WO2006028085A1

WO2006028085A1 - X-ray ct device, image processing program, and image processing method

Info

Publication number: WO2006028085A1
Application number: PCT/JP2005/016326
Authority: WO
Inventors: Masakazu Okabe; Ken Ueda
Original assignee: Hitachi Medical Corporation
Priority date: 2004-09-09
Filing date: 2005-09-06
Publication date: 2006-03-16
Also published as: JPWO2006028085A1; JP5019879B2

Abstract

An X-ray CT device includes: an X-ray source for irradiating X-rays to an examinee; an X-ray detector arranged to oppose to the X-ray source for detecting X-rays which have transmitted through the examinee and outputting X-ray image data on the examinee; rotation means for rotating the X-ray source and the X-ray detector by a predetermined angle; spatial displacement amount correction information generation means for calculating a displacement amount of the spatial position of the X-ray source and the X-ray detector and generating spatial displacement amount correction information for subjecting the X-ray image data to the position correction based on the displacement amount; and image reconfiguration means for performing position correction of the X-ray image data according to the spatial displacement amount correction information, performing image reconfiguration calculation according to the X-ray image data after the position correction, and generating the X-ray CT image of the examinee.

Description

Specification

X-ray CT apparatus, image processing program, and image processing method

Technical field

[0001] 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 under 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.

Background art

[0002] A conventional cone beam X-ray CT apparatus includes an X-ray source that irradiates a subject with X-radiating X-rays, an imaging unit that is disposed opposite to the X-ray source and that transmits a transmitted X-ray intensity image transmitted through the subject; An imaging system comprising: a rotating means for rotating the imaging system around the subject; a reconstructing means for reconstructing a reconstructed image of the subject from the transmitted X-ray intensity image; and a transmission X-ray through the rotation center axis of the imaging system Rotation center axis projection position setting means for changing the rotation center axis projection position, which is the position projected on the intensity image, and reconstruction using the rotation center axis projection position set by the rotation center axis projection position setting means Based on the contrast of the reconstructed image obtained, the rotation center axis projection position of the imaging system is estimated, and the reconstructed image force reconstructed at the estimated rotation center axis projection position. And X-ray 3D image is generated, and the X-ray tomogram or Show Z and X-ray 3-dimensional image. (For example, Patent Document 1)

In the above Patent Document 1, the projection position of the rotation center axis of the imaging system is estimated on the premise that the spatial position of the X-ray source two-dimensional X-ray detector is not displaced.

Patent Document 1: JP 2000-201918 A.

Disclosure of the invention

Problems to be solved by the invention

[0003] However, in Patent Document 1 described above, an X-ray CT apparatus in which the spatial position of an X-ray source—two-dimensional X-ray detector is displaced by the influence of gravity or centrifugal force (for example, A method to accurately form a three-dimensional X-ray CT image on a C-arm X-ray CT system) It is not considered.

An object of the present invention is to form a three-dimensional X-ray CT image even on an X-ray CT apparatus in which the spatial position of the X-ray source two-dimensional X-ray detector is displaced by rotation. Is to provide a reliable X-ray CT system.

Means for solving the problem

[0005] The X-ray CT apparatus of the present invention includes an X-ray source that irradiates a subject with X-rays, and an X-ray source that is disposed so as to face the X-ray source and that has passed through the subject to detect the X-ray. An X-ray detector that outputs X-ray image data of a subject; a rotating means that rotates and moves the X-ray source and the X-ray detector at predetermined angles; and A spatial displacement amount for calculating a displacement amount of a spatial position of the X-ray source and the X-ray detector and generating spatial displacement correction information for correcting the position of the X-ray image data based on the displacement amount. Based on the correction information generation means and the spatial displacement correction information, the position of the X-ray image data is corrected, the image reconstruction calculation is performed based on the corrected X-ray image data, and the subject And an image reconstruction means for generating an X-ray CT image.

[0006] The image processing program according to the present invention includes an X-ray source provided in an X-ray CT apparatus and the X-ray source generated when the X-ray detector is rotated at a predetermined angle. Calculates the displacement amount of the spatial position of the line detector and generates spatial displacement correction information for correcting the position based on the displacement amount for the X-ray image data acquired by the X-ray CT device force A spatial displacement correction information generating step, a reading step of reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus, and the X-ray image based on the spatial displacement correction information V Correct the position of the data and perform image reconstruction based on the X-ray image data! Image reconstruction step to generate the X-ray CT image of the subject and display the X-ray C τ image And causing the computer to execute a display step.

[0007] The image processing method according to the present invention includes the X-ray source and the X-ray generated when the X-ray source and the X-ray detector provided in an X-ray CT apparatus are rotated at predetermined angles. The displacement amount of the spatial position of the line detector is calculated, and spatial displacement amount correction information for correcting the position based on the displacement amount with respect to the X-ray image data acquired from the X-ray CT apparatus is generated. Spatial displacement correction information generation step and X obtained by imaging the subject by the X-ray CT apparatus Based on the reading step to read line image data and the spatial displacement correction information! The position of the X-ray image data is corrected and the X-ray image data is used! The method includes an image reconstruction step for performing an image reconstruction operation and generating an X-ray CT image of the subject, and a display step for displaying the X-ray CT image.

The invention's effect

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 two-dimensional X-ray detector is displaced.

Brief Description of Drawings

FIG. 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. 2 is a conceptual diagram showing a Hall chart 18 used for generating an image distortion correction table.

[Figure 3] A wire phantom 50 is placed on the bed 17 using the phantom holder 50a.

It is a conceptual diagram for demonstrating the state imaged by rotation.

FIG. 4 is a conceptual diagram showing a state where the phantom of FIG. 3 is placed on a bed.

[Figure 5] Phantom projection image of 50 wire-like phantoms collected by 2D X-ray detector 12

FIG.

FIG. 6 is a flowchart showing a procedure in which geometric parameter calculation means 300 in the embodiment of the present invention performs a geometric parameter calculation process.

FIG. 7 is a diagram showing a wire reconstructed cross-sectional image when the projection of the rotation center axis has an error in the + u direction.

