JP5784290B2 - X-ray CT system - Google Patents

Description

  Embodiments described herein relate generally to an X-ray CT apparatus.

  An X-ray CT (Computed Tomography) apparatus has a rotating part in which an X-ray tube and an X-ray detector are attached to and confronted with an annular frame. The subject is positioned inside the frame, and the rotating part is The X-ray tube emits X-rays while rotating around the subject at high speed, and the subject is scanned by detecting X-rays transmitted through the subject with an X-ray detector (X-rays). Computed tomography equipment).

  In the X-ray CT apparatus, since a rotating unit including an X-ray tube and an X-ray detector rotates at a high speed, vibration is generated in a gantry. When the natural frequency of the gantry and the vibration due to the rotation resonate, the vibration is amplified, and artifacts are generated in the reconstructed image, thereby degrading the image quality.

JP 2010-12106 A

  The object of the present invention is to reduce the vibration of the gantry of the X-ray CT apparatus.

The X-ray CT apparatus of the first embodiment includes a gantry, an X-ray tube and an X-ray detector facing each other, and is rotatably attached to the gantry and includes a rotating unit that rotates around the subject. An X-ray CT apparatus, a storage means for storing a natural vibration parameter related to the natural vibration of the gantry when the rotating unit is stopped, and a vibration for detecting a vibration parameter related to the vibration of the gantry generated based on the rotation of the rotating unit A parameter detection unit, a resonance determination unit that compares the stored natural vibration parameter and the vibration parameter detected by the vibration parameter detection unit to determine whether or not the resonance occurs; and a braking device to change the rack stand rigid with, based on the result of said resonant determination means, the brake control unit that controls the braking device to change the gantry stiffness Provided.

1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to a first embodiment of the present invention. It is a perspective view which shows the internal structure of the gantry apparatus of an X-ray CT apparatus. It is a side view which shows the state which fixed the tilt part to the base with the brake device. It is a side view which shows the state which cancelled | released fixing to the base of the tilt part by a brake device. It is a flowchart explaining the procedure in the case of scanning the subject P and changing the natural frequency of the gantry. It is a side view which shows the internal structure of the mount apparatus of the X-ray CT apparatus of the 2nd Embodiment of this invention. It is a side view which shows the internal structure of the mount apparatus of the X-ray CT apparatus of the 3rd Embodiment of this invention. It is a figure which shows the 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Example 1]
FIG. 1 is a block diagram showing a schematic configuration of the X-ray CT apparatus according to the first embodiment of the present invention. The X-ray CT apparatus includes a gantry 1, a bed (not shown), and an operation console unit 2.

  The gantry 1 includes a gantry controller 4, a high voltage generator 5, a rotation driver 6, a tilt driver 7, a brake device 8, an X-ray tube 9, an X-ray detector 10, and a data collector. 11, a rotation unit 12 (see FIG. 2), a tilt unit 13 (see FIG. 2), a natural vibration parameter calculation unit 14, and a vibration parameter detection unit 15.

  The bed apparatus (not shown) includes a bed base (not shown), a bed driving unit (not shown), and a bed top plate (not shown).

  The operation console unit 2 includes a system control unit 210, an input device 209, a preprocessing unit 19, an X-ray projection data storage unit 20, a reconstruction processing unit 21, an image storage unit 205, and an image processing unit 23. The display control unit 207 and the display unit 24 are provided.

  The gantry control unit 4 controls each unit in the gantry 1 based on an input from the input device 209 of the operation console unit 2.

  The high voltage generator 5 supplies a high voltage for irradiating X-rays from the X-ray tube 9 to the X-ray tube 9 in accordance with a control signal from the gantry controller 4.

  The X-ray tube 9 emits X-rays with a high voltage supplied from the high voltage generator 5. X-rays emitted from the X-ray tube 9 are fan-shaped or cone-shaped beams.

