JP2019191072A - Ct imaging device and imaging method - Google Patents

Abstract

To provide a CT imaging apparatus that reduces a cone beam artifact and a photographing method that reduces the cone beam artifact.SOLUTION: A CT imaging apparatus irradiates a subject 100 with cone-beam radiation. A placing surface 45 of a stage 4 on which the subject 100 is placed is tilted so that an end surface 71 of a region of interest 7 in the subject 100 and a focal point F of the radiation lie on the same plane, and all the body axis cross-sections of the region of interest 7 and one of radiation transmission paths become parallel once during rotation of the stage 4 and irradiation of the radiation.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a CT imaging apparatus and an imaging method.

  In the CT imaging apparatus, for example, a radiation source that irradiates an X-ray beam as radiation and a detector that detects the X-ray beam of the radiation source with two-dimensional resolution are arranged to face each other. A stage for placing the subject is disposed between the radiation source and the detector, and the subject placed on the stage is interposed between the radiation source and the detector. By rotating the stage once during irradiation with the X-ray beam, the X-ray beam is irradiated from all directions of the subject, and a large number of transmission images are acquired. Volume data and various cross-sectional images are reconstructed from the transmission image and displayed on the display unit.

  When irradiating a fan beam-shaped X-ray beam, in order to obtain a plurality of body axis cross sections along the body axis of the subject, the position is changed along the body axis direction of the subject. The stage must be rotated once while irradiating. On the other hand, when irradiating a cone-beam X-ray beam, that is, when irradiating a radiation beam having an opening angle also in the body axis direction of the subject, the X-ray beam is irradiated over a wide range in the body axis direction of the subject. Therefore, only by rotating the stage once while irradiating the X-ray beam, a plurality of body axis cross sections can be obtained along the body axis of the subject. Therefore, a CT imaging apparatus that irradiates a cone-beam X-ray beam has an advantage that an image of a region of interest of a subject can be obtained at high speed.

JP 2006-214841 A

  However, when a cone-beam X-ray beam is irradiated, a phenomenon called cone beam artifact occurs. That is, the contour of the body axis cross section perpendicular to the rotation axis of the subject is clear with respect to the body axis cross section on or near the optical axis of the X-ray beam, but the body axis becomes farther away from the optical axis of the X-ray beam. The outline of the cross section becomes unclear and the layers of the body axis cross section cannot be clearly distinguished.

  An object of the present embodiment is to provide a CT imaging apparatus that reduces cone beam artifacts and an imaging method that reduces cone beam artifacts in order to solve the above-described problems.

  To achieve the above object, a CT imaging apparatus according to the present embodiment is a CT imaging apparatus that images a region of interest in a subject, a radiation source that irradiates cone-beam radiation, and the radiation. A detector to detect, a stage on which the subject is placed on a placement surface, and the subject is interposed between the radiation source and the detector, and a set of the radiation source and the detector, or the An image of the region of interest based on a rotation mechanism that rotates the stage around a rotation axis that is orthogonal to the optical axis of the radiation, and transmission images in each direction obtained by the detector by rotation and radiation irradiation by the rotation mechanism. An image processing unit for reconfiguring the stage, wherein the stage mounting surface includes all body axis cross sections in the region of interest and one of the radiation transmission paths diffusing from the focal point of the radiation source, Rotation and rotation by rotation mechanism As once during irradiation of the radiation to be parallel, that is inclined a predetermined angle with respect to a direction orthogonal to the rotation axis, characterized by.

  In order to achieve the above object, a CT imaging apparatus according to another aspect of the present embodiment is a CT imaging apparatus that images a region of interest in a subject, and a mounting for mounting the subject. A stage having a placement surface; a radiation source that emits cone-beam-shaped radiation toward the subject on the stage; and the radiation that is positioned opposite to the radiation source across the stage and that has passed through the subject A detector for detecting a radiation source, a set of the radiation source and the detector, or a rotation mechanism for rotating the stage about a normal line perpendicular to the mounting surface, and a rotation mechanism for rotating the detector. An image processing unit that reconstructs an image of the region of interest based on the obtained transmission images in each direction, and the radiation source diffuses from all body axis sections in the region of interest and the focal point of the radiation. Each radiation transmission path One and is, during rotation and irradiation of the radiation by the rotating mechanism, once so as to be parallel, that is inclined a predetermined angle with respect to a direction orthogonal to the rotation axis, characterized by.

