JP2007111150A - Parallel link table and tomographic imaging equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parallel link table and tomographic imaging equipment, capable of limiting the movement of a top plate in the body axis direction to a prescribed range regardless of the lifting position of the parallel link table. <P>SOLUTION: The parallel link table comprises a stopper member 66 attached to the top plate 12, an upper structure 63 on which the top plate is mounted for driving the top plate in the direction of the body axis of a subject, four-joint parallel links L1 and L2 whose one end is rotatably attached to a pedestal 61 on the floor surface and whose other end is rotatably attached to the upper structure for rotatably supporting the upper structure while keeping the upper structure parallel to the floor surface, an actuator 62 for rotating the links in the direction of the body axis of the subject, a frame member 71 supported by the upper structure in such a way as slidable in the direction of the body axis of the subject, a stopper member 72 attached to the frame member, and a link L3 whose one end is rotatably attached to the middle point of the link L1 or L2 and whose other end is rotatably attached to the frame member, having half the length of the link L1 or L2. The range of movement of the top plate in the direction of the body axis of the subject is limited by the effect of engagement between the stopper members 66 and 72. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a parallel link table and a tomographic imaging apparatus, and more particularly to a parallel link table and a tomographic imaging apparatus that place a subject and convey it to an imaging region.

  With the spread of tomography devices (CT) today, there are many cases where CT is installed in a relatively small examination room, and in order to operate CT safely in such an installation environment, a patient or an engineer takes an imaging table. It is necessary to limit the moving range of the imaging table (top plate) according to the installation environment so that it is not sandwiched between the camera and the wall.

Conventionally, a top plate for mounting a patient is supported by a four-node parallel link, and the link is rotated in the direction of the subject's body axis to raise and lower the top plate while maintaining its horizontal posture. A so-called parallel link type imaging table is known (Patent Document 1). Since the imaging table of this system is simple in structure, it can be configured compactly and inexpensively, and when the link is retracted, the top plate part descends and at the same time is sufficiently separated from the gantry cavity part, so that the patient can get on and off freely without using a platform. In addition, since a large empty space can be secured in front of the gantry, preparation for shooting can be performed safely and easily. On the other hand, when the link advances, the top plate rises and approaches the gantry cavity at the same time, so that the top plate (patient) can be transported deeply into the gantry cavity during imaging.
Japanese Examined Patent Publication No. 02-036098 (page 3, Fig. 2) JP 2004-173756 (Abstract, FIG. 3)

  However, when imaging a subject, it is necessary to adjust the imaging center (affected part) of the subject to the height of the gantry rotation center ISO, but patients with various physiques (for example, breast thickness 140 mm to 200 mm) have a height of ISO. Since the position of the lifted top plate projects in the direction of the body axis (initial position) differs depending on its height, if the subject is subsequently imaged according to a common scan plan, There is a risk that the top plate may exceed the safe area of the installation environment, and the top plate may come into contact with the wall or an engineer may be sandwiched between the top plate and the wall.

  In order to solve this, there is a method of limiting the range of movement of the top plate by software control in consideration of the initial position of the top plate, but the danger cannot be avoided if the software runs away. In some cases, the drive unit is unlatched and the top plate is manually operated. In this case, software control is useless.

  Conventionally, there is known an imaging table in which a top plate supported by a four-node parallel link can be vertically moved up and down on the front surface of the gantry (Patent Document 2). However, a mechanism for vertically moving a heavy top plate portion is expensive.

  The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to limit the moving range of the top plate in the body axis direction to a certain level regardless of the elevation position of the parallel link table. It is an object of the present invention to provide a parallel link table and a tomographic imaging apparatus that can be used.

  The above problem is solved by the configuration of FIG. That is, the parallel link table of the present invention (1) includes a top plate 12 on which a subject is placed, a first stopper member 66 attached to the top plate, and the subject body axis by mounting the top plate. The upper structure 63 that is driven in the direction, one end is attached to the pedestal 61 on the floor surface, and the other end is rotatably attached to the upper structure body, and the upper structure is rotated while keeping parallel to the floor surface. The first and second four-node parallel links L1 and L2 that can be supported, the actuator 62 for rotating the first and second links in the direction of the subject body axis, and the upper structure. A frame member 71 slidably supported in the body axis direction, a second stopper member 72 attached to the frame member, one end at the midpoint of the first or second link, and the other end at the frame Each of the members is rotatably attached to the first or second member. And a third link L3 having a length ½ of the second link, and the top plate moves in the direction of the subject body axis by the engaging action between the first and second stopper members. The range is limited.

