JP3964155B2 - X-ray image correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  According to the present invention, cone beam X-ray CT imaging, that is, a subject is fixedly held, and an X-ray generator and a two-dimensional X-ray imaging unit are disposed opposite to each other with the subject as a center, and the X-ray generator is used to detect the subject. By rotating the X-ray generator and the two-dimensional X-ray imaging means within an angle range according to imaging conditions while locally irradiating an X-ray cone beam including only a local site to be imaged, In X-ray imaging in which an X-ray image of a local part is captured, and this X-ray image is processed to calculate a three-dimensional X-ray absorption coefficient of the local part, an X-ray image of the subject and the X-ray original image of the subject is obtained. Correcting positional deviationX-ray image correction methodAbout.
[0002]
[Prior art]
  In X-ray CT (Computed Tomography) imaging, as a two-dimensional X-ray imaging means, an image intensifier is abbreviated to an X-ray II (X-ray fluorescence multiplier) and a CCD camera (hereinafter referred to as “XII imaging tube”). In the case of this XII imaging tube, the X-ray light receiving surface is a curved surface, whereas the light receiving surface of a CCD camera that converts the light visualized here into an electric signal is a flat surface. , Tube distortion caused by detecting a curved surface in a plane, and distortion such as magnetic distortion due to geomagnetism during imaging, that is, positional deviation between the subject and the X-ray original image of the subject is corrected. Various proposals have been made.
[0003]
  FIG. 10A is a view showing an example of a conventional image correction phantom used for correcting the tube surface distortion, and FIG. 10B is a basic configuration diagram of an X-ray CT imaging apparatus using the image correction phantom. No. 24248.
[0004]
  The image correction phantom 121 shown in FIG. 10A is obtained by forming X-ray transparent holes 121b in a square lattice shape on a metal flat plate 161a that is X-ray opaque, and is preferably used for correcting the tube surface distortion. However, it took a lot of work to process the hole 121b in the metal flat plate 121a, and the cost was high.
[0005]
  In the X-ray CT imaging apparatus shown in FIG. 10B, an X-ray generator 101 and a two-dimensional X-ray imaging unit 102 arranged opposite to each other with a subject O interposed therebetween are installed on a rotating plate 103 and rotated. Then, the X-ray generator 101 turns and irradiates the subject O with the X-ray cone beam, obtains an X-ray image of the subject O by the two-dimensional X-ray imaging means 102, and the image acquisition processing device 106 obtains the obtained X-ray. The image is corrected using a position correspondence table, etc., and the corrected X-ray image is reconstructed to obtain a three-dimensional X-ray absorption coefficient (reconstruction data) of the subject O, which is displayed as an image. In this case, the image correction phantom 121 was mounted on the tube surface of the two-dimensional X-ray imaging unit 102 and used for image correction.
[0006]
  Further, as a cause of the positional deviation between the subject and the X-ray original image of the subject, a rotation center axis for rotating the X-ray generator and the two-dimensional X-ray imaging means arranged opposite to each other about the subject is used. There have been various proposals for correcting this, as well as the rotational center axis, the axial displacement of the X-ray generator and the two-dimensional X-ray imaging means.
[0007]
  FIG. 11A is a view showing another example of such an image correction phantom, and FIG. 11B is a basic configuration diagram of an X-ray CT imaging apparatus using the image correction phantom, which is described in JP-A-9-173330. It is a thing.
[0008]
  An image correction phantom 221 shown in FIG. 11A is obtained by vertically arranging a plurality of X-ray opaque spheres 221b inside an X-ray transparent support 221a, and corrects the shake of the rotation center axis. However, data processing up to the creation of the correction table is complicated by the amount of the sphere 221b.
[0009]
  The X-ray CT imaging apparatus shown in FIG. 11 (b) is indispensable for X-ray CT imaging as in FIG. 10 (b), and the X-ray generator 201 and two-dimensional X-ray imaging arranged opposite to each other with the subject O interposed therebetween. In addition to means 202, rotating plate 203, image processing means 206, etc., in order to correct an X-ray original image using image correction phantom 221, image distortion correction means 206 a, image distortion correction table creation means 261, etc. are provided. It was.
[0010]
  FIG. 12A is a diagram showing another example of the same image correction phantom, and FIG. 12B is a basic configuration diagram of an X-ray CT imaging apparatus using the same, which is described in Japanese Patent Laid-Open No. 2000-201918. Is.