  In order to achieve the above object, the imaging method of the CT imaging apparatus according to the present embodiment places a subject on a stage and irradiates the subject with cone-beam radiation from each angle from a radiation source. An imaging method for a CT imaging apparatus that detects radiation by a detector and reconstructs a region of interest in an object as an image, wherein the radiation source and the detector set or the stage is used as the light of the radiation. Rotating about a rotation axis orthogonal to the axis, irradiating radiation, all body axis cross sections in the region of interest and one of each radiation transmission path diffusing from the focal point of the radiation are the rotation and the The stage mounting surface is inclined at a certain angle with respect to a direction orthogonal to the rotation axis of the stage so as to be parallel once during irradiation of radiation.

  In addition, in order to achieve the above object, an imaging method of a CT imaging apparatus according to another aspect of the present embodiment includes placing a subject on a stage and radiating cone beam radiation from each angle with respect to the subject. Is an imaging method of a CT imaging apparatus in which a region of interest in a subject is reconstructed as an image by detecting radiation from a radiation source, and a set of the radiation source and the detector, or the stage Is rotated around a rotation axis orthogonal to the optical axis of the radiation while irradiating the radiation, and all body axis cross sections in the region of interest and one of each radiation transmission path diffusing from the focal point of the radiation are The radiation source is tilted at a certain angle with respect to a direction in which the optical axis of the radiation source is orthogonal to the rotation axis so that the rotation and the radiation are parallel once.

It is a figure which shows the structure of CT imaging apparatus which concerns on this embodiment. It is a schematic diagram which shows the structure of a stage. It is a schematic diagram explaining the inclination angle of a mounting surface. It is a block diagram which shows the structure of a control part and an image process part. It is a flowchart which shows operation | movement of CT imaging device. It is an image which shows the position of the radiation transmission path | route parallel to a body-axis cross section in each inclination angle and each irradiation angle. It is an image which shows the sagittal cross section of the subject at each tilt angle. It is an image of a body axis section of a subject at each tilt angle. It is a schematic diagram which shows the other structure of a stage. It is a figure which shows the other structure of CT imaging device.

  Hereinafter, the CT imaging apparatus according to the present embodiment will be described in detail with reference to the drawings. In addition, each figure may be exaggerated from a viewpoint of clarification, and is not limited to the scale in a figure. For example, the actual tilt angle α is different from the tilt angle α in the drawing, but is not limited to the tilt angle α in the drawing.

  FIG. 1 is a diagram illustrating an overall configuration of a CT imaging apparatus 1 according to the present embodiment. The CT imaging apparatus 1 is used for nondestructive inspection and medical applications by imaging the inside of the subject 100. The CT imaging apparatus 1 irradiates a subject 100 with a radiation beam over 360 ° with a rotation axis R as a rotation center, and collects transmission images of a plurality of views. The CT imaging apparatus 1 creates volume data from the transmission images of a plurality of views, and further creates a cross-sectional image of the subject 100 from the volume data.

  The transmission image is two-dimensional distribution data of radiation intensity attenuated in the process of passing through the subject 100. Volume data is a three-dimensional distribution of CT values. CT values are expressed by relatively expressing linear attenuation coefficients according to the elemental composition and density of each part of the subject 100 with reference to the linear attenuation coefficients of water and air. It is a converted value. The cross-sectional image is an image of the body axis cross section of the subject 100, in other words, an image of an axial cross section that extends in parallel with the optical axis CL of the radiation beam. In addition, as a cross-sectional image, a sagittal cross-section, a coronal cross-section, an oblique cross-section, and an MPR image may be generated.

  The CT imaging apparatus 1 includes a radiation source 2, a detector 3, a stage 4, a control unit 5, and an image processing unit 6. The radiation source 2 and the detector 3 are arranged to face each other. The stage 4 is disposed between the radiation source 2 and the detector 3. The control unit 5 is connected to the radiation source 2, the detector 3, and the stage 4 through a signal line so that control signals can be transmitted and received. The image processing unit 6 is connected by a signal line so as to receive a signal output from the detector 3. The control unit 5 and the image processing unit 6 are a processing device 8 including a so-called computer. The processor and the program that execute instructions according to the program are expanded, and the memory and the program that temporarily stores the execution results and data of the instructions are stored. It comprises a storage and an interface capable of transmitting / receiving control signals or data to / from each part of the CT imaging apparatus 1.

  The radiation source 2 irradiates the subject 100 with a radiation beam. The radiation is, for example, X-rays. The radiation beam is a cone beam having a focal point F of the radiation source 2 as an apex and having a cone angle and expanding in a conical shape. The radiation source 2 is, for example, a reflective or transmissive X-ray tube. In an X-ray tube, a filament and a target such as tungsten are placed opposite to each other in a vacuum, and a tube voltage is applied between the cathode on the filament side and the anode on the target side. Then, electrons are emitted from the filament, and the electrons are accelerated toward the target and collide with the target. X-rays are generated during this collision. The radiation beam includes, for example, γ rays and neutron rays, and the radiation source 2 may emit γ rays or neutron rays.