  In the present invention (1), the frame member 71 having the second stopper member 72 is supported by the upper structure 63 so as to be slidable in the direction of the subject body axis, and the frame member 71 is connected to the third link L3. Thus, with the configuration that can be lifted only in the vertical direction, the movement limit of the top plate 12 can be kept constant regardless of the lift position of the parallel link. In this case, since the structure in which only the frame member 71 (that is, the second stopper member 72) is vertically moved up and down can be configured with a simple structure and lightweight, the entire table can be provided in a small size and at low cost.

  In the present invention (2), in the present invention (1), the setting position of the second stopper member is configured to be manually set within a predetermined range in the subject body axis direction. Therefore, the movable range of the top plate 12 can be set easily.

  In the present invention (3), in the present invention (1), the setting position of the second stopper member can be set remotely by a driving means within a predetermined range in the direction of the subject body axis. Therefore, the movable range of the top 12 can be easily set remotely from a remote location.

  Further, the above problem is solved by the configuration of FIG. That is, the parallel link table of the present invention (4) includes a top plate 12 on which the subject is placed, a first stopper member 66 attached to the top plate, and the subject body axis mounted with the top plate. The upper structure 63 that is driven in the direction, one end is attached to the pedestal 61 on the floor surface, and the other end is rotatably attached to the upper structure body, and the upper structure is rotated while keeping parallel to the floor surface. Four-node parallel type first and second links L1 and L2 that are supported in a possible manner, an actuator 62 that rotates the first and second links in the direction of the subject body axis, and the first or second link Detection means 90 for detecting the rotation angle of the link, a second stopper member 72 attached to the upper structure, and attached to the upper structure, and based on the detected detection angle, The second stopper portion in a direction that cancels out the movement in the specimen body axis direction And drive means for controlling the settings position, the engagement action between the first and second stopper members, is obtained by limiting the range of movement of the subject body axis direction of the top plate.

  In the present invention (4), the second stopper member 72 is supported by the upper structure 63 so as to be slidable in the direction of the subject body axis, and the subject body of the upper structure is based on the separately detected rotation angle of the link. With the configuration in which the setting position of the second stopper member is automatically controlled in a direction that cancels the movement in the axial direction, the movement limit of the top plate 12 can be kept constant regardless of the elevation position of the parallel link.

  In the present invention (5), in the above-mentioned present inventions (1) to (4), the actuator can be pivoted at one end to the base and the other end to the upper half of the first or second link. It is composed of a telescopic actuator attached to the. Such actuators include hydraulic type, ball screw type, and sliding screw type.

  In the tomographic imaging apparatus of the present invention (6), an X-ray imaging system including an X-ray tube and an X-ray detector facing each other with the subject interposed therebetween is rotated around the subject body axis to obtain projection data. A scanning gantry to be acquired, and a parallel link table according to the present invention (1) to (5) for loading and unloading a subject mounted on a top board into and out of the cavity of the scanning gantry, and the scanning gantry Information processing means for reconstructing a tomographic image of the subject based on the acquired projection data. The parallel link table of the present invention is suitable for application to an X-ray CT apparatus.

  As described above, according to the present invention, it is possible to limit the movement range of the top plate in the body axis direction regardless of the elevation position of the parallel link table, so that the parallel link can be used even in a relatively narrow installation environment. The mold table can be operated safely, and thus greatly contributes to the spread of tomographic imaging apparatuses.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings. FIG. 1 is a configuration diagram of an X-ray CT apparatus according to an embodiment. The X-ray CT apparatus includes an imaging table 10 on which a subject 100 is placed and moved in the direction of the subject body axis (z-axis), and a scanning gantry 20 that collects axial / helical scan data of the subject using an X-ray fan beam. Remote control of the imaging table 10 and the scanning gantry 20, and an operation console 1 on which an operator performs various setting operations.

