WO2015022888A1 - 放射線断層像撮影装置 - Google Patents
放射線断層像撮影装置 Download PDFInfo
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Definitions
- the present invention relates to a radiation tomography apparatus such as an X-ray CT apparatus, and more particularly to an image reconstruction method in a radiation tomography apparatus having a mechanism for moving a bed in a direction perpendicular to the body axis direction of a subject during imaging.
- the present invention also relates to a technique for imaging a region of interest existing along a direction substantially parallel to the body axis direction of a subject with high spatial resolution.
- An X-ray CT apparatus is an apparatus that images a tomographic image of a subject by placing the subject in the central opening of a rotating disk in which an X-ray source and an X-ray detector are placed facing each other and rotating the rotating disk. is there.
- an X-ray CT apparatus when the region of interest exists along a direction substantially parallel to the body axis direction of the subject, the positions of the subject and the rotating disk are relatively changed in the body axis direction.
- a plurality of tomographic images are acquired for a predetermined region along the body axis direction, and an image of the site of interest is extracted from these tomographic images.
- Patent Document 1 proposes to perform imaging by moving a region of interest to the imaging center.
- the photographing center is moved for each photographing region and photographing is performed.
- the site of interest such as a blood vessel does not always run parallel to the body axis direction, the site of interest cannot always be placed at the imaging center.
- This invention makes it a subject to provide the method of solving the subject which exists in radiation tomography apparatuses, such as X-ray CT mentioned above.
- the radiological tomography apparatus of the present invention moves the bed on which the subject is placed in a direction perpendicular to the body axis direction of the subject or changes the angle of the scanner during imaging,
- image reconstruction there is provided means for reconstructing an image using movement information (movement information in a direction orthogonal to the body axis) of the bed being photographed or an angle change amount of the scanner.
- the radiation tomography apparatus of the present invention is configured such that a subject is placed and a bed that can move in the body axis direction of the subject, and a radiation source that irradiates radiation and a radiation detector are placed across the bed.
- a rotating table that rotates around the bed, and an image creation unit that reconstructs a tomographic image of the subject based on radiation data detected by the radiation detector during rotation of the rotating table A position of the bed and / or a mechanism that changes an angle with respect to the vertical plane of the rotating disk, a controller that controls the mechanism, and a movement of the bed in a direction perpendicular to the body axis direction during shooting
- a movement amount setting unit for setting the amount and / or the angle change amount of the rotating disk.
- the control unit performs shooting by controlling the mechanism unit in accordance with the movement amount of the bed and / or the angle change amount of the rotating disk set in the movement amount setting unit.
- the image creating unit creates an image using movement information in a direction orthogonal to the body axis direction of the bed during photographing and / or angle information of the rotating disk.
- the site of interest of the subject when the site of interest of the subject has a structure that continues in a predetermined direction, such as a blood vessel, a digestive tract, and a spine, the site of interest is always almost at the center of imaging. Can be arranged. As a result, it is possible to obtain an image with a low spatial exposure and a high spatial resolution for the region of interest.
- FIG. 4 is a diagram illustrating the effects of the imaging method and the image reconstruction method according to the present invention, where (a) is a diagram illustrating projection data and a reconstructed image according to a conventional imaging method, and (b) is a projection by imaging with horizontal movement of the bed.
- the figure which shows the reconstruction image by data and the conventional reconstruction method (c) is the figure which shows the projection data by imaging
- This figure shows the relationship between the subject size and the X-ray detector size, where (a) shows that the detector size is large enough to cover the entire subject, and (b) shows that the detector size is small. This shows a case where the entire subject cannot be covered.
- the figure explaining bed movement photography by a third embodiment It is a figure explaining the bed movement photography by a 4th embodiment, (a) shows the sampling density of a conventional method, (b) shows the sampling density of a 4th embodiment.
- FIGS. 4A and 4B are diagrams for explaining bed movement shooting according to the fourth embodiment, in which FIG. 4A is an image reconstruction when a bed movement is not performed (conventional method), and FIG. Embodiment)
- FIGS. 6A and 6B are diagrams illustrating image synthesis in the fifth embodiment, where FIG. 5A is a diagram illustrating one image before synthesis, and FIG. 5B is a diagram illustrating an image after synthesis.
- the X-ray CT apparatus of the present embodiment includes a bed (20) on which a subject is placed and movable in the body axis direction of the subject, and an X-ray source (11) that irradiates X-rays across the bed (20).
- the X-ray detector (12) are arranged to face each other, the rotating plate (scanner 10) rotating around the bed, and the X-ray detected by the X-ray detector (12) during the rotation of the rotating plate Image creation unit (reconstruction calculation unit 32, image processing unit 33) that reconstructs a tomographic image of the subject based on the data, and changes the position of the bed and / or the angle with respect to the vertical plane of the turntable
- a mechanism unit (mechanism unit 25, tilt mechanism unit 151), a control unit (central control device 40) for controlling the mechanism unit, a movement amount of the bed in a direction perpendicular to the body axis direction during photographing, and / or Alternatively, a movement amount setting unit (bed movement amount setting unit 31) for setting the angle change amount of the rotating disk is provided.
- the control unit (40) performs shooting by controlling the mechanism units (25, 151) in accordance with the movement amount of the bed and / or the angle change amount of the turntable set in the movement amount setting unit (31).
- the image creation unit (32, 33) creates an image using movement information in a direction orthogonal to the body axis direction of the bed and / or angle information of the turntable during photographing.
- the image creation unit creates an image using, for example, the amount of movement of the bed in the direction orthogonal to the body axis direction set in the movement amount setting unit and / or the angle change amount of the turntable.
- the mechanism unit (25, 151) is a measuring unit (bed movement measurement unit 23) that measures the amount of movement of the bed in the direction perpendicular to the body axis direction and / or the amount of change in the angle of the rotating disk during shooting.
- the image creating unit creates an image using the movement amount of the bed and / or the angle change amount of the turntable recorded in the measuring unit (23).
- FIG. 1 is a diagram showing the external appearance of the X-ray CT apparatus 100 of the present embodiment
- FIG. 2 is a diagram showing the overall configuration.
- This X-ray CT apparatus includes a scanner 10 for imaging a subject, a bed 20 for laying the subject, and an operation unit 300.
