converted into the coordinates of the rotational coordinate system (s, t) in the projection angle β direction set in step S381 (S382).

(Step S383)
The theoretical projection position 51 on the two-dimensional X-ray detector 12 is calculated from the coordinate value (s) calculated in step S382 (S383).

(Step S384)
The actual wire projection position 52 calculated in step S370 is compared with the theoretical projection position 51 calculated in step S383, the displacement amount 65 is calculated, and a spatial displacement correction value is output (S384).

(Step S385)
It is determined whether or not all projection angles β have been processed. Otherwise, the processing from step S381 is repeated for the next projection angle β.

  FIG. 13 shows a wire reconstructed cross-sectional image 57 obtained as a result of three-dimensional reconstruction of the projection image 35 of the wire phantom 50 using the spatial displacement correction information stored in step S390. When the spatial displacement of the X-ray source 11-2D X-ray detector 12 generated at each projection angle of the C-type arm 13 is reproducible (this is common because of the mechanical characteristics of the C-type arm). Then, the image is formed on the wire reconstructed cross-sectional image fixed in step S360. When the spatial displacement amount of the X-ray source 11-2D X-ray detector 12 generated at each projection angle of the C-arm 13 is reproducible, once the spatial displacement correction information is generated, any subject 40 can be obtained. Even in this case, the three-dimensional X-ray CT image can be formed.

  In this embodiment, a phantom made of wire is used to adjust the geometric parameters. After step S390, the rotation determined in step S350 is performed while visually confirming that the metal artifact is uniform. The center axis projection position can be further finely adjusted manually.

<Second embodiment>
The second embodiment is a mode in which the wire line and the subject 40 are imaged simultaneously in the first embodiment described above.
In addition to the X-ray CT apparatus 1 according to the first embodiment, the cone beam X-ray CT apparatus 1a according to the second embodiment includes an alignment reconstruction unit 400 that aligns the wire 70, and Wire extraction means 410 is provided.

  FIG. 15 is a conceptual diagram showing a state in which a high-contrast wire wire 70 is fixed to the back surface of the bed 17.

  The second embodiment provides an embodiment for aligning a three-dimensional X-ray CT image when the subject 40 is rotated and imaged while the C-arm 13 repeatedly rotates. . The spatial positions of the C-arm 13 and the bed 17 can be roughly adjusted by referring to the display value of the cone beam X-ray CT apparatus 1, but there is not enough accuracy to superimpose as a three-dimensional X-ray CT image. Is normal. In such a case, the position of the wire line 70 is extracted from the X-ray image data of the subject 40 including the wire line 70 with high contrast by the same method as in the first embodiment described above, and the wire line 3D reconstruction while generating spatial displacement correction information of the X-ray source 11-2D X-ray detector 12 during the image reconstruction calculation so that the position 70 is backprojected to the target reconstruction point I do.

(Step S400)
Next, the flow of processing of the X-ray CT apparatus 1a according to the second embodiment will be described based on the flowchart of FIG. FIG. 17 is a flowchart showing a detailed process of the wire extraction process which is one process shown in FIG.

(Step S201)
First, pre-processing S201 pre-processes X-ray transmission images of a plurality of subjects 40 obtained by repeated imaging on the X-ray absorption coefficient distribution images of the subject 40, bed 17 and wire wire 70. .

(Step S202)
Next, the image distortion correction process S202 corrects the image distortion of the X-ray absorption coefficient distribution image of the subject 40, the bed 17 and the wire wire 70.

(Step S410)
The wire extraction process S410 divides the X-ray absorption coefficient distribution image of the subject 40, the bed 17 and the wire wire 70 into two regions of the wire wire 70 and the subject 40, and then extracts wire projection data. Hereinafter, based on FIG. 17, the detail of wire extraction process S410 is demonstrated.

(Step S411)
As shown in FIG. 15, since the wire line 70 is fixed to the bed 17, the projection position in the X-ray transmission image of the wire line 70 can be roughly predicted for each projection angle direction. Therefore, the wire existence range cutout process S411 cuts out a range where the X-ray transmission image of the wire line 70 exists from the X-ray absorption coefficient distribution image of the wire line 70 whose image distortion has been corrected by the image distortion correction process S202. .