  The detector 3 is an area detector that is arranged to face the focal point F of the radiation source 2 and detects a transmission image of a plurality of views. The detector 3 is, for example, a flat panel detector (FPD). In the FPD, radiation detection elements are arranged two-dimensionally. Each detection element has a scintillator surface and a photodiode. The scintillator surface is made of cesium iodide that emits light when excited by radiation. The photodiode converts and accumulates the fluorescent image on the scintillator surface into electric charge, and outputs the accumulated electric charge when an ON signal is given to the TFT switch. The detector 3 may be constituted by, for example, an image intensifier (II) and a camera.

  The stage 4 has a placement surface 45 on which the subject 100 is placed, and the subject 100 is positioned between the radiation source 2 and the detector 3. FIG. 2 is a schematic diagram showing a detailed configuration of the stage 4. As shown in FIG. 2, the stage 4 is supported by a rotation mechanism 41, a shift mechanism 42, an elevating mechanism 43, and a tilting mechanism 44.

  The rotation mechanism 41 rotates the stage 4 once around the rotation axis R. The rotation axis R extends perpendicular to the optical axis CL of the radiation beam and passes through the center of the stage 4. The shift mechanism 42 moves the stage 4 in a direction orthogonal to the rotation axis R along the optical axis CL of the radiation beam, and moves the stage 4 closer to or away from the radiation source 2. The shift mechanism 42 moves the stage 4 in a direction orthogonal to the rotation axis R. The lifting mechanism 43 moves the stage 4 along the rotation axis R. The tilt mechanism 44 tilts the placement surface 45 of the stage 4. In other words, the tilt mechanism 44 makes the normal line N of the mounting surface 45 obliquely intersect the rotation axis R.

  The rotation mechanism 41, the shift mechanism 42, and the lifting mechanism 43 are configured by a ball screw mechanism as an example. That is, a rail, a rotary motor, a shaft, and a slider are provided. The rail is placed on the moving object and extends in the moving direction. The rotation motor rotates the shaft. The shaft extends in parallel with the rail, is threaded, and is prevented from moving in the extending direction. The slider is screwed to the shaft and connected to the moving object. When the rotary motor is operated, the shaft rotates, the slider moves along the shaft, and the moving object connected to the slider slides along the rail. For example, the shift mechanism 42, the lifting mechanism 43, the rotation mechanism 41, the tilting mechanism 44, and the placement surface 45 of the stage 4 are stacked in this order from the lower layer, and all the upper layers are set as moving targets.

  The tilt mechanism 44 is, for example, a gonio stage. The gonio stage has a base 441 and a sliding portion 442. The base 441 is pivotally supported by the rotation mechanism 41, and the sliding portion 442 supports the placement surface 45. The base 441 has a concave curved surface 441a, the sliding portion 442 has a convex curved surface 442a, the concave curved surface 441a and the convex curved surface 442a have the same curvature, and the concave curved surface 441a and the convex curved surface 442a are It is rubbed together. The circle center C of the concave curved surface 441a and the convex curved surface 442a of the base 441 and the sliding portion 442 is located on the extension line of the shaft of the rotation mechanism 41, in other words, on the rotation axis R.

  The tilt mechanism 44 tilts the placement surface 45 of the stage 4 so that the end surface 71 of the region of interest 7 and the focal point F of radiation are placed on the same plane S. The region of interest 7 is also called a ROI, and is a spatial region in the subject 100 that is noticed by the user. The end surface 71 is one of the surfaces parallel to the placement surface 45. This tilting mechanism 44 has the mounting surface 45 of the stage 4 by a certain tilting angle α expressed by the following formula (1) because the end surface 71 of the region of interest 7 and the focal point F of radiation are placed on the same plane S. Tilt. The tilt angle α is an angle formed between the normal line N perpendicular to the mounting surface 45 of the stage 4 and the rotation axis R, in other words, an angle formed between the mounting surface 45 and the direction orthogonal to the rotation axis R. Further, the tilt angle α is constant, and the tilt angle α does not change during the rotation of the stage 4.

  Here, as shown in FIG. 3, FCD in the above formula (1) is a distance from the focal point F of the radiation to the center of rotation on the optical axis CL. The rotation center is the intersection of the optical axis CL and the rotation axis R. FOVx is the length in the optical axis CL direction in the spatial range in which the region of interest 7 extends by precession. H is the distance from the position away from the focal point F along the optical axis CL by the distance FCD to the boundary of the spatial range in which the region of interest 7 extends by precession in the direction orthogonal to the optical axis CL. When the region of interest 7 is accommodated in the entire effective field of view where image reconstruction is possible, the tilt angle α is an angle formed by the optical axis CL and the irradiation limit line of the radiation beam as a result of following the above equation (1), that is, Half the cone angle.