  The operation console 1 includes an input device 2 that receives input from an operator, a central processing unit (CPU) 3 that performs image reconstruction processing, a data collection buffer 5 that collects projection data acquired by the scanning gantry 20, and a projection A monitor 6 that displays a CT image reconstructed from data, and a storage device 7 that stores programs and data for realizing the functions of the apparatus and X-ray CT images are provided. The imaging table 10 includes an elevating mechanism and a top plate (cradle) 12 for placing a subject on and off of the subject to and from a bore (cavity) of the scanning gantry 20.

   The scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22 that controls the tube voltage and tube current of the X-ray tube 21, and a collimator that controls the thickness (slice thickness) of the X-ray fan beam in the z-axis direction. 23, a multi-row X-ray detector 24, a data acquisition device DAS (Data Acquisition System) 25, an X-ray tube 21, a multi-row X-ray detector 24, and the like are rotatably supported around the subject body axis. A rotation unit 15, a rotation unit controller 26 that controls the rotation unit 15, and a control controller 29 that exchanges control signals with the operation console 1 and the imaging table 10 are provided.

  Collection of projection data in this X-ray CT apparatus is performed as follows. First, with the subject positioned in the cavity of the scanning gantry 20, the position in the z-axis direction is fixed, and the subject is irradiated with the X-ray fan beam from the X-ray tube 21 (projection of X-rays). The transmitted X-ray is detected by the multi-row X-ray detector 24. The transmission X-ray is detected by rotating the X-ray tube 21 and the multi-row X-ray detector 24 around the subject {ie, changing the projection (view) angle} N (for example, N = 1000) view direction, data collection for 360 degrees is performed.

Each detected transmission X-ray is converted into a digital value by the data acquisition unit 25 and is projected as projection data d (ch, view) (ch: channel, view: view) via the data acquisition buffer 5 via the operation console 1. Forwarded to This operation is called one scan. Then, the scan position is sequentially moved by a predetermined amount in the z-axis direction, and the next scan is performed. Such a scanning method is called a conventional (or axial) scanning method. Further, in this conventional scan method, a scan method that continuously scans for a plurality of rotations is called a cine scan method. In addition, a method of moving the imaging table 10 at a predetermined speed in synchronization with a change in the projection angle and collecting projection data while moving the scan position is called a helical scan method. The present invention can be applied to any of a conventional scan method, a cine scan method, and a helical scan method.

  The operation console 1 stores the projection data transferred from the scanning gantry 20 in the storage device 7 of the central processing unit 3, and performs, for example, a predetermined reconstruction function and a superimposition operation, and a tomographic image of the subject by back projection processing. Reconfigure. Here, the operation console 1 can reconstruct a tomographic image in real time from projection data sequentially transferred from the scanning gantry 20 during the scanning process, and always display the latest tomographic image on the monitor 6. Furthermore, it is also possible to call up the projection data stored in the storage device 7 and perform image reconstruction again.

  2 and 3 are configuration diagrams (1) and (2) of the imaging table according to the first embodiment, and FIG. 2 shows a state in which the imaging table 10 is returned to a relatively low position in front of the scanning gantry 20. The side structure is shown. The imaging table 10 is provided on a pedestal 61 and a top plate (cradle) 12 on which the subject 100 is mounted, an upper structure 63 on which the top plate 12 is mounted and moved in the direction of the subject (z) axis. And a lift mechanism that rotates the upper structure 63 including the top plate 12 in the yz plane while maintaining the level with the floor surface by the four-node parallel links L1 and L2.

  The top plate 12 includes a first stopper member 66 fixed at a predetermined position below the top plate 12. The upper structure 63 supports the top plate 12 so as to be slidable in the z-axis direction by a roller member 65 and a drive unit 64 provided on the upper surface thereof. Further, the upper structure 63 includes first and second brackets 67 and 68 that project downward at a predetermined interval and at an equal length. Although not shown, such first and second brackets and structures related thereto are provided symmetrically toward the subject.

  Further, a pair of rotating rollers r1, r2 and r3, r4 are provided inside the first and second brackets 67, 68, respectively, between the rollers r1 and r2 and between the rollers r3 and r4. Is sandwiched by a frame member 71 extending in the z-axis direction. Thereby, the frame member 71 is supported by the upper structure 63 so as to be slidable in the z-axis direction.