(Step S412)
The blurred image generation process S412 performs a smoothing filter process on the distribution image of the X-ray absorption coefficient of the wire 70 cut out in the wire existence range cutout process S411, and generates the blurred image.

(Step S413)
The difference process S413 performs a subtraction process on the distribution image of the X-ray absorption coefficient of the wire line 70 and the blur image generated in the blur image generation process S412 to extract a candidate image of a thin structure such as a wire line. To do.

(Step S414)
The binarization process S414 performs a binarization process using a predetermined threshold process on the fine structure candidate image extracted in the difference process S413. A candidate image of a fine structure having a contrast equal to or higher than a predetermined threshold is extracted as wire projection data.

(Step S415)
The wire area storage process S415 stores the wire projection data extracted in the binarization process S414.

(Step S300)
The geometric parameter calculation process S300, based on the wire projection data extracted by the wire region extraction process S410, calculates the spatial displacement correction information of the X-ray source 11-2D X-ray detector 12 as in the first embodiment. Generate.
After generating the spatial displacement correction information, the wire projection area included in the X-ray transmission image of the subject 40 may be removed using the wire data extracted in the wire area storing process S415.

(Step S203)
The filtering process S203 performs a filtering process on the X-ray transmission image of the subject 40 in which the image distortion of the X-ray absorption coefficient distribution image is corrected by the image distortion correction process S202.

(Step S204)
The backprojection process S204 performs a backprojection process based on the spatial displacement correction information generated by the geometric parameter calculation process S300 on the X-ray transmission image subjected to the filtering process in the filtering process S203, so that the subject 40 A three-dimensional X-ray CT image is generated.

  The first embodiment is based on the premise that the amount of spatial displacement of the X-ray source 11-2D X-ray detector 12 is reproducible. In the second embodiment, the X-ray of the subject 40 is used. Since the wire line 70 serving as a reference for alignment is reflected in the transmission image, a three-dimensional X-ray CT image can be formed even if the spatial displacement is not reproducible.

  In addition, according to the second embodiment, it becomes possible to superimpose a three-dimensional X-ray CT image generated by a plurality of rotational imaging without any difference on the basis of the wire line 70, and before and after surgery. Comparison, changes over time from the contrast agent injection timing, diagnosis of the relationship between blood vessels (communication, short circuit), etc. when contrasted blood vessels are selectively changed, or diastole when applied to lung diagnosis Comparison diagnosis with systole becomes possible.

  In the second embodiment, the high-contrast wire wire 70 is used as an alignment index body. Instead of adding the wire wire 70, a thin groove is dug in the back of the patient bed, and the thin wire wire 70 is added. It is also possible to align using the groove as a phantom. Moreover, it may replace with a wire wire and may use the phantom which consists of a microsphere.

<Third embodiment>
In the third embodiment, the above-described second embodiment is applied to digital subtraction (hereinafter referred to as “DSA”) imaging. DSA imaging is a three-dimensional image of a contrasted blood vessel obtained by imaging a rotation image (hereinafter referred to as “mask image”) before injection of a contrast agent and a rotation image (hereinafter referred to as “live image”) at the time of injection of a contrast agent. This is a method for calculating a standard X-ray CT image.

  A cone beam X-ray CT apparatus 1b according to the present embodiment will be described with reference to FIG. The cone beam X-ray CT apparatus 1b in FIG. 18 is an alignment DSA in which the reconstruction means 200 of the cone beam X-ray CT apparatus 1 in FIG. Reconstruction means 500, wire extraction means 410, and difference means 540 for subtracting mask data from live data.

  Next, a processing flow of the cone beam X-ray CT apparatus 1b according to the present embodiment will be described.