- the operation unit 300 includes an arithmetic device 30 that performs operations such as image reconstruction, and an input / output device 35 that includes an input unit 36, a display unit 37, and the like.
- the scanner 10 has a rotating disk (not shown) in which an X-ray generator 11 and an X-ray detector 12 are arranged opposite to each other and is housed in a gantry having an opening in the center, and the rotating disk is rotated at a predetermined circumferential speed. Shooting is performed.
- the scan method is not limited, but is a rotate-rotate method (third generation).
- a high voltage generator 13 that supplies a high voltage to the X-ray generator 11, and an X-ray controller 41 that controls the high voltage generator 13 to emit X-rays from the X-ray generator.
- a collimator control device 44 that controls the control devices 41 to 44 and a central control device 40 that controls the control devices 41 to 44 are housed.
- the X-ray detector 12 is, for example, a multi-row detector (two-dimensional detector) in which a plurality of detector rows in which a number of X-ray detection elements are arranged along the circumferential direction of the rotating disk are arranged in a direction orthogonal to the circumferential direction. Each detection element generates an electrical signal corresponding to the detected X-ray dose.
- the scanner 10 includes a preamplifier 18 that amplifies the output of the X-ray detector 12 and an A / D converter 19. The digital signal that is the output of the A / D converter 19 is input to the arithmetic unit 30.
- the scanner 10 can include a tilt mechanism 151 that can change the angle with respect to the upper surface of the bed 20.
- a tilt angle When a plane perpendicular to the longitudinal direction of the bed 20 is used as a reference plane, the angle of the scanner (rotary disc) 10 with respect to the reference plane is called a tilt angle.
- the range in which the tilt angle can be changed is a range in which the opening of the scanner 10 does not interfere with the bed 20 and is usually about ⁇ 30 °.
- the bed 20 includes a support table 21 and a top plate part 22 thereon, and can move the top plate part 22 in a direction along the body axis direction of the subject (here, the Z direction).
- the subject placed on the bed 20 can be carried to the imaging position within the opening of the scanner 10.
- the bed 20 is perpendicular to the Z direction, for example, the vertical direction (vertical direction, Y direction) and the left and right (horizontal direction perpendicular to the body axis direction, X direction).
- a known drive mechanism such as a stepping motor or a linear motor can be used.
- the mechanism unit 25 is controlled by the bed control device 43.
- the bed control device 43 can drive the mechanism unit 25 during photographing to change the position of the bed 20 in the X direction or the Y direction.
- a bed movement measuring device 23 that measures the amount of movement of the bed 20 in each direction and outputs it to the arithmetic device 30 as movement information is provided.
- the couch movement measuring device 23 is preferably provided, but is not essential. When the couch movement measurement device 23 is provided, the couch position information measured by the couch movement measurement device 23 is sent to the calculation device 30 and used for image creation.
- the input / output device 35 of the operation unit 300 includes an input unit 36 such as a pointing device such as a keyboard or a mouse, a display unit 37, and a storage unit 38 that stores parameters, data, calculation results, and the like necessary for calculation of the calculation device 30. ing.
- the calculation device 30 operates under the control of the central control device 40, and includes a reconstruction calculation unit 32 that performs image reconstruction calculation using a signal sent from the X-ray detector 12 via the A / D converter 19, and a reconstruction calculation unit 32.
- An image processing unit 33 that performs correction of the image reconstructed by the configuration calculation unit 32 is provided.
- the reconstruction calculation unit 32 and the image processing unit 33 function as an image creation unit of the present invention.
- the arithmetic device 30 further includes a movement amount setting unit 31 for setting the movement amount of the bed.
- a control signal is sent from the X-ray controller 41 to the high-voltage generator 13, the high voltage is applied to the X-ray generator 11, and the subject is irradiated with X-rays from the X-ray generator 11
- a control signal is sent from the scanner control device 42 to the drive device 15, and the X-ray generator 11, the X-ray detector 12, and the preamplifier 18 are circulated around the subject.
- the bed on which the subject is placed is moved in the body axis direction (Z direction) of the subject in accordance with the imaging method.
- the imaging method is a method in which the movement of the bed in the body axis direction is performed step by step, for example, every rotation of the scanner (referred to here as the normal scan method) (a), and the movement in the body axis direction
- the normal scan method referred to here as the normal scan method
- a continuous method helical scan method
- a method in which movement in the body axis direction is performed in both forward and reverse directions shuttle scan method
- the X-ray emitted from the X-ray generator 11 is limited in the irradiation area by the collimator 16, absorbed (attenuated) by each tissue in the subject, passes through the subject, and is detected by the X-ray detector 12. .
- X-rays detected by the X-ray detector 12 are converted into current, amplified by a preamplifier 18, A / D converted by an A / D converter, and then input to the arithmetic unit 30 as a projection data signal.
- the projection data signal input to the arithmetic device 30 is subjected to image reconstruction processing by the reconstruction arithmetic unit 32 in the arithmetic device 30.
- the reconstructed image is stored in the storage unit 38 in the input / output device 35 and displayed as a CT image on the display unit 37.
- the image is displayed on the display unit 37 as a CT image.
- the bed movement amount setting unit 31 sets the bed movement amount, and based on the set movement amount, the bed 20 is perpendicular to the Z direction (vertical direction and / or Alternatively, it is characterized in that shooting is performed while moving in the left-right direction) or shooting is performed while changing the tilt angle of the scanner system.
- FIG. 4 is a diagram illustrating the moving direction of the bed
- FIG. 5 is a diagram illustrating an operation procedure.
- the top plate portion of the bed 20 on which the subject is laid is substantially parallel to the floor surface, and the longitudinal direction thereof coincides with the body axis direction (Z direction) of the subject.
- the direction orthogonal to the Z direction is an arbitrary direction in the plane orthogonal to the Z axis, but here, a case where the subject can move in the horizontal direction (X direction) and the vertical direction (Y direction) will be described. .
- pre-shooting is performed (S501).
- Prior imaging is performed in order to obtain information on a subject necessary for subsequent main imaging, and image data is obtained at a relatively low resolution.
- Any of the imaging methods shown in FIG. 3 may be used, and in order to achieve low resolution, for example, the movement speed in the body axis direction with respect to the rotational speed of the rotating disk is increased, and the volume projection data is obtained in a short time with low exposure.