  The frame member 71 includes a third bracket 74 that protrudes downward at the same height as the first and second brackets 67 and 68 at a substantially central portion thereof. The head of the frame member 71 is engaged with a first stopper member 66 fixed to the top plate 12 to stop further movement of the top plate 12 in the direction of the gantry 20. The second stopper member 72 is attached so that the setting position on the frame member 71 can be arbitrarily changed by manual operation. Preferably, by providing the scale 73 on the side surface of the frame member 71, the operator can accurately set the second stopper member 72 at a desired position. It is preferable that this scale can easily (intuitively) recognize the insertion limit position of the top plate 12 in the body axis direction.

  On the other hand, the upper surface of the base 61 is provided with the first and second brackets 67 and 68 and fourth and fifth brackets 81 and 82 provided at equal intervals in the z-axis direction. And between these 1st, 4th brackets 67 and 81 and between 2nd and 5th brackets 68 and 82, the rotary coupling | bond part c1-1 by the 1st, 2nd link L1, L2 of equal length. It connects so that it can rotate freely in yz plane via c4. Thus, the first and second links L1 and L2 constitute a four-node parallel type parallel link.

Further, an extendable actuator 62 is connected between the second link L2 and the bracket 83 provided on the pedestal 61 so as to be rotatable in the yz plane via rotary coupling portions c7 and c8. ing. An example of the actuator 62 is a cylinder having a piston rod built therein, and is configured to extend and contract the piston rod by, for example, hydraulic pressure. The upper structure 63 is moved up and down in a state in which the upper structure 63 is maintained parallel to the base 61 by the expansion and contraction of the piston rod.

  Further, between the just center portion of the first link L1 (that is, the position of ½ of the link length) and the third bracket 74 of the frame member 71, exactly ½ of the first link L1. The third link L3 having the length of is connected to the yz plane so as to be rotatable through rotary coupling portions c5 and c6. The frame member 71 moves up and down only in the vertical direction of the pedestal 61 while maintaining the horizontal posture with the pedestal 61 by the action of the third link L3. Next, this operation will be described.

FIG. 6 is a diagram for explaining the vertical lifting operation by the link L3. In the figure, a link L3 having a length d is connected to the midpoint of the link L1 having a length 2d. In this state, isosceles triangles c2, c5, c6 and isosceles triangles c1, c5, c6 are always formed. Therefore, if the angle formed between each link and the horizontal direction is α and the angle formed between each link and the vertical direction is β, the angle between α and β is
π-2α + π-2β = π
The relationship always holds. This
α + β = π / 2
The relationship always holds. This is the same even when the link L1 falls to the position indicated by the dotted line in the figure. Accordingly, the vertex c6 of the link L3 is always raised and lowered only in the direction perpendicular to the base 61 (arrow b).

  FIG. 3 shows a side structure in a state where the imaging table 10 is driven to a relatively high position in front of the scanning gantry 20. When the cylinder of the actuator 62 extends, the parallel links L1 and L2 rotate in the clockwise direction (arrow a), and accordingly, the upper structure 63 also rotates in the clockwise direction. However, since the frame member 71 is connected to the third link L3 in a slide-free state, the frame member 71 slides freely between the rotation rollers r1 to r4 regardless of the movement of the upper structure 63 in the z-axis direction. However, it rises only in the vertical (arrow b) direction. Therefore, the second stopper member 72 can be held at a predetermined fixed position regardless of the elevation position of the top 12.

  Thus, when the imaging center (affected part) of the subject 100 reaches a height that coincides with the gantry rotation center ISO, the drive by the actuator 62 stops. When imaging the subject 100, the top 12 is moved in the body axis direction by the drive unit 64 to convey the subject 100 into the gantry cavity, and tomography is performed. Even in this case, when the top plate 12 advances to a predetermined region (dangerous region) set in advance, the first and second stopper members 66 and 72 are engaged, and beyond that of the top plate 12 by a mechanical stop action. Progress is limited.