  The control unit 5 is a so-called computer, a processor that executes instructions according to the program, a memory in which the program is expanded, a memory that temporarily stores the execution result and data of the instruction, a storage that stores the program, and the radiation source 2 and the detector 3. And an interface for outputting a control signal to the stage 4. As shown in FIG. 4, the control unit 5 includes an ROI setting unit 51, a tilt angle calculation unit 52, and a tilt control unit 53, aligns the region of interest 7 with the effective field of view (FOV) of the radiation beam, 1) is calculated, and the mounting surface 45 of the stage 4 is further tilted to the tilt angle α. When the region of interest 7 is matched with the effective visual field, the calculation of the above formula (1) by the tilt angle calculation unit 52 may be omitted, and a cone angle stored in advance may be used.

  That is, the control unit 5 operates the shift mechanism 42 and the lifting mechanism 43 to match the region of interest 7 with the effective visual field. An operation unit 54 such as a keyboard or a mouse and a display unit 55 such as a monitor are connected to the control unit 5. The control unit 5 displays the temporarily captured transmission image on the display unit 55 and accepts an input of the region of interest 7 using the operation unit 54. Typically, a rectangular figure having a user-desired position and size is drawn on the transmission image using the operation unit 54, and the control unit 5 recognizes the rectangular figure as the region of interest 7 and draws the drawn region of interest. The stage 4 is moved so that 7 matches the effective visual field.

  Further, the control unit 5 serves as the tilt angle calculation unit 52, the distance FCD from the focal point F of the radiation to the center of rotation on the optical axis CL, and the length FOVx in the direction of the optical axis CL in the range in which the region of interest 7 extends by precession. And the distance H from the position away from the focal point F along the optical axis CL by the distance FCD to the boundary of the range in which the region of interest 7 is precessed in the direction orthogonal to the optical axis CL. And the control part 5 calculates the inclination angle (alpha) according to said Formula (1) from these FCD, FOVx, and H as the inclination angle calculation part 52. FIG. Then, the control unit 5 operates the tilt mechanism 44 as the tilt control unit 53, and mounts the normal line N perpendicular to the mounting surface 45 of the stage 4 so that the normal line N is tilted with respect to the rotation axis R by the tilt angle α. Tilt surface 45. The direction of tilting may be any.

  The image processing unit 6 is a so-called computer, a processor that executes instructions according to a program, a program that is expanded, a memory that temporarily stores execution results and data of instructions, a storage that stores programs, and a detector 3 outputs It consists of an input interface that receives signals. The image processing unit 6 and the control unit 5 may be configured by a single computer. As shown in FIG. 4, the image processing unit 6 includes a reconstruction unit 61 that reconstructs an image in the subject 100 from transmission images of a plurality of views, and a correction unit 62 that corrects the inclination of the three-dimensional CT image. I have. A three-dimensional CT image is a three-dimensional image represented by volume data.

  The reconstruction unit 61 receives transmission images of each direction of the subject 100 tilted by the tilt angle α from the detector 3, generates volume data from these transmission images, and generates a cross-sectional image from the volume data. In this reconstruction, for example, the FDK (Feldkamp, Davis, Kress) method, the filtered back projection method, or the ART (Algebraic Reconstruction Technique) method, the successive approximation method, or the like is used. When the subject 100 is tilted and imaged by the tilt mechanism 44, the correction unit 62 corrects the tilt of the image caused by this tilt to erect the three-dimensional CT image. The correction unit 62 performs coordinate conversion in which the coordinates of the CT values included in the volume data are rotated and moved by the tilt angle α, contrary to the tilted direction.

  The operation of the CT imaging apparatus 1 will be described in detail with reference to FIG. FIG. 5 is a flowchart showing the operation of the CT imaging apparatus 1. First, the CT imaging apparatus 1 sets the region of interest 7 (step S01).

  In step S01, first, the subject 100 is placed on the stage 4, imaging conditions such as tube voltage and tube current are set, and provisional imaging is started. In this first imaging, the imaging magnification (= FDD / FCD) may be set small so that the subject 100 surely falls within the effective visual field. The stage 4 makes the normal line N perpendicular to the mounting surface 45 coincide with the rotation axis R, that is, the tilt angle α is set to zero. The radiation source 2 emits a radiation beam while the stage 4 is not rotated, and the detector 3 detects a transmission image of the subject 100. The image processing unit 6 displays the transmission image received from the detector 3 on the display unit 55. The user draws a rectangular figure representing the region of interest 7 using the operation unit 54 on the displayed transmission image.