- This volume projection data is converted into image data (hereinafter referred to as pre-captured image data) by a known image reconstruction method.
- pre-captured image data image data
- a volume image with low spatial resolution is acquired as a positioning image in order to place a target region of a subject at an appropriate position in an imaging system. You may use this positioning image for the pre-photographed image data of this embodiment.
- the bed movement curve is a curve in which a movement amount of the bed (a direction perpendicular to the body axis direction, for example, a movement amount in the X direction and / or the Y direction) is set with respect to the view angle.
- the specific shape of the bed movement curve varies depending on the purpose of imaging and the site of interest of the subject.For example, the movement of the bed necessary to position the site of interest of the subject at the imaging center (the center of rotation of the turntable) There are curves that show quantities, curves that change linearly within a certain range, and the like.
- a pre-photographed image can be displayed on a display device and an inspector can interactively set the pre-photographed image data on the display screen.
- an inspector can interactively set the pre-photographed image data on the display screen.
- the photographing method may be any of the photographing methods shown in FIG. 3, and is the same as the normal photographing except that the bed 20 is moved in the X direction / Y direction as the turntable rotates.
- the image is reconstructed using the projection data (S504).
- a known reconstruction algorithm such as a filter-corrected back projection method, an extended method thereof (for example, a method described in Patent Document 2 or Patent Document 3), a successive approximation reconstruction method, or the like can be used.
- the position coordinates of the photographing center are converted using the position information for each view.
- the position information can be obtained from the bed movement curve set in step S502.
- the X-ray CT apparatus includes the bed movement measurement device 23 of the bed 20, the position information of the bed measured by the bed movement measurement device 23 can be used. Since this position information uses an actual position, it is possible to perform image reconstruction with higher accuracy than in the case of using a set bed movement curve.
- the X-ray CT apparatus of the present embodiment is characterized in that the position of the bed is controlled so that the imaging center moves along the center line of the region of interest during imaging. That is, the movement amount setting unit that sets the movement amount of the bed sets the movement amount of the bed so that the target site of the subject is located at the rotation center (imaging center) of the rotating disk.
- a sleeper movement curve is set based on the image data obtained by the pre-shooting (S501) (S502). Although the setting of the couch movement curve can be automatically performed, a procedure in the case of performing interactively by designation by the operator will be described below.
- a pre-captured image (here, a coronal image) 600 is displayed on the display unit 37.
- a control point P is set at the position of interest to be moved to the photographing center.
- a cross section for setting the control point P on the image may be specified, the cross section images 601 to 603 may be displayed on the sub-screen, and the control point P may be set on the tomographic images 601 to 603. .
- the couch movement amount setting unit 31 of the arithmetic device 30 connects the plurality of designated control points P to create a couch movement curve L.
- the bed movement curve L is a movement curve that moves the bed in the left-right direction (X direction) of the subject.
- control points are designated on the tomographic images 601 to 603, a movement curve including movement in the vertical direction as well as the horizontal direction is obtained.
- the bed movement curve may be formed by linearly connecting a plurality of control points P, or may be formed by nonlinear interpolation such as a spline curve.
- the bed movement curve is a curve indicating the amount of movement in the horizontal direction and / or the vertical direction with respect to the position in the body axis direction, but the position in the body axis direction of the bed being photographed is the view angle (fan beam projection angle) ⁇ . Therefore, it can be described by the following equations (1-1) and (1-2).
- the pre-captured image may be the sagittal plane image 700 shown in FIG.
- control points may be specified on the image 700, or cross-sectional images at a plurality of positions different in the body axis direction may be displayed, and control points may be specified on these tomographic images.
- the couch movement curve When setting the couch movement curve automatically, distinguish the features (pixel value distribution and feature amount) on the image of the target region, and use the pixel that satisfies the feature or the center pixel of the region that satisfies the feature as the control point. It can be a connecting bed movement curve.
- the range of movement of the bed is restricted by the bed movement mechanism in the vertical and horizontal directions.
- the range in which the bed can be moved in the vertical and horizontal directions within the time required to move from one point to the next is This is limited by the moving speed of the bed and the movable range of the bed. Therefore, in the X-ray CT apparatus of the present embodiment, the limit value of the movement amount in the direction orthogonal to the body axis direction of the bed is calculated, and the movement of the bed in the direction orthogonal to the body axis direction is calculated based on the limit value. Control.
- a range (settable range) that can be set as a control point is set next.
- the settable range can be calculated by the computing device 30 according to the moving speed in the Z direction from the moving speed of the bed up and down, left and right, the moving range of the bed, and the like. Moreover, you may have the setting value of the settable range as a default.
- next control point is specified within a movable range for a certain control point, it is set as the next control point, and if it is specified beyond this range, the control point is It may be set to prompt re-designation without setting, or to move to the nearest position within this range. If it is a problem that the control points cannot be set, if the cause is the vertical / horizontal movement speed of the bed, the movement speed (so-called beam pitch) of the bed in the body axis direction is decreased or the rotation speed of the scanner is decreased. It is also possible to change these settings. When the condition is changed, the control point can move within the movable range even after being set once.
- the settable range may be displayed on the display device.
- FIG. 8A shows the case where the coronal image 810 is displayed
- FIG. 8B shows the case where the sagittal image 820 is displayed.
- the settable range W is indicated by a line, but the display method is not limited to the example shown in FIG.
- FIG. 8 shows a case where a two-dimensional image is displayed
- the settable range is also applied when a bed movement curve along a lumen is generated from a volume image.
- step S503 After setting the bed movement curve in this way, scanning is started and the bed 20 is moved in the body axis direction, and the bed 20 is moved in a direction orthogonal to the body axis direction according to the set bed movement curve (step S503).
- the couch movement measuring device 23 if the couch movement measuring device 23 is provided, the couch movement trajectory actually moved at the time of photographing is measured as a couch movement curve.
- the measured bed movement trajectory is used in place of the set bed movement curve in image reconstruction when there is a large error between the bed movement curve assumed in advance and the bed movement curve actually moved.
- an image is created using the projection data for each view detected by the X-ray detector 12 by photographing (S504).
