JP7148267B2 - CT imaging device and imaging method - Google Patents

Description

An embodiment of the present invention relates to a CT imaging apparatus and imaging method.

In a CT imaging apparatus, for example, a radiation source that emits an X-ray beam as radiation and a detector that detects the X-ray beam from the radiation source with two-dimensional resolution are arranged to face each other. A stage on which an object is placed is arranged between the radiation source and the detector, and the object placed on the stage is interposed between the radiation source and the detector. By rotating the stage once while irradiating the X-ray beam, the X-ray beam is irradiated from all directions on the object to be inspected, and a large number of transmission images are obtained. Volume data and various cross-sectional images are reconstructed from this transmission image and displayed on the display unit.

In the case of irradiating a fan-shaped X-ray beam, in order to obtain a plurality of body-axis cross-sections along the body axis of the subject, the position of the subject is changed along the body axis direction, and the X-ray beam The stage must be rotated once while irradiating . On the other hand, in the case of irradiating a cone-beam X-ray beam, that is, in the case of irradiating a radiation beam having an opening angle also in the body axis direction of the subject, the X-ray beam should be irradiated over a wide range in the body axis direction of the subject. can be obtained, a plurality of body-axis cross-sections can be obtained along the body axis of the subject by rotating the stage only once while irradiating the X-ray beam. Therefore, a CT imaging apparatus that irradiates a cone-shaped X-ray beam has the advantage of being able to obtain an image of a region of interest of a subject 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 cross section becomes sharper as the distance from the optical axis of the X-ray beam increases. 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 with reduced cone beam artifacts and an imaging method with reduced cone beam artifacts in order to solve the above problems.

In order to achieve the above object, a CT imaging apparatus according to the present embodiment is a CT imaging apparatus for imaging a region of interest within a subject, comprising: a radiation source that emits cone-beam radiation; a detector for detection, a stage on which the subject is placed on a mounting surface so that the subject is interposed between the radiation source and the detector, a set of the radiation source and the detector, or the A rotation mechanism that rotates the stage around a rotation axis orthogonal to the optical axis of the radiation, and an image of the region of interest based on transmission images in each direction obtained by the detector through rotation by the rotation mechanism and radiation irradiation. and an image processing unit that reconstructs the It is characterized in that it is tilted at a certain angle with respect to the direction orthogonal to the rotation axis so that the rotation by the rotation mechanism and the radiation are parallel once.

Further, 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 within a subject, and includes a mount on which the subject is placed. a stage having a placement surface; a radiation source that emits cone-beam radiation toward a subject on the stage; and the radiation that passes through the subject and is positioned opposite to the radiation source with the stage interposed therebetween. a detector that detects the radiation source and the detector, or a rotation mechanism that rotates 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, and the detector is rotated by the rotation by the rotation mechanism an image processing unit that reconstructs an image of the region of interest based on the transmission images obtained in each direction, wherein the radiation source diffuses from all axial cross sections in the region of interest and the focal point of the radiation one of the radiation transmission paths is tilted at a certain angle with respect to a direction orthogonal to the rotation axis so as to be parallel once during the rotation by the rotation mechanism and the irradiation of the radiation. Characterized by

In order to achieve the above object, the imaging method of the CT imaging apparatus according to the present embodiment includes placing a subject on a stage and irradiating the subject with cone-beam radiation from a radiation source at each angle. and detecting the radiation with a detector, and reconstructing an image of a region of interest in the subject, wherein the combination of the radiation source and the detector or the stage is irradiated with the light of the radiation. Radiation is emitted while rotating about a rotation axis orthogonal to the axis, and all axial cross-sections in the region of interest and one of each radiation transmission path diverging from the focus of the radiation are aligned with the rotation and the The mounting surface of the stage is tilted at a certain angle with respect to a direction perpendicular to the axis of rotation of the stage so as to be parallel once during radiation irradiation.

In order to achieve the above object, an imaging method for a CT imaging apparatus according to another aspect of the present embodiment includes placing a subject on a stage and emitting cone-beam radiation from each angle to the subject. is irradiated from a radiation source, the radiation is detected by a detector, and a region of interest within a subject is reconstructed as an image, comprising a set of the radiation source and the detector, or the stage is rotated around a rotation axis perpendicular to the optical axis of the radiation, and all the body-axis cross-sections in the region of interest and one of the radiation transmission paths diverging from the focus of the radiation and tilting the radiation source 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 once parallel during irradiation.