FIG. 8 is a diagram showing a wire reconstructed cross-sectional image when the projection of the rotation center axis has an error in the u direction.

FIG. 9 is a flowchart showing a procedure in which a rotation center axis projection position determining unit 350 determines a rotation center axis projection position.

FIG. 10 is a schematic diagram showing a cross-sectional image of a wire reconstruction when a spatial displacement of the X-ray source—two-dimensional X-ray detector remains.

[Fig. 11] Spatial displacement correction information generating means 380 for generating spatial displacement correction information It is a flowchart which shows.

[12] It is a conceptual diagram for explaining the geometric calculation for generating the spatial displacement correction information.

[13] Rotation center axis projection position and X-ray source—This is a schematic diagram showing a state where the correction of the spatial displacement of the two-dimensional X-ray detector has been completed and an image is formed on the wire reconstruction cross-sectional image force ^ point.

[14] FIG. 14 is a block diagram for explaining a second embodiment of the present invention.

15] A conceptual diagram for explaining a second embodiment of the present invention, showing a state where the wire wire 70 is fixed to the back surface of the bed 17 with high contrast.

16) A flowchart showing a procedure for the alignment reconstruction means 400 in the second embodiment of the present invention to perform alignment reconstruction processing.

FIG. 17 is a flowchart showing a detailed procedure of wire extraction processing, which is one processing shown in FIG.

FIG. 18 is a C-arm type cone beam X-ray CT apparatus lb to which the present invention is applied.

It is a block diagram which shows schematic structure of the cone beam X-ray CT apparatus lb applied to SA. 19] FIG. 19 is a first flowchart showing a procedure in which the alignment DSA reconstruction means 500 in the third embodiment of the present invention performs alignment DSA reconstruction processing.

20] FIG. 20 is a second flowchart showing a procedure in which the alignment DSA reconstruction means 500 in the third embodiment of the present invention performs alignment DSA reconstruction processing.

FIG. 21 is a C-arm type cone beam X-ray CT apparatus lc to which the present invention is applied.

FIG. 2 is a block diagram showing a schematic configuration of a cone beam X-ray CT apparatus 1 c equipped with a two-dimensional X-ray detector using PD. Explanation of symbols

1 ··· Cone beam X-ray CT device, 10 ··· Radioscope, 11 ··· X-ray source, llt to X-ray tube, 11c ··· Collimator, 12 ··· 2D 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 ··· Bed, 18 ··· Hall chart, 18h… Hall, 20 ··· Control operation unit, 30 ··· Rotating raceway surface (midplane), 31 ··· Rotational center axis, 32 ··· · · · Rotation center, 33 · · · projection of the rotation axis to the X-ray entrance plane, 35 · · · phantom projection image, 40 ... Subject, 50 ... Wire phantom, 50a ... Phantom holder, 51 ... Geometrically correct wire projection position, 52 ... Shifted wire projection position, 53 ... Wire reconstruction image, 54 ... Wire reconstruction cross-sectional image when the rotation center axis projection has an error in the + u direction, 55 ... Wire reconstruction cross-section image when the projection of the rotation center axis has an error in the u direction, 56 to X-ray source 11 — Wire reconstruction cross-sectional image when spatial displacement of 2D X-ray detector 12 remains, 56a… Reference wire reconstruction image, 57 ··· Reconstruction cross-sectional image after fixing the wire reconstruction point, 65 · ··· Displacement amount 70 ··· High-contrast wire arranged on the back of the patient bed · · · Display device · 90 · Input device · 100 · Imaging unit control means · 101 · Imaging system rotation control means · 102 · Imaging System position control means, 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 ... 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 generation means, 390 ... Spatial displacement correction information storage means, 400 ... Alignment reconstruction means, 410 ··· Wire extraction means, 500 ··· Alignment DSA reconstruction means, 540 ... Difference means

BEST MODE FOR CARRYING OUT THE INVENTION

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.

FIG. 1 is a C-arm type cone-beam X-ray CT apparatus 1 to which the present invention is applied, and includes an X-ray image intensifier 12i and a television camera that captures a visible light image by the X-ray image intensifier 12i. FIG. 12 is a block diagram showing a schematic configuration of an X-ray CT apparatus having an X-ray detector consisting 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 in FIGS. 1 and la is an imaging unit that irradiates a subject 40 with X-rays and captures an X-ray transmission image of the subject 40 to obtain X-ray image data. 10 and each component of the imaging unit 10, and based on the X-ray image data, 3D X-ray C of the subject 40 And a control operation unit 20 for reconstructing the T image. Further, the display device 80 includes an image display device 80 and an input device 90 that also has a trackball and a mouse force for inputting an instruction to move the position of the image displayed on the display device 80.

[0013] (shooting unit 10)

The imaging unit 10 is installed at a position facing the X-ray source 11, the bed 17 on which the subject 40 is placed, the X-ray source 11 that irradiates the subject 40 placed on the bed 17, and 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-arm 13 that mechanically connects the X-ray source 1 1 and the two-dimensional X-ray detector 12 Is provided. 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 shown in FIG. And a ceiling rail 16 that is movably supported in the two-dimensional direction.

[0014] The X-ray source 11 includes an X-ray tube lit that generates X-rays, and a collimator 11c that controls the direction of X-ray irradiation from the X-ray tube lit in a circular or quadrangular pyramid shape.

[0015] 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. Is provided. The X-ray CT apparatus and the two-dimensional X-ray detector 12 shown in FIG. 1 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 May be replaced with a flat panel detector (FPD) using TFT elements.

[0016] When imaging the subject 40, the C-type arm 13 rotates about the rotation center axis 31 for each predetermined projection angle. 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, the rotational movement of the C-arm 13 causes a rotational 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 The rotation center 32 is an intersection of the rotation center axis 31 and the rotation track surface 30.

[0017] In principle, these geometric parameters are determined from the design data of the photographing unit 10, but in practice, due to production errors of the photographing unit 10 and deformation of members, individual cone beams X Value specific to line CT system 1.