- the subject position is shifted in the vertical and horizontal directions based on the bed movement curve. For example, when imaging is performed while moving the bed to the right by 1 mm in each view, the subject centered at the first view position is 1 mm to the right in the next second view. If such projection data is directly reconstructed by a conventional image reconstruction method, artifacts due to movement of the subject and distortion of the subject shape are generated. Therefore, in this embodiment, reconstruction is performed while moving the reconstruction center position for each view according to the bed movement curve.
- a fan beam image reconstruction method corresponding to a conventional helical scan will be described.
- a tomographic image is generated by calculation using the following equation (2).
- the reconstruction of the present embodiment shows that the pixel positions x and y are corrected by the vertical and horizontal position data ⁇ x and ⁇ y of the bed. It can be seen that the vertical and horizontal position data ⁇ x and ⁇ y of the bed are functions of the view, that is, equivalent to moving the reconstruction center for each view.
- Equation (2) is a fan beam image reconstruction method, but it uses a fan-para conversion method that converts fan beam projection to parallel beam projection for the purpose of speeding up computation and improving image quality uniformity. It has been.
- the conventional parallel beam image reconstruction can be expressed, for example, by the following equation (4).
- Reconstruction filter processing is expressed, for example, by the following equations (6-1) and (6-2).
- the above equations (7-3) and (7-4) are apparently the same as the equations (4-3) and (4-4) of the conventional parallel beam reconstruction, but the equations (7-3),
- the pixel positions x and y used in (7-4) are corrected by the vertical and horizontal position information ⁇ x and ⁇ y of the bed, respectively. That is, it can be seen that the vertical / horizontal position data ⁇ x and ⁇ y of the bed are functions of the view and are equivalent to moving the reconstruction center for each view.
- the above expression is a circulation function using the parallel beam projection angle ⁇ and the pixel positions x and y as parameters, and the circulation number (number of loops) of this circulation function is sufficient to be about several times.
- the image reconstruction method has been described using an equation, but even when the imaging method is different, the coordinates of the reconstruction center position used for reconstruction are adjusted for each view according to the bed movement curve. By changing, image reconstruction can be performed similarly. As a result, an image free from artifacts associated with moving the bed up and down and left and right can be obtained.
- Fig. 9 shows the result of image reconstruction for a thin cylindrical phantom.
- the upper three figures in FIG. 9 are projection data
- the lower three figures are tomographic images after image reconstruction
- (a) is taken without moving the bed
- (b) is the bed.
- (c) is when shooting while moving the bed in the X and Y directions and performing image reconstruction of this embodiment Is shown.
- the projection data reflects the movement of the photographing center.
- an X-ray CT that captures an image while moving the bed so that the region of interest of the subject is positioned substantially at the imaging center, and has no artifacts due to the movement of the bed and high spatial resolution of the region of interest.
- the basic posture of the scanner 10 is such that a straight line connecting the X-ray source of the X-ray generator 11 and the center of the X-ray detector is orthogonal to the moving direction (Z direction) of the bed. It is such a vertical posture.
- the scanner 10 can take an inclined posture (tilt posture) from the vertical posture as long as the top plate portion 22 of the bed 20 that moves through the opening does not interfere with the opening.
- tilt posture the spatial resolution in the Z direction can be improved as compared with the vertical posture, and a method of performing a helical scan in the tilt posture is conventionally known.
- the tilt angle changes during scanning, an error occurs during image reconstruction and a large amount of artifacts are generated, so that the tilt angle is conventionally fixed.
- the tilt angle is changed in accordance with the shape of the site of interest, and the site of interest is continuously imaged with high spatial resolution.
- pre-shooting (S501) and setting a bed movement curve based on the pre-shot image (S5021) are the same as in the first embodiment, and the pre-shot image uses a positioning image. .
- an angle change amount ⁇ with respect to the Z direction of the set bed movement curve is calculated.
- the angle change amount ⁇ can be calculated by, for example, Expression (8).
- ⁇ represents the range of the predetermined view angle.
- the tilt angle ⁇ is calculated as a function of the view angle ⁇ (S5022).
- the tiltable range of the scanner can be set like the movable range in the first embodiment.
- the tilt angle is limited to a range in which the couch top and the opening do not interfere with each other.
- the tiltable range changes in a state where the top plate portion is moved up, down, left and right. Since the tiltable range ( ⁇ maximum angle in both directions) is determined by the position of the bed in the vertical and horizontal directions, the computing device uses the angle calculated by the above equation (8) as the bed position in the view (the set movement It is determined whether or not the angle is an allowable angle (position when moved by the amount). If the angle exceeds the allowable angle, the maximum allowable angle is set.
- the set tilt angle is used for later image reconstruction. Further, when a device for measuring and recording the tilt angle of the scanner is provided, angle information from the recording device is used for image reconstruction. Thus, even when there is an error between the set tilt angle and the actual tilt angle, image reconstruction without error can be performed.
- the tilt angle change amount is set in this way, actual photographing is started, and photographing is performed while changing the tilt angle of the scanner 10 corresponding to the view angle while moving the bed 20 in the Z direction (S503).
- the bed movement curve When the movement amount in the X direction and the Y direction of the bed 20 is set by the bed movement curve, the bed may be moved in the vertical and horizontal directions together with the change of the tilt angle of the scanner.
- various methods shown in FIG. 3 can be adopted as the photographing method.
- reconstruction is performed using the projection data collected by the X-ray detector 12 (S504).
- the reconstruction can be performed using, for example, the following formula (9).
- Equations (9) and (9-1) to (9-3) described above correspond to (2) and (2-1) to (2-3) of the first embodiment, but the scanner is tilted. As a result, the position “y I ” in the Y direction of the target pixel used in these equations is changed to “y ′ I ” shown in equation (9-5). Further, the position “z s ” in the Z direction of the radiation source used in the equation (2-3) is changed to “z ′ s ” shown in the equation (9-4).
- the region of interest of the subject is bent (in many cases), or along the body axis direction (Z direction) but has an angle with respect to the Z direction
- a good image can be obtained.
- an artifact-free image can be obtained despite changing the tilt angle.
- the present embodiment is characterized in that when the subject size is larger than the size of the X-ray detector 12, the bed moving range is set so as to expand the FOV and cover the subject.
- the relationship between the subject size and the X-ray detector size will be described with reference to FIG. Fig. 12 (a) shows the case where the detector size is large enough to cover the entire subject, and Fig. 12 (b) shows the case where the detector size is too small to cover the whole subject. Yes.