[0011]
  An image correction phantom 321 shown in FIG. 12A has an X-ray opaque rod 321b installed in the vertical direction inside an X-ray transparent support 321a. Can be suitably used to correct the vertical misalignment of the detector and the two-dimensional X-ray imaging means. However, in order to create a correction table, the data irradiated to the entire phantom 321 is necessary, which is complicated. It was processing.
[0012]
  The X-ray CT imaging apparatus shown in FIG. 12 (b) is indispensable for X-ray CT imaging as in FIG. 11 (b), and an X-ray generator 301 and two-dimensional X-ray imaging arranged opposite to each other with the subject O interposed therebetween. Means 302, a rotating plate 303, a data processing unit 306 corresponding to an image processing unit, and the like, and a geometry estimation unit corresponding to an image distortion correction unit in order to correct an X-ray original image using the image correction phantom 361. 306a and the like.
[0013]
[Problems to be solved by the invention]
  However, although these conventional image correction phantoms achieve the intended purpose, they still have the problems to be solved as described above.
[0014]
  The present invention is intended to solve such problems and solves various problems derived from the purpose of distortion correction.Image correction methodThe purpose is to provide.
[0015]
[Means for Solving the Problems]
  The X-ray image correction method according to claim 1 comprises:The cone beam X-ray CT that irradiates the subject with cone beam X-rays from the X-ray generator while rotating the X-ray generator and the two-dimensional imaging means arranged opposite to each other with the subject interposed therebetween. The axial displacement of the rotation center axis during shootingX-ray image correction method for correctionThe X-ray transparent support body accommodates two spheres having a higher X-ray absorption coefficient than the support body, and the support body is installed at a position away from the rotation center axis by a predetermined position. The X-ray generator and the two-dimensional imaging means are inverted 180 degrees around the rotation center axis, and the original X-ray images of the two spheres obtained on the two-dimensional imaging means at the respective positions. On the other hand, a predetermined calculation is performed to calculate the reference position of the X-ray original image on the two-dimensional imaging means.
[0016]
  Claim 2The X-ray image correction method described inIn claim 1,A center axis deviation correction table is created to correct the axial position deviation of the rotation center axis of X-ray CT imaging.,thisAn image correction table is created for each rotation angle of X-ray CT imaging using the center axis deviation correction table, and each X-ray original image is corrected using the image correction table.
[0017]
  The correction method is the correction according to claim 1.MethodThe X-ray original image is corrected by an image correction table created using a center axis deviation correction table that corrects distortion that may occur during X-ray CT imaging while effectively utilizing is doing.
  Claim 3The X-ray image correction method described in claim 12In the X-ray image correction method, two spheres having an X-ray absorption coefficient higher than that of the support are accommodated in the X-ray support, and the support is substantially the same as the sphere in X-ray CT imaging. The angle and shift amount used for correction from the average value of the movement in the coordinate direction on the image of the two spheres installed at the subject holding position so as to be up and down in the rotation center axis directionAnd calculatingThe image correction table is created.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
  Of the present inventionEmbodiments will be described with reference to the accompanying drawings.
[0019]
  FIG. 1 (a) shows the present invention.Used inA front view showing an example of an image correction phantom, (b) is a longitudinal sectional view showing a state in which the image correction phantom is mounted on a two-dimensional X-ray imaging means, and (c) is an example of an original X-ray image taken in (b). FIG.
[0020]
  An image correction phantom 21 shown in FIG. 1A is composed of an X-ray transmissive printed board 21a and a small circle 21b having a high X-ray absorption coefficient, and as shown in the figure, a grid-like shape is formed on the printed board 21a. Assuming a lattice, small circles 21b are arranged at positions that are intersections of the lattice.
[0021]
  The printed circuit board 21a may be a plate-like body formed of a material having a low X-ray absorption coefficient such as a plastic material such as an acrylic resin, vinyl chloride, or polycarbonate in addition to a synthetic resin, for example, a glass epoxy resin or a phenol resin. Specifically, a printed circuit board that is widely used for arranging and arranging electronic devices can be obtained at low cost and is suitable.
[0022]
  As the X-ray opaque material of the small circular body 21b, metals such as copper, tungsten, iron-nickel-chromium alloy, and stainless steel are preferable, and the small circular body 21b has a diameter of about 1.5 mm. However, the present invention is not limited to this, and is relatively determined according to the overall size of the phantom, that is, the size of the tube surface of the two-dimensional X-ray imaging means on which the phantom is mounted. .