  The X-ray detector 10 detects X-rays irradiated from the X-ray tube 9 and transmitted through the subject P. In the case of a single slice CT apparatus, the X-ray detector 10 is configured by arranging, for example, 1000 channels of X-ray detection elements in a line in a fan shape or a straight line shape. In the case of a multi-slice CT apparatus, the X-ray detector 10 includes a plurality of X-ray detector elements arranged in an array in each of two directions (slice direction and channel direction) orthogonal to each other. It constitutes a detector.

  The data collection unit 11 includes data collection elements arranged in an array similar to the X-ray detection elements of the X-ray detector 10, and X-rays (actually detection signals detected by the X-ray detector 10). ) In correspondence with the data collection control signal output from the gantry control unit 4. This collected data becomes X-ray projection data.

  The rotation drive unit 6 drives the rotation unit 12 to rotate according to a control signal output from the gantry control unit 4.

  The natural vibration parameter calculation means 14 calculates a natural vibration parameter of the gantry when the rotating unit is stopped. The natural vibration parameter is a parameter derived from natural vibration, which is a specific vibration detected when an object is vibrated freely. For example, the natural frequency can be used. The natural frequency, which is a natural vibration parameter, is affected by rigidity and the like. The obtained natural vibration parameters are stored in a storage unit such as a memory of the system control unit 210. When the vibration parameter of the gantry accompanying the rotation of the rotating unit 12 becomes close to the natural vibration parameter, a resonance phenomenon occurs and the amplitude increases. For example, when the vibration frequency of the gantry and the natural frequency of the gantry substantially coincide with the rotation of the rotating unit 12, a resonance phenomenon occurs. The natural vibration parameter calculation means 14 in this embodiment hits a stand with an impulse hammer, and measures acceleration and the like with an acceleration pickup (vibration parameter detection means 15) attached to the stand. The natural vibration parameter can be calculated by performing FFT analysis on the result.

  The vibration parameter detection unit 15 detects a parameter derived from vibration generated with the rotation of the rotating unit 12. As the vibration parameter, the frequency can be used. As the vibration parameter detection means 15, an acceleration sensor, a speed sensor, a displacement sensor, a position sensor, or the like is used.

  In this embodiment, the vibration parameter changing means 3 is mainly composed of a brake device 8.

  The resonance determining unit 16 in the operation console unit 2 compares the vibration parameter of the gantry 1 calculated by the natural vibration parameter calculating unit 14 in advance with the vibration parameter detected by the vibration parameter detecting unit 15 to determine whether resonance has occurred. Judge whether or not.

  The resonance determining unit 16 may be provided in the gantry 1.

  The vibration parameter changing unit 3 changes the vibration parameter of the gantry 1 accompanying the rotation of the rotating unit 12 based on the determination result of the resonance determining unit 16. In this embodiment, in order to change the vibration frequency that is the vibration parameter of the gantry 1 accompanying the rotation of the rotating unit 12, the gantry rigidity that affects the vibration frequency is changed. A method of adjusting the gripping force of the brake device 8 is employed to change the gantry rigidity.

  The brake device 8 changes its gripping force based on the control signal output from the gantry control unit 4 based on the determination result of the resonance determination unit 16.

  The tilt drive unit 7 rotates the tilt unit 13 to an arbitrary angle based on the control signal output from the gantry control unit 4 based on the determination result of the resonance determination unit 16.

  The bed driving unit (not shown) moves the bed base (not shown) in the vertical direction based on the input from the input device 209 of the operation console unit 2, and the bed top plate (not shown) in the longitudinal direction. Move. A subject P is placed on the couch top, and the body axis direction of the subject P coincides with the longitudinal direction of the couch top.

  The input device 209 includes a keyboard, a touch panel, a mouse, and the like, and performs various input operations for driving the X-ray CT apparatus.

  The system control unit 210 generates a control signal based on an input from the input device 209, and sends this control signal to each unit in the gantry control unit 4, the bed driving unit, and the operation console unit 2.