- the X-ray CT apparatus of the present embodiment continuously captures images while changing the position of the bed (subject), and reconstructs an image using the position information of the bed, so that the detector size is relatively Even when the size is small, the substantial FOV can be enlarged, and a large-sized subject can be handled.
- pre-photographing is performed (S501), and a pre-photographed image is displayed on the display device to determine a range in which the bed moving photographing according to the present embodiment is performed.
- Sleeper moving shooting refers to shooting performed while moving the bed up and down and / or left and right. For example, when taking a whole image of the subject from the head to the foot, the head and foot are shown in Fig. 12 (a), even if the detector can cover the whole, the chest and abdomen are May not be covered. In such a case, a slice for starting the couch moving shooting is specified, and a slice for ending the couch moving shooting is specified, and a range (a range in the Z direction) for the couch moving shooting is determined. Without specifying the range of the bed movement shooting, the bed movement shooting may be performed on the entire shooting range, and in this case, the range determination step is omitted.
- the movement range in the vertical and horizontal directions of the couch is determined, and a couch movement curve is set (S502).
- the movement range of the bed in the vertical and horizontal directions may be set to a predetermined movement range based on the abdominal circumference of the subject measured in advance or the height from the top surface of the top panel to the top surface of the subject.
- a pre-captured tomographic image of a slice within the range for performing the bed moving imaging may be displayed on the display device and designated on the tomographic image.
- the movement range to be set is within the restriction range.
- the number of views in the movement range is set, and the bed movement curve is determined.
- the number of views is preferably M ⁇ 1.5 or more, where M is the number of views at 360 °.
- M is the number of views at 360 °.
- the couch movement curve is a straight line (formula (11-1)) that linearly changes the couch position from one point in the vertical and horizontal directions (one end of the moving range) to one point (the other end of the moving range) with respect to the view. (11-2)).
- a and b represent constants, and (x0, y0) represent the coordinates of the photographing center at the start of bed movement photographing.
- the shooting method can be any of the shooting methods shown in Fig. 3, and in the case of normal scan, the specified number of views is displayed at each slice position where movement in the Z direction is stopped while intermittently moving the bed in the Z direction. Take a sleeper shot.
- imaging is performed while moving the bed continuously in the Z direction and moving the bed (moving in the X and Y directions). The same applies to the shuttle scan.
- the couch moving shooting is performed only for the set range, and outside the range, the shooting is performed with the couch fixed in the XY direction.
- FIG. 13 shows an example in which the bed movement is photographed for one section.
- FIG. 13 shows an example in which the bed is moved only in the left-right direction (X direction), but the direction in which the bed is moved may be a vertical direction or a direction that combines the vertical direction and the left-right direction.
- the imaging center moves to the right for each view from a position closer to the left than the center of the subject as the bed moves.
- the subject has a portion that protrudes from the spread of the fan beam received by the X-ray detector 12, but the scanner (rotary plate) makes one and a half turns, so that CT can be performed from all regions of the subject.
- Data necessary for image reconstruction is obtained. Specifically, when the scanner position at the center of FIG. 13 and 0 °, with the view to 0 ° from -270 ° (left), used for reconstruction of the object portion including the point P R of the subject rightmost projection data is obtained for, the view from 0 ° to + 270 ° (right end), the projection data to be used for reconstruction of the object portion including the point P L of the subject left is obtained.
- FIG. 13 shows a case where the scanner is rotated once and a half
- the projection data for the two images may be obtained by rotating the scanner twice. That is, the imaging starts at the bed position where the center of the subject is almost the imaging center, starts to move to the left side of the bed at the scanner angle of ⁇ 360 ° (0 °), and the scanner angle of ⁇ 270 ° (the left end of FIG. 13). ) To reach the left edge and turn it back. Similarly, at the scanner angle + 270 °, the bed position is folded back at the right end, and returned to the same bed position as 0 ° at + 360 ° (position where the center of the subject is almost the imaging center).
- Equation (3-1) and Equation (2) modified by Equations (3-1) and (3-2) for fan beam reconstruction, and Equation (7) for parallel beam reconstruction. It is the same as that of 1st embodiment to perform using. However, as the bed movement curve ⁇ , the bed movement curve shown in Expression (11) is used. Alternatively, when the couch movement measuring device 23 is also provided here, reconstruction is performed using the couch movement trajectory (position information) actually moved at the time of shooting.
- the X-ray detection apparatus size is smaller than the subject size, and the subject Even when a part of the specimen protrudes from the fan beam, no data is lost and a good image can be obtained for the entire specimen.
- continuous shooting is performed, so there is no influence of the subject's posture change between shots and the image quality caused by the posture change is low. There is no problem of deterioration.
- the present embodiment is characterized in that the sampling density determined by the detector size is increased and the spatial resolution is improved by adopting bed moving imaging.
- the fan beam sampling pitch is determined by the detector size (element size).
- element size the smaller the element size of the detector, the smaller the sampling pitch and the higher the sampling density.
- the element size is about 1 mm in each of the channel direction and the detector row direction, and the sampling pitch near the imaging center is about 0.6 mm.
- the spatial resolution of about 0.35 mm near the center of rotation is achieved by shifting the sampling position between the opposing data. Is realized.
- This embodiment realizes a spatial resolution equivalent to or higher than that of the quarter offset detector by adopting bed movement shooting. Details of this embodiment will be described below with reference to FIGS.
- the processing procedure refers to the imaging procedure shown in FIG. 5 as necessary.
- the vertical and / or horizontal movement of the bed during shooting is the same as in the above-described embodiment, but in this embodiment, the setting of the bed movement curve using a pre-captured image is omitted.
- the bed movement curve is determined in consideration of the sampling pitch at the photographing center (S501). A case where the sampling pitch is 1/3 will be described as an example.
- the sampling pitch is a predetermined pitch (referred to as a basic pitch) determined by the detector size.
- the same slice is spread over three rounds. Photograph and ensure that the same slice is photographed three times at the same projection angle.
- the bed position is shifted, for example, in the X direction so that the photographing center is shifted by 1/3 pitch from the basic pitch every round.
- the sampling pitch is 1/3 of the basic pitch, that is, the sampling density is tripled, and the spatial resolution can be improved.
- the bed movement curve may be continuously moved during one round of the scanner, and may be a continuous movement, or as shown in FIG.