It is a figure which shows the structure of the CT imaging device which concerns on this embodiment. 3 is a schematic diagram showing the configuration of a stage; FIG. It is a schematic diagram explaining the inclination angle of a mounting surface. 3 is a block diagram showing the configuration of a control unit and an image processing unit; FIG. It is a flow chart which shows operation of a CT imaging device. It is an image showing the position of the radiation transmission path parallel to the body axis section at each tilt angle and each irradiation angle. It is an image showing a sagittal section of the subject at each tilt angle. It is the image of the body axis section of the subject at each tilt angle. FIG. 10 is a schematic diagram showing another configuration of the stage; It is a figure which shows the other structure of a CT imaging device.

A CT imaging apparatus according to this embodiment will be described in detail below with reference to the drawings. Each figure may be exaggerated from the viewpoint of clarity, and the scale in the figure is not limited. For example, the actual tilt angle α is different from the tilt angle α in the drawing, but the tilt angle α in the drawing is not limiting.

FIG. 1 is a diagram showing the overall configuration of a CT imaging apparatus 1 according to this embodiment. The CT imaging apparatus 1 images the inside of the subject 100 for nondestructive inspection and medical purposes. This 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. Then, the CT imaging apparatus 1 creates volume data from transmission images of a plurality of views, and further creates a cross-sectional image of the subject 100 from the volume data.

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

This CT imaging apparatus 1 includes a radiation source 2 , a detector 3 , a stage 4 , a control section 5 and an image processing section 6 . A radiation source 2 and a detector 3 are arranged opposite to each other. A stage 4 is arranged 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 by signal lines so as to be able to transmit and receive control signals. The image processing unit 6 is connected by a signal line so as to be able to receive the signal output by the detector 3 . The control unit 5 and the image processing unit 6 are a processing device 8 made up of a so-called computer, and include a processor that executes commands according to a program, a memory that stores the program, a memory that temporarily stores results of command execution and data, and a program that stores the program. It is composed of a storage and an interface capable of transmitting/receiving control signals or data to/from each part of the CT imaging apparatus 1 .

This radiation source 2 irradiates a radiation beam toward the subject 100 . Radiation is, for example, X-rays. The radiation beam is a cone beam that has the focal point F of the radiation source 2 as its apex and spreads conically with a cone angle. This 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 each other in a vacuum, and a tube voltage is applied between a cathode on the filament side and an anode on the target side. Electrons are then emitted from the filament, 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 beams, and the radiation source 2 may emit γ-rays or neutron beams.

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

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

The rotation mechanism 41 rotates the stage 4 around the rotation axis R once. The axis of rotation 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 along the optical axis CL of the radiation beam in a direction orthogonal to the rotation axis R to bring the stage 4 closer to or away from the radiation source 2 . Also, the shift mechanism 42 moves the stage 4 in a direction perpendicular to the rotation axis R. As shown in FIG. The lifting mechanism 43 moves the stage 4 along the rotation axis R. As shown in FIG. The tilting mechanism 44 tilts the mounting surface 45 of the stage 4 . In other words, the tilting mechanism 44 obliquely crosses the normal line N of the mounting surface 45 with respect to the rotation axis R. As shown in FIG.

The rotating mechanism 41, the shift mechanism 42, and the lifting mechanism 43 are configured by, for example, a ball screw mechanism. That is, rails, rotary motors, shafts and sliders are provided. The rail carries the object to be moved and extends in the direction of movement. The rotary motor rotates the shaft. The shaft extends parallel to the rail, is screwed with a thread groove, and is prevented from moving in the direction of extension. The slider is screwed onto the shaft and connected to the object to be moved. When the rotary motor operates, 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 rotating mechanism 41, the tilting mechanism 44, and the mounting surface 45 of the stage 4 are stacked in this order from the bottom layer, and all the upper layers are the objects to be moved.

The tilting mechanism 44 is, for example, a goniometer stage. The goniometer stage has a base 441 and a sliding portion 442 . The base 441 is pivotally supported by the rotating mechanism 41 , and the sliding portion 442 supports the mounting 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 slid together. A 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 positioned on the extension line of the axis of the shaft of the rotation mechanism 41, in other words, on the rotation axis R.