  The preprocessing unit 19 performs sensitivity correction, X-ray intensity correction, and the like on the X-ray projection data output from the data collection unit 11. The X-ray projection data that has been subjected to processing such as sensitivity correction in the preprocessing unit 19 is temporarily stored in the X-ray projection data storage unit 20.

  The reconstruction processing unit 21 reconstructs image data by performing a back projection process on the X-ray projection data stored in the X-ray projection data storage unit 20. This back projection method is the same as a known method. Further, when interpolation processing is performed on X-ray projection data, X-ray projection data at a target slice position is obtained by a known interpolation method such as 360-degree interpolation method or 180-degree interpolation method (opposite data interpolation method). .

  The reconstructed image data is temporarily stored in the image storage unit 205 and then sent to the image processing unit 23. Based on the input from the input device 209, the image processing unit 23 converts the image data into image data such as a tomographic image of an arbitrary cross section, a projection image from an arbitrary direction, or a three-dimensional image by rendering processing by a known method. And output to the display unit 24 via the display control unit 207. An image based on the image data is displayed on the display unit 24.

  FIG. 2 shows the tilt unit 13, the rotation unit 12, the tilt drive unit 7, and the brake device 8 provided on the gantry 1. The tilt unit 13, the rotation unit 12, the tilt drive unit 7, and the brake device 8 are mounted on a base 25 and covered with an exterior case 26 (see FIGS. 3 and 4). An opening (not shown) through which the subject P placed on the bed top is taken in and out is formed at the center of the outer case 26.

  The base 25 includes a rectangular frame-shaped base portion 25a and a pair of support column portions 25b erected from the base portion 25a.

  The tilt portion 13 includes a pair of side plates 13 a supported by the support shaft 27 on the upper end portion of the support column portion 25 b and an annular frame 13 b fixed between the pair of side plates 13 a. Can be rotated. The support shaft 27 may be fixed to the support column 25b and interposed with a bearing between the tilt plate 13 and the side plate 13a, or may be fixed to the support plate 25a of the tilt unit 13 and between the support plate 25b. A bearing may be interposed.

  The vibration parameter detection means 15 may be provided on a support shaft 27 that is a tilt axis in the gantry 1 and at a place where vibrations appear remarkably, such as the uppermost end or the lowermost end of the tilt unit 13. That is, you may provide on the flame | frame 13b and the support | pillar part 25b. The vibration parameter detection unit 15 detects a vibration parameter derived from vibration in a direction along the rotation axis of the rotating unit 12 and / or a vibration parameter derived from vibration in a direction orthogonal to the direction along the rotation axis. Alternatively, a vibration parameter derived from vibration in an arbitrary direction is detected.

The resonance determination unit 16 determines whether resonance has occurred in the gantry 1. Whether or not resonance has occurred is determined as follows.
The FFT detection is performed on the waveform detected by the vibration parameter detection means 15. If the resulting frequency matches the natural vibration parameter measured earlier, it is determined as resonance.
If the amplitude of the waveform detected by the vibration parameter detection means 15 exceeds a certain threshold value, it is determined as resonance.

  When resonance occurs, the resonance determining unit 16 causes the vibration parameter changing unit 3 to change the vibration parameter of the gantry accompanying the rotation of the rotating unit 12 via the gantry controller 4.

  The tilt drive unit 7 is a mechanism that rotates the tilt unit 13 around the support shaft 27 at an arbitrary angle and holds the tilt unit 13 at the rotated angles. The tilt drive unit 7 can be extended and contracted, and one end of the tilt drive unit 7 is rotatably connected to the base unit 25 a and the other end is connected to the side plate 13 a of the tilt unit 13 so as to be rotatable. By extending and retracting the tilt drive unit 7, the tilt unit 13 rotates around the support shaft 27. By stopping the expansion and contraction of the tilt drive unit 7, the tilt unit 13 is held at the rotated angle.