[0018] (Control arithmetic unit 20)

The control calculation unit 20 includes an imaging unit control unit 100 that controls the imaging unit 10, an image collection unit 110 that collects and stores the X-ray image data output from the imaging unit 10, and the acquired X-ray image data. Next, the reconstruction means 200 for reconstructing a three-dimensional X-ray CT image and the mechanical manufacturing error of the imaging unit 10 are numerically expressed, and correction data is obtained when the reconstruction means 200 performs three-dimensional reconstruction. And a geometric parameter calculation means 300 for obtaining a geometric parameter to be used. Furthermore, an image display means 210 for displaying the three-dimensional X-ray CT image generated by the reconstruction means 200 is provided.

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

[0020] (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 unit 201 is a unit for converting the X-ray image data collected by the image collection unit 110 into a distribution image of X-ray absorption coefficients. In the present embodiment, first, natural logarithmic conversion calculation 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, a distribution image of the X-ray absorption coefficients of the subject 40 and the bed 17 is obtained.

[0022] The image distortion correction unit 202 is a method for calculating the distribution image of the X-ray absorption coefficient generated by the preprocessing unit 201. Correct image distortion. This image distortion is image distortion that occurs when an X-ray transmission image is converted into a visible light image by the X-ray image intensifier 12i, and is stored in the image distortion correction table storage means 330 described later. Using the table, the image distortion of the X-ray absorption coefficient distribution image obtained by the preprocessing means 201 is corrected.

[0023] The filtering means 203 performs filtering processing in X-ray CT image reconstruction.

[0024] The back projection means 204 performs a back projection operation based on the filtered X-ray image data, and generates a three-dimensional X-ray CT image. Back projection means 204 detects the X-ray source and X-ray detection based on the spatial displacement correction information for each X-ray image data after filtering (X-ray image data obtained by photographing each projection angular force)! Correct the amount of spatial displacement with the vessel. Next, the back projection means 204 generates a projection image based on each X-ray image data. Then, the back projection means 204 generates an X-ray CT image by performing a back projection operation on this projection image.

[0025] Further, the back projection means 204 generates a projection image from each X-ray image data after the filtering process. Next, the back projection means 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 this projection image. Then, the back projection means 204 may generate an X-ray CT image by performing a back projection operation on the corrected projection image.

[0026] (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 the image distortion caused by the rotation orbit plane 30, the rotation center axis 31, and the X-ray image intensifier eye 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. An amount correction information generation unit 380 and a spatial displacement amount correction information storage unit 390 are provided. Each component of the geometric parameter calculation means 300 will be described later.

The image distortion correction table generating unit 320 generates an image distortion correction table used by the above-described image distortion correcting unit 202 using the hall chart 18 shown in FIG. The hole chart 18 in FIG. 2 is formed by drilling a number of small holes 18h in a lattice arrangement on a plate made of a material that easily absorbs X-rays. To generate an image distortion correction table First, the Hall 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 Hall chart 18 (hereinafter referred to as “Hall chart distortion projection image”) is taken. 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 Hall chart 18 is projected onto the X-ray incident surface without distortion. Then, 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 rotating the image.

[0028] The image distortion correction table storage means 330 stores the image distortion correction table generated by the image distortion correction table generation means 320 on a magnetic disk or the like. Then, 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, save the detector mounting correction angle. In the case of FPD, this correction angle is read when correcting the rotation of the X-ray transmission image.

[0029] As shown in FIGS. 3 and 4, the cone beam X-ray CT apparatus 1 is an X-ray transmission image (hereinafter referred to as “phantom projection image”!) Of an index body, for example, a wire phantom 50. , And output phantom X-ray image data.

[0030] The rotation center axis projection position determining means 350 is based on the phantom X-ray image data, and serves as a rotation center axis projection meter serving as a reference for forming a three-dimensional X-ray CT image of the phantom projection image 35. To decide. The method by which the rotation center axis projection position determining means 350 determines the rotation center axis projection parameters will be described later.

The spatial displacement correction information generating unit 380 calculates the spatial displacement 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 parameters determined by the rotation center axis projection position determining means 350, and the resulting wire phantom 50 is reconstructed. Spatial displacement correction information is generated to form the sectioned image (hereinafter referred to as “wire reconstructed cross-sectional image”) at one point.

[0032] The spatial displacement correction information storage means 390 is generated by the spatial displacement correction information generation means 380. The generated spatial displacement correction information is stored in a magnetic disk or the like. Then, when the back projection means 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 out.

[0033] The specification example of the C-arm type cone beam X-ray CT apparatus 1 is as follows. The distance between the X-ray tube l it 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 1 2, that is, the X-ray image intensifier 12i The distance is 400mm, the X-ray image intensifier 12i has a circular X-ray entrance surface size of 400mm, and the image size is 1024 X 1024 (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 the 2D X-ray detector 12 from the left hand direction of the subject 40 (one 100 °) to the ceiling direction (0 °), and to the right hand direction of the subject 40 (+ 100 °), that is, the X-ray tube l it passes from the right hand direction of the subject 40 (+ 100 °) to the ceiling direction (0 °) and to the left hand direction of the subject 40 (one 100 °). By moving, a two-dimensional X-ray transmission image of the subject 40 is taken over a projection angle of 200 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 an operation 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 propeller rotation of the C-arm 13. After the rotation acceleration period, the X-ray irradiation control means 103 irradiates the X-ray tube l it with X-rays. The detection system control means 105 starts taking a visible light image by the television camera 12c. The X-ray irradiated with the X-ray tube l it force 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 captured by the television camera 12c. The television camera 12c converts a visible light image into a video signal, and the video signal undergoes AZD conversion, and then is recorded in the image collecting means 110 as two-dimensional X-ray image data such as a digital signal. The standard scanning mode for shooting with the TV 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 the 200-degree rotation imaging is completed, the X-ray irradiation control means 103 ends the X-ray irradiation of the X-ray tube lit, and the imaging system rotation control means 10 1 stops rotating.