  The cone beam X-ray CT apparatus 1b obtains a set of X-ray image data (a plurality of projection images for obtaining one reconstructed image) by photographing the subject before injecting the contrast agent. The cone beam X-ray CT apparatus 1b performs respective processes on the X-ray image data by the preprocessing unit 201, the image distortion correction unit 202, the filtering unit 203, and the back projection unit 204 in the same manner as in the first embodiment, and a mask image. Is generated. The back projection unit 204 acquires the spatial displacement amount correction information from the spatial displacement amount correction information storage unit 390, corrects the spatial displacement amount between the X-ray source and the X-ray detector, and generates a mask image. Similarly, the cone beam X-ray CT apparatus 1b captures a subject after injecting a contrast agent to obtain a set of X-ray image data, and generates a live image based on the set of X-ray image data. . The cone beam X-ray CT apparatus 1b aligns the mask image and the live image based on the respective spatial displacement correction information, and then performs a differential process to generate a DSA image.

  Hereinafter, based on the flowchart of FIG. 19 thru | or FIG. 20, the flow of a process of the X-ray CT apparatus 1b concerning 3rd Embodiment is demonstrated. In the third embodiment, the mask image and the live image are photographed together with the wire lines 70 while the subject is placed on the bed. The relative positional relationship between the wire 70 and the subject remains unchanged in the mask image and the live image unless the subject moves. Therefore, by generating a mask image and a live image so that the wire line 70 forms an image at a single point, as a result, the subject imaged in the mask image and the subject imaged in the live image can be aligned. It becomes possible to perform DSA processing. Hereinafter, a first example and a second example of the present embodiment will be described. In the first embodiment, DSA processing is performed on a mask image (reconstructed image) and a live image (reconstructed image) configured using projection data of the wire 70. In the second embodiment, DSA processing is performed on projection data of a mask image and live image projection data captured in the same view, and a contrast image (blood vessel image) is generated based on the difference data.

(Step S500)
First, an alignment DSA reconstruction process S500, which is a first example of the third embodiment, will be described with reference to the flowchart of FIG.

(Step S501)
First, pre-processing S501 of mask X-ray image data pre-processes the X-ray absorption coefficient distribution image of the subject 40, the bed 17 and the wire wire 70 on the mask X-ray transmission image of the subject 40.

(Step S502)
Next, the image distortion correction processing S502 of the mask X-ray image data corrects the image distortion of the mask X-ray transmission image of the subject 40 and the distribution image of the X-ray absorption coefficient of the bed 17 and the wire wire 70.

(Step S410m)
In the wire extraction process S410m of the mask X-ray image data, the mask X-ray transmission image of the subject 40, the distribution image of the X-ray absorption coefficients of the bed 17 and the wire wire 70 are divided into two regions of the wire line 70 and the subject 40. After dividing, wire projection data is extracted.

(Step S300m)
The geometric parameter calculation processing S300m of the mask X-ray image data is based on the wire projection data at the time of mask imaging extracted by the wire region extraction processing S410m, as in the first embodiment. Spatial displacement correction information for the line detector 12 is generated.

(Step S511)
First, pre-processing S511 of live X-ray image data pre-processes the X-ray absorption coefficient distribution images of the subject 40, the bed 17 and the wire wire 70 on the live X-ray transmission image of the subject 40.

(Step S512)
Next, the image distortion correction processing S512 of the live X-ray image data corrects the image distortion of the live X-ray transmission image of the subject 40 and the distribution image of the X-ray absorption coefficient of the bed 17 and the wire wire 70.

(Step S410L)
The wire extraction process S410L of the live X-ray image data converts the live X-ray transmission image of the subject 40 and the distribution images of the X-ray absorption coefficients of the bed 17 and the wire wire 70 into two regions of the wire line 70 and the subject 40. After dividing, wire projection data is extracted.

(Step S300L)
The geometric parameter calculation process S300L of the live X-ray image data is based on the wire projection data at the time of live imaging extracted by the wire region extraction process S410m, as in the first embodiment. Spatial displacement correction information for the line detector 12 is generated.

(Step S521)
The mask X-ray image data filtering process S521 performs a filtering process on the mask X-ray transmission image of the subject 40 in which the image distortion of the X-ray absorption coefficient distribution image is corrected by the image distortion correction process S502.

(Step S522)
The mask X-ray image data backprojection process S522 performs a backprojection process based on the spatial displacement correction information generated by the geometric parameter calculation process S300m on the mask X-ray transmission image subjected to the filtering process in the filtering process S521. Then, a mask three-dimensional X-ray CT image of the subject 40 is generated.