  When the region of interest 7 is input by drawing, the control unit 5 moves the amount of movement of the stage 4 where the region of interest 7 and the effective field of view coincide with each other, and the rotation axis R of the normal N perpendicular to the placement surface 45 of the stage 4. The tilt angle α with respect to is calculated (step S02). Then, the shift mechanism 42, the elevating mechanism 43, and the tilt mechanism 44 move the stage 4 according to the amount of movement and the tilt angle α under the control of the control unit 5 (step S03), and the mounting surface 45 of the stage 4 Is tilted (step S04).

  In step S02 and step S03, the control unit 5 calculates a movement amount for making the center of the region of interest 7 coincide with the center of the effective visual field. For example, the number of vertical and horizontal pixels and the center coordinates of the region of interest 7 and the effective visual field drawn on the display unit 55 are calculated. Next, a movement amount in which the center coordinates of the region of interest coincide with the center coordinates of the effective visual field is calculated. That is, since the center of the region of interest 7 and the center of the effective field of view coincide with each other, the number of pixels in the direction along the optical axis CL, the direction of the rotation axis R, and the direction orthogonal to the optical axis CL and the rotation axis R. Calculate whether to move. The calculated amount of pixels in each direction is converted based on the relationship between the distance in real space and the number of pixels stored in advance to obtain the movement amount.

  Further, the control unit 5 calculates the amount of movement of the stage 4 for matching the size of the region of interest 7 and the size of the effective visual field. That is, from the state where the center of the region of interest 7 and the center of the effective field of view coincide with each other, the ratio for matching the number of vertical and horizontal pixels of the region of interest 7 with the number of vertical and horizontal pixels of the effective field of view, in other words, the photographing magnification ( = FDD / FCD). Then, the movement amount of the stage 4 is calculated based on the calculated FDD value and FCD value.

  Furthermore, in step S02 and step S04, the control unit 5 calculates the tilt angle α satisfying the above formula (1) by calculating the FCD value, the FOVx value, and the H value as the tilt angle calculation unit 52. The sliding portion 442 of the tilting mechanism 44 moves along the concave curved surface 441a of the base 441 under the control of the tilt control unit 53 of the control unit 5, and tilts around one point on the rotation axis R as the center of the circle. Change direction by α.

  Next, the CT imaging apparatus 1 starts main imaging of the subject 100 (step S05). At this time, the rotation mechanism 41 of the stage 4 rotates the stage 4 once around the rotation axis R. The subject 100 placed on the placement surface 45 of the stage 4 also makes one rotation around the rotation axis R. During this rotation, the radiation source 2 emits a radiation beam, and the detector 3 outputs a transmission image of the subject 100 to the image processing unit 6.

  During the main imaging of the subject 100, the subject 100 tilts by the tilt angle α with respect to the rotation axis R and performs precession. FIG. 6 is each image showing the position of the radiation transmission path parallel to the cross section of the body axis at each tilt angle and each irradiation angle. In each image, the white streaks represent the positions of radiation transmission paths parallel to the body axis cross section.

  As shown in FIG. 6, when the tilt angle is 0 °, that is, when the placement surface 45 and the rotation axis R are orthogonal, the precession of the subject 100 does not occur, and therefore, over the entire rotation angle of the stage 4, A radiation transmission path parallel to only the cross section of the body axis parallel to the optical axis CL is generated. On the other hand, when the tilt angle is tilted to about 2.5 °, that is, about half of the tilt angle α, the position of the parallel radiation transmission path changes according to the rotation of the stage 4.

  Furthermore, as shown in FIG. 6, when the tilt angle is about 5 °, that is, when tilted to the tilt angle α where the end surface 71 of the region of interest 7 and the radiation focus F are placed on the same plane S, according to the rotation angle of the stage 4, The position of the radiation path parallel to the body axis section changes along the body axis direction of the subject 100, that is, along the rotation axis R. Here, the subject 100 is tilted so that the end surface 71 of the region of interest 7 and the focal point F of the radiation are on the same plane S. Accordingly, during rotation, a parallel radiation transmission path is created once for all the body axis cross sections of the region of interest 7.

  Then, when the main imaging of the subject 100 is completed, the image processing unit 6 generates volume data of the subject 100 (step S06). The volume data is tilted by the tilt angle α. Therefore, when the volume data is generated, the image processing unit 6 corrects the inclination of the volume data as the correction unit 62 (step S07), and erects the three-dimensional CT image represented by the volume data.

  When the volume data is generated and corrected, the image processing unit 6 selects an image of a selected section such as a body axis section, a sagittal section, an annular section, an oblique section, or an MPR image from the volume data according to the operation section 54. Is generated (step S08), and the generated image is displayed on the display unit 55 (step S09).

  FIG. 7 is an image showing a sagittal section of the subject 100 at each tilt angle. The imaged subject 100 is formed by stacking discs such as CDs and DVDs in multiple layers. The subject 100 has an overlapping disk fixed with an adhesive tape. The subject 100 was photographed at a tilt angle of 0 °, a tilt angle of about 2.5 °, that is, half of the tilt angle α, and a tilt angle of about 5 °, that is, the tilt angle α.