[0036] 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, and performs image reconstruction based on the X-ray image data Calculation is performed to reconstruct the 3D X-ray CT image of the subject 40. The image display means 210 displays a three-dimensional X-ray CT image on a display device 80 composed of a CRT device, a liquid crystal display device, or the like. 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 a state where the state of FIG. 3 is 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. FIG. 6 is a flowchart showing a procedure in which the geometric parameter calculation means 300 performs a geometric parameter calculation process. Hereinafter, description will be made in the order of steps in FIG.

[0038] (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.

[0039] (Step S320)

The image distortion correction table generating means 320 generates an image distortion correction table based on the 150 Hall chart distortion projection images obtained in step S310.

[0040] (Step S330)

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

[0041] (Step S340)

Shoot the wire phantom 50 (S340). As shown in FIG. 3, the phantom holder 50a is placed on the bed 17. The phantom holder 50a is shown in FIGS. Similarly, the wire-like phantom 50 is positioned so as to protrude from the bed 17 as close as possible to the rotation center axis 31. 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 means 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.

[0042] (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 serves as a reference for imaging a three-dimensional X-ray CT image. The rotation center axis projection parameter is determined (S350). Details of the specific processing of the calculation will be described later with reference to FIGS. In the following process, it is sufficient to perform the process using the phantom X-ray image data limited to the rotation path plane (mitd plane) 30, and this can reduce the amount of calculation.

[0043] (Step S360)

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

[0044] (Step S370)

Based on the phantom X-ray image data collected in step S340, the projection position 52 of the wire phantom 50 is estimated for each phantom projection image 35, and the left and right coordinates (u) and the body axis direction are estimated. There is a straight line with coordinates (V)!ヽ finds the u coordinate of the intersection of the straight line representing the projection position 52 and the rotating orbital plane 30 (S370). Here, as a method for estimating the projection position 52 in the phantom projection image 35, the projection data profile in the u-axis direction is used. There is a method that takes an aisle, finds the minimum value, or obtains the second-order differential force of several image values adjacent in the U-axis direction, and assigns the minimum value to prevent errors due to mixing of bad data. Furthermore, the same processing can be performed with 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.

[0045] (Step S380)

X-ray source generated at each projection angle 11-Reconstruction of wire phantom 50 reconstructed by correcting the spatial displacement of the two-dimensional X-ray detector 12 and using the rotation center axis projection parameters obtained in step S350 Spatial displacement correction information is generated to form a cross-sectional image at one point (S380). Details of the specific processing of the calculation will be described later with reference to FIGS.

[0046] (Step S390)

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

Next, details of the rotation center axis projection position determining means 350 and the spatial displacement amount correction information generating means 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 in the rotation center axis projection position determining means 350. A flowchart of the projection position determination process (step S350), FIG. 10 is a conceptual diagram showing a wire reconstruction cross-sectional image obtained as a result of the rotation center axis projection position determination process.

First, a 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. FIG. 7 and 8 also show the force in the foot direction of the subject 40. For simplicity, only the X-ray image intensifier 12i and the TV camera 12c are shown, and the others are omitted. The X-ray image intensifier 12i and the television camera 12c pass from the direction of the left hand of the subject 40 to the direction of the ceiling and pass from the direction of the right hand of the subject 40. Move with.

[0049] Fig. 7 shows the image reconstruction process 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). The results are shown. In this case, the reconstructed cross-sectional image 54 of the wire-like phantom 50 does not form a single point, but draws a semicircular arc opened on the right side as shown in FIG. The position (geometrically positive U, wire projection position 51: dotted line) is equal to the displacement of force. On the other hand, Fig. 8 shows that the projection of the rotation center axis 31 on the two-dimensional X-ray detector 12 is the actual wire projection position. The result of image reconstruction when there is an error in the u direction with reference to 52 (solid line) is shown. In this case, the reconstructed cross-sectional image 55 does not form a single point, but draws a semicircular arc that opens to the left, and its radius is the correct position of the projection position (geometrically correct wire projection position 51: dotted line). ) It becomes equal to the shift of force.

[0050] The reconstructed cross-sectional images 54 and 55 shown in FIGS. 7 and 8 are forces that also have a plurality of semicircular forces. This is because the source 11 is drawn assuming that there is a spatial displacement of the two-dimensional X-ray detector 12.

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

[0052] (Step S351)

The rotation center axis projection position (hereinafter referred to as center) is set to the initial position (design position) (S 351).

[0053] (Step S352)

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

[0054] (Step S353)

The image distortion correction unit 202 performs image distortion correction processing on the phantom X-ray image data that has been preprocessed in step S352 (S353).

[0055] (Step S354)

The filtering means 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). [0056] (Step S355)

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

[0057] (Step S356)

A wire region is extracted from the wire reconstructed image 53 generated in step S355, and the radius of the arc with 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.

[0058] (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 is terminated. If it cannot be regarded as zero, the process proceeds to step S358.

[0059] (Step S358)

If 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 a wire reconstructed image 53 after the rotation center axis projection position determination process (step S350). FIG. 10 shows that the wire reconstruction cross-sectional image 56 is imaged at three positions because the spatial displacement of the X-ray source 11—two-dimensional 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 appears in the projection angle direction. In many cases, it will be drawn.

Therefore, in step S360 described above, of the plurality of wire reconstruction points displayed in FIG. 10, the wire reconstruction point having the highest contrast is fixed to the reference wire reconstruction image 56a. 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 below with reference to FIGS. FIG. 11 shows that the spatial displacement correction information generation means 380 generates spatial displacement correction information. It is a flowchart which shows the procedure to perform. FIG. 12 is a conceptual diagram for explaining the geometric calculation for generating the spatial displacement correction information. This will be described below in the order of steps in FIG.

[0062] (Step S381)

The projection angle 13 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 13 direction set in step S381 (S382).

[0063] (Step S383)

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

[0064] (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 65 is calculated, and the spatial displacement correction value is output (S384).

[0065] (Step S385)

It is determined whether or not the force has been processed for all projection angles j8. Otherwise, the processing from step S381 is repeated for the next projection angle j8.