  Although not shown, preferably, a proximity sensor is provided between the first and second stopper members 66 and 72, and the safety function is activated when the sensor detects an approach of a predetermined level or more. The drive of the plate 12 is stopped. Therefore, a large engagement load is not applied between the first and second stopper members 66 and 72. As the proximity sensor, various types of known proximity sensors that detect a change in light, magnetic field, or electric field caused by the approach of two objects can be used. Further, even when the drive unit 64 is not powered on, or when the top plate 12 is unlatched from the drive unit and manually slid freely, the mechanical force between the first and second stopper members 66 and 72 can be reduced. The forward movement of the top plate 12 is surely stopped by the proper engaging action. Therefore, it is safe even when the top plate 12 is manually operated.

  Then, after the imaging, the operation for carrying the subject 100 out of the scanning gantry 20 is the reverse of the above. Although not shown, the top plate 12 at the time of retraction is mechanically stopped at a predetermined home position by a method similar to the conventional method.

  FIG. 4 is a block diagram of the imaging table according to the second embodiment. The third link L3 is provided on the second link L2 side, and the frame member 71 is connected to the third link L3. An example is shown. Since the operation of the parallel link can be easily inferred from the description of the operation according to the first embodiment, the description is omitted.

  Further, in the second embodiment, a guide rail 77 is attached to the frame member 71, and a second stopper member 72 is slidably attached to the guide rail 77. In addition, the geared motor 75 is fixed to the frame member 71, and the second stopper member 72 is screwed onto the rotating shaft that has been cut off. In this configuration, for example, when the motor 75 rotates to the left, the stopper member 72 moves backward in the body axis direction, and when the motor 75 rotates to the right, the stopper member 72 moves forward. Therefore, according to this configuration, the setting position of the second stopper member 72 can be remotely controlled as desired from an operation panel (not shown) on the surface of the imaging table 10 or from the operation console 1.

  FIG. 5 is a block diagram of an imaging table according to the third embodiment. The conventional simple four-barrel parallel link structure is used as it is, and the inclination angle of the parallel link is separately detected and based on the detected angle. In this example, the setting position of the second stopper member 72 is automatically corrected in a direction that cancels out the movement of the upper structure in the subject body axis direction.

  In the figure, when the cylinder of the actuator 62 extends, the parallel links L1 and L2 rotate in the clockwise direction (arrow a), and accordingly, the upper structure 63 also rotates in the clockwise direction. In the present embodiment, a guide rail 77 is provided on the upper structure 63, and a second stopper member 72 is slidably attached to the guide rail 77 in the z-axis direction. The geared motor 75 is fixed to the upper structure 63, and the second stopper member 72 is screwed onto the rotary shaft 76 that has been cut off. In this configuration, for example, when the motor 75 rotates to the left, the stopper member 72 moves backward in the body axis direction, and when the motor 75 rotates to the right, the stopper member 72 moves forward. The initial position of the stopper member 72 can be set remotely in advance from the operation panel on the surface of the imaging table 10 or from the operation console 1 in the same manner as described above with reference to FIG.

On the other hand, an angle sensor 90 is provided at the lower end portion of the link L2 via the rotation shaft of the rotary coupling portion c3. The angle sensor 90 can measure the rotation angle θ from the surface of the base 61 of the link L2. It has become. The measured rotation angle θ is input to, for example, the CPU 3, and the offset position of the third bracket 68 in the z-axis direction with respect to the rotation angle θ is calculated here. Assuming that the length of the link L2 is now 2d, this position is from the position where the coupling part c3 is located,
H = 2d cos θ
The position is offset in the z-axis direction.

The CPU 3 obtains a movement amount Δh in the body axis direction of the upper structure 63 in real time based on the detected rotation angle θ of the link L2 in conjunction with the driving of the actuator 62. Assuming that the rotation angle of the link L2 has changed from θ1 to θ2 (> θ1), the movement amount Δh of the upper structure 63 in the body axis direction is
Δh = 2d (cos θ1−cos θ2)
It is obtained by. In response to this, the CPU 3 returns the position of the second stopper member 72 by Δh, so that the initial setting position of the second stopper member 72 is always kept constant regardless of the horizontal movement of the upper structure 63. it can. Accordingly, it is possible to appropriately prevent the top plate 12 from excessively passing during subsequent photographing.