  As shown in FIG. 7, when the subject 100 is imaged without tilting, the distinction between the upper and lower layers of the disc is unclear. On the other hand, when the subject 100 is tilted to half the tilt angle α, the range in which the contour of the body axis cross-section is clear is enlarged. Further, when the subject 100 is tilted by the tilt angle α so that the end surface 71 of the region of interest 7 and the focal point F of the radiation lie on the same plane S, the outline of each disk is clearly seen over the entire subject 100. However, the disc layers are clearly distinguished.

  Thus, cone beam artifacts are reduced across the region of interest 7. That is, when the subject 100 is tilted by the tilt angle α, the resolution in the body axis direction is improved and each body axis section is clearly distinguished. The radiation transmission path parallel to the body axis section has only information on the body axis section or only information outside the body axis section, so the layers are considered to be clearly distinguished. .

  FIG. 8 is an image showing the vicinity of the optical axis CL, a layer slightly below the optical axis CL, and a layer further below the optical axis CL in the body axis cross section of the subject 100, and the tilt angle α. The image was taken with the subject 100 tilted, and the image was taken without tilting the subject 100. The imaged subject 100 is formed by stacking discs such as CDs and DVDs in multiple layers. The subject 100 has an overlapping disk fixed with an adhesive tape.

  As shown in FIG. 8, when the subject 100 is imaged with an inclination angle α, that is, an inclination angle of about 5 ° so that the end surface 71 of the region of interest 7 and the focal point F of radiation are on the same plane S, the optical axis CL is obtained. The disk having the cross section of the body axis in the vicinity is as clear as the upper and lower disks than the optical axis CL, and the characters on the disk surface can be discriminated. On the other hand, if the subject 100 is photographed without tilting, the inside of the body axis section near the optical axis CL is very unclear, and the characters on the disk surface cannot be discriminated.

  This is because if a radiograph is taken at an inclination angle α, a radiation transmission path that intersects the cross section of the body axis near the optical axis CL is generated. Therefore, the transmission distance of the cross section of the body axis near the optical axis CL is shortened, and radiation is attenuated. This is thought to be because the amount of radiation is suppressed, and the difference in attenuation of radiation due to characters on the disk surface increases. On the other hand, if imaging is performed without tilting the subject 100, a radiation transmission path that is nearly parallel to the body axis section is generated for the body axis section near the optical axis CL, and the transmission distance of the body axis section is long. It is considered that the inside of the body axis section in the vicinity of the optical axis CL is unclear because the length is long, the amount of radiation attenuation is large, and the difference in the amount of radiation attenuation due to characters on the disk surface is reduced.

  As described above, in the CT imaging apparatus 1 that irradiates the cone-beam-shaped radiation, the placement surface 45 of the stage 4 is tilted so that the end surface 71 of the region of interest 7 and the focal point F of the radiation are placed on the same plane S. The subject 100 was photographed while precessing. That is, all body axis cross sections of the region of interest 7 and one of the radiation transmission paths are made parallel once during the rotation of the stage 4 and the radiation irradiation.

  Therefore, the resolution in the body axis direction of the subject 100, that is, the direction of the normal N perpendicular to the placement surface 45 is improved, cone beam artifacts are reduced, and the layers can be clearly distinguished. Further, since a radiation transmission path intersecting with the body axis cross section near the optical axis CL is generated, the transmission distance of the body axis cross section near the optical axis CL is shortened, and the body axis cross section near the optical axis CL becomes clear.

  Here, a radiation transmission path parallel to all the body axis cross sections in the region of interest 7 may be created once, and a parallel radiation transmission path may be created beyond the region of interest 7. This also clearly distinguishes the body axis section in the region of interest 7. That is, the placement surface 45 may be inclined so that the plane S on which the end surface 71 of the region of interest 7 is placed intersects the optical axis CL extending from the focal point F. In other words, it may be tilted to a tilt angle α or more shown by the above formula (1). For example, the angle formed by the normal line N of the mounting surface 45 with respect to the rotation axis R may be within 30 °.

  However, if the tilt angle is more than 3 ° larger than the tilt angle α that satisfies the above formula (1), the resolution of the body axis cross section near the optical axis CL starts to drop below the peak value. It is considered that the radiation transmission path that intersects the body axis section near the optical axis CL also passes through the adjacent body axis section. Further, it is considered that as the tilt angle α is larger, the FOVx becomes larger, so that the resolution of the body axis section is lowered. On the other hand, if the tilt angle α is within the range of the tilt angle α + 3 °, the radiation transmission path crossing the body axis cross section near the optical axis CL is less likely to pass through the adjacent body axis section, or several layers. The possibility of passing through the body axis cross section is low, and the FOVx is not excessively increased, so that a good resolution of the body axis cross section near the optical axis CL is maintained.