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. X-ray source generated at each projection angle of C-type arm 13-When the spatial displacement of 2D X-ray detector 12 is reproducible (This is common because of the mechanical characteristics of C-type arm ) To the wire reconstructed cross-sectional image fixed in step S360. X-ray source generated at each projection angle of the C-arm 13 11—When the spatial displacement of the two-dimensional X-ray detector 12 is reproducible, any object can be obtained as long as the spatial displacement correction information is generated. Even in the case of 40, the 3D X-ray CT image can be formed.

[0067] In the present embodiment, a phantom made of wire is used for adjusting the geometric parameters. After step S390, it is possible to manually fine-tune the rotation center axis projection position determined in step S350 while visually confirming that the metal arch features are equalized.

[0068] <Second embodiment>

The second embodiment is a mode in which the wire line and the subject 40 are simultaneously imaged in the first embodiment described above.

The cone beam X-ray CT apparatus la that works well in the second embodiment is an alignment reconfiguration that aligns the wire 70 in addition to the X-ray CT apparatus 1 that works in the first embodiment. Means 400 and wire extraction means 410 are provided.

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

[0070] The second embodiment is an implementation for aligning a three-dimensional X-ray CT image when the subject 40 is rotated while the C-arm 13 is repeatedly rotated. Provide form. The spatial position 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 device 1.There is not enough precision 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 The spatial displacement correction information of the X-ray source 11—2D X-ray detector 12 is generated during the image reconstruction calculation so that the position of the line 70 is backprojected to the target reconstruction point. Make the configuration.

[0071] (Step S400)

Next, based on the flowchart of FIG. 16, the flow of processing of the X-ray CT apparatus 1a which is useful for the second embodiment will be described. FIG. 17 is a flowchart showing a detailed process of the wire extraction process which is one process shown in FIG.

[0072] (Step S 201)

First, pre-processing S201 pre-processes the X-ray absorption coefficient distribution images of the subject 40, the bed 17 and the wire wire 70 for the X-ray transmission images of the plurality of subjects 40 obtained by repeated imaging. . [0073] (Step S202)

Next, the image distortion correction processing 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.

[0074] (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, the details of the wire extraction processing S410 will be described with reference to FIG.

[0075] (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 cut-out process S411 cuts out the 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 is corrected by the image distortion correction process S202. .

[0076] (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 by the wire existence range cutout process S411, and generates the blurred image.

[0077] (Step S413)

Difference processing S413 performs bow I calculation processing of the distribution image of the X-ray absorption coefficient of the wire 70 and the blurred image generated by the blur image generation processing S412. Extract images.

[0078] (Step S414)

The binary key process S414 performs a binarization process by using a predetermined threshold process for the fine structure candidate image extracted in the difference process S413. A fine structure candidate image having a contrast equal to or greater than a predetermined threshold is extracted as wire projection data.

[0079] (Step S415)

Wire area storage processing S415 is the wire projection data extracted in binary key processing S414. Is stored.

[0080] (Step S 300)

The geometric parameter calculation process S300 is based on the wire projection data extracted by the wire region extraction process S410, and the spatial displacement correction information of the X-ray source 11—two-dimensional X-ray detector 12 is the same as in the first embodiment. Is generated.

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.

[0081] (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.

[0082] (Step S 204)

The back projection process S 204 performs a back projection process on the X-ray transmission image subjected to the filtering process in the filtering process S 203 based on the spatial displacement correction information generated by the geometric parameter calculation process S300. Then, a three-dimensional X-ray CT image of the subject 40 is generated.

[0083] In the first embodiment, the force based on the premise that the amount of spatial displacement of the X-ray source 11—two-dimensional X-ray detector 12 is reproducible. Since the wire wire 70, which is the alignment reference, is shown in the X-ray transmission image, even if the spatial displacement is not reproducible, it is possible to form a three-dimensional X-ray CT image.

[0084] In addition, according to the second embodiment, it is possible to superimpose a three-dimensional X-ray CT image generated by a plurality of rotational imaging without any difference in size with respect to the wire line 70, and preoperatively. 'Comparison after surgery, changes in contrast agent injection timing over time, contrasted blood vessels when selectively changing blood vessels (connection, short circuit), etc. Enables comparative diagnosis between diastolic and systolic phases.

[0085] In the second embodiment, instead of adding the force wire wire 70, a thin groove is formed on the back of the patient bed. It is also possible to dig and align the narrow grooves as phantoms. Moreover, it may replace with a wire wire and may use the phantom which also has microsphere power. [0086] <Third embodiment>

In the third embodiment, the second embodiment described above is applied to digital subtraction (hereinafter referred to as “DSA”) imaging. DSA imaging is a rotation image (hereinafter referred to as “mask image”) before injection of contrast agent and a rotation image (hereinafter referred to as “live image”) at the time of contrast agent injection. This is a method to calculate a dimensional X-ray CT image.

A cone beam X-ray CT apparatus lb according to the present embodiment will be described with reference to FIG. The cone beam X-ray CT apparatus lb in Fig. 18 is reconstructed by combining the mask and live imaging geometric systems in the reconstruction method 200 of the cone beam X-ray CT apparatus 1 in Fig. 1. Alignment DSA reconstruction means 500, wire extraction means 410, and difference means 540 for subtracting mask data from live data are provided.

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

The cone beam X-ray CT apparatus lb obtains a set of X-ray image data (a plurality of projection images for obtaining one reconstructed image) by imaging a subject before injecting a contrast agent. As in the first embodiment, the cone beam X-ray CT apparatus lb performs a process 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, and a mask image. Is generated. The back projection unit 204 acquires the spatial displacement correction information from the spatial displacement correction information storage unit 390, and corrects the spatial displacement between the X-ray source and the X-ray detector to generate a mask image. Similarly, the cone beam X-ray CT apparatus lb obtains a set of X-ray image data by photographing the subject after the contrast medium is injected, and performs live based on the X-ray image data set. Generate an image. The cone beam X-ray CT apparatus lb 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.