(Step S531)
The live X-ray image data filtering process S531 performs a filtering process on the live X-ray transmission image of the subject 40 in which the image distortion of the X-ray absorption coefficient distribution image is corrected by the image distortion correction process S512.

(Step S532)
The live X-ray image data backprojection process S532 performs a backprojection process based on the spatial displacement correction information generated by the geometric parameter calculation process S300L on the live X-ray transmission image subjected to the filtering process in the filtering process S531. And a live three-dimensional X-ray CT image of the subject 40 is generated.

(Step S533)
The live CT image-mask CT image difference processing S533 is performed by performing mask X-ray image data back projection processing S522 from a live three-dimensional X-ray CT image of the subject 40 generated by live X-ray image data back projection processing S532. The generated mask three-dimensional X-ray CT image of the subject 40 is subtracted to generate a three-dimensional DSA reconstructed image (angiogram) of the subject 40.

(Step S500a)
Next, an alignment DSA reconstruction process S500a, which is a second example of the third embodiment, will be described with reference to the flowchart of FIG. Steps S501 to S300L are the same as those in the first embodiment described above, and a description thereof will be omitted.

(Step S541)
In the mask-live geometric system comparison process S541, the spatial displacement correction information at the time of mask imaging calculated in the geometric parameter calculation process S300m of the mask X-ray image data is converted into the geometric parameter calculation process S300L of the live X-ray image data. Generates relative spatial displacement correction information to align the mask X-ray image data with the live X-ray image data on the projection data, compared to the calculated spatial displacement correction information during live imaging To do.

(Step S542)
In the mask X-ray image data translation processing S542, the mask X-ray image data is converted into a live X-ray image on the projection data based on the relative spatial displacement correction information generated in the mask-live geometric system comparison processing S541. The translation is performed so as to overlap the data.

(Step S543)
The live image-mask image difference process S543 subtracts the mask X-ray image data aligned on the projection data by the mask X-ray image data translation process S542 from the live X-ray image data.

(Step S551)
The difference image data filtering process S551 performs a filtering process on the difference projection data generated by the live image-mask image difference process S543.

(Step S552)
In the difference image data backprojection processing S552, the difference projection data subjected to the filtering processing in the filtering processing S551 is subjected to backprojection processing based on the spatial displacement amount correction information generated by the geometric parameter calculation processing S300L. A live three-dimensional DSA reconstructed image (angiogram) of the specimen 40 is generated.
In the second embodiment S500a, a live image-mask image is subtracted on the projection data and then backprojection processing is performed to generate a three-dimensional DSA reconstructed image of the subject 40. Compared to S500, there is an advantage that the calculation time can be greatly shortened.
On the other hand, since the mask X-ray image data translation in step S542 is an approximation of a three-dimensional spatial displacement on two-dimensional projection data, it is not a three-dimensional perfect alignment. Note that in step S542 of the above operation, the alignment is limited to the alignment by parallel movement, but by adding rotation processing or deformation processing by translation different for each local coordinate, the alignment with three-dimensional magnification correction is added. It is also possible to do it.
Since the calculation time and the three-dimensional perfect alignment are a trade-off, it is one method to enable selection of the first embodiment S500 and the second embodiment S500a according to various cases. .

<Fourth embodiment>
The fourth embodiment is an embodiment in which the present invention is applied to an X-ray CT apparatus provided with an X-ray detector comprising a flat panel detector (FPD), which is a C-arm type cone beam X-ray CT apparatus. . Below with reference to FIG. 21, it described the embodiment. FIG. 21 is a block diagram showing a schematic configuration of the X-ray CT apparatus according to the present embodiment.

In the cone beam X-ray CT apparatus 1c of FIG. 21, the same components as those of the cone beam X-ray CT apparatus 1 of FIG.