  Further, the CT imaging apparatus 1 of the present embodiment automatically matches the effective visual field and the region of interest 7, but the effective visual field and the region of interest 7 may be manually matched, or the effective visual field may be changed. If the region of interest 7 fits, the effective visual field and the region of interest 7 do not have to be matched. As a manual method, the shift mechanism 42 and the lifting mechanism 43 may be operated according to the input content of the operation unit 54. When the effective visual field and the region of interest 7 are not matched, the above formula (1) is useful. When the effective visual field and the region of interest 7 are matched, the above formula (1) is omitted and the half of the cone angle is omitted. Just tilt it at an angle.

  In addition, the CT imaging apparatus 1 further includes a tilt mechanism 44 that tilts at a certain angle, but instead, a member is sandwiched between the subject 100 and the placement surface 45 to tilt the subject 100. You may do it.

  In addition, the tilt mechanism 44 is a gonio stage and is tilted with the point on the rotation axis R as the center of rotation. Thus, the length FOVx in the optical axis CL direction can be shortened in the range covered by the region of interest 7 due to precession. Therefore, the resolution of the image to be reconstructed can be improved.

  However, the tilt mechanism 44 is not limited to the gonio stage, and any mechanism that can tilt the mounting surface 45 may be used. For example, as shown in FIG. 9, a hinge 45b connected to the base 45a is attached to one side of the mounting surface 45, and an expansion / contraction rod 45c that expands and contracts by air pressure or the like is fixed to the opposite side to the side to which the hinge 45b is attached. The mounting surface 45 may be inclined with the hinge 45b as a base point by expansion and contraction of the telescopic rod 45c.

  The CT imaging apparatus 1 is further provided with a tilt angle calculation unit 52 that calculates a constant tilt angle α, and the tilt mechanism 44 is tilted according to the calculation result of the tilt angle calculation unit 52. Thereby, the placement surface 45 of the stage 4 is such that all the body axis cross sections in the region of interest 7 and one of the respective radiation transmission paths diffusing from the focal point F of the radiation source 2 rotate the stage 4 and irradiate the radiation. It can be tilted with high precision so that it is parallel once. Alternatively, the user may calculate the tilt angle α, and the user may apply an external force to the sliding portion 442 of the tilt mechanism 44 to tilt the placement surface 45 manually.

  Further, the CT imaging apparatus 1 includes a correction unit 62 that corrects the inclination of the three-dimensional CT image generated in the process of reconstruction. Thereby, even if the subject 100 is tilted and photographed, an image that does not give the user a sense of incongruity can be reconstructed.

  In the CT imaging apparatus 1 of the present embodiment, the mounting surface 45 is inclined, but it is sufficient that the subject 100 precesses relative to the radiation beam. For example, as shown in FIG. 10, the radiation source 2 and the detector 3 are connected by an arm (not shown). The tilt mechanism 44 supports the arm and tilts the set of the radiation source 2 and the detector 3 through the arm. The tilt angle α is an angle of the optical axis CL with respect to the direction orthogonal to the rotation axis R. On the other hand, the normal N perpendicular to the mounting surface 45 is made to coincide with the rotation axis R. This also ensures that all body axis cross-sections in the region of interest 7 and one of the respective radiation transmission paths diffusing from the focal point F of the radiation during the rotation of the radiation source 2 and detector 3 array and irradiation of radiation. Once parallel. Therefore, an image in which the layers of the body axis section are clearly distinguished is obtained, and the body axis section near the optical axis CT becomes clear.

  In the CT imaging apparatus 1 of the present embodiment, the stage 4 is rotated, but the set of the radiation source 2 and the detector 3 may be rotated. For example, the radiation source 2 and the detector 3 are connected by an arm. The rotation mechanism 41 may support an arm, and the pair of the radiation source 2 and the detector 3 may be rotated about one point on the rotation axis R via the arm. At this time, since the rotation axis R coincides with the normal line N when the tilt angle of the mounting surface 45 is 0 °, it is not necessary to tilt the subject 100 when the subject 100 contains liquid, etc. The liquid level and the mounting surface 45 can be maintained in parallel.