- the bed position may be moved every lap.
- the amount of change in the couch movement per round may be “integer multiple of basic pitch + 1/3 pitch” instead of 1/3 of the basic pitch.
- a relatively large change amount can be set as the change amount from the first view of the first lap to the final view of the third lap. Control of the part becomes easy.
- 14 shows only the movement amount in the X direction, the movement direction of the bed may be the Y direction or both the X direction and the Y direction.
- the imaging method may be either normal scan, lieutenant helical scan, or shuttle scan.
- Three pieces of projection data with different positions of the photographing center are obtained by photographing. These three projection data, for example, is a function of view ⁇ and the channel angle (fan angle) .alpha.
- I detector row positions v I as shown in the following equation (12).
- the image reconstruction after shooting is performed by using data closest to a predetermined pixel among data sampled at a high density by shooting a plurality of times as data of the pixel (S504).
- FIG. FIG. 16A is a diagram for explaining the conventional reconstruction
- FIG. 16B is a diagram for explaining the reconstruction according to the present embodiment.
- the raw projection data is fan beam-like projection data as viewed from the body axis direction, but since it can be converted from a fan beam to a parallel beam by fan-para conversion, the case of a parallel beam is shown here for ease of explanation. ing.
- data of a predetermined pixel (pixel at a position indicated by ⁇ in the figure) 161 is interpolated with projection data adjacent thereto.
- the data of the pixel 161 interpolated with the nearest neighbor data has higher accuracy than the data interpolated with the projection data of the conventional method.
- reconstruction is performed using Equation (7) or Equation (4).
- the sampling density can be increased by shifting the position of the shooting center to 1/2, 1/3, etc. of the element size (arrangement pitch), etc. It is difficult to move the bed accurately with a movement amount smaller than the element size.
- the movement amount equal to or larger than the element size is set as the maximum movement amount of the bed and the bed is moved continuously up to the maximum movement amount, the bed can be controlled easily.
- the sampling density determined by the detector size is increased and the spatial resolution is improved by adopting the bed moving imaging.
- the X-ray CT apparatus of the fourth embodiment has a function of reconstructing the projection data with a high density
- the X-ray CT apparatus of the present embodiment has a plurality of images with different sampling positions. It differs in that it is reconstructed and combined.
- different points will be mainly described.
- the same slice is photographed over four rounds in order to obtain four images having different photographing center positions.
- the amount of movement of the bed is determined so that the amount of movement in the vertical and horizontal directions per round coincides with the image shift amount (S502).
- the image shift amount is set to an equal interval so that the sampling position of one image is in the middle of the sampling position of another image.
- the second cycle is a position shifted by 1/2 pitch in the right direction
- the third cycle is a position shifted by 1/2 pitch upward from the position of the second cycle.
- the amount of bed movement is determined so that the fourth round is a position shifted by a half pitch with respect to the position of the third round (that is, a position shifted upward from the position of the first round).
- the amount of movement of the couch may be changed in each view of each circumference, or may be fixed for each circumference (see FIG. 15 of the fourth embodiment).
- photographing is performed based on the determined amount of bed movement (S503), and projection data for each circumference is obtained. These projection data are reconstructed to obtain an image (S504).
- image For reconstruction, fan beam reconstruction can be performed using equation (2) or the like, and parallel beam reconstruction can be performed using equation (4) or the like.
- correction using the bed position information is performed using equation (3) or equation (7) or the like.
- the couch position information may be the movement amount set in S502, or when the couch movement measuring device 23 is provided, the couch movement trajectory (position information) actually moved at the time of photographing is used.
- the synthesized image has four times the number of pixels of the original image, but the spatial resolution itself is the same as the original image.
- the resulting quadruple density sampling image is subjected to blur correction such as frequency enhancement processing to obtain a high spatial resolution image.
- the frequency enhancement process a known super-resolution technique can be used.
- the present embodiment is characterized in that a CPR image is directly created using bed position information.
- a CPR image is an image along the lumen.
- volume data three-dimensional image data
- the volume data is used as the center of the lumen.
- the movement information of the bed is displayed as the center point of the lumen.
- the CPR surface can be defined based on the coordinates and angle of its center line (the angle with the body axis as the rotation axis), and the reconstruction center coordinate for the ⁇ I coordinate of the CPR surface is (x 0 ( ⁇ I ),
- the CPR plane s ⁇ coordinate and XYZ coordinate when y 0 ( ⁇ I )) can be correlated as shown in the following equation.
- ⁇ I is the angle of the CPR plane (the angle with the body axis as the rotation axis of the CPR plane)
- s I is the coordinate position perpendicular to the z axis on the CPR plane
- ⁇ I is the s along the CPR plane
- the coordinate perpendicular to the axis, ⁇ is a function that defines the travel of the CPR plane.
- the fan beam image reconstruction for the CPR plane according to the present embodiment can be expressed by the following equation (14).
- the image reconstruction according to the formula (14) or (15) described above is based on the premise that the bed position is moved in the vertical and horizontal directions during shooting.
- the present embodiment can also be applied to the case where the angle of the scanner is changed as described above.
- the angle information of the scanner of each slice is used as the angle of the CPR plane, and the coordinates of the photographing center are set as the center coordinates of the CPR plane, so that the CPR image using the above formulas (14) and (15) is used. Reconfiguration is possible.
- the CPR image can be directly applied by applying the image reconstruction of this embodiment even if the vertical / horizontal movement of the bed or the change of the scanner tilt angle is not performed.
- This embodiment is a technique that can also be applied to an X-ray CT apparatus that does not involve bed moving imaging.
- the center point of the lumen is always taken as the imaging center by performing the bed movement imaging, it is possible to obtain a CPR image that best depicts the spatial resolution of the lumen.
- This embodiment is characterized in that an image reconstruction selection function is added to the X-ray CT apparatus having the CPR image creation function according to the sixth embodiment described above, and in particular, a GUI for selection. There is a feature.
- the illustrated display screen 200 includes an image display unit 210, a subject information display unit 220, an imaging condition display unit 230, a reconstruction condition display unit 240, a status display unit 250, and the like.
- image display unit 210 for example, a positioning image of a subject imaged in advance imaging, a CT image after image reconstruction, and a CPR image are displayed.