Cone-beam X-ray CT apparatus 1c is provided with a two-dimensional X-ray detector 12 with a FPD device 12 f. The shape of the FPD 12 f may be any shape that is circular or square. The two-dimensional X-ray detector 12 is installed such that its detector element array is parallel (0 °) or 90 ° to the rotation center axis 31. For example, when a rectangular flat panel detector (FPD) is used as the two-dimensional X-ray detector 12, if the long side is installed at an angle of 90 ° with the central axis of rotation, a cross-sectional image of a large field of view such as the chest and abdomen can be obtained. It is suitable for photographing, and it is useful for photographing the head and neck, limbs, etc. if the long side is installed at an angle parallel to the rotation center axis (0 °). The two-dimensional X-ray detector 12 may be configured such that its detector element array can be rotated manually or electrically by a predetermined reference angle with respect to the rotation center axis 31.

In cone-beam X-ray CT apparatus 1c with a FPD device 12 f, as geometrical parameters, likewise rotating raceway surface and the cone-beam X-ray CT apparatus 1 in FIG. 1 (midplane) 30, the rotation center shaft 31, and the center of rotation In addition to these, there is also a deviation from the reference angle (0 ° or 90 °) of the detector mounting angle. When a flat panel detector (FPD) is used as the two-dimensional X-ray detector 12, there is no image distortion, but in this case, the two-dimensional X-ray detector 12 is installed in parallel with the rotation center axis 31 without any errors. There is no deviation from the reference angle (0 ° or 90 °) of the detector mounting angle described above. When the FPD is used, it is necessary to correct this detector mounting angle shift by image rotation means as image distortion correction.

Therefore, the cone-beam X-ray CT apparatus 1c in Fig. 21, instead of the image distortion correcting unit 202 of FIG. 1, for correcting the deviation from the reference angle of the detector mounting angle of the FPD device 12 f (0 ° or 90 °) The inclination angle correction information is acquired from the inclination angle correction information storage means 330a and the inclination angle correction information storage means 330a for storing the inclination angle correction information, and the X-ray image data output from the two-dimensional X-ray detector 12 is obtained. An inclination angle correction unit 202a for correction is provided. The inclination angle correction unit 202a reads the correction angle when correcting the rotation of the X-ray image data. The geometric parameter calculation means 300 calculates the rotation track surface 30, the rotation center axis 31, and the detector mounting angle.

  When a flat panel detector (FPD) is used as the two-dimensional X-ray detector 12, the X-ray incident surface has a rectangular shape of 400 mm × 300 mm, the image size is 2048 × 1536, and the pixel pitch is 0. .2 mm.

  When a flat panel detector (FPD) is used, it is first converted into light by a light emitter such as CsI on the X-ray incident surface, and the optical signal is converted into electric charge by a photodiode. The accumulated charge is converted into a digital signal by a TFT element at a constant frame rate and read out. In the rotational imaging mode, two-dimensional X-ray image data is read at 30 frames per second and an image size of 1024 × 768. An X-ray CT image is reconstructed based on the two-dimensional X-ray image data. Other configurations are the same as those of the cone beam X-ray CT apparatus 1 of FIG. Thus, the second and third embodiments have been described based on the cone beam X-ray CT apparatus 1 of the first embodiment, but can be similarly implemented by the cone beam X-ray CT apparatus 1c described in the fourth embodiment. is there.

  In the cone beam X-ray CT apparatus 1 that generates and displays a three-dimensional X-ray CT image by the geometric parameter calculation means 300 described above, the positional relationship between the X-ray source 11 and the two-dimensional X-ray detector 12 is displaced. In this case, the back projection unit 204 can correct the geometric parameter for generating a clear three-dimensional X-ray CT image, the projection position of the rotation center axis, and the amount of spatial displacement. In the cone beam X-ray CT apparatus that generates a three-dimensional X-ray CT image from the two-dimensional X-ray image by installing the geometric parameter calculation means, the positions of the X-ray source and the two-dimensional X-ray detector Even when the relationship is displaced, a clear three-dimensional X-ray CT image can be generated and displayed. As a result, contrast imaging of the head, abdomen, and the like, and diagnostic performance in the field of shaping of the teeth, jaws, lumbar vertebrae, and limbs can be improved.