The processing flow of the X-ray CT apparatus lb according to the third embodiment will be described below based on the flowcharts of FIGS. 19 to 20. 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 line 70 and the subject remains unchanged in the mask image and the live image unless the subject moves. For this reason, a mask image and a live image are generated so that the wire 70 forms an image at a point, and as a result, the mask image is captured. It is possible to align the specimen and the subject photographed in the live image and perform DSA processing. Hereinafter, a first example and a second example of the present embodiment will be described. In the first embodiment, a mask image (reconstructed image) and a live image (reconstructed image) constructed using projection data of the wire 70 are subjected to DSA processing. In the second embodiment, DSA processing is performed on the projection data of the mask image and the projection data of the live image taken in the same view, and a contrast image (blood vessel image) is generated based on the difference data. It is processing.

[0091] (Step S 500)

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.

[0092] (Step S 501)

First, pre-processing of mask X-ray image data S501 performs pre-processing on the X-ray absorption coefficient distribution images of the subject 40, the bed 17 and the wire wire 70 for the mask X-ray transmission image of the subject 40.

[0093] (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, the X-ray absorption coefficient distribution image of the bed 17 and the wire wire 70.

[0094] (Step S410m)

Wire extraction processing of mask X-ray image data S410m is a mask X-ray transmission image of the subject 40, the X-ray absorption coefficient distribution image of the bed 17 and the wire wire 70, and two regions of the wire wire 70 and the subject 40. Then, wire projection data is extracted.

[0095] (Step S 300m)

Geometric parameter calculation processing for mask X-ray image data S300m is the same as in the first embodiment, based on the wire projection data extracted by wire region extraction processing S410m, as in the first embodiment. Spatial displacement correction information for detector 12 is generated.

[0096] (Step S511)

First, pre-processing S511 of live X-ray image data is applied to the live X-ray transmission image of the subject 40. And pre-process the X-ray absorption coefficient distribution images of the subject 40, bed 17 and wire 70.

[0097] (Step S 512)

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, the X-ray absorption coefficient distribution image of the bed 17 and the wire wire 70.

[0098] (Step S410L)

Wire extraction processing of live X-ray image data The S410L uses live X-ray transmission images of the subject 40, X-ray absorption coefficient distribution images of the bed 17 and the wire wire 70, and two regions of the wire wire 70 and the subject 40. Then, wire projection data is extracted.

[0099] (Step S300L)

Geometric parameter calculation processing of live X-ray image data S300L is the same as in the first embodiment based on the wire projection data extracted by wire region extraction processing S410m. Spatial displacement correction information for detector 12 is generated.

[0100] (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.

[0101] (Step S522)

The mask X-ray image data backprojection process S 522 is 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 S 521. Then, a back projection process is performed to generate a mask 3D X-ray CT image of the subject 40.

[0102] (Step S531)

Live X-ray image data filtering processing S 531 performs filtering processing on the live X-ray transmission image of the subject 40 corrected for image distortion in the distribution image of the X-ray absorption coefficient by image distortion correction processing S 512. . [0103] (Step S532)

The live X-ray image data backprojection processing S532 is based on the spatial displacement correction information generated by the geometric parameter calculation processing S300L to the live X-ray transmission image filtered in the filtering processing S531! A live 3D X-ray CT image of the subject 40 is generated by applying a back projection process.

[0104] (Step S 533)

Live CT image-mask CT image difference processing S533 is a back projection process of live X-ray image data S Back-projection process of mask X-ray image data from live 3D X-ray CT image of subject 40 generated by S532 S522 By subtracting the mask 3D X-ray CT image of the subject 40 generated by the above, a 3D DSA reconstructed image (angiogram) of the subject 40 is generated.

[0105] (Step S 500a)

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. Step S501 to step S300L are the same as those in the first embodiment described above, and a description thereof will be omitted.

[0106] (Step S 541)

Mask-live geometric system comparison process S541 is a geometric parameter calculation process for mask X-ray image data. The spatial displacement correction information at the time of mask imaging calculated by S300m is used to calculate geometric parameters for live X-ray image data. Relative spatial displacement correction information for aligning the mask X-ray image data with the live X-ray image data on the projection data compared to the spatial displacement correction information at the time of live shooting calculated by S300L Is generated.

[0107] (Step S542)

Mask X-ray image data translation processing S542 is a mask-live geometric system comparison process. Based on the relative spatial displacement correction information generated in S541, the mask X-ray image data is live on the projection data. The translation is performed so as to overlap the X-ray image data.

[0108] (Step S543)

Live image—mask image difference processing S543 is a mask X-ray image that is aligned on the projection data by live mask X-ray image data translation processing S542 from live X-ray image data. Subtract image data.

[0109] (Step S551)

Difference Image Data Filtering Processing S551 performs filtering processing on the difference projection data generated by the live image-mask image difference processing S543.

[0110] (Step S 552)

Difference image data backprojection processing S 552 is the backprojection processing based on the spatial displacement correction information generated by the geometric parameter calculation processing S300L to the difference projection data filtered in the filtering processing S551. To generate a live three-dimensional DSA reconstructed image (angiographic image) of the subject 40.

In the second embodiment S500a, the live image-mask image is subtracted on the projection data, and the back projection process is performed by force, so that the three-dimensional DSA reconstructed image of the subject 40 is generated. Compared to the embodiment 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 the three-dimensional spatial displacement on the two-dimensional projection data, it is not a three-dimensional perfect alignment. In step S542 in the above operation, it was limited to alignment by translation, but by adding deformation processing by rotation or translation that differs for each local coordinate,

It is also possible to perform alignment with a three-dimensional magnification correction.

There is a trade-off between calculation time and 3D perfect alignment, so it is possible to select the first embodiment S500 and the second embodiment S500a according to various cases. is there.

[0111] <Fourth embodiment>

The fourth embodiment is an implementation in which the present invention is applied to an X-ray CT apparatus provided with an X-ray detector such as a flat panel detector (FPD), which is a C-arm type cone-beam X-ray CT apparatus. It is an aspect. Hereinafter, the present embodiment will be described with reference to FIG. FIG. 19 is a block diagram showing a schematic configuration of the X-ray CT apparatus according to the present embodiment.