- subject information display unit 220 displays information about the subject such as the name, sex, date of birth, and ID of the subject.
- the imaging condition display unit 230 and the reconstruction condition display unit 240 function as a GUI that prompts input to the input unit 36 and displays the input, and the imaging conditions (tube current, tube voltage, circuit Speed, bed movement speed in the body axis direction), and reconstruction conditions (reconstruction mode, image FOV, reconstruction filter, image slice thickness, reconstruction slice position) are set.
- the status display unit 250 displays the current status of the X-ray CT apparatus (whether imaging is being performed or stopped) and the selected mode.
- the shooting condition display unit 230 displays a GUI for selecting bed bed up / down / left / right moving shooting or scanner tilt angle changing shooting.
- a GUI may be displayed in a state where the positioning shooting is completed and the positioning image is displayed on the image display unit 210, and at that time, the bed up / down / left / right moving shooting and / or the scanner tilt angle changing shooting is selected. It may be possible.
- the bed moving curve can be set interactively with the operator as described in the first embodiment, The apparatus can determine the couch movement curve from the positioning image.
- the reconstruction condition display unit 240 displays either the volume mode or the CPR mode as the reconstruction mode.
- a GUI for selecting is displayed.
- the GUI may be a CPR selection button that allows CPR to be selected when the button is pressed, or a check box or the like.
- a GUI for selecting the standard mode or the straight line mode is displayed.
- the CPR image is an image along a vessel such as a blood vessel, but the display mode that displays the running direction of the vessel as it is is the standard mode, and the running direction of the vessel matches the Y direction (vertical direction) on the screen.
- the display mode to be performed is the straight line mode.
- FIG. 20 shows the flow of processing when the operator operates the image reconstruction condition display unit 240 of such a display screen.
- the image reconstruction described in the sixth embodiment is performed, and a CPR image (straight line image or standard image) is directly formed without reconstructing the volume image. And displayed on the image display unit 210.
- the image reconstruction described in the first embodiment and the second embodiment is performed, and volume image data is created.
- the volume image data is displayed on the image display unit 210 after image processing such as known volume rendering is performed. It is also possible to create a CPR image from this volume image.
- the operator can smoothly advance the bed up / down / left / right moving shooting / scanner tilt angle changing shooting, and can smoothly set the conditions associated with the shooting.
- the present invention it is possible to provide photographing that accompanies the movement of the bed up and down, left and right, or photographing that involves changing the tilt angle of the scanner, and a novel image reconstruction method corresponding thereto. Thereby, a high spatial resolution image effective for diagnosis can be displayed.
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Abstract
Description
X線検出器12で検出されたX線は、電流に変換され、プリアンプ18で増幅され、A/DコンバータでA/D変換された後、投影データ信号として演算装置30に入力される。演算装置30に入力された投影データ信号は、演算装置30内の再構成演算部32で画像再構成処理される。
本実施形態のX線CT装置は、撮影中に撮影中心を着目部位の中心線に沿って移動していくように寝台の位置を制御することが特徴である。すなわち、寝台の移動量を設定する移動量設定部は、被検体の着目部位が、回転盤の回転中心(撮影中心)に位置するように寝台の移動量を設定する。
xI、yI、zI:対象画素位置[mm]
L:線源から対象画素までの距離[mm]
R:線源と周回中心との間の距離[mm]
β:ファンビームの投影角度[rad]
fPfan:フィルタ補正ファンビーム投影データ
αI:チャネル角(ファン角)[rad]
vI:検出器列位置[mm]
xs、ys、zs:線源位置[mm]
SID:線源と検出器の距離
T: 寝台移動速度(Z方向)[mm/回転]
これに対し、本実施形態では上述した式(2-1)、(2-2)で用いられるxI及びyIの値として、式(1)の寝台移動曲線κx、κyから求められるX方向及びY方向の移動量を加えたものを用いて、式(2)の計算を行う。すなわち、式(2-1)~(2-3)を次式(3-1)~(3-3)のとおり変更する。