  In addition, this invention is not limited to the said embodiment, It can deform | transform variously in the range which does not deviate from the summary of this invention. For example, in the above-described embodiment, the C-arm type cone beam X-ray CT apparatus is used. However, the present invention can also be applied to a cone-beam X-ray CT apparatus other than the C-type arm type. Further, the present invention can also be applied to a case where the total angle of rotational shooting is other than 200 degrees.

  The present invention is not limited to a process of generating a medical image based on X-ray transmission data obtained by imaging a subject, and all X-ray CT apparatuses in which the spatial positions of an X-ray source and an X-ray detector are displaced. Can be applied to.

Claims (20)

An X-ray source for irradiating the subject with X-rays;
An X-ray detector disposed opposite to the X-ray source, detecting the X-ray transmitted through the subject and outputting X-ray image data of the subject;
Rotating means for rotating the X-ray source and the X-ray detector for each predetermined projection angle;
The index body X-ray image data generated by photographing the index body arranged in the vicinity of the rotation center axis of the rotational movement while rotating at every predetermined projection angle is set to the rotation center axis projection position that is initially set. Index body image reconstruction means for performing back projection processing using the indicated value and generating an index body reconstruction image;
An area where the index body is imaged is extracted from the index body reconstructed image, and a value indicating the initial rotation center axis projection position is set so that the area matches the theoretical shape of the index body. A rotation center axis projection position determining means to be corrected;
Of the index object reconstructed image reconstructed using the value indicating the corrected rotation center axis projection position, a region having the highest contrast is set as a reference index object reconstructed image, and the index object reconstructed image is the reference object reconstructed image. A space for correcting the amount of spatial displacement for each projection angle in the rotation orbit plane perpendicular to the rotation center axis of the X-ray source and the X-ray detector so as to form an index body reconstructed image. Spatial displacement correction information generating means for generating displacement correction information;
The spatial displacement amount included in the X-ray image data for each predetermined projection angle of the subject is corrected using the spatial displacement correction information for the projection angle of the X-ray image data, and the corrected X-ray image Image reconstruction means for performing back projection processing using data and generating an X-ray CT image of the subject;
Display means for displaying an X-ray CT image of the subject;
An X-ray CT apparatus comprising: The indicator body is an indicator body having a circular cross-sectional shape orthogonal to the rotation center axis,
The rotation center axis projection position determining means is initialized so that the radius of the arc with the highest contrast becomes 0 in the area where the index body extracted from the index body reconstruction image is captured. Correct by adding or subtracting the value indicating the rotation center axis projection position,
The X-ray CT apparatus according to claim 1. The spatial displacement correction information generating means corrects a displacement amount between a position where the index body is projected on the X-ray detector and a position where the reference index body reconstructed image is projected at each projection angle. Generating the spatial displacement correction information;
The X-ray CT apparatus according to claim 2 . The indicator is a wire extending parallel to the rotation center axis, or a thin groove parallel to the rotation center axis carved on the back of a bed positioned between the X-ray source and the X-ray detector. ,
The X-ray CT apparatus according to any one of claims 1 to 3 . An alignment unit configured to perform alignment using an X-ray image data portion corresponding to the index body among a plurality of sets of X-ray image data;
The X-ray CT apparatus according to claim 1, wherein The alignment means extracts an X-ray image data portion corresponding to the index body from each X-ray image data, and detects a position where the difference between the X-ray image data portions corresponding to the index body is the smallest. Align with
The X-ray CT apparatus according to claim 5 . A difference unit that generates a difference image obtained by subtracting the two images;
The X-ray detector is configured to inject mask X-ray image data obtained by imaging a blood vessel and the index body of the subject before the contrast agent is injected into the blood vessel of the subject, and the contrast agent. And outputting live X-ray image data obtained by imaging the blood vessel of the subject and the index body,
The alignment means includes a projected image of the index body included in the mask projection image based on the mask X-ray image data photographed at the same projection angle, and an index body projection included in the live projection image based on the live X-ray image data. Alignment based on the image,
The difference means is subjected to difference processing between the mask projection image and the live projection image that are photographed at the same projection angle and aligned, to generate a difference projection image for each projection angle, and the image reconstruction means includes: Reconstruct a contrast-enhanced blood vessel image by reconstructing differential projection images at all projection angles ;