[0112] In the cone beam X-ray CT apparatus lc of FIG. 19, the same components as those of the cone beam X-ray CT apparatus 1 of FIG.

[0113] The cone beam X-ray CT apparatus lc includes a two-dimensional X-ray detector 12 including an FPD12F. The shape of the FPD12F may be any circular or square shape. 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 the large field of view such as the chest and abdomen It is useful for photographing the head and neck, limbs, etc. if the long side is set 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.

[0114] In the cone beam X-ray CT apparatus lc equipped with FPD12F, the geometric parameters are the same as the cone beam X-ray CT apparatus 1 in Fig. 1, the rotating orbital plane (mitsubrain) 30, the rotation center axis 31, and the rotation Forces with center 32 In addition to these, there is a deviation of the reference angle (0 ° or 90 °) of the detector mounting angle. When a flat panel detector (FPD) is used as the 2D X-ray detector 12, there is no image distortion, but in this case, the 2D X-ray detector 12 is parallel to the rotation center axis 31 without any errors. There is a deviation from the reference angle (0 ° or 90 °) of the detector mounting angle described above. When using FPD, it is necessary to correct the deviation of the detector mounting angle by image rotation means as an image distortion correction.

[0115] Therefore, the cone beam X-ray CT apparatus lc in Fig. 19 compensates for the deviation of the reference angle (0 ° or 90 °) of the detector mounting angle of the FPD12F instead of the image distortion correction means 202 in Fig. 1. The inclination angle correction information storage means 330a for storing the inclination angle correction information for correction and the inclination angle correction information from the inclination angle correction information storage means 330a are acquired, and the X output from the two-dimensional X-ray detector 12 is acquired. Tilt angle correction means 202a for correcting line image data is provided. The inclination angle correction unit 202a reads out 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.

[0116] When a flat panel detector (FPD) is used as the two-dimensional X-ray detector 12, the X-ray entrance surface has a rectangular shape of 400 mm X 300 mm, the image size is 2048 X 1536, and the pixels The pitch is 0.2mm. [0117] When a flat panel detector (FPD) is used, light is first converted into light by a light emitter such as Csl 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 fixed frame rate and read out. In the rotational imaging mode, 2D X-ray image data is read out at 30 frames per second with an image size of 1024 X 768. Based on this 2D X-ray image data, an X-ray CT image is reconstructed. Other configurations are the same as those of the cone beam X-ray CT apparatus 1 in FIG. Therefore, the second and third embodiments can be similarly implemented by the cone beam X-ray CT apparatus 1 c described in the fourth embodiment based on the cone beam X-ray CT apparatus 1 of the first embodiment. is there.

[0118] 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 X-ray source 11 and the two-dimensional X-ray detector 12 Even when the positional relationship is displaced, the back projection means 204 can correct the geometric parameters 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 addition, by installing a geometric parameter calculation means, the 2D X-ray image force can also be detected by a cone-beam X-ray CT system that generates a 3D X-ray CT image. A clear 3D X-ray CT image can be generated and displayed even when the positional relationship with the instrument is displaced. As a result, the imaging performance of the head, abdomen, and the like, and the diagnostic performance in the orthopedic field such as the tooth jaw, the lumbar vertebra, and the limbs can be improved.

Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, the above embodiment can be applied to a cone beam X-ray CT apparatus other than the force C-arm type using a C-type arm type cone beam X-ray CT apparatus. It can also be applied when the rotational angle is not 200 degrees.

Industrial applicability

[0120] The present invention is not limited to the process of generating a medical image based on X-ray transmission data obtained by imaging a subject, but the spatial position of the X-ray source and the X-ray detector is displaced. It can be applied to all line CT devices.

Claims

The scope of the claims

[1] An X-ray source that irradiates the subject with X-rays,

An X-ray detector that is disposed opposite to the X-ray source, detects the X-ray transmitted through the subject, and outputs X-ray image data of the subject;

Rotating means for rotating the X-ray source and the X-ray detector by a predetermined angle, and calculating a displacement amount of a spatial position of the X-ray source and the X-ray detector for each predetermined angle. Spatial displacement correction information generating means for generating spatial displacement correction information for correcting the position of the X-ray image data based on the displacement;

Based on the spatial displacement correction information, the position of the X-ray image data is corrected, the image reconstruction operation is performed based on the X-ray image data, and the X-ray CT image of the subject is generated. Image reconstruction means;

Display means for displaying the X-ray CT image;

An X-ray CT apparatus comprising:

[2] The image reconstruction means corrects the position of the X-ray image data based on the spatial displacement correction information, and generates a projection image based on the X-ray image data after the position correction. , Perform image reconstruction based on the projected image,

The X-ray CT apparatus according to claim 1, wherein:

[3] The image reconstruction means is based on the X-ray image data! Then, a projected image is generated, the position of the projected image is corrected based on the spatial displacement correction information, and image reconstruction calculation is performed based on the projected image after the position correction.

The X-ray CT apparatus according to claim 1, wherein:

[4] A projected image of the index body generated by the X-ray detector taking an image of the index body arranged between the X-ray source and the X-ray detector while rotating at predetermined angles. Including index body Image reconstruction calculation based on X-ray image data! A marker body reconstructed image generating means for generating a reconstructed image of the index body;

The spatial displacement correction information generating means calculates the displacement based on a positional relationship between the reconstructed image and the projected image;

The X-ray CT apparatus according to claim 1, wherein:

[5] The apparatus further comprises alignment means for performing alignment between a plurality of sets of X-ray image data using an X-ray image data portion corresponding to the index body.

The X-ray CT apparatus according to claim 4, wherein:

[6] The positioning means extracts an X-ray image data portion corresponding to the index body from each X-ray image data, and determines a position where the difference of the X-ray image data portion corresponding to the index body is the smallest. Align by detecting

The X-ray CT apparatus according to claim 5, wherein:

[7] It further comprises a bed on which the subject is placed,

The X-ray CT apparatus according to claim 4, wherein the index body is extended along a body axis direction of the subject placed on the bed.