The tilting 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 the radiation are placed on the same plane S. The region of interest 7, also called ROI, is a spatial region within the subject 100 that the user pays attention to. The end surface 71 is one surface parallel to the mounting surface 45 . Since 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 tilting mechanism 44 tilts the mounting surface 45 of the stage 4 by a constant tilting angle α represented by the following equation (1). tilt the The tilt angle α is the angle between the normal N perpendicular to the mounting surface 45 of the stage 4 and the rotation axis R, in other words, the angle between the mounting surface 45 and the direction perpendicular to the rotation axis R. Further, the tilt angle α is constant, and does not change during the rotation of the stage 4 .

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

The control unit 5 is a so-called computer, and includes a processor that executes commands according to a program, a memory in which the program is developed and temporarily stores the results of command execution and data, a storage that stores the program, the radiation source 2, and the detector 3. , an interface for outputting control signals 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. The region of interest 7 is aligned with the effective field of view (FOV) of the radiation beam, and the above formula ( 1) is calculated, and the mounting surface 45 of the stage 4 is tilted at the tilt angle α. When the region of interest 7 is aligned with the effective field of view, the calculation of the above formula (1) by the tilt angle calculator 52 may be omitted, and a pre-stored cone angle 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 causes the display unit 55 to display the provisionally captured transmission image, and receives an input of the region of interest 7 using the operation unit 54 . Typically, a rectangular figure of a position and size desired by the user is drawn on the transmission image using the operation unit 54, and the control unit 5 recognizes this rectangular figure as the region of interest 7, and draws the drawn region of interest. The stage 4 is moved so that 7 coincides with the effective field of view.

In addition, the control unit 5, as the tilt angle calculation unit 52, calculates the distance FCD from the focus F of the radiation to the center of rotation on the optical axis CL, the length FOVx in the direction of the optical axis CL in the range over which the region of interest 7 extends due to the precession motion. , and the distance H from the position a distance FCD away from the focal point F along the optical axis CL to the boundary of the range spanned by the region of interest 7 by precession in the direction orthogonal to the optical axis CL. Then, the controller 5, as the tilt angle calculator 52, calculates the tilt angle α from these FCD, FOVx and H according to the above equation (1). Then, the control unit 5 operates the tilting mechanism 44 as the tilting control unit 53 so that the normal line N perpendicular to the mounting surface 45 of the stage 4 is tilted with respect to the rotation axis R by the tilting angle α. The surface 45 is tilted. The direction of inclination may be any.

The image processing unit 6 is a so-called computer, and includes a processor that executes commands according to a program, a memory in which the program is developed, a memory in which the command execution results and data are temporarily stored, a storage in which the program is stored, and an output from the detector 3. It consists of an input interface that receives signals. The image processing section 6 and the control section 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 inside the subject 100 from transmission images of a plurality of views, and a correction unit 62 that corrects the tilt of the three-dimensional CT image. I have it. A three-dimensional CT image is a three-dimensional image represented by volume data.

The reconstruction unit 61 receives transmission images in 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 cross-sectional images from the volume data. In this reconstruction, for example, the filtered back projection method of the FDK (Feldkamp, Davis, Kress) method or the iterative approximation method of the ART (Algebraic Reconstruction Technique) is used. When the subject 100 is imaged while being tilted by the tilting mechanism 44, the correction unit 62 corrects the tilt of the image caused by this tilt, and erects the three-dimensional CT image. The correcting unit 62 performs coordinate transformation by rotating the coordinates of each CT value included in the volume data by a tilt angle α opposite to the tilted direction.

The operation of such a CT imaging apparatus 1 will be described in detail with reference to FIG. FIG. 5 is a flow chart showing the operation of the CT imaging apparatus 1. As shown in FIG. 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. For this first imaging, the imaging magnification (=FDD/FCD) should be set small so that the subject 100 is surely within the effective field of view. The stage 4 aligns the normal N perpendicular to the mounting surface 45 with the rotation axis R, that is, sets the tilt angle α to zero. The radiation source 2 emits a radiation beam while the stage 4 remains non-rotating, and the detector 3 detects a transmitted image of the subject 100 . The image processing unit 6 causes the display unit 55 to display the transmission image received from the detector 3 . The user uses the operation unit 54 to draw a rectangular figure representing the region of interest 7 on the displayed transmission image.

When the region of interest 7 is input by drawing, the controller 5 determines the amount of movement of the stage 4 so that the region of interest 7 coincides with the effective field of view, and the rotation axis R of the normal N perpendicular to the mounting surface 45 of the stage 4. is calculated (step S02). Then, the shift mechanism 42, the lifting mechanism 43, and the tilting mechanism 44 move the stage 4 according to the movement amount and the tilting angle α under the control of the control unit 5 (step S03). is tilted (step S04).