The X-ray CT apparatus according to claim 6 . Positioning means for aligning two reconstructed images in which the index body is imaged based on an area in which the index body is imaged,
Difference means for generating a difference image obtained by subtracting two images, and
The image reconstruction means includes a cross section of the index body based on mask X-ray image data obtained by imaging the blood vessels and the index body of the subject before the contrast medium is injected into the blood vessels of the subject. the so focused on one point with reconstructing a mask image, the subject of the blood vessel and the index body based on a live X-ray image data obtained by photographing the index body after the contrast agent has been injected The live image is reconstructed by forming the cross section of
The alignment means aligns the mask image and the live image with reference to a cross section of the index body included in each ,
The difference means generates a contrast-enhanced blood vessel image by differentially processing the mask image and the live image after alignment ,
The X-ray CT apparatus according to claim 1, wherein Inclination angle correction information storage means for storing inclination angle correction information for correcting a deviation from a reference angle of the detector mounting angle of the X-ray detector;
Tilt angle correction means for correcting X-ray image data of the subject based on the tilt angle correction information,
The X-ray detector uses a flat panel detector,
The inclination angle correction information storage means stores inclination angle correction information for correcting a deviation of the mounting angle of the flat panel detector from a reference angle.
The X-ray CT apparatus according to claim 1, wherein Index body X-ray image data generated by photographing an index body arranged in the vicinity of the rotation center axis of the rotational movement of the X-ray source and the X-ray detector while rotating at predetermined projection angles, An index body image reconstruction step for performing a back projection process using a value indicating the initially set rotation center axis projection position and generating an index body reconstruction image;
An area where the index body is imaged is extracted from the index body reconstructed image, and a value indicating the initial rotation center axis projection position is set so that the area matches the theoretical shape of the index body. A rotation center axis projection position determination step to be corrected;
Of the index object reconstructed image reconstructed using the value indicating the corrected rotation center axis projection position, a region having the highest contrast is set as a reference index object reconstructed image, and the index object reconstructed image is the reference object reconstructed image. A space for correcting the amount of spatial displacement for each projection angle in the rotation orbit plane perpendicular to the rotation center axis of the X-ray source and the X-ray detector so as to form an index body reconstructed image. A spatial displacement correction information generating step for generating displacement correction information;
A reading step of reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus;
The displacement amount included in the X-ray image data for each predetermined projection angle of the subject is corrected using the spatial displacement correction information with respect to the projection angle of the X-ray image data, and the corrected X-ray image data is obtained. An image reconstruction step for performing back projection processing based on the generated X-ray CT image of the subject;
A display step for displaying the X-ray CT image;
An image processing program for causing a computer to execute. The indicator body is an indicator body having a circular cross-sectional shape orthogonal to the rotation center axis,
In the rotation center axis projection position determination step, the initial setting is performed such that the radius of the arc having the highest contrast is 0 in the region where the index body extracted from the index body reconstruction image is captured. Correct by adding or subtracting the value indicating the rotation center axis projection position,
The image processing program according to claim 10. In the spatial displacement amount correction information generation step, the displacement amount between the position where the index body is projected on the X-ray detector and the position where the reference index body reconstruction image is projected is corrected at each projection angle. Generating the spatial displacement correction information;
The image processing program according to claim 11 , wherein: An alignment step of aligning the plurality of X-ray image data;
In the reading step, a plurality of sets of X-ray image data are read,
In the alignment step, alignment is performed using an X-ray image data portion corresponding to the index body between the plurality of sets of X-ray image data .
13. The image processing program according to claim 10 , wherein the image processing program is any one of claims 10 to 12. In the alignment step, an X-ray image data portion corresponding to the index body is extracted from each X-ray image data, and a position where the difference between the X-ray image data portions corresponding to the index body is minimized is detected. Align with
The image processing program according to claim 13. A difference step for generating a difference image obtained by subtracting the two images;
In the reading step, the mask X-ray image data obtained by imaging the blood vessel and the index body of the subject before the contrast agent is injected into the blood vessel of the subject, and after the contrast agent is injected Read live X-ray image data obtained by imaging the blood vessel of the subject and the index body,