[0023]
  The correction phantom 21 uses a general-purpose X-ray transmissive printed board 21a as a plate-like object for arranging small circles 21b having a high X-ray absorption coefficient serving as a reference point for correction in a grid pattern. It will be very cheap. In addition, the lattice arrangement can be achieved by simply forming the small circles 21b on the printed circuit board 21a by etching, thereby reducing the cost.
[0024]
  The two-dimensional X-ray image pickup means 2 is an XII image pickup tube as shown in FIG. 1B, and is a well-known one, but its configuration will be briefly described. An input window 2a that is a tube surface, an input surface substrate. 2b, input phosphor screen 2c, photocathode 2d, focus electrode 2e, anode 2f, output phosphor screen 2g, output window 2h, optical lens 2i, CCD camera 2j, focus power supply E1, anode power supply E2, etc. Upon receiving the incident line, this is converted into visible light, and the visible light is imaged by a CCD camera and output as an electrical signal.
[0025]
  The two-dimensional X-ray imaging means 2 is provided with an attachment frame 25 for attaching the image correction phantom 21 to the input window 2a.
[0026]
  As shown in FIG. 1B, the image correction phantom 21 is used by being attached to the tube surface of the two-dimensional X-ray imaging means 2 by this attachment frame 25. In this state, X The line original image IO is shown in FIG.
[0027]
  The correction table indicating the relative positional relationship between the small-circle image IO (21b) constituting the X-ray original image IO and the small-circle body 21b of the image correction phantom 21 is used to correct the tube surface distortion of the two-dimensional X-ray imaging means. Then, distortion such as magnetostriction due to geomagnetism during imaging, that is, positional displacement between the subject and the X-ray original image of the subject is corrected. This correction table is called a tube surface distortion correction table.
[0028]
  FIGS. 2A to 2C are conceptual diagrams of a correction method using the image correction phantom of FIG. 1, and the creation of the tube surface distortion correction table will be described using these.
[0029]
  1) Binarization of X-ray original image IO: This is for obtaining the position of the small circle image IO (21b) in the original image IO. FIG. 2A shows one small circular body 21b of FIG. 1A and a grid surrounding it. Here, since the size of the lattice is 3 mm and the diameter of the small circle 21b is 1.5 mm, the area ratio of the small circle image IO (21b) is
    π * (1.5 / 2) * (1.5 / 2) /3*3≈0.196
It becomes. This is a threshold for the X-ray original image IO. Here, “*” means multiplication, and “/” means division.
[0030]
  Next, as shown in FIG. 2B, an X-ray original image IO of 320 pixels * 240 pixels is extrapolated by applying a mirror image process to the image data within the boundary around the field boundary in the region of 512 pixels * 512 pixels. The result is subjected to FFT (Fourier transform), then a band pass filter as shown in FIG. 2C is applied in the frequency domain, and further IFFT (inverse Fourier transform) is performed. .196)).
[0031]
  2) Creation of correction table: This indicates the positional relationship between the original image IO and the small circle 21b of the phantom 21. As shown in FIG. 2 (d), this problem generally occurs from four points A, B, C, D on the xy coordinate system to four points A ′, B ′, C ′, on the uv coordinate system. It can be understood that this is a conversion problem to D ′. Here, in addition to simple rotation and enlargement of the coordinate system, the enlargement ratio changes, so the following extended affine transformation is used.
   u = a11 * xy + a10 * x
+ a01 * y + a00
   v = b11 * xy + b10 * x
+ b01 * y + b00
  In this case, there are four coefficients for each equation of u and v, which is suitable for obtaining the relationship between the four points as in this problem.
[0032]
  3) Define the whole affine transformation by a set of small area affine transformations.
[0033]
  As shown in FIG. 2 (e), the entire affine transformation is defined as a set of small area affine transformations corresponding to the hatched portion on the left side.
[0034]
  By such a procedure, a tube surface distortion correction table is obtained. In this state, the tilt of the imaging system and the vertical and horizontal tilts, that is, the rotation center axis shake of X-ray CT imaging and the rotation center axis of X-ray CT imaging. In order to achieve this, it is necessary to create a center axis shake correction table and a center axis deviation correction table using two types of image correction phantoms described below. There is.
[0035]
3A and 3B are external views showing a reference example of the image correction phantom, and FIG. 4 is a conceptual diagram of a correction method using the image correction phantom of FIG.