In steps S02 and S03, the control unit 5 calculates the amount of movement for matching the center of the region of interest 7 with the center of the effective field of view. For example, the number of vertical and horizontal pixels and the central coordinates of the region of interest 7 and the effective visual field drawn on the display unit 55 are calculated. Next, the amount of movement is calculated so that the center coordinates of the region of interest match the center coordinates of the effective field of view. That is, since the center of the region of interest 7 coincides with the center of the effective field of view, the number of pixels in the direction along the optical axis CL, in the direction of the rotation axis R, and in the direction orthogonal to the optical axis CL and the rotation axis R is increased. Move or calculate. The calculated number of pixels in each direction is converted based on the relationship between the distance and the number of pixels in the real space stored in advance to obtain the amount of movement.

The control unit 5 also 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 field of view. That is, from the state where the center of the region of interest 7 and the center of the effective field of view match, 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 imaging magnification ( =FDD/FCD) is calculated. Then, the amount of movement of the stage 4 is calculated based on the calculated FDD value and FCD value.

Furthermore, in steps S02 and S04, the controller 5, as the tilt angle calculator 52, calculates the FCD value, the FOVx value, and the H value, and calculates the tilt angle α that satisfies the above equation (1). Then, 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 tilting control portion 53 of the control portion 5, and tilts at a point on the rotation axis R as the center of the circle. Change the direction by α.

Next, the CT imaging apparatus 1 starts actual imaging of the subject 100 (step S05). At this time, the rotation mechanism 41 of the stage 4 rotates the stage 4 around the rotation axis R once. The subject 100 mounted on the mounting surface 45 of the stage 4 also rotates about the rotation axis R once. 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 section 6 .

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

As shown in FIG. 6, when the tilt angle is 0°, that is, when the mounting surface 45 and the rotation axis R are perpendicular to each other, the precession of the subject 100 does not occur. Parallel radiation transmission paths occur only in body-axis cross sections parallel to the optical axis CL. On the other hand, when the tilt angle is about 2.5°, that is, about half the tilt angle α, the positions of the parallel radiation transmission paths change according to the rotation of the stage 4 .

Furthermore, as shown in FIG. 6, when the tilt angle is about 5°, that is, when the end face 71 of the region of interest 7 and the radiation focus F are tilted to the tilt angle α on the same plane S, depending on 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 . 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 lie on the same plane S. Therefore, parallel radiation transmission paths will be created once for all axial cross-sections of the region of interest 7 during rotation.

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 tilt angle α. Therefore, when the volume data is generated, the image processing section 6 corrects the tilt of the volume data as the correction section 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 converts the volume data into an image of a selected cross section such as a body axial cross section, a sagittal cross section, an annular cross section, an oblique cross section, or an MPR image, according to the operation unit 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. A photographed subject 100 is composed of multiple layers of discs such as CDs and DVDs. This test object 100 has overlapping discs fixed with an adhesive tape. This subject 100 was imaged at a tilt angle of 0°, a tilt angle of about 2.5°, half 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 photographed without tilting, the distinction between the upper layer and the lower layer of the disc is unclear. On the other hand, when the subject 100 is tilted to half the tilt angle α and photographed, the range in which the contour of the body axis section is clear is expanded. Furthermore, when the subject 100 is tilted by the tilt angle α so that the end face 71 of the region of interest 7 and the focus F of the radiation are placed on the same plane S, the outline of each disk can be clearly seen over the entire subject 100. and the layers of the disc are clearly separated.

Thus, cone beam artifacts are reduced throughout 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. Since the radiation transmission path parallel to the axial cross-section has either only the information of the axial cross-section or only the information outside the axial cross-section, it is considered that the layers are 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. The tilt angle α The image is taken with the subject 100 tilted only, and the image is taken without tilting the subject 100 . A photographed subject 100 is composed of multiple layers of discs such as CDs and DVDs. In this test object 100, overlapping discs are fixed with an adhesive tape.

As shown in FIG. 8, when the subject 100 is tilted by a tilt angle α, that is, by a tilt angle of about 5° so that the end surface 71 of the region of interest 7 and the focus F of the radiation lie on the same plane S, the optical axis CL The disc, which is a body-axis section in the vicinity, is as clear as the discs above and below the optical axis CL, and characters on the disc surface are also identifiable. On the other hand, when the subject 100 is photographed without tilting, the inside of the body-axis cross section near the optical axis CL is extremely unclear, and the characters on the disk surface cannot be identified.