φ:パラレルビームの投影角[rad]
Wp(φ):パラレルビーム用ビュー重み
F:逆投影する位相幅(画素に対して逆投影されるビューの角度幅)
またファンビーム投影からパラレルビーム投影への並べ替え処理(ファン-パラ変換)は、たとえば次式(5)のように表される。
本実施形態でも、着目部位に合わせて撮影中心位置を変化させることは第一実施形態と同様であるが、本実施形態では寝台位置を移動するのではなく、着目部位の傾きの変化に合わせてスキャナのチルト角を変更することが特徴である。以下、第一実施形態と異なる点を中心に本実施形態を説明する。
本実施形態は、X線検出器12のサイズに対し被検体サイズが大きいときに、FOVを拡大し被検体をカバーするように寝台移動範囲を設定することが特徴である。まず被検体サイズとX線検出器サイズとの関係について図12を参照して説明する。図12(a)は、検出器サイズが被検体全体をカバーするのに十分な大きさを持つ場合、図12(b)は、検出器サイズが小さく、被検体全体をカバーできない場合を示している。
本実施形態は、寝台移動撮影を採用することによって、検出器サイズで決定されるサンプリング密度を増加し、空間分解能を向上することが特徴である。
寝台移動を伴わない場合には、図14(a)に示すように、サンプリングピッチは検出器サイズで決まる所定のピッチ(基本ピッチという)となるが、本実施形態では、同一スライスを3周にわたり撮影し、同一スライスが同一投影角度で3回撮影されるようにする。
この際、1周毎に撮影中心が基本ピッチから1/3ピッチずれるように寝台位置をたとえばX方向にずらす。これにより3回の撮影終了時点で、図14(b)に示すように、サンプリングピッチは基本ピッチの場合の1/3、すなわちサンプリング密度は3倍となり空間分解能を向上することができる。
また図14ではX方向の移動量のみを示しているが、寝台の移動方向はY方向でもよいし、X方向とY方向の両方でもよい。
本実施形態も、寝台移動撮影を採用することによって、検出器サイズで決定されるサンプリング密度を増加し、空間分解能を向上することは、第四実施形態と同様である。ただし第四実施形態のX線CT装置は、投影データを高密度化し再構成する機能を持つものであったのに対し、本実施形態のX線CT装置は、サンプリング位置をずらした画像を複数枚再構成し、合成する点で異なる。以下、異なる点を中心に説明する。
この際、1周の間で寝台を連続移動する場合には、式(3)等又は式(7)等を用いて寝台位置情報を用いた修正を行う。寝台位置情報は、S502で設定した移動量でもよいし、寝台移動計測装置23が備えられている場合には、撮影時に実際に移動した寝台移動軌跡(位置情報)を用いる。
本実施形態は、寝台の位置情報を用いて直接CPR像を作成することが特徴である。
その場合、各スライスのスキャナの角度情報はCPR面の角度として用い、また撮影中心の座標をCPR面の中心座標とすることで、上述した式(14)、(15)を用いたCPR像の再構成が可能である。
本実施形態は、上述した第六実施形態によるCPR像作成機能を備えたX線CT装置に対し、画像再構成の選択機能を追加したことを特徴とするものであり、特に選択のためのGUIに特徴がある。
Claims (17)
- 被検体を載せ、前記被検体の体軸方向に移動可能な寝台と、前記寝台を挟んで、放射線を照射する放射線源と放射線検出器とを対向させて配置し、前記寝台の周りを回転する回転盤と、前記回転盤の回転中に前記放射線検出器が検出した放射線のデータをもとに前記被検体の断層像を画像再構成する画像作成部と、前記寝台の前記体軸方向と直交する方向の位置及び/又は前記回転盤の垂直面に対する角度を変更する機構部と、前記機構部を制御する制御部と、撮影中における前記寝台の前記体軸方向と直交する方向の移動量及び/又は前記回転盤の角度変化量を設定する移動量設定部と、を備え、
前記制御部は、前記移動量設定部に設定された前記寝台の移動量及び/又は前記回転盤の角度変化量に従い、前記機構部を駆動して撮影を行い、前記画像作成部は、撮影中における前記寝台の前記体軸方向と直交する方向の移動情報及び/又は前記回転盤の角度情報を用いて画像を作成することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記制御部は、前記寝台の前記体軸方向の移動と連動して、前記寝台の前記体軸方向と直交する方向の移動を制御することを特徴とする放射線断層像撮影装置。 - 請求項2に記載の放射線断層像撮影装置であって、
前記制御部は、前記寝台の前記体軸方向の位置毎に、前記寝台の前記体軸方向と直交する方向の移動量の制限値を算出する制限値算出部を備えることを特徴とする放射線断層像撮影装置。 - 請求項3に記載の放射線断層像撮影装置であって、
前記画像作成部が作成した画像を表示する表示部を備え、
前記制御部は、前記制限値算出部が算出した移動量の制限値を、前記表示部に表示させることを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記画像作成部は、前記移動量設定部に設定された前記寝台の前記体軸方向と直交する方向の移動量及び/又は前記回転盤の角度変化量を用いて画像を作成することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記機構部は、撮影中の前記寝台の前記体軸方向と直交する方向の移動量及び/又は前記回転盤の角度変化量を計測する計測部を備え、前記画像作成部は、前記計測部に記録された前記寝台の移動量及び/又は前記回転盤の角度変化量を用いて画像を作成することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記移動量設定部は、前記被検体の事前撮影画像データをもとに、前記寝台の前記体軸方向と直交する方向の移動量及び/又は前記回転盤の角度変化量を設定することを特徴とする放射線断層像撮影装置。 - 請求項7に記載の放射線断層像撮影装置であって、
前記移動量設定部は、前記被検体の着目部位が、前記回転盤の回転中心に位置するように前記寝台の移動量を設定することを特徴とする放射線断層像撮影装置。 - 請求項7に記載の放射線断層像撮影装置であって、
前記移動量設定部は、前記回転盤の角度が、前記被検体の着目部位の前記体軸方向に対する傾きの変化に追従するように前記回転盤の角度変化量を設定することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記移動量設定部は、撮影のビュー角度に対し線形に変化させるように前記寝台の前記体軸方向と直交する方向の移動量を設定することを特徴とする放射線断層像撮影装置。 - 請求項10に記載の放射線断層像撮影装置であって、
前記移動量設定部は、前記放射線検出器のサイズと前記被検体の撮影対象面積との差に基き、前記寝台の前記移動方向と直交する方向の移動量を算出することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記制御部は、同一スライス位置について、一枚の断層像に必要なビュー数より多いビュー数の撮影を行い、同一スライス位置について、前記放射線検出器の素子サイズよりも細かいピッチで前記寝台を前記被検体の体軸方向と直交する方向に移動することを特徴とする放射線断層像撮影装置。 - 請求項1に記載の放射線断層像撮影装置であって、
前記画像作成部は、前記寝台の前記体軸方向と直交する方向における位置が異なる複数の画像を作成し、当該複数の画像を合成して合成画像を作成することを特徴とする放射線断層像撮影装置。 - 請求項13に記載の放射線断層像撮影装置であって、
前記画像作成部は、前記合成画像に対し、周波数強調フィルタリングして一枚の画像とすることを特徴とする。 - 請求項1に記載の放射線断層像撮影装置であって、
前記画像作成部は、前記寝台を前記被検体の体軸方向に移動しながら、前記寝台の前記体軸方向と直交する方向の位置及び/又は前記回転盤の前記垂直面に対する角度を変化させて撮影した投影データを用いて、前記被検体の着目部位に沿ったCPR像を作成することを特徴とする放射線断層像撮影装置。 - 請求項15に記載の放射線断層像撮影装置であって、
前記画像作成部に作成させる画像として、三次元画像とCPR像のいずれかを操作者に選択させる入力装置を備えたことを特徴とする放射線断層像撮影装置。 - 被検体を載せ、前記被検体の体軸方向に移動可能な寝台と、前記寝台を挟んで、放射線を照射する放射線源と放射線検出器とを対向させて配置し、前記寝台の周りを回転する回転盤と、前記回転盤の回転中に前記放射線検出器が検出した放射線のデータをもとに前記被検体の断層像を画像再構成する画像作成部と、前記被検体の着目部位の、前記体軸方向に沿った座標の変化を記録する記録部とを備え、
前記画像作成部は、前記記録部に記録された前記被検体の着目部位の座標の変化と、前記被検体の体軸方向に沿って収集された投影データとを用いて、前記被検体の着目部位に沿ったCPR像を作成することを特徴とする放射線断層像撮影装置。
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