[0036]
  The image correction phantom 22 is composed of an X-ray transparent support 22a and two medium spheres 22b (A) and 22b (B) having a high X-ray absorption coefficient. The spheres 22b (A) and 22b (B) are arranged so that when the support 22a is placed at the subject holding position, these spheres 22b are vertically moved substantially in the direction of the rotation center axis 3a of X-ray CT imaging. (See FIG. 7).
[0037]
  Here, the material of the support 22a is preferably an acrylic resin having a good X-ray transparency, transparent, easily available and easy to process. The material of the intermediate sphere 22b is preferably a steel ball having a high X-ray absorption coefficient, and its diameter is preferably 3 mm to 15 mm, but is not limited thereto.
[0038]
  The correction phantom 22 has a simple configuration and can be manufactured at a low cost, and it becomes easy to create a correction table using the phantom.
[0039]
  The phantom 22 is used to create a center axis shake correction table for correcting the rotation center axis shake in X-ray CT imaging. For this purpose, the phantom 22 is placed on a support base 26 as shown in FIG. It is set so that its position is almost the vicinity of the rotation center axis 3a in FIG. FIG. 4 shows a method of performing X-ray imaging in this state and calculating the rotation center axis shake from the obtained X-ray original image.
[0040]
  Further, the correction phantom 22 may be a rectangular parallelepiped as shown in FIG. 3A or a cylindrical body as shown in FIG.
[0041]
  In FIG. 4, the images of the two spheres 22 b (A) and 22 b (B) are simply indicated by the symbols A and B.
[0042]
  First, A and B in this figure need to be corrected by the tube surface distortion correction table (the same applies to FIG. 6). Here, the purpose is to obtain the angle θ and the shift amount XS.
[0043]
  Since A and B move to the left and right as shown in the figure by the rotation of the swivel arm 360, the points A 'and B' can be easily obtained by obtaining the average value of the x coordinates of A and B. Thus, the angle θ and the shift amount XS are calculated. More precisely, the movement of A and B in the x-coordinate direction can be subjected to Fourier transform, and the respective DC components can be used as the x-coordinates of the points A ′ and B ′.
[0044]
  Since it is assumed that the angle θ is small, the y-coordinates of A and B are constant (average value), and it can be assumed that A and B only move in the horizontal direction. Further, only one set of the angle θ and the shift amount XS is calculated for the 360 degree rotation of the swing arm 3.
[0045]
  FIG.Other examples of image correction phantomFIG. 6 is a conceptual diagram of a correction method using the image correction phantom of FIG.
[0046]
  The image correction phantom 23 is composed of an X-ray transparent support 23a and two small spheres 23b (A) and 23b (B) having a high X-ray absorption coefficient. The small spheres 23b (A) and 23b (B) are arranged so that the small spheres 23b are vertically arranged in the direction of the rotation center axis of X-ray CT imaging when the support 23a is placed at the subject holding position. (See FIG. 7).
[0047]
  Here, the material of the support 23a may be the same as that of the support 22a. The material of the small sphere 23b may be the same as that of the intermediate sphere 22b, and the diameter is preferably 1 to 3 mm, but is not limited thereto.
[0048]
  The correction phantom 23 has a simple configuration and can be manufactured at a low cost, and it becomes easy to create a correction table using the phantom.
[0049]
  The phantom 23 is used to create a center axis deviation correction table for correcting the axial position deviation of the rotation center axis of X-ray CT imaging. For this purpose, the phantom 23 is shown in FIG. Then, it is placed on the support base 27 so that the position thereof is substantially away from the rotation center axis 3a in FIG. 7, that is, a position away from the subject holding position by a predetermined distance. FIG. 6 shows a method of performing X-ray imaging in this state and calculating the axial displacement of the rotation center axis from the obtained X-ray original image.
[0050]
  In FIG. 6, the two small spheres 23b (A) and 23b (B) are simply indicated by the symbols A and B. Reference numeral 1 denotes an X-ray generator, reference numeral 2 denotes a two-dimensional X-ray imaging means, and reference numeral 3a denotes a rotation center axis 3a of the swivel arm 3 (see FIG. 7).
[0051]
  Reference numerals a1 and b1 denote the X-ray sources of the small spheres A and B when the X-ray generator 1 is irradiated with the X-ray generator 1 in the position farthest away from the small spheres A and B (indicated by a one-dot chain line). The vertical positions on the image, the symbols a2 and b2, are the positions where the X-ray generator 1 is closest to the small spheres A and B (that is, positions rotated 180 degrees around the rotation center axis 3a from the previous position). The vertical positions of the small spheres A and B on the X-ray original image when these are irradiated in the state (shown by a solid line). Reference symbol c is the vertical position occupied by the reference position of the X-ray original image with respect to the rotation center axis 3a.
[0052]
  Between the four positions a1, b1, a2, b2 thus obtained and the vertical position c of the rotation center shaft 3a,
   (a1-c) / (a2-c) =
(b1-c) / (b2-c)
The relationship of
    c = (a2 * b1-b2 * a1) / ((a2-b2)-(a1-b1))
It becomes.
[0053]
  Thus, the vertical position c is obtained, and this vertical position c becomes the vertical position of the X-ray original image with respect to the rotation center axis 3a on the machine, so that the vertical movement type of the coordinate axis can be generated, and this becomes the central axis deviation correction table. . In addition, what is necessary is just to prepare one set of this correction table about the perimeter of irradiation.
[0054]
  Thus, when a tube surface distortion correction table is obtained for each turning angle of X-ray CT imaging, and a set of center axis shake correction table and center axis deviation correction table is obtained for the entire circumference, the tube surface distortion correction table is obtained. Then, coordinate axis rotation conversion by the center axis shake correction table and coordinate axis movement conversion by the center axis deviation correction table are performed, and an image correction table is created for each turning angle of X-ray CT imaging.
[0055]
  Such an image correction table uses a tube surface distortion correction table, a center axis shake correction table, and a center axis deviation correction table for correcting all possible distortions that may occur during X-ray CT imaging. Can be removed.
[0056]
  It should be noted that those having different sizes as the correction reference points, such as the middle sphere 22b of the correction phantom 22 for the center axis shake correction table and the small sphere 23b of the correction phantom 23 for the center axis deviation correction table, It corresponds to each correction purpose.
[0057]
  In other words, in the case of the center axis blur correction, the correction phantom 22 is placed almost in the vicinity of the rotation center axis, that is, in the subject holding position, but this position is in the middle of the X-ray generator 1 and the two-dimensional X-ray imaging means 2. Yes, during turning, the size of the X-ray image of the middle sphere 22b of the correction phantom does not change much. Therefore, if the size of each image of the two spheres 22b is reflected on the imaging surface of the two-dimensional X-ray imaging means 2, the size is as described above.
[0058]
On the other hand, in the case of center axis deviation correction, it is necessary to install the correction phantom 23 at a position away from the rotation center axis and at a predetermined distance from the subject holding position. The size of the X-ray image of the small sphere 23b changes from large to small. Therefore, even when the size of the X-ray image of the small sphere 23b is maximized at the rotational position where the correction phantom 23 is closest to the X-ray generator 1, the respective surfaces of the two-dimensional X-ray imaging means 2 are set on the imaging surface. If the images of the two small spheres 23b are captured, the small sphere 23b is smaller than the middle sphere 22b used in the correction phantom of the center axis shake.
[0059]
  FIG.Image correction phantomFIG. 8 is a detailed configuration diagram of the image correction unit in FIG. 7.
[0060]
  The X-ray CT imaging apparatus 20 includes an X-ray imaging unit A, an X-ray beam adjusting unit B, a turning arm drive control unit C, an arithmetic processing unit 6, a display monitor E, a subject holding unit 4 that holds the subject O fixedly, a subject A subject position moving unit 5 for moving the holding unit 4, a main frame 10, an operation unit 11, an operation panel 10 e and the like are provided.
[0061]
  The X-ray imaging means A has a swivel arm 3, and the swivel arm 3 is suspended from the X-ray generator 1 and the two-dimensional X-ray imaging means 2.
[0062]
  The X-ray beam adjusting means B provided in the X-ray generator 1 has an X-ray beam width limiting means B1, an X-ray beam controller B2, and an emission control slit B3, and the X-ray beam emitted from the X-ray tube Is adjusted by the X-ray beam width limiting means B1, so that an X-ray cone beam 1a having a desired beam width can be emitted.
[0063]
  One two-dimensional X-ray imaging means 2 converts X-rays hitting a scintillator layer provided on the surface of X-ray II into visible light, converts the visible light into electrons by a photoelectric converter, and multiplies the electrons. This electron is converted into visible light by a phosphor and photographed with a CCD (solid-state imaging device) camera arranged two-dimensionally through a lens.
[0064]
  In addition to this, known two-dimensional X-ray imaging means such as an X-ray two-dimensional imaging means such as cadmium tellurium (CdTe) or a MOS sensor, or a CCD imaging means using a combination of a scintillator, a glass fiber, and a CCD are used. it can.
[0065]
  The revolving arm 3 is provided with an XY table 31, an elevation control motor 32, and a rotation control motor 33. By controlling the X-axis control motor 31a and the Y-axis control motor 31b, the rotation center 3a is set in the XY direction. The position of the revolving arm 3 can be moved up and down by driving the elevating control motor 32 and the revolving arm 3 can be rotated around the subject O by driving the rotation control motor 33 at a constant speed during photographing. The lift control motor 32 constitutes an arm vertical position adjusting means for the swing arm 3.
[0066]
  Further, the rotation center 3a of the swivel arm 3, that is, the swivel axis is provided vertically, the swivel arm 3 rotates horizontally, and the X-ray cone beam 1a is locally irradiated horizontally, so that the apparatus occupies a small floor space. It can be configured as a vertical type.
[0067]
  This rotation control motor 33 constitutes a turning drive means for the turning arm 3, and uses a motor that can freely control its rotation speed and rotation position, such as a servo motor. The shaft is directly connected to the rotation center 3a.
[0068]
  Therefore, the swivel arm 3 can be rotated at a constant speed or a variable speed, and the rotation position can be known along the time axis. It is convenient for taking out a transmission image, and there is no center shake, and cone beam X-ray CT imaging can be effectively performed.
[0069]
  A hollow portion 3 b is provided at the rotation center 3 a of the turning arm 3. In order to provide such a hollow portion 3b, it is necessary to provide a hollow hole in all the related parts on the rotation center 3a. For example, the rotation control motor 33 is a servo using a hollow shaft. A motor can be used.
[0070]
  The hollow portion 3b is used for arranging a connection line between the X-ray generator 1 and the two-dimensional X-ray imaging means 2 suspended from the swivel arm 3 and the operation unit 11 provided on the main frame 10 side. belongs to.
[0071]
  When electrical wiring is connected to the rotating portion, the arrangement method of the connecting wire becomes a problem. However, if the connecting wire is arranged through the rotation center 3a of the swivel arm 3 as described above, the influence of twisting due to rotation, etc. Can be minimized, and a favorable effect can be obtained from the aesthetics of the wiring.
[0072]
  In this embodiment, the swing arm drive control means C is configured by combining the position adjusting means 31 composed of an XY table, the motor 32 after lift control, and the rotation control motor 33, but is not limited to such a configuration. . In the simplest structure, the center 3a of the swivel arm 3 may be set at an arbitrary position by operating a handwheel handle.
[0073]
  The subject holding means 4 includes a chair 4b that holds the subject (patient) O in a sitting position, and a head fixing means 4a provided on the back of the chair 4b.
[0074]
  The subject position moving unit 5 includes an X-axis control motor 51 that moves the subject holding unit 4 left and right, a Y-axis control motor 52 that moves back and forth, and a Z-axis control motor 53 that moves up and down.
[0075]
  The X-axis, Y-axis, and Z-axis linear movement tables (not shown) driven by these motors 51 to 54 are each composed of a well-known cross roller guide or a combination of ordinary bearings and guides. Can be moved linearly. Moreover, the movement of these X-axis, Y-axis, and Z-axis linear movement tables by the motors 51 to 54 can be applied with a rack and pinion method, a ball screw method, a method using a normal screw shaft, or the like. What can be positioned is desirable.
[0076]
  In this way, the subject O is seated on the chair 4 b, the head of the subject O is fixedly held by the head fixing means 4 a, and the subject position moving means 5 is used to bring the inside of the subject O into the rotation center 3 a of the swivel arm 3. It can be adjusted to the center of the local site. On the other hand, instead of moving the subject holding means 4 by the subject position moving means 5, the rotation arm 3 side is moved using the XY table 31 and the lifting control motor 32, and the rotation center 3 a of the turning arm 3 is moved to the subject O It is also possible to match with the center of the local site inside.
[0077]
  In this apparatus 20, in order to align the rotation center 3a, that is, to set the X-ray imaging position, the subject position moving means 5 for moving the subject side, and the XY table 31 for moving the swivel arm 3 on the irradiation side, Although both the lift control motors 32 are provided, only one of them may be provided. In the case of cone beam X-ray CT imaging, it is important that there is no blurring of the rotation center 3a. Therefore, it is desirable that only the turning arm 3 is turned and the turning center 3a is fixed.
[0078]
  The arithmetic processing means 6 includes an arithmetic processor that operates at high speed for image processing analysis, and after pre-processing the X-ray transmission image generated on the two-dimensional X-ray imaging means 2, executes predetermined arithmetic processing. Thus, the three-dimensional X-ray absorption coefficient data inside the object through which X-rays are transmitted are calculated, and calculation such as projection of this data on the projection surface is performed, and the projection image or An X-ray panoramic image is displayed and stored as image information in a necessary storage medium.
[0079]
  In this imaging apparatus, the arithmetic processing unit 6 includes an image correction unit 6a that creates the above-described image correction table and corrects an X-ray original image using the image correction table.
[0080]
  In order to achieve this object, the image correction unit 6a performs correction processing unit 61 that performs various correction processes and arithmetic processes, and an image correction table that stores and saves the generated image correction table for each rotation angle of X-ray CT imaging. A memory 62, a tube surface distortion correction table memory 63, a center axis shake correction table memory 64, and a center axis deviation correction table memory 65 are provided.
[0081]
  FIG. 9 (a)X-ray CT imaging systemFIG. 2B is a side view of the outer appearance of the example, FIG.
[0082]
  The X-ray CT imaging apparatus 20 is configured with a main frame 10 that is a portal-type extremely rigid structure as an overall support.
[0083]
  The main frame 10 has an arm 10a for rotatably supporting a swing arm 3 suspended from the X-ray generator 1 and the two-dimensional X-ray imaging means 2, and a base end portion of the arm 10a is fixed. A pair of horizontal beams 10b that are held, a pair of vertical beams 10c that support the horizontal beams 10b, and a pair of vertical beams 10c are fixedly mounted, and are composed of a base 10d that forms the basis of the entire apparatus 20. Has been.
[0084]
  The members constituting the main frame 10 are each made of a steel material having high rigidity, and are appropriately provided with braces or corner reinforcing members to be resistant to deformation. The rotation center 3a is not changed.
[0085]
  As described above, the main frame 10 has a structure that prevents the swing arm 3 from swinging. Therefore, the main frame 10 is particularly suitable as an X-ray CT imaging apparatus that requires no swing swing.
[0086]
  The operation panel 10e is provided on the surface of one vertical beam 10c of the main frame 10 at a position where the operator can easily operate in a standing position. The chair 4b of the subject holding means 4 is placed on the subject position moving means 5 described in FIG. 7, and the chair 4b is moved in the X, Y, and Z directions, that is, in the front-rear, left-right, up-down directions, Further, the back plate 4ba of the chair 4b can be tilted to hold the head of the subject O tilted.
[0087]
  In the present invention, as shown in FIGS. 9B and 9C, phantom support bases 26 and 27 are attached to the head fixing means 4a of the subject holding means 4 so as to be detachable and replaceable. The above-described image correction phantoms 22 and 23 can be placed on the support bases 26 and 27.
[0088]
  The phantom support 26 is for positioning the image correction phantom 22 in the vicinity of the rotation center axis 3a of the swivel arm 3, as shown in FIG.
[0089]
  As can be seen from FIGS. 9 and 3, the phantom 22 is installed in the vicinity of a so-called subject holding position by simply placing the image correction phantom 22 on the phantom support base 26, and the sphere 22 b incorporated in the phantom 22. (A) and 22b (B) are arranged at predetermined intervals substantially in the direction of the rotation center axis 3a.
[0090]
  As shown in FIG. 9C, the phantom support base 27 is for positioning the image correction phantom 23 at a position further away from the rotation center axis 3 a of the swivel arm 3 in the horizontal direction than the support base 26. .
[0091]
  As can be seen from FIGS. 9 and 5, the image correction phantom 23 is installed at a position away from a so-called subject holding position by a predetermined distance only by placing the image correction phantom 23 on the phantom support 27, and is built in the phantom 23. The small spheres 23b (A) and 23b (B) thus arranged are arranged at predetermined intervals substantially in the direction of the rotation center axis 3a.
[0092]
【The invention's effect】
  Claim1X-ray image correction described inMethodAccording toAn X-ray image correction method for correcting an axial displacement of a rotation center axis in cone beam X-ray CT imaging in which a subject is irradiated with cone beam X-rays from an X-ray generator. , Which contains two spheres having a higher X-ray absorption coefficient than this support, this support is placed at a predetermined position away from the rotation center axis, and the X-ray generator and the two-dimensional imaging means are rotated. X-rays on the two-dimensional imaging means are obtained by performing a predetermined operation on the two spherical X-ray images obtained on the two-dimensional imaging means at respective positions, inverted by 180 degrees around the central axis. Since the reference position of the original image is calculated, it is easy to create a correction table.
[0093]
  Claim2According to the X-ray image correction method according to claim 1, the correction according to claim 1.MethodEffectively corrects distortion that may occur during X-ray CT imaging while demonstrating its effectsAn X-ray original image can be corrected by an image correction table created using the center axis deviation correction table, and all possible distortions that may occur during X-ray CT imaging can be removed.
[0094]
  Claim3The X-ray image correction method described in3. The X-ray image correction method according to claim 2, wherein two spheres having an X-ray absorption coefficient higher than that of the support are accommodated in an X-ray support, and the support is formed by X-ray CT imaging. The image correction table is calculated by calculating the angle and the shift amount used for correction from the average value of the movement in the coordinate direction on the image of the two spheres. Therefore, it becomes easy to create a correction table.
[Brief description of the drawings]
1A is a front view showing an example of an image correction phantom of the present invention, FIG. 1B is a longitudinal sectional view showing a state in which the image correction phantom is mounted on a two-dimensional X-ray imaging means, and FIG. Showing an example of an original X-ray image captured by
2A to 2E are conceptual diagrams of a correction method using the image correction phantom of FIG.
FIG. 3 is an external view showing a reference example of an image correction phantom.
4 is a conceptual diagram of a correction method using the image correction phantom of FIG.
FIG. 5 is an external view showing another example of the image correction phantom of the present invention.
6 is a conceptual diagram of a correction method using the image correction phantom of FIG.
FIG. 7 is a basic configuration diagram of an example of an X-ray CT imaging apparatus using the image correction phantom of the present invention.
FIG. 8 is a detailed configuration diagram of the image correction unit in FIG. 7;
9A is an external front view of the X-ray CT imaging apparatus of FIG. 7, FIG. 9B is a side view, and FIG. 9C is a partial side view.
10A is a diagram showing an example of a conventional image correction phantom, and FIG. 10B is a basic configuration diagram of an X-ray CT imaging apparatus using the image correction phantom.
11A is a diagram showing another example of a conventional image correction phantom, and FIG. 11B is a basic configuration diagram of an X-ray CT imaging apparatus using the image correction phantom.
12A is a diagram showing another example of a conventional image correction phantom, and FIG. 12B is a basic configuration diagram of an X-ray CT imaging apparatus using the image correction phantom.
[Explanation of symbols]
      1 X-ray generator
      1a X-ray cone beam
      2 Two-dimensional X-ray imaging means
      21 X-ray image correction phantom
      21a Printed circuit board
      21b small circle
      22 X-ray image correction phantom
      22a Support
      22b Medium sphere
      23 X-ray image correction phantom
      23a Support
      23b small sphere
      3 swivel arm
      3a Rotation center axis
      4 Subject holding means
      4a chair
      4b Head fixing means
      6 Image processing means
      6a Image correction means
    20 X-ray CT imaging system

Claims (3)

Cone beam X-ray CT imaging that irradiates a subject with cone beam X-rays from an X-ray generator while rotating an X-ray generator and a two-dimensional imaging unit opposed to each other with the subject interposed therebetween. An X-ray image correction method for correcting a positional deviation in the axial direction of the rotation center axis in
An X-ray transparent support body accommodates two spheres having an X-ray absorption coefficient higher than that of the support body.
This support is installed at a position away from the rotation center axis by a predetermined position,
The X-ray generator and the two-dimensional imaging means are inverted 180 degrees around the rotation center axis, and the X-ray original images of the two spheres obtained on the two-dimensional imaging means at the respective positions are obtained. An X-ray image correction method characterized in that a predetermined calculation is performed to calculate a reference position of an X-ray original image on the two-dimensional imaging means. In claim 1,
A center axis deviation correction table for correcting the axial position deviation of the rotation center axis of the X-ray CT imaging is created , and an image correction table for each turning angle of the X-ray CT imaging is created using this center axis deviation correction table. And correcting each original X-ray image using the image correction table. In claim 2,
Further, two spheres having an X-ray absorption coefficient higher than that of the support are accommodated in the X-ray support, and the support is vertically moved in the direction of the rotation center axis in X-ray CT imaging. The image correction table is created by calculating the angle and shift amount used for correction from the average value of the movement in the coordinate direction on the image of the two spheres. X-ray image correction method.

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