This is because when photographing is performed by tilting at the tilt angle α, a radiation transmission path intersects the body axis cross section near the optical axis CL. It is believed that this is because the amount of radiation is suppressed and the difference in radiation attenuation due to the characters on the disk surface increases. On the other hand, if the subject 100 is photographed without tilting, a radiation transmission path nearly parallel to the body-axis cross-section near the optical axis CL is generated, and the transmission distance of the body-axis cross-section is increased. It is conceivable that the inside of the body axis section near the optical axis CL is unclear because the difference in the amount of attenuation of the radiation due to the characters on the disk surface is reduced.

As described above, in the CT imaging apparatus 1 that irradiates cone-beam radiation, the mounting 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 is photographed while precessing. That is, all body-axis cross sections of the region of interest 7 and one of the radiation transmission paths were made parallel once during the rotation of the stage 4 and irradiation of the radiation.

Therefore, the resolution in the direction of the body axis 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. In addition, since a radiation transmission path intersects the body-axis cross section near the optical axis CL, 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, parallel radiation transmission paths need only be created once for all axial cross-sections within the region of interest 7 , and parallel radiation transmission paths may be created beyond the region of interest 7 . This also clearly distinguishes the body-axis cross section in the region of interest 7 . That is, the mounting surface 45 may be tilted so that the plane S on which the end surface 71 of the region of interest 7 rests intersects the optical axis CL extending from the focal point F. In other words, it may be tilted more than the tilt angle α shown in 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 greater than 3° from the tilt angle α that satisfies the above formula (1), the resolution of the body-axis cross-section near the optical axis CL begins to fall below the peak value. This is probably because the radiation transmission path that intersects the body-axis cross-section near the optical axis CL also passes through the adjacent body-axis cross-section. In addition, it is considered that the larger the tilt angle α, the larger the FOVx, and the lower the resolution of the body-axis cross-section. On the other hand, within the range of the tilt angle α or more and the tilt angle α+3°, the possibility that the radiation transmission path that intersects the body-axis cross section near the optical axis CL also passes through the adjacent body-axis cross section is low, or A good resolution of the body-axis cross-section near the optical axis CL is maintained because the possibility of passing through the body-axis cross-section is low and the FOVx is not excessively increased.

Moreover, although the CT imaging apparatus 1 of the present embodiment automatically matches the effective field of view and the region of interest 7, the effective field of view and the region of interest 7 may be matched manually, or If the region of interest 7 fits, the effective field of view and the region of interest 7 do not have to match. As a manual method, the shift mechanism 42 and the elevating mechanism 43 may be operated according to the input contents of the operation unit 54 . When the effective field of view and the region of interest 7 do not match, the above formula (1) is useful. It should be tilted at an angle.

The CT imaging apparatus 1 further includes a tilting mechanism 44 that tilts the subject 100 by a predetermined angle. You may do so.

Further, the tilting mechanism 44 is a goniometer stage, and is tilted with a point on the rotation axis R as the center of rotation. This makes it possible to shorten the length FOVx in the direction of the optical axis CL within the range that the region of interest 7 extends due to the precession. Therefore, it is possible to improve the resolution of the image to be reconstructed.

However, the tilting mechanism 44 is not limited to the goniometer 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 a base 45a is attached to one side of the mounting surface 45, and an extensible rod 45c that expands and contracts by air pressure or the like is fixed to the side opposite to the side to which the hinge 45b is attached. Alternatively, the mounting surface 45 may be tilted with the hinge 45b as a base point by extending and retracting the extendable rod 45c.

The CT imaging apparatus 1 further includes a tilt angle calculator 52 for calculating a constant tilt angle α, and the tilting mechanism 44 is tilted according to the calculation result of the tilt angle calculator 52 . As a result, on the mounting surface 45 of the stage 4, all the body-axis cross-sections in the region of interest 7 and one of the radiation transmission paths diverging from the focal point F of the radiation source 2 are aligned with the rotation of the stage 4 and irradiation of radiation. It can be tilted with high precision so that it is parallel once inside. Alternatively, the user may calculate the tilting angle α and apply an external force to the sliding portion 442 of the tilting mechanism 44 to manually tilt the placement surface 45 .

Further, the CT imaging apparatus 1 is provided with a corrector 62 for correcting the tilt of the three-dimensional CT image generated in the process of reconstruction. As a result, even if the subject 100 is tilted and photographed, an image can be reconstructed that does not give the user a sense of discomfort.

In the CT imaging apparatus 1 of this embodiment, for example , as shown in FIG. 10, the radiation source 2 and the detector 3 are connected by an arm (not shown). A tilting mechanism 44 supports an arm and tilts the radiation source 2 and detector 3 set via the arm. The tilt angle α is the 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 aligned with the rotation axis R. As shown in FIG. This also ensures that all axial cross-sections within the region of interest 7 and one of each radiation transmission path diverging from the focal point F of the radiation are: parallel once. Therefore, an image in which the layers of the axial section are clearly distinguished is obtained, and the axial section near the optical axis CT becomes clear.

Moreover, although the stage 4 is rotated in the CT imaging apparatus 1 of the present embodiment, the combination of the radiation source 2 and the detector 3 may be rotated. For example, the radiation source 2 and detector 3 are connected by an arm. The rotating mechanism 41 may support an arm and rotate the set of the radiation source 2 and the detector 3 around a point on the rotation axis R via the arm. At this time, the rotation axis R coincides with the normal line N when the tilt angle of the mounting surface 45 is 0°. and the mounting surface 45 can be kept parallel.

(Other embodiments)
Although embodiments of the invention have been described herein, the embodiments are provided by way of example and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. The embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and its equivalents.

1 CT imaging device 2 Radiation source 3 Detector 4 Stage 41 Rotation mechanism 42 Shift mechanism 43 Elevating mechanism 44 Tilting 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 surface 8 Processing device CL Optical axis R Rotational axis S Same plane 100 Subject Specimen

Claims (10)

A CT imaging apparatus for imaging a region of interest within a subject,
a radiation source that emits cone-beam radiation;
a detector that detects the radiation;
a stage for placing the subject on a placement surface to interpose the subject between the radiation source and the detector;
a rotation mechanism that rotates the set of the radiation source and the detector or the stage about a rotation axis orthogonal to the optical axis of the radiation;
an image processing unit that reconstructs an image of the region of interest based on transmission images in each direction obtained by the detector through rotation by the rotation mechanism and radiation irradiation;
with
The mounting surface of the stage is such that all body-axis cross-sections in the region of interest and one of each radiation transmission path diverging from the focus of the radiation source are rotated by the rotation mechanism and once during irradiation of the radiation. is inclined at a certain angle with respect to the direction orthogonal to the rotation axis so that the
The angle α°, which is the constant angle, is in the range shown by the following formula (1),
A CT imaging apparatus characterized by:

the edge of the region of interest and the focal point of the radiation source lie in the same plane, or the plane on which the edge of the region of interest lies is tilted at an angle until it intersects the optical axis of the radiation;
The CT imaging apparatus according to claim 1, characterized by: The constant angle is within 30°,
3. The CT imaging apparatus according to claim 1 or 2, characterized by: The angle α°, which is the constant angle, is in the range shown by the following formula (2) ,
The CT imaging apparatus according to claim 1 , characterized by:

further comprising a tilting mechanism for tilting the constant angle;
5. The CT imaging apparatus according to any one of claims 1 to 4 , characterized by: the tilting mechanism is a goniometer stage;
The CT imaging apparatus according to claim 5 , characterized by: tilting the goniometer stage about a point on the rotation axis as a center of rotation;
The CT imaging apparatus according to claim 6 , characterized by: further comprising a tilt angle calculation unit that calculates the constant angle;
tilting the tilting mechanism according to the calculation result of the tilt angle calculator;
8. The CT imaging apparatus according to any one of claims 5 to 7 , characterized by: The image processing unit includes a correction unit that corrects the tilt of the three-dimensional CT image generated in the reconstruction process;
9. The CT imaging apparatus according to any one of claims 1 to 8 , characterized by: A CT that places the subject on a stage, irradiates the subject with cone-beam radiation from a radiation source at each angle, detects the radiation with a detector, and reconstructs an image of the region of interest within the subject. A photographing method of a photographing device,
irradiating 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;
Placement of the stage so that all body-axis cross-sections in the region of interest and one of each radiation transmission path diverging from the focus of the radiation are once parallel during the rotation and irradiation of the radiation. tilting the surface at a certain angle with respect to a direction orthogonal to the rotation axis of the stage;
The angle α°, which is the constant angle, is in the range shown by the following formula (1),
An imaging method for a CT imaging apparatus characterized by:

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