(Other embodiments)
In the present specification, an embodiment according to the present invention has been described. However, this embodiment is presented as an example, and is not intended to limit the scope of the invention. The embodiment as described above can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The embodiments and the modifications thereof are included in the scope of the invention and the scope of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 CT imaging apparatus 2 Radiation source 3 Detector 4 Stage 41 Rotation mechanism 42 Shift mechanism 43 Elevating mechanism 44 Tilt mechanism 441 Base 441a Concave curved surface 442 Sliding part 442a Convex curved surface 45 Mounting surface 45a Base 45b Hinge 45c Telescopic rod 5 Control Unit 51 ROI setting unit 52 tilt angle calculation unit 53 tilt control unit 54 operation unit 55 display unit 6 image processing unit 61 reconstruction unit 62 correction unit 7 region of interest 71 end face 8 processing device CL optical axis R rotation axis S coplanar 100 covered Specimen

Claims (13)

A CT imaging apparatus for imaging a region of interest in a subject,
A radiation source that emits cone-beam radiation;
A detector for detecting the radiation;
A stage for placing the subject on a placement surface and interposing the subject between the radiation source and the detector;
A rotation mechanism for rotating the set of the radiation source and the detector or the stage around a rotation axis perpendicular to the optical axis of the radiation;
An image processing unit that reconstructs an image of the region of interest based on a transmission image in each direction obtained by the detector through rotation by the rotation mechanism and radiation irradiation;
With
The stage mounting surface is such that all body axis cross-sections in the region of interest and one of each radiation transmission path diffusing from the focal point of the radiation source are rotated once by the rotation mechanism and during irradiation of the radiation. Are inclined at a certain angle with respect to the direction perpendicular to the rotation axis so that they are parallel to each other,
CT imaging device characterized by the above. A CT imaging apparatus for imaging a region of interest in a subject,
A stage having a placement surface on which the subject is placed;
A radiation source that emits cone-beam radiation toward the subject on the stage;
A detector that is positioned opposite to the radiation source across the stage and that detects the radiation transmitted through the subject;
A rotation mechanism for rotating the set of the radiation source and the detector, or the stage about a normal line perpendicular to the mounting surface as a rotation axis;
An image processing unit for reconstructing an image of the region of interest based on a transmission image in each direction obtained by the detector by rotation by the rotation mechanism;
With
The radiation source is configured such that all body axis sections in the region of interest and one of the radiation transmission paths diffusing from the focal point of the radiation are parallel once during rotation by the rotation mechanism and irradiation of the radiation. So that it is inclined at a certain angle with respect to the direction orthogonal to the rotation axis,
CT imaging device characterized by the above. The end face of the region of interest and the focal point of the radiation source are on the same plane, or the plane on which the end face of the region of interest is placed is inclined at a certain angle until it intersects the optical axis of the radiation;
The CT imaging apparatus according to claim 1 or 2. The constant angle is within 30 °;
The CT imaging apparatus according to any one of claims 1 to 3. The angle α °, which is the constant angle, is a range represented by the following formula (1):
The CT imaging apparatus according to claim 4.
The angle α °, which is the constant angle, is a range represented by the following formula (2).
The CT imaging apparatus according to claim 4.
Further comprising a tilting mechanism for tilting the constant angle;
A CT imaging apparatus according to claim 1, wherein: The tilt mechanism is a gonio stage;
The CT imaging apparatus according to claim 7. The gonio stage is tilted around a point on the rotation axis;
The CT imaging apparatus according to claim 8. A tilt angle calculator for calculating the constant angle;
The tilt mechanism is tilted according to a calculation result of the tilt angle calculator;
A CT imaging apparatus according to any one of claims 7 to 9. The image processing unit includes a correction unit that corrects an inclination of a three-dimensional CT image generated in the reconstruction process;
The CT imaging apparatus according to claim 1, wherein: CT that places the subject on the stage, irradiates the subject with cone-beam radiation from various angles, detects the radiation with a detector, and reconstructs the region of interest as an image A photographing method of a photographing apparatus,
While rotating the set of the radiation source and the detector or the stage around a rotation axis orthogonal to the optical axis of the radiation, the radiation is irradiated,
Placement of the stage so that all body axis sections in the region of interest and one of each radiation transmission path diffusing from the focal point of the radiation are parallel once during the rotation and irradiation of the radiation. Tilting the surface at a certain angle with respect to the direction orthogonal to the rotation axis of the stage;
An imaging method of a CT imaging apparatus characterized by the above. CT that places the subject on the stage, irradiates the subject with cone-beam radiation from various angles, detects the radiation with a detector, and reconstructs the region of interest as an image A photographing method of a photographing apparatus,
While irradiating the radiation while rotating the set of the radiation source and the detector or the stage around a rotation axis orthogonal to the optical axis of the radiation,
The radiation source so that all body axis sections in the region of interest and one of each radiation transmission path diffusing from the focal point of the radiation are parallel once during the rotation and irradiation of the radiation; Tilting the optical axis of the radiation source by a certain angle with respect to the direction orthogonal to the rotation axis,
An imaging method of a CT imaging apparatus characterized by the above.