In the alignment step, the projected image of the index object included in the mask projection image based on the mask X-ray image data photographed at the same projection angle and the index object projection included in the live projection image based on the live X-ray image data Alignment based on the image,
In the difference step, a differential projection image is generated by performing a differential process on the mask projection image and the live projection image that are photographed at the same projection angle and aligned,
In the image reconstruction step, a contrasted blood vessel image is reconstructed by reconstructing differential projection images at all projection angles.
The image processing program according to claim 14. An alignment step of aligning two reconstructed images in which the index body is imaged based on an area in which the index body is imaged;
A difference step for generating a difference image obtained by subtracting the two images; and
In the image reconstruction step, a cross section of the index body based on mask X-ray image data obtained by imaging the blood vessel and the index body of the subject before the contrast medium is injected into the blood vessel of the subject The index body is reconstructed on the basis of live X-ray image data obtained by imaging the blood vessel and the index body of the subject after the contrast agent is injected. The live image is reconstructed by forming the cross section of
In the alignment step, the mask image and the live image are aligned based on a cross section of the index body included in each,
In the difference step, a differential blood vessel image is generated by performing a differential process on the mask image after the alignment and the live image,
13. The image processing program according to claim 10, wherein the image processing program is any one of claims 10 to 12. A tilt angle correcting step of correcting the X-ray image data of the subject based on tilt angle correction information for correcting a deviation from a reference angle of a detector mounting angle of the X-ray detector;
The X-ray detector uses a flat panel detector,
In the inclination angle correction step, a deviation from a reference angle of the mounting angle of the flat panel detector is corrected,
The image processing program according to claim 10, wherein the image processing program is any one of claims 10 to 16. Index body X-ray image data generated by photographing an index body arranged in the vicinity of the rotation center axis of the rotational movement of the X-ray source and the X-ray detector while rotating at predetermined projection angles, An index body image reconstruction step for performing a back projection process using a value indicating the initially set rotation center axis projection position and generating an index body reconstruction image;
An area where the index body is imaged is extracted from the index body reconstructed image, and a value indicating the initial rotation center axis projection position is set so that the area matches the theoretical shape of the index body. A rotation center axis projection position determination step to be corrected;
Of the index object reconstructed image reconstructed using the value indicating the corrected rotation center axis projection position, a region having the highest contrast is set as a reference index object reconstructed image, and the index object reconstructed image is the reference object reconstructed image. A space for correcting the amount of spatial displacement for each projection angle in the rotation orbit plane perpendicular to the rotation center axis of the X-ray source and the X-ray detector so as to form an index body reconstructed image. A spatial displacement correction information generating step for generating displacement correction information;
A reading step of reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus;
The displacement amount included in the X-ray image data for each predetermined projection angle of the subject is corrected using the spatial displacement correction information with respect to the projection angle of the X-ray image data, and the corrected X-ray image data is obtained. An image reconstruction step for performing back projection processing based on the generated X-ray CT image of the subject;
A display step for displaying the X-ray CT image;
An image processing method comprising: An alignment step of aligning the plurality of X-ray image data;
In the reading step, a plurality of sets of X-ray image data are read,
In the alignment step, alignment is performed using an X-ray image data portion corresponding to the index body between the plurality of sets of X-ray image data .
The image processing method according to claim 18. A difference step for generating a difference image obtained by subtracting the two images;
In the reading step, the mask X-ray image data obtained by imaging the blood vessel and the index body of the subject before the contrast agent is injected into the blood vessel of the subject, and after the contrast agent is injected Reading live X-ray image data obtained by imaging the blood vessel of the subject and the index body,
In the alignment step, the mask projection image based on the mask X-ray image data photographed at the same projection angle and the live projection image based on the live X-ray image data are aligned based on the index object projection image,
In the difference step, a differential projection image is generated by performing a differential process on the mask projection image and the live projection image that are photographed at the same projection angle and aligned,
In the image reconstruction step, a contrasted blood vessel image is reconstructed by reconstructing differential projection images at all projection angles.
The image processing method according to claim 19.

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