  In the above embodiment, the case where the actuator 62 is a hydraulic cylinder has been described. However, the present invention is not limited to this. In addition, an extendable actuator composed of a geared motor and a ball screw may be used. Alternatively, instead of using the telescopic actuator, the rotation shaft of the geared motor may be directly connected to the lower end portion of the link L1 or L2, and the link L1 or L2 may be directly rotated.

  In the above-described embodiment, the application example to the X-ray CT apparatus is described as an example of the tomography apparatus to which the present invention is applied. However, the present invention is not limited to this. The imaging table of the present invention detects and images a pair of γ-rays (two photons) generated when positrons contained in a radiopharmaceutical (positron nuclide) taken into the subject disappear. The present invention can also be applied to a PET apparatus.

  Moreover, although several embodiment suitable for the said invention was described, it cannot be overemphasized that the structure of each part, a control, a process, and these combinations can be variously changed within the range which does not deviate from this invention. .

1 is a configuration diagram of an X-ray CT apparatus according to an embodiment. It is a block diagram (1) of the imaging | photography table by 1st Embodiment. It is a block diagram (2) of the imaging | photography table by 1st Embodiment. It is a block diagram of the imaging | photography table by 2nd Embodiment. It is a block diagram of the imaging | photography table by 3rd Embodiment. It is a figure explaining the vertical raising / lowering operation | movement by the link L3.

Explanation of symbols

1 Operation console 10 Shooting table 20 Scanning gantry 12 Top plate (cradle)
61 Pedestal 62 Actuator 63 Upper structure 64 Drive portion 65 Roller member 66, 72 Stopper member 67, 68 Bracket 71 Frame member 75 Geared motor 76 Shaft 77 Guide rail 90 Angle sensor 100 Subject c1 to c4 Linking portion L1 to L3 Link r1 ~ R4 roller

Claims (6)

A top plate on which the subject is placed;
A first stopper member attached to the top plate;
An upper structure mounted with the top plate and driven in the direction of the subject body axis;
A four-joint parallel type first that has one end attached to a pedestal on the floor and the other end rotatably attached to the upper structure, and supports the upper structure rotatably while keeping parallel to the floor. , The second link,
An actuator for rotating the first and second links in the direction of the subject body axis;
A frame member that is slidably supported in the axial direction of the subject by the upper structure;
A second stopper member attached to the frame member;
A third end having one end pivotally attached to the midpoint of the first or second link and the other end pivotally attached to the frame member, and having a length ½ of the first or second link. With a link
A parallel link table characterized in that the range of movement of the top plate in the direction of the subject body axis is limited by the engaging action between the first and second stopper members. The parallel link table according to claim 1, wherein the setting position of the second stopper member is configured to be manually set within a predetermined range in the direction of the subject body axis. 2. The parallel link table according to claim 1, wherein the setting position of the second stopper member can be set remotely by a driving means within a predetermined range in the direction of the subject body axis. A top plate on which the subject is placed;
A first stopper member attached to the top plate;
An upper structure mounted with the top plate and driven in the direction of the subject body axis;
A four-joint parallel type first that has one end attached to a pedestal on the floor and the other end rotatably attached to the upper structure, and supports the upper structure rotatably while keeping parallel to the floor. , The second link,
An actuator for rotating the first and second links in the direction of the subject body axis;
Detecting means for detecting a rotation angle of the first or second link;
A second stopper member attached to the upper structure;
Driving means attached to the upper structure and for controlling the setting position of the second stopper member in a direction that cancels out the movement of the upper structure in the direction of the subject body axis based on the detected detection angle; With
A parallel link table characterized in that the range of movement of the top plate in the direction of the subject body axis is limited by the engaging action between the first and second stopper members. 5. The actuator includes an extendable actuator having one end attached to the base and the other end rotatably attached to the upper half of the first or second link. The parallel link type table according to any one of the above. A scanning gantry for obtaining projection data by rotating an X-ray imaging system including an X-ray tube and an X-ray detector opposed to each other with the subject interposed therebetween;
A parallel link table according to any one of claims 1 to 5, wherein a subject mounted on a top board is carried into and out of a cavity of the scanning gantry;
An tomographic imaging apparatus comprising: information processing means for reconstructing a tomographic image of a subject based on projection data acquired by the scanning gantry.

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