[8] The image reconstructing means is based on 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. A mask image is reconstructed by forming an image of the cross section of the index body at one point, and the live X-ray image data obtained by imaging the blood vessel of the subject and the index body after the contrast agent is injected. Based on the cross-section of the wire line, the live image is reconstructed by forming the cross-section of the wire line at one point, and the mask image and the live image are aligned based on the cross-section of the index body included in each! The X-ray CT apparatus according to claim 7, further comprising difference means that generates a contrasted blood vessel image by processing.

[9] The X-ray detector includes 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 the contrast agent. And the live X-ray image data obtained by photographing the blood vessel of the subject and the index body after being injected,

The image reconstruction means aligns a mask projection image based on mask X-ray image data photographed in the same view and a live projection image based on live X-ray image data based on the index object projection image. After that, differential processing is performed to generate a differential projection image for each view, and a contrasted blood vessel image is reconstructed by reconstructing the differential projection images of all views. The X-ray CT apparatus according to claim 7, wherein:

[10] The spatial displacement correction information generating means generates the spatial displacement correction information so that a rotation center axis is fixed to one when the X-ray source and the X-ray detector are rotationally moved. The X-ray CT apparatus according to claim 1, wherein:

[11] Calculate the amount of displacement of the spatial position of the X-ray source and X-ray detector that occurs when the X-ray source and the X-ray detector provided in the X-ray CT apparatus are rotated at a predetermined angle. A spatial displacement correction information generating step for generating spatial displacement correction information for correcting the position based on the displacement with respect to the X-ray image data acquired from the X-ray CT apparatus;

A reading step for reading X-ray image data obtained by imaging the subject by the X-ray CT apparatus;

Based on the spatial displacement correction information, the position of the X-ray image data is corrected, and based on the X-ray image data, an image reconstruction operation is performed to obtain an X-ray CT image of the subject. Generating an image reconstruction step;

A display step for displaying the X-ray CT image;

An image processing program for causing a computer to execute.

[12] A projected image of the index body generated by the X-ray detector taking an image of the index body arranged between the X-ray source and the X-ray detector while rotating at a predetermined angle. Including index body Image reconstruction calculation based on X-ray image data!指標, further comprising an index body reconstructed image generating step for generating a reconstructed image of the index body,

The spatial displacement correction information generation step calculates the displacement based on a positional relationship between the reconstructed image and the projected image.

The image processing program according to claim 11, wherein:

[13] In the reading step, a plurality of sets of X-ray image data are read,

An alignment step of performing alignment 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 program according to claim 12, wherein:

[14] In the reading step, before the contrast agent is injected into the blood vessel of the subject, the subject Reading first X-ray image data obtained by imaging a blood vessel of a specimen, and second X-ray image data obtained by imaging the blood vessels of the subject after the contrast medium is injected, In the image reconstruction step, a mask image is reconstructed based on the first X-ray image data, and a live image is reconstructed based on the second X-ray image data, and the alignment step Then, the mask image and the live image are aligned based on the reconstructed image of the index body.

A difference step of generating a contrast-enhanced blood vessel image by performing a difference process on the aligned mask image and the live image;

The image processing program according to claim 13.

[15] In the reading step, first X-ray image data obtained by imaging the blood vessel of the subject before the contrast agent is injected into the blood vessel of the subject, and after the contrast agent is injected And the second X-ray image data obtained by imaging the blood vessel of the subject, and the first X-ray image captured in the same view in the image reconstruction step. The first projection image based on the data and the second projection image based on the second X-ray image data are aligned based on the index object projection image, and then subjected to differential processing to generate a differential projection image for each view. And reconstruct the contrast-enhanced blood vessel image by reconstructing the differential projection images of all views.

The image processing program according to claim 13.

[16] Calculate the displacement of the spatial position of the X-ray source and X-ray detector that occurs when the X-ray source and the X-ray detector provided in the X-ray CT apparatus are rotated at a predetermined angle. A spatial displacement correction information generating step for generating spatial displacement correction information for correcting the position based on the displacement with respect to the X-ray image data acquired from the X-ray CT apparatus;

Based on the spatial displacement correction information, the position of the X-ray image data is corrected, and based on the X-ray image data, an image reconstruction operation is performed to obtain an X-ray CT image of the subject. Generating an image reconstruction step; A display step for displaying the X-ray CT image;

An image processing method comprising:

[17] A projected image of the index body generated by photographing the X-ray detector while rotating and moving the index body arranged between the X-ray source and the X-ray detector at predetermined angles. Including index body Image reconstruction calculation based on X-ray image data!指標, further comprising an index body reconstructed image generating step for generating a reconstructed image of the index body,

The image processing method according to claim 16.

[18] In the reading step, a plurality of sets of X-ray image data are read,

The image processing method according to claim 17, wherein:

[19] In the reading step, first X-ray image data obtained by imaging a blood vessel of the subject before the contrast agent is injected into the blood vessel of the subject, and after the contrast agent is injected The second X-ray image data obtained by imaging the blood vessel of the subject is read, and the mask image is regenerated based on the first X-ray image data in the image reconstruction step. And a live image is reconstructed based on the second X-ray image data, and the mask image and the live image are based on the reconstructed image of the index body in the alignment step. Align,

The image processing method according to claim 18, wherein:

[20] In the reading step, first X-ray image data obtained by imaging a blood vessel of the subject before the contrast agent is injected into the blood vessel of the subject, and after the contrast agent is injected And the second X-ray image data obtained by imaging the blood vessel of the subject, and the first X-ray image captured in the same view in the image reconstruction step. A first projection image based on the data and a second projection image based on the second X-ray image data; After performing alignment based on the index object projection image, differential processing is performed to generate a differential projection image for each view, and the contrast projection blood vessel image is reconstructed by reconstructing the differential projection images of all the views. ,

The image processing method according to claim 18, wherein: