JP2011136027A - X-ray ct imaging apparatus, and reconfiguration processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing the generation of an artifact in a CT image. <P>SOLUTION: The X-ray CT imaging apparatus includes: an X-ray generation part for radiating an X-ray cone beam toward a subject; an X-ray detection part for detecting the X-ray cone beam; a support part for supporting the X-ray generation part and the X-ray detection part so as to face each other holding the subject therebetween; a turning drive part for performing X-ray CT imaging by rotary driving the support part and turning the X-ray generation part and the X-ray detection part around the object; and an arithmetic processing part for reconfiguring projection data acquired in the X-ray CT imaging and generating three-dimensional data. The arithmetic processing part uses only the projection data obtained by radiating the X-ray cone beam from respective directions of a projection angle of just 180 degrees as the processing object of a reconfiguration operation for any point inside the X-ray CT imaging area. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for generating three-dimensional data from projection data obtained by X-ray irradiation.

  2. Description of the Related Art Conventionally, X-ray CT imaging apparatuses are known that acquire scan data by irradiating an affected area of a subject with X-rays, acquire projection data, and reconstruct this to acquire three-dimensional data. For example, Patent Document 1 describes a configuration of an X-ray CT imaging apparatus and an X-ray CT imaging method.

  Specifically, an X-ray cone beam made up of a bundle of X-rays is rotated at an angle of 180 degrees by adding the fan angle (angle of spread in the rotation direction) of the X-ray cone beam to 180 degrees. Irradiate toward. Then, X-ray projection data is collected by detecting X-rays transmitted through the subject. In this way, by irradiating the X-ray cone beam having a rotation angle corresponding to the angle obtained by adding the fan angle to 180 degrees, X-rays from all directions in the range of at least 180 degrees are applied to all points in the imaging target area of the subject. Irradiated projection data can be acquired.

JP 2007-125174 A

  However, in a conventional X-ray CT imaging apparatus, when a CT image is generated from reconstructed three-dimensional data, artifacts that should not originally exist, such as a pattern extending in the vertical direction or the horizontal direction, are generated in the CT image. There is. In order to improve the accuracy of image diagnosis, it is desired to suppress the occurrence of such artifacts.

  The present invention has been made in view of the above problems, and an object thereof is to provide a technique for suppressing the occurrence of artifacts in CT images.

  In order to solve the above problems, a first aspect includes an X-ray generation unit that irradiates an X-ray cone beam toward a subject, an X-ray detection unit that detects the X-ray cone beam, and the X-ray generation unit. And the X-ray detection unit so as to oppose each other with the subject interposed therebetween, and the support unit is driven to rotate so that the X-ray generation unit and the X-ray detection unit are moved around the subject. X-ray CT provided with a turning drive unit that performs X-ray CT imaging by turning, and an arithmetic processing unit that reconstructs the projection data acquired by the X-ray CT imaging and generates three-dimensional data An imaging apparatus, wherein the arithmetic processing unit only applies projection data obtained by irradiating the X-ray cone beam from each direction with a projection angle of exactly 180 degrees at any point in the X-ray CT imaging region. The target of the reconstruction operation.

  Further, the second aspect is the X-ray CT imaging apparatus according to the first aspect, wherein the rotation drive unit uses an angle obtained by adding 180 degrees to the angle spreading in the rotation direction of the X-ray cone beam, The X-ray CT imaging is performed by turning the X-ray generation unit and the X-ray detection unit.

  Further, the third aspect is the X-ray CT imaging apparatus according to the second aspect, wherein the X-ray generation part partially blocks the passage of the X-ray by adjusting the size of the opening, A control unit that controls an irradiation range of the X-ray cone beam, and a projection angle of 180 degrees for all points in the CT imaging region by the operation of the control unit during the X-ray CT imaging; The X-ray cone beam is irradiated from each direction.

  Further, according to a fourth aspect, in the X-ray CT imaging apparatus according to the third aspect, the restriction unit is configured to start X-ray cone beam irradiation on the subject according to a turning angle of the support unit. The operation gradually increases the irradiation range of the X-ray cone beam on the subject.

  According to a fifth aspect, in the X-ray CT imaging apparatus according to the third aspect, at the time before the restriction portion reaches the end point of the X-ray cone beam irradiation on the subject, The passage of the X-ray is regulated so as to gradually reduce the irradiation range of the X-ray cone beam according to the turning angle.

  Further, according to a sixth aspect, in the X-ray CT imaging apparatus according to the third aspect, the restriction unit is configured to start the irradiation of the X-ray cone beam with respect to the subject according to the turning angle of the support unit. The X-ray cone beam irradiation range for the subject gradually operates, and at a time before reaching the end point of the X-ray cone beam irradiation on the subject, according to the turning angle of the support unit. The X-ray CT imaging apparatus for restricting the passage of the X-rays so as to gradually reduce the irradiation range of the X-ray cone beam. The seventh aspect is any one of the aspects from the second to the sixth aspects. In the X-ray CT imaging apparatus, X-rays can be obtained from each direction of the projection angle of 180 degrees with respect to all the points in the X-ray CT imaging region among the projection data acquired by the X-ray CT imaging. By extracting only radiation data, further comprising an operation unit, which performs a predetermined reconstruction processing.

  According to an eighth aspect, in the X-ray CT imaging apparatus according to any one of the second to seventh aspects, the X-ray detection unit has a plurality of detection elements that detect X-rays in a planar shape. By limiting the X-ray detectable range of the detection surface, all the points in the X-ray CT imaging region are projected from each direction with a projection angle of 180 degrees. Projection data irradiated with the X-ray cone beam is acquired.

  According to a ninth aspect, in the X-ray CT imaging apparatus according to the eighth aspect, the X-ray detection unit sets the turning angle of the support unit at the start of irradiation of the X-ray cone beam onto the subject. In response, the X-ray detection range on the detection surface is gradually increased.

  According to a tenth aspect, in the X-ray CT imaging apparatus according to the eighth aspect, the X-ray detection unit is configured to execute the X-ray cone beam irradiation on the subject before reaching the end point of the X-ray cone beam irradiation. The X-ray detection range on the detection surface is gradually reduced according to the turning angle of the support portion.

  Further, an eleventh aspect is the X-ray CT imaging apparatus according to the eighth aspect, wherein the X-ray detection unit has a turning angle of the support unit at the start of the irradiation of the X-ray cone beam to the subject. Accordingly, the X-ray detection range on the detection surface is gradually increased, and gradually before reaching the end point of irradiation of the X-ray cone beam on the subject, depending on the turning angle of the support portion. The X-ray detection range on the detection surface is reduced.

  In a twelfth aspect, in a reconstruction processing method for reconstructing three-dimensional data from X-ray projection data related to a subject, the X-ray generation unit and the X-ray detection unit face each other with the subject interposed therebetween. Data for collecting X-ray projection data by performing X-ray CT imaging in which the X-ray detection unit detects an X-ray cone beam emitted from the X-ray generation unit toward the subject while turning around the subject. And a calculation step of generating three-dimensional data by performing a predetermined reconstruction calculation process on the projection data acquired in the data collection step. In the calculation step, the X-ray At any point in the CT imaging region, only projection data obtained by irradiating the X-ray cone beam from each direction with a projection angle of 180 degrees is set as a processing target.

  According to the X-ray CT imaging apparatus according to the first to ninth aspects, since only the projection data irradiated with X-rays from each direction in the range of the projection angle of 180 degrees is the processing target for the reconstruction calculation, It is possible to achieve an excellent effect that the generation of artifacts due to the processing of the projection data irradiated with X-rays from the direction exceeding the angle of 180 degrees can be suppressed.

  In particular, according to the X-ray CT imaging apparatus according to the second aspect, by rotating the X-ray generation unit and the X-ray detection unit to an additional angle that the X-ray cone beam spreads, With respect to a point, it is possible to obtain an excellent effect that projection data irradiated with X-rays from each direction corresponding to a projection angle of 180 degrees can be acquired. That is, it is possible to produce an effect that the generation of artifacts can be suppressed only by rotating the X-ray cone beam by an extra angle corresponding to the spread angle.

  In particular, according to the X-ray CT imaging apparatus according to the third to sixth aspects, it is possible to acquire projection data with the minimum necessary X-ray exposure. Therefore, an excellent effect that the X-ray exposure amount of the subject can be minimized can be obtained.

  In particular, according to the X-ray CT imaging apparatus according to the seventh aspect, it is possible to achieve an excellent effect that projection data irradiated with X-rays from a direction exceeding a range corresponding to a projection angle of 180 degrees can be easily eliminated.

  In particular, according to the X-ray CT imaging apparatus according to the eighth to eleventh aspects, the occurrence of artifacts can be suppressed only by controlling the X-ray detectable range of the X-ray detection element relatively easily.

  Further, according to the X-ray CT imaging method according to the twelfth aspect, only the projection data irradiated with X-rays from each direction within the range of the projection angle of 180 degrees in the calculation step, regardless of the mechanical configuration, Since it is a processing target of reconstruction calculation, it is possible to achieve an excellent effect that it is possible to suppress the occurrence of artifacts due to processing of projection data irradiated with X-rays from a direction exceeding the projection angle of 180 degrees.

It is a figure which shows the outline | summary of the X-ray CT imaging apparatus which concerns on 1st Embodiment. It is a fragmentary sectional view which shows a support part and an upper frame with the internal structure. It is a fragmentary sectional view showing an upper frame with the internal structure. It is a longitudinal cross-sectional view which shows an X-ray generation part. It is a perspective view which shows a beam shaping mechanism. It is a front view which shows a turning arm. It is a perspective view which shows a detector holder. It is a block diagram which shows the structure of a X-ray CT imaging apparatus. It is a conceptual diagram which shows the operation | movement of X-ray CT imaging by X-ray CT imaging apparatus. It is a figure which shows a mode that the irradiation range of an X-ray cone beam is controlled at the time of X-ray CT imaging. It is a figure which shows a mode that the irradiation range of an X-ray cone beam is controlled at the time of X-ray CT imaging in 2nd Embodiment. It is a figure which shows a mode that the irradiation range of an X-ray cone beam is controlled at the time of irradiation start and the time of completion | finish of irradiation. It is a figure which shows a mode that the detection range of an X-ray cone beam is controlled at the time of X-ray CT imaging | photography in 3rd Embodiment. It is a figure which shows a mode that the detection range of an X-ray cone beam is controlled at the time of X-ray CT imaging | photography in 4th Embodiment. It is a figure which shows the functional block implement | achieved by CPU of the information processing main-body part which concerns on 5th Embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings. However, the configuration described in this embodiment is merely an example, and is not intended to limit the scope of the present invention.

<1. First Embodiment>
<1.1. Overview>
FIG. 1 is a diagram showing an outline of an X-ray CT imaging apparatus 100 according to the first embodiment. The X-ray CT imaging apparatus 100 according to the present embodiment is a medical X-ray imaging apparatus, and an X-ray generation unit 10 and an X-ray detection unit 20 are set to an imaging target region for a subject M1 fixed at a predetermined position. The projection data is collected by irradiating the X-ray cone beam B1 generated by the X-ray generator 10 while rotating around the center of the (biological organ or the like). The X-ray CT imaging apparatus 100 reconstructs the collected projection data to generate three-dimensional data (volume data), and based on the three-dimensional data, a CT image (tomographic plane image, volume) about the imaging target region. Rendering image, etc.).

  As a result of investigating the cause of artifacts in a CT image generated by a conventional X-ray CT imaging apparatus, when reconstructing three-dimensional data, the projection angle exceeds 180 degrees for a part of the imaging target region. It has been found that artifacts may occur due to projection data obtained by irradiating X-rays from each direction. Although the projection angle will be described in detail later, the X-ray CT imaging at a certain point in time during the X-ray CT imaging with respect to the traveling direction of the X-ray passing through a certain point at the X-ray irradiation start point. It is defined as an angle formed by the traveling direction of X-rays passing through a specific point.

  On the other hand, the X-ray CT imaging apparatus 100 according to the present embodiment has the configuration described below, so that any point in the imaging target region is exactly the projection angle of 180 degrees (that is, the projection angle is 0 degrees). Only the projection data obtained by irradiating X-rays from each direction in the range of from 180 degrees to just 180 degrees is the target of the reconstruction calculation process. Thereby, the X-ray CT imaging apparatus 100 is configured to be able to generate a CT image in which the occurrence of artifacts is suppressed.

<1.2. Configuration and Function of X-ray CT Imaging Apparatus>
The X-ray CT imaging apparatus 100 shown in FIG. 1 performs X-ray CT imaging, and collects projection data, and processes the projection data collected in the main body 1 to generate various images. It is roughly divided into the processing device 8.

  The main body 1 detects an X-ray generator 10 that emits a pyramid-shaped X-ray cone beam B1 formed of a bundle of X-rays toward the subject M1, and detects the X-rays emitted by the X-ray generator 10. X-ray detection unit 20, support unit 30 that supports X-ray generation unit 10 and X-ray detection unit 20 facing each other, elevating unit 40 configured to be movable up and down in the vertical direction, and vertical A column 50 extending in the direction and a main body control unit 60 are provided. At the time of X-ray imaging, the X-ray generation unit 10 and the X-ray detection unit 20 are supported by the support unit 30 so as to face each other with the subject M1 interposed therebetween, and turn around the subject M1.

  In the example shown in the figure, the support portion 30 is composed of a revolving arm that revolves around the mechanical revolving shaft 31, but is not particularly limited to the revolving arm, and various configurations are conceivable. For example, the support unit 30 is configured by an annular member that rotates around the center of a predetermined circle, and the X-ray generation unit 10 and the X-ray detection unit 20 are provided to face the annular member. It may be what you have.

  The X-ray generation unit 10 and the X-ray detection unit 20 are respectively suspended and fixed at both ends of the support unit 30 and supported so as to face each other. The support part 30 is suspended and fixed to the elevating part 40 via a turning shaft 31 extending in the vertical direction.

  Here, in the following description, a direction parallel to the axial direction of the turning shaft 31 (here, a vertical direction) is referred to as a “z-axis direction”, a direction intersecting the z-axis is referred to as an “x-axis direction”, and A direction intersecting the x-axis direction and the z-axis direction is defined as a “y-axis direction”. Although the x-axis and y-axis directions can be arbitrarily determined, here, the left and right directions of the subject when the subject who is the subject M1 is positioned in the X-ray CT imaging apparatus 100 and directly faces the column 50 are shown. The x-axis direction is defined, and the front-rear direction of the subject is defined as the y-axis direction.

  On the other hand, for the three-dimensional coordinates on the support unit 30 that turns, the direction in which the X-ray generation unit 10 and the X-ray detection unit 20 face each other is “Y-axis direction”, and the horizontal direction is orthogonal to the Y-axis direction. Is the “X-axis direction”, and the vertical direction perpendicular to the X- and Y-axis directions is the “Z-axis direction”. In the present embodiment and subsequent embodiments, the z-axis direction is the same direction as the Z-axis direction. Moreover, the support part 30 of this embodiment turns around the turning axis 31 extended in a perpendicular direction. Therefore, the XYZ orthogonal coordinate system rotates around the z axis (= Z axis) with respect to the xyz orthogonal coordinate system.

  The raising / lowering part 40 is engaged with the support | pillar 50 standingly arranged so that it may extend along a perpendicular direction. The elevating part 40 has a substantially U-shaped structure in which the upper frame 41 and the lower frame 42 protrude on the opposite side of the side engaged with the support column 50.

  An upper end portion of the support portion 30 is attached to the upper frame 41. Thus, the support part 30 is suspended by the upper frame 41 of the raising / lowering part 40, and when the raising / lowering part 40 moves along the support | pillar 50, the support part 30 moves up and down.

  The lower frame 42 is provided with a subject fixing portion 421 including an ear rod that fixes the subject M1 (here, the head of the human body) from the left and right, a chin rest that fixes the chin, and the like. The support unit 30 is moved up and down according to the height of the subject M1 and adjusted to an appropriate position, and the subject M1 is fixed to the subject holding unit 421 in this state.

  As shown in FIG. 1, the X-ray generation unit 10, the X-ray detection unit 20, the support unit 30, and the elevating unit 40 are accommodated in an X-ray prevention chamber 70. A main body control unit 60 is provided inside the X-ray detection unit 20. The main body control unit 60 is provided with a display unit 61 composed of a liquid crystal monitor and an operation panel 62 composed of various buttons. The operation panel 62 is also used to designate the position of an imaging region such as a living organ.

  In addition, an operation display unit 600 is provided outside the wall of the X-ray chamber 70. The operation display unit 600 is provided with a display unit 61a composed of a liquid crystal monitor or the like and an operation panel 62a composed of various buttons.

  The information processing device 8 can transmit and receive various data to and from the main body 1 using a communication cable. However, data may be exchanged between the main body 1 and the information processing apparatus 8 wirelessly.

  The information processing apparatus 8 includes an information processing main body unit 80 configured by, for example, a computer or a workstation, and processes the projection data acquired by the main body unit 1 to display three-dimensional data (volume) expressed by voxels. Data). To the information processing main body 80, for example, a display unit 81 including a display device such as a liquid crystal monitor and an operation unit 82 including a keyboard and a mouse are connected. The operator can give various commands to the information processing apparatus 8 via the operation unit 82. The display unit 81 can also be configured with a touch panel. In this case, a part or all of the functions of the operation unit 82 are provided.

  FIG. 2 is a partial cross-sectional view showing the support 30 and the upper frame 41 together with the internal structure thereof. FIG. 3 is a partial cross-sectional view showing the upper frame 41 together with its internal structure. 2 is a diagram showing the state of the support unit 30 and the upper frame 41 when the X-ray CT imaging apparatus 100 is viewed from the side. FIG. 3 shows the state of the upper frame 41 when viewed from above. FIG.

  The upper frame 41 is a table configured by a Y table 35Y that moves the support portion 30 in the front-rear direction (Y-axis direction) and an X table 35X that is supported by the Y table 35Y and moves in the horizontal direction (X-axis direction). 35. The upper frame 41 connects the Y-axis motor 60Y that drives the Y table 35Y, the X-axis motor 60X that moves the X table 35X in the X direction with respect to the Y table 35Y, and the X table 35X and the support unit 30. A turning motor 60 </ b> R for turning the support portion 30 around the turning shaft 31 is provided. In this embodiment, the turning shaft 31 is configured to extend along the vertical direction, but the turning shaft may be inclined at an arbitrary angle with respect to an arbitrary vertical direction.

  A bearing 37 is interposed between the turning shaft 31 and the support portion 30 to facilitate the rotation of the support portion 30 with respect to the turning shaft 31. The turning motor 60 </ b> R is fixed inside the support portion 30, and the turning power is transmitted to the turning shaft 31 by the belt 38 to turn the support portion 30. The turning shaft 31, the bearing 37, the belt 38, and the turning motor 60R are examples of a turning mechanism that turns the support portion 30, and the turning mechanism of the support portion 30 is not limited to this.

  In the X-ray CT imaging apparatus 100, the support unit 30 can be turned by driving the control motors of the X-axis motor 60X, the Y-axis motor 60Y, and the turning motor 60R according to a predetermined program. The X table 35X and the Y table 35Y can be moved back and forth (Y direction) and left and right (X direction). The X-ray generation unit 10 and the X-ray detection unit 20 rotate around the axis of the rotation axis 31 by the rotation of the support unit 30 around the axis of the rotation axis 31.

  In addition, the X table 35X and the Y table 35Y move the swivel shaft 31 to a specific position in a two-dimensional plane (in each case a horizontal plane), and then swivel the support unit 30 around the axis, The X-ray detection unit 20 can be rotated. In this case, the positions of the rotation axes of the X-ray generation unit 10 and the X-ray detection unit 20 coincide with the position of the turning shaft 31.

  Further, in the X-ray imaging apparatus 100, the support unit 30 can be swung around the swivel axis 31 while the swivel axis 31 is moved in the two-dimensional plane by driving the X table 35X and the Y table 35Y. . The X-ray generation unit 10 and the X-ray detection unit 20 are swung by the combined movement of the movement of the support unit 30 in the horizontal plane due to the movement of the swivel shaft 31 and the swivel of the support unit 30 around the swivel shaft 31. It can be rotated around the axis of a specific rotation axis set at a position different from the position of the axis 31. As an example of setting the rotation axes of the X-ray generation unit 10 and the X-ray detection unit 20 at a place different from the mechanical turning axis 31 as described above, X-ray CT imaging described in Japanese Patent Application Laid-Open No. 2007-29168. It is also possible to apply the configuration of the apparatus as appropriate.

  As will be described later, in X-ray CT imaging, the X-ray generator 10 rotates while irradiating the X-ray cone beam B1 toward the X-ray detector 20. Therefore, the X-ray cone beam B1 also rotates about a center C1 shown in FIG. The rotation center C1 of the X-ray cone beam is also the rotation axis of the X-ray generation unit 10 and the X-ray detection unit 20. X-rays, which are electromagnetic waves, are components that do not move and stay in space, but X-ray cone beams are composed of X-ray bundles and are irradiated in a certain cone shape. Is done. Therefore, in this embodiment, the state in which the X-ray bundle rotates is considered as the rotation of the X-ray cone beam.

{X-ray generator 10}
FIG. 4 is a longitudinal sectional view showing the X-ray generator 10. FIG. 5 is a perspective view showing the beam forming mechanism 16. As shown in FIG. 4, the X-ray generation unit 10 includes a housing 11 for housing each component included in the X-ray generation unit 10. The housing 11 is connected to the support portion 30 via the rotation mechanism 12.

  The rotation mechanism 12 includes a rotation motor 121 fixed inside the support portion 30, a vertical shaft 122 fixed to the support portion 30, a gear mechanism 123 that connects the rotation motor 121 and the vertical shaft 122, and the housing 11. And a fixing member 124 fixed to the vertical shaft 122.

  The housing 11 is configured to be rotatable around a vertical axis 122 in a horizontal plane by driving a rotary motor 121 that operates based on a control signal from the main body control unit 60. Such a rotation mechanism 12 is used, for example, at the time of cephalometric photography.

  An X-ray detector 14 containing an X-ray tube 13 which is an X-ray generation source is accommodated inside the X-ray generation unit. The X-ray detector 14 is configured by a housing which is an X-ray blocking case, and the X-ray tube 13 is the X-ray detector 14 except for a portion facing the X-ray detection unit 20 (left side in FIG. 4). Covered with a case. The X-ray generator 14 includes a beam shaping plate 15 in a region facing the X-ray detection unit 20. The beam shaping plate 15 is attached to the beam shaping mechanism 16.

  As shown in FIG. 5, the beam shaping mechanism 16 has a block 163 supported so as to be movable up and down along a plurality of vertical guide rails 162 via a plurality of guide rollers 161. The block 163 includes an X-ray passage hole 164 (see FIG. 4) that guides the X-ray emitted from the X-ray tube 13 toward the X-ray detection unit 20.

  The block 163 is connected to a lifting motor 165 fixed to the housing 11 via a screw mechanism. By driving the lifting motor 165, the X-ray generation unit 10 can move the X-ray irradiation angle in the Z-axis direction. Thereby, the X-ray irradiation angle can be moved up and down without moving the X-ray generator 10 up and down.

  A beam shaping plate 15 provided with a plurality of beam shaping slits for shaping the X-ray beam emitted from the X-ray tube 13 is disposed in front of the block 163 (outside the X-ray passage hole 164). The beam shaping plate 15 is a restricting part that restricts the irradiation range. The beam shaping plate 15 is supported by a plurality of guide rollers 166 fixed to the front surface of the block 163 so as to be movable in the horizontal direction.

  A connection arm 167 is connected to one end of the beam shaping plate 15. A nut 168 is attached to the connecting arm 167. The block 163 rotatably supports a screw shaft 169 extending in the longitudinal direction of the beam shaping plate 15. The nut 168 is screwed to the screw shaft 169, and the screw shaft 169 is connected to the motor 170 fixed to the block 163.

  The beam shaping plate 15 moves the front part of the block 163 in one direction in the horizontal direction, that is, in a direction intersecting with the X-ray beam, by driving a motor 170 that operates based on a control signal from the main body control unit 60.

  In the present embodiment, the beam shaping plate 15 is formed with three types of X-ray passage openings (primary slits and collimators). These three types of X-ray passage openings have a rectangular or square CT imaging beam passage hole 151 for shaping the X-ray beam into a cone shape (including a pyramid shape), and an elongated X-ray beam. A vertically long beam passage hole 152 for panoramic photography for forming a slit beam by forming into a strip shape and a vertically long cephalometric photography beam passage hole 153 are included.

  For example, when the CT imaging beam passage hole 151 is opposed to the X-ray tube 13, an X-ray cone beam extending in a truncated pyramid shape is emitted from the X-ray generation unit 10 toward the X-ray detection unit 20. If the longitudinal and lateral lengths of the CT imaging beam passage hole 151 are the same, the X-ray beam has a substantially square cross section perpendicular to the X-ray traveling direction. The CT imaging beam passage hole 151 is not limited to a square shape, and an appropriate shape can be adopted. For example, by forming the beam passage hole 151 in a circular shape, it is not hindered to irradiate a cone-shaped X-ray cone beam and to make the imaging target region spherical.

  In the present embodiment, the horizontal width of the X-ray passage hole 164 of the block 163 is the same as the horizontal width of the beam passage hole 151. The opening of the X-ray exit hole formed by the X-ray passage hole 164 and the beam passage hole 151 is adjusted by the movement of the beam shaping plate 15 driven by the motor 170, and the horizontal spread of the X-ray cone beam is adjusted. The width of is adjusted.

  For example, by displacing the beam shaping plate 15 with respect to the block 163, the beam passage hole 151 of the beam shaping plate 15 is moved to a position overlapping the X-ray passage hole 164, and passes through the X-ray passage hole 164. Do not disturb the line. Thereby, the width of the horizontal spread of the X-ray cone beam can be set to the maximum width.

  Further, by displacing the beam shaping plate 15 with respect to the block 163, the beam passage hole 151 of the beam shaping plate 15 is in a position where the X-rays passing through the X-ray passage hole 164 are partially blocked (restricted). Move. Thereby, the width of the horizontal spread of the X-ray cone beam can be made smaller than the maximum width.

  Thus, in the present embodiment, the horizontal spread of the X-ray cone beam is determined by controlling the position of the beam shaping plate 15. Note that the configuration for controlling the spread of the X-ray cone beam in the horizontal direction is not limited to this, and can be realized by other configurations.

  For example, an X-ray diaphragm apparatus that controls X-rays in which a plurality of mask plates 4 and 5 disclosed in FIG. Can be applied.

  That is, although not shown in the drawings, a sub beam shaping plate in which a beam passage hole having a horizontal width substantially the same as (or more than) the beam passage hole 151 is formed either before or after the beam shaping plate 15. Provide. By changing the position of the beam passage hole of the sub beam shaping plate relative to the beam passage hole 151 of the beam shaping plate 15, the X-ray cone is partially blocked by opening the beam passage hole 151 partially. The horizontal spread of the beam can be controlled.

  As the drive motor for driving the auxiliary beam shaping plate, the same motor as the drive motor 170 for driving the beam shaping plate 15 can be employed. Further, by connecting the auxiliary beam shaping plate to a guide mechanism provided in the same manner as the guide roller 166, the auxiliary beam shaping plate can be moved in the same direction as the beam shaping plate 15.

  In such a configuration, by displacing the secondary beam shaping plate relative to the beam shaping plate 15, the beam passage hole of the secondary beam shaping plate is not disturbed by X-rays passing through the beam passage hole 151. Then, the beam is moved to a position overlapping with the beam passage hole 151. Thereby, the width of the horizontal spread of the X-ray cone beam can be set to the maximum width.

  Further, by displacing the secondary beam shaping plate relative to the beam shaping plate 15, the beam passage hole of the secondary beam shaping plate is partially blocked (restricted) by X-rays passing through the beam passage hole 151. ) Move to position. Thereby, the width of the horizontal spread of the X-ray cone beam can be made smaller than the maximum width.

  In such an aspect, the horizontal spread of the X-ray cone beam is determined by the relative position of the sub beam shaping plate with respect to the beam shaping plate 15.

  When the beam passage hole 152 for panoramic imaging or the beam passage hole 153 for cephalometric imaging is opposed to the X-ray tube 13, the transverse section is substantially flat from the X-ray generation unit 10 toward the X-ray detection unit 20. A plate-like (but strictly speaking, a truncated pyramid) X-ray beam is emitted.

  In addition, although illustration is abbreviate | omitted, the cephalostat used at the time of a cephalo imaging is provided in the tip of the arm fixed to the raising / lowering part 40 and extended in a predetermined direction. Specifically, as the cephalostat, various types including the cephalostat disclosed in JP-A-2003-245277 can be employed. Such a cephalostat is provided with, for example, a fixture for fixing the head in a fixed position and an x-ray detector for cephalo imaging.

{X-ray detector 20}
FIG. 6 is a front view showing the support portion 30. FIG. 6 also shows a part of the inside of the X-ray detection unit 20. The X-ray detection unit 20 includes a housing 200 for housing each component of the X-ray detection unit 20.

  The housing 200 includes an X-ray detector 21 for detecting X-rays, a detector holder 22 that holds the X-ray detector 21 therein, and a guide that supports the detector holder 22 so as to be slidable in the horizontal direction. The rail 23 and the moving motor 24 attached to the housing 200 are provided.

  The X-ray detector 21 includes an X-ray sensor having a detection surface that is configured by two-dimensionally arranging a semiconductor imaging device, which is a detection device for detecting X-rays, in a two-dimensional plane in the vertical and horizontal directions. . The X-ray sensor may be, for example, an X-ray sensor such as a MOS sensor or a CCD sensor, but is not limited thereto, and is not limited to a flat panel detector (FPD) such as a CMOS sensor or an X-ray fluorescence multiplier (XII). Other solid-state image sensors can be used as appropriate.

  The detector holder 22 is in contact with a roller attached to the rotating shaft of the moving motor 24. The detector holder 22 is driven by a moving motor 24 that operates based on a control signal from the main body control unit 60, and moves in the horizontal direction along the guide rail 23.

  FIG. 7 is a perspective view showing the detector holder 22. The detector holder 22 has beam passage holes (secondary forming slits or collimators) 221 and 222 on the side facing the X-ray generation unit 10. The beam passage holes 221 and 222 correspond to the shapes of the beam passage holes 151 and 152 described above. For example, an X-ray beam passing through the beam passage hole 151 is shaped with higher accuracy at the beam passage hole 221. And projected onto the X-ray detector 21. The members provided with the beam passage holes (secondary forming slits or collimators) 221 and 222 may be omitted.

  The X-ray detector 21 includes a detection element group 211 configured by arranging image pickup elements in a square shape corresponding to the rectangular beam passage holes 151, and a vertically long image pickup element corresponding to the vertically long beam passage holes 152. And a detection element group 212 configured in an array. The X-ray detector 21 is inserted into a slot 224 formed by the detector holder 22.

  When the X-ray detector 21 is set in the slot 224, the substantially square detection element group 211 is disposed behind the approximately square beam passage hole 221. The detection element group 212 is disposed behind the beam passage hole 222. During X-ray CT imaging, the detection element group 211 moves to a position irradiated with X-rays that have passed through the beam passage hole 151, and during panoramic imaging, the detection element group 212 passes through the beam passage hole 153. The movement of the detector holder 22 is controlled so that the detector holder 22 moves to a position where the line is irradiated.

  In the present embodiment, the detection element groups 211 and 212 are provided in the X-ray detector 21, but only the detection element group 211 is provided, and in X-ray CT imaging and panoramic imaging, the beam passage hole 151 and the beam passage hole are provided. One of 153 may be selected as appropriate, and the same detection element group 211 may be configured to detect X-rays. In that case, the transmission efficiency of the image signal which is projection data can be improved by controlling to read out elements only in the range irradiated with X-rays.

  FIG. 8 is a block diagram illustrating a configuration of the X-ray CT imaging apparatus 100. As shown in FIG. 8, the turning motor 60R, the X-axis motor 60X, the Y-axis motor 60Y, and the subject holding unit 421 serve as a drive source for moving the support unit 30 relative to the subject M1 at a predetermined position. The drive part 65 is comprised. The driving unit 65 and the subject holding unit 421 serve as a moving mechanism that moves the X-ray generation unit 10 including the X-ray tube 13 and the X-ray detection unit 20 including the X-ray detector 21 relative to the subject M1. Function. The drive unit 65 is an example of a turning drive unit that drives the support unit 30 to turn.

  The main body control unit 60 includes a CPU 601 that executes various control programs including a program PG1 that controls the drive unit 65, a fixed disk such as a hard disk, a storage unit 602 that stores various data and programs PG1, a ROM 603, The RAM 604 is configured as a general computer connected to the bus line.

  The operation display unit 600 can also perform operations and displays related to the main body control unit 60. Note that the operation functions and display functions of the main body control unit 60 and the operation display unit 600 may be overlapped, but the operation display unit 600 may perform specific operations and displays. Further, the operation display unit 600 may be provided with a control function to share a part of the control of the main body control unit 60, or the main body control 60 itself may be provided in the operation display unit 600.

  The CPU 601 executes the program PG1 stored in the storage unit 602 on the RAM 604, so that the X-ray generation unit control unit 601a and the X-ray detection unit 20 control the X-ray generation unit 10 according to various imaging modes. Functions as an X-ray detection unit control unit 601b.

  Note that the CPU 601 constituting the main body control unit 60 and the CPU 801 constituting the information processing main body unit 80 collectively constitute a control system.

  An operation panel 62 added to the main body control unit 60 includes a plurality of operation buttons and the like. In addition to the operation buttons, a keyboard, a mouse, a touch pen, or the like can be used as an input device instead of the operation panel 62 or used together with the operation panel 62. Further, a voice command may be received and recognized by a microphone or the like. That is, the operation panel 62 is an example of an operation unit. Therefore, any operation means may be used as long as it can accept the operation of the operator. In addition, the display unit 61 can be configured by a touch panel. In this case, the display unit 61 includes a part or all of the functions of the operation panel 62.

  Various information necessary for the operation of the main body unit 1 is displayed on the display unit 61 as characters, images, and the like. However, the display content displayed on the display unit 81 of the information processing apparatus 8 may be displayed on the display unit 61. Further, various commands may be issued to the main body unit 1 through a pointer operation with a mouse or the like on a character or image displayed on the display unit 61.

  The main body unit 1 locally performs CT imaging of an imaging target region (biological organ or the like) R1 of the subject M1 in accordance with a command from the operation panel 62 or the information processing device 8. The main body 1 receives various commands, coordinate data, and the like from the information processing device 8, and transmits X-ray projection data acquired by imaging to the information processing device 8.

  The information processing main unit 80 includes a CPU 801 that executes various programs, a fixed disk such as a hard disk, and a general storage unit 802 that stores various data and programs PG2, a ROM 803, and a RAM 804 connected to a bus line. It has a configuration as a simple computer.

  The CPU 801 executes the program PG2 stored in the storage unit 802 on the RAM 804, calculates the coordinates of the region specified by the operation unit 82, and specifies the imaging region specifying unit R801, and the projection It functions as an arithmetic processing unit 801b that performs arithmetic processing such as reconstructing three-dimensional data from data.

  The programs PG1 and PG2 may be acquired by the main body control unit 60 or the information processing main body unit 80 via a predetermined network line or the like, or stored in a portable medium (CD-ROM or the like). Alternatively, the programs PG1 and PG2 may be acquired by being read by a predetermined reading device.

  In the present embodiment, the imaging target region R1 is designated by the operator via the operation panel 62 or the operation unit 82. Specifically, a screen (illustration, panoramic image, or the like) that displays a part or the whole of the living body is displayed on the display unit 61 or the display unit 81, and an area that the operator wants to photograph is displayed via the operation panel 62 or the operation unit 82. By designating, the imaging target region R1 is designated. Alternatively, the region may be directly specified by inputting the name of the region or inputting the code from the operation panel 62 or the operation unit 82 without displaying the region specifying screen on the screen.

<1.3. Operation of X-ray CT imaging apparatus>
Next, the operation of the X-ray CT imaging apparatus will be described. The operation of the X-ray CT imaging apparatus 100 described below is controlled by the main body control unit 60 or the information processing main body unit 80 unless otherwise specified.

  FIG. 9 is a conceptual diagram showing an operation of X-ray CT imaging by the X-ray CT imaging apparatus 100. FIG. 9 shows a state in which the X-ray generation unit 10, the X-ray cone beam B1, the X-ray detection unit 20, and the like are viewed from the axial direction of the turning shaft 31 of the support unit 30.

  When the operator gives an instruction to perform X-ray CT imaging for a specific imaging target region R1, the main body control unit 60 rotates the support unit 30 by driving the driving unit 65 such as the rotation motor 60R. At this time, as shown in FIG. 9, an X-ray cone beam B1 is emitted from the X-ray generation unit 10, and the cone beam B1 is rotated about the center C1. That is, the X-ray generation unit 10 And the support part 30 turns so that the X-ray detection part 20 rotates centering on the center C1.

  While the X-ray cone beam B1 rotates around the center C1, the region that is always imaged by X-ray irradiation is the imaging target region R1 for X-ray CT imaging. When the subject M1 is positioned, the relative position of the subject M1 with respect to the support unit 30 is adjusted as appropriate so that the region (region of interest) that the operator wants to shoot is the shooting target region.

  Here, in order to image the entire imaging target region R1 at a constant magnification, the distances between the X-ray generation unit 10, the center C1, and the X-ray detection unit 20 are maintained from the start of irradiation to the end of irradiation. There is a need. Therefore, at the time of X-ray CT imaging, the main body control unit 60 controls the X-axis motor 60X and the Y-axis motor 60Y to rotate the turning shaft 31 about the center C1, and simultaneously controls the turning motor 60R. Then, by rotating the support portion 30, the X-ray cone beam B1 is rotated with the center C1 as the center of rotation.

  In addition, after driving the X table 35X and the Y table 35Y to move the turning shaft 31 to a specific position and stopping it, the support portion 30 is turned around the turning shaft 31 and the X-ray generating portion 10 is moved. The X-ray detection unit 20 may be rotated.

  In addition, in order to perform X-ray CT imaging stably, it is desirable to provide a run-up section for accelerating until the support unit 30 reaches a constant turning speed. Thus, in the present embodiment, for example, the X-ray generation unit 10 starts to rotate slightly before the position L0 shown in FIG. In addition, the movement locus of the X-ray generation unit 10 during the movement in the approach section does not necessarily need to be set at a position on a perfect circle that constitutes a locus during X-ray CT imaging.

  While the X-ray CT imaging apparatus 100 rotates the X-ray cone beam B1, the X-ray detection unit 20 collects projection data for a predetermined number of times. Specifically, the main body control unit 60 monitors the turning motor 60R, and collects X-ray detection data from the X-ray detector 21 as projection data each time the support unit 30 turns by a predetermined angle. . In the present embodiment, the X-ray cone beam B1 is always irradiated to the imaging target region R1 while the support unit 30 is turning.

  However, the X-ray irradiation method is not limited to this. For example, the X-ray generation unit 10 may be configured to emit the X-ray cone beam B1 toward the imaging target region R1 at the timing when the X-ray detection unit 20 detects X-rays. In this case, since the subject M1 is intermittently irradiated with X-rays, the amount of X-ray exposure can be reduced.

  The collected projection data is sequentially transferred to the information processing apparatus 8 and stored in the storage unit 802, for example. The collected projection data is processed in the arithmetic processing unit 801b and reconstructed into three-dimensional data. The reconstruction calculation processing in the calculation processing unit 801b includes predetermined preprocessing, filter processing, back projection processing, and the like. Various arithmetic processing techniques including known techniques can be applied to these arithmetic processes.

  As shown in FIG. 9, in the present embodiment, the rotation angle around the rotation center C1 of the X-ray cone beam B1 in one X-ray CT imaging is spread in the rotation direction of the X-ray cone beam B1 at 180 degrees. (Which is hereinafter referred to as fan angle θ1) is an angle (less than 360 degrees). The rotation angle around the rotation center C1 of the X-ray cone beam B1 is also the rotation angle around the axes of the X-ray generation unit 10 and the X-ray detection unit 20 with the center C1 as the rotation axis.

The X-ray generator 10 rotates from position L0 to position L1. Note that the fan angle θ1 here is an X-ray cone in a range in which the X-ray cone beam B1 emitted from the X-ray generation unit 10 passes through the entire imaging target region R1 and can be detected by the X-ray detection unit 20. This is the angle of spread of the beam B1. In other words, the X-ray generation unit 10 and the X-ray detection unit 20 rotate by an angle obtained by adding the fan angle θ1 to 180 degrees from the start to the end of the X-ray CT imaging. Strictly speaking, the positions L0 and L1 are focal positions which are the origins where the X-rays of the X-ray tube 13 are generated.

  Here, the concept of the projection angle will be described. The projection angle in the present embodiment refers to the X-ray passing through a specific point in the imaging target region R1 at the X-ray irradiation start time (specifically, when the X-ray generator 10 reaches the position L0). An angle formed by the traveling direction of X-rays passing through the specific point at each time point of X-ray CT imaging with respect to the traveling direction. Hereinafter, a case where the specific point is a point PS1 on the center C1, which is the rotation center of the X-ray cone beam B1, will be described as a specific example.

  At the start of irradiation with the X-ray cone beam B1, X-rays in the traveling direction DR1 pass from the X-ray generation unit 10 at the position L0 toward the X-ray detection unit 20 at the point PS1. Here, assuming that projection data for N times is acquired in one X-ray CT imaging, at the point Tn when the projection data is acquired at the nth (where n is an integer value from 1 to N), the point PS1. The traveling direction DRn of the X-rays passing through. An angle formed by the traveling direction DRn with respect to the traveling direction DR1 is a projection angle PRn.

  In other words, the X-ray cone beam B1 irradiates the imaging target region R1 while rotating about the center C1. However, with respect to a specific point (for example, the point PS1) in the imaging target region R1, When viewed from the axial direction, a reference straight line (specifically, a straight line LS parallel to the traveling direction DR1) is incident on the specific point projected on the X-ray detection unit 20 at a certain time (or The angle formed by the X-rays passing through is the projection angle. Specifically, the X-ray projection angle PRn when the X-ray generator 10 is at each of the positions L0, L1, and L2 is projected at the position L0, the projection angle is 0 degrees, the position L2 is projected at 180 degrees, and the position L1 is projected. The angle is (180 degrees + θ1).

  Assuming that one projection data is acquired every time the X-ray cone beam B1 rotates by 1 degree (that is, the support unit 30 rotates by 1 degree), the projection angle PRn for the point PS1 is Each time it increases once, one projection data is acquired. As shown in FIG. 9, when the X-ray generator 10 moves from the position L0 to the position L2, the projection angle at the point PS1 becomes 180 degrees. That is, when the X-ray generation unit 10 is at the position L2, 181 projection data are acquired including X-ray imaging at the irradiation start time (when the X-ray generation unit 10 is at the position L0). Become.

  Here, if the rotation angle of the X-ray generator 10 in X-ray CT imaging is set to 180 degrees, the X-ray generator 10 rotates from the position L0 to the position L2. In this case, the intersection P1 between the outer edge of the X-ray cone beam B1 emitted from the position L0 and the outer edge of the imaging target region R1 is irradiated with X-rays only from a direction in a range smaller than the projection angle of 180 degrees. Absent. In the projection data, when there is a point in the imaging target region R1 that has not been irradiated with X-rays from each direction within the range of the projection angle of 180 degrees, a highly accurate CT image is generated from the reconstructed three-dimensional data. It becomes difficult.

  On the other hand, when the rotation angle of the X-ray generation unit 10 in X-ray CT imaging is set to an angle obtained by adding a fan angle to 180 degrees as in the present embodiment, the projection angle 180 degrees also at the intersection P1 shown in FIG. X-rays can be irradiated from each direction of the minute. In other words, projection data obtained by X-ray irradiation from each direction corresponding to a projection angle of 180 degrees can be collected for all points in the imaging target region R1, so that a living organ or the like in the imaging target region R1 is obtained from the three-dimensional data. It is possible to generate a highly accurate CT image with a clear outline and shape.

  In the present embodiment, as described above, the three-dimensional data is reconstructed from only the data obtained by irradiating X-rays from the respective directions corresponding to the projection angle of 180 degrees for all the points in the imaging target region R1. Therefore, when the irradiation with the X-ray cone beam B1 as shown in FIG. 9 is continued, there is a portion for acquiring projection data irradiated with the X-ray from each direction where the projection angle exceeds 180 degrees. Therefore, unnecessary X-ray irradiation is eliminated by executing the following control.

  FIG. 10 is a diagram showing how the irradiation range of the X-ray cone beam B1 is controlled during X-ray CT imaging. FIGS. 10A to 10E show X-ray CT imaging states arranged in chronological order, and FIG. 10A shows a position L0 about the rotation center C1 of the X-ray cone beam B1. When the rotation angle of rotation of the X-ray generator 10 starting from is (180 ° −θ1), (b) is when the rotation angle is not less than (180 ° −θ1) and not more than 180 °, and (c) is When the rotation angle is 180 °, (d) shows the case where the rotation angle is 180 ° or more and (180 ° + θ1) or less, and (e) shows the case where the rotation angle is (180 ° + θ1). Since the X-ray generation unit 10 is rotated by the support unit 30, the rotation angle of the X-ray generation unit 10 is also the turning angle of the support unit 30.

  As shown in FIG. 10A, the X-ray generator 10 rotates around the imaging target region (X-ray CT imaging region) R1 in a predetermined direction (clockwise here) from the position L0 to the position L01. When the X-ray cone beam B1 is irradiated to the imaging target region R1, the point P2 at which the X-ray irradiation from each direction within the range of the projection angle of 180 degrees (projection angle from 0 to 180 degrees) is completed is the imaging target region. Occurs at R1. Here, the position L01 is geometrically a value obtained by subtracting the fan angle θ1 from the rotation angle of 180 degrees, and the point P2 is an outer edge in the rotation direction of the X-ray cone beam B1 emitted from the position L01. And the intersection of the outer edges of the subject area R1.

  More generally, in the imaging target region R1, the portion on the side where the X-ray generator 10 moves relative to the line segment connecting the position L0 of the X-ray generator 10 and each position during irradiation (FIG. 10 ( In a) to (e), the region indicated by hatching is completed with X-ray irradiation in the direction corresponding to the projection angle of 180 degrees.

  For example, as shown in FIG. 10B, when the X-ray generator 10 is at the position L02, the region R2 outside the line segment LN1 connecting the position L0 and the position L02 in the imaging target region R1. For X, X-ray irradiation in each direction for a projection angle of 180 degrees has already been performed. Therefore, in the present embodiment, as shown in FIG. 10B, the irradiation range of the X-ray cone beam B1 is controlled to be reduced so that the region R2 is not irradiated with X-rays. The line segment LN1 is a line segment that connects the position β of the X-ray generation unit 10 after the position L01 and the position α of the X-ray generation unit 10 at the position L01, such as positions L02, L03,.

  In this reduction control, the X-ray generation unit control unit 601a slides the beam shaping plate 15 of the X-ray generation unit 10 shown in FIG. This is realized. As for the shielding degree of the X-ray cone beam B1, when the X-ray generation unit 10 is at the position L01 as a reference (= rotation angle is zero), the rotation angle of the X-ray generation unit 10 is ω, The cone beam B1 is controlled so that the fan angle becomes a value obtained by subtracting (ω / 2) from θ1.

  To explain this control from another angle, the position of the X-ray generation unit 10 at the position L01 is α, and the position of the X-ray generation unit 10 after the position L01 is set as β like the positions L02, L03,. The position of the X-ray generator 10 at the position L0 is denoted by γ. When ∠αγβ (angle αγβ) is an angle ψ, the fan angle of the X-ray cone beam B1 is controlled to have a value of (θ1−ψ). Further, according to the circumference angle theorem, the value of ∠αγβ (= ψ) is ω / 2, which is half of the value of ∠αC1β (= ω).

  For example, in the state shown in FIG. 10C, the rotation angle from the position L01 of the X-ray generation unit 10 is θ1 (= the fan angle of the X-ray cone beam B1 that is not restricted at all). The fan angle of B1 is (θ1 / 2) (= θ1- (θ1 / 2)). When the X-ray generator 10 passes through the position L04 shown in FIG. 10D and reaches the position L1 shown in FIG. 10E, the X-ray cone beam B1 is completely blocked. In this way, it is possible to collect only projection data irradiated with X-rays from all directions corresponding to a projection angle of 180 degrees for all points in the imaging target region R1.

  As described above, in the present embodiment, control is performed so that the irradiation range of the X-ray cone beam B1 is reduced before reaching the end point of X-ray irradiation. This embodiment is control in the case where the irradiation range of the X-ray cone beam is gradually reduced according to the turning angle of the support unit 30 as the end point of the irradiation of the X-ray cone beam B1 approaches.

  As described above, the X-ray irradiation range is controlled in accordance with the rotation angle, so that any point in the imaging target region R1 is X only from each direction within the range of the projection angle of 180 degrees. Irradiated projection data can be acquired. In addition, the range of just the projection angle of 180 degrees is an angle of a continuous range (0 degrees to 180 degrees) that is not interrupted in the middle. When three-dimensional data is reconstructed from such projection data, it is not necessary to perform correction processing for projection data irradiated with X-rays from a direction exceeding the projection angle of 180 degrees. Therefore, the occurrence of artifacts in the CT image can be reduced, and the image quality of the CT image can be improved. Thereby, it is possible to accurately perform image diagnosis.

<2. Second Embodiment>
In the above embodiment, the X-ray cone beam B1 is controlled so that the irradiation range of the X-ray cone beam B1 is reduced as the end point of the X-ray irradiation approaches, but the method of controlling the X-ray irradiation range is limited to this. It is not something that can be done. In the following description, elements having the same functions as those in the first embodiment are appropriately denoted by the same reference numerals and description thereof is omitted.

  FIG. 11 is a diagram illustrating a state in which the irradiation range of the X-ray cone beam B1 is controlled during X-ray CT imaging in the second embodiment. FIGS. 11A to 11F show X-ray CT imaging states arranged in time series.

  The X-ray cone beam B1 has a fan angle of θ1 at the stage indicated by (e) and (f). However, until the stage of (e), the fan angle is smaller than θ1, and the fan angle is It increases as the rotation of the X-ray generator 10 proceeds from the zero state at the start of irradiation.

  FIG. 11A shows the rotation angle of the X-ray generator 10 centering on the center C1 and starting from L0 is 0 °, and FIG. 11B shows the rotation angle of 0 ° or more and θ1 or less. c) when the rotation angle is θ1, (d) when the rotation angle is not less than θ1 and not more than (2 · θ1), (e) is when the rotation angle is (2 · θ1), and (f) is the rotation angle. Is shown when (180 ° + 2 · θ1). In addition, a range indicated by fine dots with respect to the imaging target region R1 is a range irradiated with the X-ray cone beam B1.

  FIG. 11A shows a state in which the X-ray generation unit 10 is at a position L0 at the start of X-ray irradiation on the imaging target region R1. At this time, the beam shaping plate 15 is disposed at a position where the X-rays emitted from the X-ray tube 13 are completely blocked, so that the X-ray cone beam B1 is not irradiated to the X imaging target region R1. Has been.

  In the imaging target region R1, a portion through which a line segment LN2 (shown by a one-dot chain line in FIG. 11) connecting the position of the X-ray generation unit 10 and the X-ray irradiation end position (position L1) passes X The irradiation range of the X-ray cone beam B1 is increased so as to perform the irradiation of the line. Specifically, as the X-ray generator 10 rotates, the beam shaping plate 15 is moved, and the amount of X-ray passing through the beam passage hole 151 is gradually increased. The line segment LN2 is a line segment connecting the position β1 of the X-ray generation unit 10 after the position L0 and the position α1 of the X-ray generation unit 10 at the position L1, as in positions L01A, L02A,.

  FIG. 11B specifically shows a state in which the X-ray generator 10 has rotated from the position L0 by an angle of (θ1) / 2 to reach the position L01A. At this time, the fan angle of the X-ray cone beam B1 is geometrically half the rotation angle (θ1 / 4). FIG. 11C shows a state in which the X-ray generator 10 has reached the position L02A after rotating by an angle of θ1 from the position L0. At this time, the fan angle of the X-ray cone beam B1 is (θ1 / 2).

  The position of the X-ray generation unit 10 at the position L0 is α1, the position of the X-ray generation unit 10 after the position L0 is β1, and the X-ray generation unit at the position L1 as in the positions L01A, L02A,. The position of 10 is γ1. When す る と α1γ1β1 (angle α1β1γ1) is an angle μ, the fan angle of the X-ray cone beam B1 is controlled to be a value of μ. Here, a line LN2 connecting the position L0 and the position L1 is a tangent to a circle that is the imaging target region R1. Therefore, as shown in FIGS. 11B and 11C, ∠α1γ1β1 = ∠β1γ1α1 = μ.

  FIG. 11D specifically shows a state in which the X-ray generation unit 10 has reached the position L03A after being rotated from the position L0 by an angle of (θ1 + (θ1 / 2)). At this time, the fan angle of the X-ray cone beam B1 is ((θ1 / 2) + (θ1 / 4)). Also at this time, the fan angle of the X-ray cone beam B1 is controlled to be a value of μ.

  Further, FIG. 11E shows a state in which the X-ray generation unit 10 has reached the position L04A after being rotated by an angle of (2 · θ1) from the position L0. At this time, the fan angle of the X-ray cone beam B1 is θ1, and the entire range of the imaging target region R1 is irradiated with X-rays. FIG. 11F shows a state in which the X-ray generation unit 10 has reached the position L1 after being rotated from the position L0 by an angle of (rotation angle 180 ° + θ1). The X-ray generation unit 10 irradiates the imaging target region R1 with the X-ray cone beam B1 having the fan angle θ1 until reaching the position L1 from the position L04A, and ends the X-ray irradiation after reaching the position L1. To do.

  As described above, even when the X-ray irradiation range is controlled from the X-ray cone beam B1 irradiation start point, as in the first embodiment, in one X-ray CT imaging, within the imaging target region R1. Also for all the points, projection data obtained by performing X-ray irradiation from each direction within a range of a projection angle of exactly 180 degrees can be acquired.

  For the control of the shielding degree of the X-ray cone beam B1, the same control as that for shielding the fan angle by ω can be applied in accordance with the rotation angle ω of the X-ray generator 10 in the first embodiment. The first embodiment is controlled at the end of X-ray irradiation, whereas the second embodiment is different in that the control is at the start of X-ray irradiation.

  The above description regarding the second embodiment is a case where the irradiation range of the X-ray cone beam B1 is gradually expanded according to the turning angle of the support unit 30 at the start of irradiation of the X-ray cone beam B1.

  In the first embodiment, as the end point of X-ray irradiation approaches, the irradiation range of the X-ray cone beam B1 is controlled to be reduced. In the second embodiment, the X-ray cone beam is started from the start point of X-ray irradiation. Although the control is performed to increase the irradiation range of B1, the irradiation range of the X-ray cone beam B1 may be increased at the start of irradiation and may be controlled to be reduced at the end. In this case, from the start of irradiation until the X-ray generation unit 10 rotates by the rotation angle θ1 (that is, the position where the rotation angle is 0 ° (position L0 in FIG. 11A) to the position θ1 (FIG. 11 ( c) until the position L02A) is reached) and until the X-ray generator 10 is rotated by the rotation angle θ1 by the end of irradiation (that is, the rotation angle is 180 ° (FIG. 10C)). The X-ray irradiation range is controlled between position L03) and (180 ° + θ1) (up to position L1 in FIG. 10E).

  More specifically, at the start of irradiation, X-ray generation starts from a state in which no X-ray cone beam B1 is irradiated until the rotation angle of the X-ray generation unit reaches the position θ1 from the position of 0 °. Control is performed to irradiate the X-ray cone beam B1 while increasing the fan angle of the X-ray cone beam B1 by the rotation angle of the rotation of the unit 10. As a result, the fan angle increases from zero to θ1 while the X-ray generator 10 rotates θ1. Thereafter, an X-ray cone beam B1 having a fan angle θ1 is irradiated onto the imaging target area. At the end of irradiation, the fan angle of the X-ray cone beam B1 is equal to the rotation angle of the X-ray generator 10 until the rotation angle reaches the position of (180 ° + θ1) from the position of 180 degrees. Control to reduce the. As a result, the fan angle decreases from θ1 to zero while the X-ray generator rotates by the rotation angle θ1, that is, the irradiation with the X-ray cone beam B1 ends. Also by performing such control, it is possible to perform only X-ray irradiation for obtaining projection data for a projection angle of 180 degrees.

  Furthermore, the method of controlling the irradiation of the X-ray cone beam B1 at the start of irradiation and at the end of irradiation is not limited to the above. FIG. 12 is a diagram showing how the irradiation range of the X-ray cone beam B1 is controlled at the start and end of irradiation.

  In FIG. 12, the X-ray generation unit 10 rotates from the irradiation start position L0 by the rotation angle T1 about the center C1 as the rotation axis, and reaches a position L02B, and the fan angle is constant from zero to θ1. And the fan angle of the X-ray cone beam B1 is constant from θ1 to zero until it reaches the position L1, which is the X-ray irradiation end position, by rotating from the position L03B by the rotation angle T2. The control to decrease is performed.

  Note that a position L01B shown in FIG. 12 is a position of the X-ray generation unit 10 in the middle of an increase in the irradiation range of the X-ray cone beam B1, and is a state of full irradiation of the X-ray cone beam B1 (fan angle is The half on the opposite side of the rotation direction of the X-ray generator 10 with respect to the state of θ1 (when viewed from above in the vertical direction, the left half toward the X-ray detector 20 from the X-ray generator 10 and the fan angle Is the position when only irradiation is performed. Further, the position L04B is the position of the X-ray generation unit 10 in a state where the irradiation range of the X-ray cone beam B1 is decreasing, and the rotation direction of the X-ray generation unit 10 with respect to the entire irradiation state The position is shown when only the side half (when viewed from above in the vertical direction is the left half from the X-ray generator 10 toward the X-ray detector 20 and the fan angle is θ1 / 2) is shown. Yes.

  As shown in FIG. 12, when the X-ray generator 10 rotates from the position L02B by the rotation angle (180 ° −θ1) and reaches the position L03B, it is the same as the point P2 shown in FIG. For the point P2B, the X-ray irradiation is completed from each direction in the range of the projection angle of 180 degrees. The rotation angle (∠L0, C1, L03B) of the X-ray generation unit 10 from the position L0 to the position 03B is (180 ° −θ1 + T1) because ∠L02B, C1, and L03B are 180 ° −θ1. Become.

The rotation angle of the X-ray generation unit 10 from the position L0 to the position L03B is a value obtained by subtracting the rotation angle T2 from the rotation angle (180 ° + θ1) from the position L0 to the position L1 (= 180 ° + θ1-T2). It becomes. In summary, the following equation holds:
∠L0, C1, L03B = 180 ° −θ1 + T1 = 180 ° + θ1−T2 (1)
The following equation is derived from the above equation (1).
T2 = 2 · θ1−T1 (2)

  According to the above formula (2), from the position L0, which is the X-ray irradiation start point, until the X-ray generation unit rotates by the rotation angle T1, the fan angle from the opposite side of the rotation direction is constant from zero to θ1. In the case of increasing, the X-ray generation unit 10 rotates from the position L0 by the rotation angle (180 ° −θ1 + T1) by the rotation angle (2 · θ1−T1) (= T2) and reaches the position L1. Until the fan angle is decreased at a constant rate from θ1 to zero from the opposite side of the rotational direction. Thereby, it is possible to acquire only projection data irradiated with X-rays having a projection angle of exactly 180 ° for all points in the imaging target region R1.

  Here, the control method described in the first embodiment corresponds to T1 = 0, T2 = 2 · θ1, and the control method described in the second embodiment is T1 = 2 · θ1, T2. This corresponds to the case of = 0.

  Note that the fan angle of the X-ray cone beam B1 does not necessarily have to be increased or decreased at a constant rate, and can be changed as appropriate within a range in which irradiation control can be performed for a projection angle of 180 °.

<3. Third Embodiment>
In the first and second embodiments, the X-ray generation unit control unit 601a controls the irradiation range of the X-ray cone beam B1, thereby limiting the range of projection data to be acquired. However, the technique for limiting the acquisition range of projection data is not limited to the above.

  In this embodiment, the X-ray cone beam B1 irradiation range with respect to the imaging target region R1 is not controlled, but the X-ray detection unit control unit 601b controls the X-ray detectable range, thereby obtaining the projection data acquisition range. Limit.

  FIG. 13 is a diagram illustrating a state in which the detection range of the X-ray cone beam B1 is controlled during X-ray CT imaging in the third embodiment. FIGS. 13A to 13C show X-ray CT imaging situations arranged in time series. In FIG. 13, the positions L0, L01, L03, and L1 of the X-ray generation unit 10 coincide with the positions shown in FIG.

  As shown in FIG. 13, also in the X-ray CT imaging of the present embodiment, the X-ray generation unit 10 uses the rotation center C1 of the X-ray cone beam B1 that is the center of the imaging target region R1 as in the first embodiment. The X-ray cone beam B1 is irradiated onto the imaging target region R1 while rotating about the rotation axis by an angle obtained by adding the fan angle θ1 to 180 degrees as the rotation angle. However, the X-ray generation unit 10 is always irradiated with the X-ray cone beam B1 all over the imaging target region R1, and the X-ray detection unit 20 is equivalent to a projection angle of 180 degrees in the imaging target region R1. Control is performed so as not to detect X-rays that have passed through the X-ray irradiation in each direction.

  Specifically, as shown in FIG. 13A, when the X-ray generation unit 10 reaches the position L01, the projection obtained by irradiating the point P2 with X-rays from each direction corresponding to the projection angle of 180 degrees. Data is acquired. Therefore, since it is not necessary to acquire any more projection data for the point P2, the X-ray detection unit 20 invalidates the X-ray detection function of this part. The irradiation range of X-rays to be invalidated is a range indicated by oblique lines in the imaging target region R1.

  Further, as shown in FIG. 13B, when the X-ray generator 10 reaches the position L03, the region R3 on the right side of the line segment connecting the position L03 and the position L0 in the imaging target region R1. The acquisition of projection data irradiated with X-rays from each direction in the range of the projection angle of exactly 180 degrees is already completed. Therefore, at this point, the function of the part that detects the X-rays transmitted through the region R3 is invalidated. Then, as shown in FIG. 13C, when the X-ray generator 10 reaches the position L1, the X-ray detectable range (shown by a thick line in FIG. 13) disappears and X-ray detection is performed. Disappear.

  In the above description regarding the third embodiment, the X-ray detection range on the detection surface is gradually reduced according to the turning angle of the support unit 30 at the time when the end of irradiation of the X-ray cone beam B1 is reached. It is an explanation.

  As described above, by limiting the detectable range of the detection surface of the X-ray detection unit 20, X-rays can be obtained from each direction within the range of the projection angle of 180 degrees at any point in the imaging target region R1. Only projection data obtained by irradiation can be acquired. In the present embodiment, in X-ray CT imaging, the X-ray cone beam B1 is always irradiated to the imaging target region R1. Therefore, the first or second embodiment is more advantageous from the viewpoint of reducing the exposure dose of X-rays.

<4. Fourth Embodiment>
In the third embodiment, control is performed to limit the X-ray detectable range by the X-ray detection unit 20 as the X-ray CT imaging end point is approached, but the method of controlling the detectable range is limited to this. It is not something that can be done.

  In the present embodiment, by controlling the X-ray detectable range from the irradiation start time of the X-ray cone beam B1, any point of the imaging target region R1 can be viewed from each direction within the range of the projection angle of 180 degrees. Only projection data irradiated with X-rays is acquired.

  FIG. 14 is a diagram illustrating a state in which the detection range of the X-ray cone beam B1 is controlled during X-ray CT imaging in the fourth embodiment. 14A to 14C show X-ray CT imaging situations arranged in time series. In FIG. 14, the positions L0, L02A, L04A, and L1 of the X-ray generation unit 10 are the same as the positions shown in FIG.

  In the X-ray CT imaging in the present embodiment, as in the third embodiment, the X-ray generation unit 10 uses the rotation center C1 of the X-ray cone beam B1 that is the center of the imaging target region R1 as the rotation axis, and the rotation angle. The X-ray cone beam B1 having a fan angle of θ1 is irradiated to the imaging target region R1 while rotating by an angle obtained by adding the fan angle θ1 to 180 degrees. However, in this embodiment, as shown in FIG. 14A, the X-ray detector 20 is controlled not to detect X-rays at the start of X-ray irradiation. The X-ray detectable range (indicated by a thick line in FIG. 14) of the X-ray detector 20 is gradually enlarged until the X-ray generator 10 rotates and reaches the position L04A. Specifically, an X-ray detection function for a part that detects X-rays that pass through a region R4 on the left side of a line segment connecting the position L1 and the position of the X-ray detection unit 20 in the imaging target region R1. Is activated.

  As described above, the X-ray detection unit 20 is controlled so as to gradually expand the X-ray detectable range on the detection surface in accordance with the turning angle of the support unit 30 from the X-ray irradiation start time, thereby obtaining an imaging target. For any point in the region R1, only projection data irradiated with X-rays from each direction in the range of the projection angle of 180 degrees can be acquired.

  In the above description regarding the fourth embodiment, the X-ray detection range on the detection surface of the X-ray detection unit 20 is gradually expanded according to the turning angle of the support unit 30 at the start of irradiation with the X-ray cone beam B1. It is an explanation of the case.

  The control of the X-ray detection unit 20 described in the third and fourth embodiments detects the X-ray cone beam B1 emitted from the X-ray generation unit 10 in the first and second embodiments. This is equivalent to enabling only the detection range of the X-ray detector 21. Therefore, as described in detail in the second embodiment, the X-ray detection range is increased at the X-ray irradiation start time, and the X-ray detection range is reached before reaching the X-ray irradiation end time. Even by controlling the X-ray detection unit 20 so as to narrow the range, only projection data irradiated with X-rays from any direction within the range of the projection angle of 180 degrees can be obtained for any point of the imaging target region R1. Needless to say, you can.

<5. Fifth Embodiment>
In the above embodiment, the X-ray generation unit 10 or the X-ray detection unit 20 is controlled to adjust the acquisition range of the projection data, so that the projection angle is exactly 180 degrees for all the points in the imaging target region R1. Only the projection data obtained by irradiating X-rays from each direction is used for the reconstruction calculation process. However, the technique for limiting the range of projection data to be processed is not limited to this.

  FIG. 15 is a diagram illustrating functional blocks realized by the CPU 801A of the information processing main body 80 according to the fifth embodiment. In the X-ray CT imaging of the present embodiment, as in the X-ray CT imaging of the first to fourth embodiments, the X-ray generation unit 10 rotates and moves by an angle obtained by adding the fan angle θ1 to the rotation angle of 180 degrees. The X-ray cone beam B1 is irradiated to the imaging target region R1. However, the X-ray generation unit 10 always irradiates the imaging target region R1 with the X-ray cone beam B1 having the fan angle θ1, and the X-ray detection unit 20 generates X-rays that pass through all points in the imaging target region R1. To detect. As a result, X-ray projection data is collected. This projection data includes projection data obtained by irradiating X-rays from a direction exceeding the range of a projection angle of 180 degrees (hereinafter referred to as “excess projection data”). Is included). Since the range of the surplus projection data is obvious from the first to fourth embodiments, detailed description thereof is omitted.

  As shown in FIG. 14, the information processing main body 80 according to the present embodiment includes a CPU 801 </ b> A that functions as a data exclusion unit 801 c by operating according to a program PG <b> 2 instead of the CPU 801. The data excluding unit 801c has a function of excluding the above-described excess projection data from all projection data. Therefore, the projection data acquired by the data excluding unit 801c includes only projection data obtained by irradiating X-rays from all directions within the range of the projection angle of 180 degrees for all the points in the imaging target region R1. It will be.

  In this way, only the projection data obtained by irradiating the X-ray cone beam from each direction with a projection angle of 180 degrees is the target of the reconstruction calculation.

  Also in the present embodiment, the arithmetic processing unit 801b reconstructs three-dimensional data from such projection data, so that a CT image with reduced artifacts can be generated. Moreover, in the case of this embodiment, since control of the X-ray generation part 10 or the X-ray detection part 20 demonstrated in 1st-4th embodiment becomes unnecessary, an apparatus structure can be simplified and manufacturing cost can be reduced. It becomes possible to suppress.

<6. Modification>
Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

  For example, in the above embodiment, the subject holding unit 421 is configured to fix the subject who is the subject M1 to a predetermined position in the standing posture in the above embodiment, but the subject M1 can be fixed in the sitting posture, for example. You may be comprised with the chair etc.

  Further, in the above embodiment, the support unit 30 is moved in the horizontal direction with respect to the subject M1 by attaching the turning shaft 31 to the horizontal movement mechanism constituted by the XY table 35. For example, the subject holding unit 421 is provided. The subject M1 may be moved relative to the support unit 30 by connecting it to a horizontal movement mechanism. Further, each of the turning shaft 31 and the subject holding unit 421 may be provided with a horizontal movement mechanism so that each of them can be moved in the horizontal direction.

  Moreover, although the X-ray CT imaging apparatus 100 of the said embodiment has a structure standing upright on the floor, it has the structure where X-ray CT imaging is performed with the subject who is the subject M1 sleeping. Needless to say, it can be applied.

  Moreover, although the functional block shown in the said embodiment was demonstrated that it implement | achieved by software, you may implement | achieve part or all of these functional blocks as hardware by a dedicated logic circuit.

  Furthermore, each structure demonstrated in the said embodiment and modification can be suitably combined or abbreviate | omitted unless a contradiction arises mutually.

DESCRIPTION OF SYMBOLS 100 X-ray CT imaging apparatus 10 X-ray generation part 13 X-ray tube 14 X-ray generator 15 Beam shaping plate 151,152,153 Beam passage hole 20 X-ray detection part 21 X-ray detector 211,212 Detection element group 30 Turning Arm 31 Rotating axis 40 Elevating part 60 Main body control part 601 CPU
601a X-ray generation unit control unit 601b X-ray detection unit control unit 60R Rotating motor 60X X-axis motor 60Y Y-axis motor 61 Display unit 62 Operation panel 65 Drive unit 70 X-ray room 8 Information processing device 80 Information processing main unit 801 , 801A CPU
801b Arithmetic processing unit 801c Data exclusion unit B1 X-ray cone beam C1 center (rotation center of X-ray cone beam B1)
M1 Subject PG1, PG2 Program R1 Target area θ1 Fan angle

Claims (12)

An X-ray generator that emits an X-ray cone beam toward the subject;
An X-ray detector for detecting the X-ray cone beam;
A support unit that supports the X-ray generation unit and the X-ray detection unit so as to face each other with the subject interposed therebetween;
A turning drive unit for performing X-ray CT imaging by turning the support unit and turning the X-ray generation unit and the X-ray detection unit around the subject;
An arithmetic processing unit for reconstructing projection data acquired by the X-ray CT imaging to generate three-dimensional data;
An X-ray CT imaging apparatus comprising:
The calculation processing unit only processes projection data obtained by irradiating the X-ray cone beam from each direction with a projection angle of 180 degrees at any point in the X-ray CT imaging region. X-ray CT imaging apparatus. The X-ray CT imaging apparatus according to claim 1,
The swivel driving unit swivels the X-ray generation unit and the X-ray detection unit with a rotation angle that is an angle obtained by adding 180 degrees to an angle that spreads in the rotation direction of the X-ray cone beam. An X-ray CT imaging apparatus that performs imaging. The X-ray CT imaging apparatus according to claim 2,
The X-ray generation unit has a regulating unit that partially blocks the passage of the X-ray by adjusting the size of the opening and regulates the irradiation range of the X-ray cone beam;
When performing the X-ray CT imaging, the X-ray CT is irradiated with the X-ray cone beam from all directions within the projection angle of 180 degrees at all points in the CT imaging region by the operation of the restriction unit. Shooting device. The X-ray CT imaging apparatus according to claim 3,
X-rays in which the restricting unit operates to gradually expand the irradiation range of the X-ray cone beam on the subject at the start of the X-ray cone beam irradiation on the subject according to the turning angle of the support unit. CT imaging device. The X-ray CT imaging apparatus according to claim 3,
The X-ray cone beam irradiation range is gradually reduced in accordance with the turning angle of the support portion before the restriction portion reaches the end point of the X-ray cone beam irradiation on the subject. X-ray CT imaging device that regulates the passage of rays. The X-ray CT imaging apparatus according to claim 3,
The regulation part is
At the start of X-ray cone beam irradiation on the subject, the X-ray cone beam irradiation range for the subject gradually increases according to the turning angle of the support unit, and
Before reaching the end point of the X-ray cone beam irradiation on the subject, the passage of the X-ray is regulated so as to gradually reduce the X-ray cone beam irradiation range according to the turning angle of the support portion. X-ray CT imaging device The X-ray CT imaging apparatus according to any one of claims 2 to 6,
Of the projection data acquired by the X-ray CT imaging, for all the points in the X-ray CT imaging area, extract only the data irradiated with X-rays from each direction of the projection angle of 180 degrees, A calculation unit for performing predetermined reconstruction calculation processing;
An X-ray CT imaging apparatus further comprising: The X-ray CT imaging apparatus according to any one of claims 2 to 7,
The X-ray detection unit has a detection surface in which a plurality of detection elements for detecting X-rays are arranged in a plane, and the X-ray CT is limited by limiting the X-ray detectable range of the detection surface. An X-ray CT imaging apparatus that acquires projection data obtained by irradiating the X-ray cone beam with respect to all points in an imaging region from directions of exactly a projection angle of 180 degrees. The X-ray CT imaging apparatus according to claim 8,
The X-ray detection unit gradually increases the X-ray detection range on the detection surface according to the turning angle of the support unit at the start of irradiation of the X-ray cone beam on the subject. . The X-ray CT imaging apparatus according to claim 8,
The X-ray detection unit gradually reduces the X-ray detection range on the detection surface according to the turning angle of the support unit before reaching the end point of irradiation of the X-ray cone beam on the subject. X-ray CT imaging device. The X-ray CT imaging apparatus according to claim 8,
The X-ray detection unit
At the start of irradiation of the X-ray cone beam on the subject, the X-ray detection range on the detection surface is gradually increased according to the turning angle of the support portion, and
An X-ray CT imaging apparatus that gradually reduces the X-ray detection range on the detection surface in accordance with the turning angle of the support portion before reaching the end point of irradiation of the X-ray cone beam on the subject. In a reconstruction processing method for reconstructing three-dimensional data from X-ray projection data relating to a subject,
The X-ray cone and the X-ray detector are turned around the subject in a state where the X-ray generator and the X-ray detector are opposed to each other with the subject interposed therebetween. A data collection step of performing X-ray CT imaging detected in step S1 and collecting X-ray projection data;
A calculation process for generating three-dimensional data by performing a predetermined reconstruction calculation process on the projection data acquired in the data collection process,
Have
In the calculation step, at any point in the X-ray CT imaging region, only projection data obtained by irradiating the X-ray cone beam from each direction with a projection angle of 180 degrees is used as a calculation processing target. Configuration processing method.

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