  The rotating unit 12 includes an annular frame 28, an X-ray tube 9 attached to the inner periphery of the frame 28, an X-ray detector 10, a power supply unit 29, and a mechanical control unit 30. ing. The rotating portion 12 is supported by the frame 13b of the tilt portion 13 via a bearing (not shown), and is rotatable about the center of the frame 13b and the frame 28. In addition, a rotation drive unit 6 such as a motor is connected to the rotation unit 12, and the rotation unit 12 is driven to rotate by the rotation drive unit 6. The X-ray tube 9 and the X-ray detector 10 are arranged at positions separated by 180 °, and face each other in the direction in which the X-ray detector 10 can detect the X-rays emitted from the X-ray tube 9.

  The brake device 8 is a device that fixes the tilt portion 13 rotated at an arbitrary angle to the base 25 at a predetermined angle with a predetermined gripping force, and includes a first gear 31 and a second gear 32.

  The first gear 31 is fixed to one side plate 13 a of the tilt portion 13, is provided so as to be rotatable around the support shaft 27 integrally with the tilt plate 13, and is formed on a convex circular arc portion centering on the support shaft 27. It has the several tooth | gear part 31a located. The first gear 31 is formed in a semicircular shape. This semicircular range is a range in which the first gear 31 can maintain meshing with the second gear 32 when the tilt portion 13 is rotated around the support shaft 27 in the maximum range.

  One end of the second gear 32 is attached to the other end of the movable piece 33 on the support column 25b so that the second gear 32 can be rotated by the support shaft 33a. The second gear 32 is attached to the movable piece 33 by restricting the rotation of the second gear 32. A solenoid (not shown) is connected to the movable piece 33. When the solenoid is turned on / off, the movable piece 33 is rotated to the position shown in FIGS. 2 and 3, and the second gear 32 is engaged with the first gear 31. Located in position. When the solenoid is turned on, the movable piece 33 rotates to the position shown in FIG. 4, and the second gear 32 is located at the mesh release position where the mesh with the first gear 31 is released.

  By controlling the current value of the solenoid that moves the movable piece 33, the force pressing the second gear 32 against the first gear 31 can be controlled. As a result, the gripping force can be increased or decreased, and the same effect can be obtained by changing the value of the current supplied to the motor, not the solenoid that moves the movable piece 33, but the motor.

  In such a configuration, the X-ray CT apparatus of the present embodiment can rotate the tilt unit 13 around the support shaft 27 by the tilt drive unit 7 and brake the tilt unit 13 rotated to an arbitrary angle. The device 8 can be fixed to the base 25 with a predetermined gripping force.

  Accordingly, it is possible to prevent the rotating unit 12 from vibrating around the support shaft 27 together with the tilt unit 13 when the rotating unit 12 rotates. Thereby, the error of the image data reconstructed based on the X-ray projection data detected by the X-ray detector 10, the position information of the X-ray tube 9, the X-ray detector 10, etc. is reduced, and the reconstructed image The quality will be higher.

  In the first embodiment, the case where the first gear 31 is formed in a semicircular shape has been described as an example. However, the shape of the first gear 31 is not limited to a semicircular shape, and is circular. It may be a fan shape. Further, the first gear may be a gear having a concave arcuate portion centered on the support shaft 27 and having a tooth portion.

  FIG. 5 is a flowchart for explaining a procedure in the case where the subject P is scanned by the X-ray CT apparatus and the vibration frequency, which is the vibration parameter of the gantry accompanying the rotation of the rotating unit 12, is changed.

  First, the natural frequency of the gantry is calculated by the natural vibration parameter calculation means 14 in a state where the rotating part is stopped (S1). In the state where the rotating unit 12 is rotated, the vibration parameter detecting means 15 detects the vibration frequency which is the vibration parameter of the gantry accompanying the rotation of the rotating unit 12 (S2). The resonance determination unit 16 determines the presence or absence of resonance based on the detected vibration parameter (S3). When the occurrence of resonance is determined (S4), the resonance determination unit 16 causes the vibration parameter changing unit 3 to change the vibration parameter of the gantry (S5).

[Example 2]
An X-ray CT apparatus according to a second embodiment of the present invention will be described with reference to FIG. Note that, in the second embodiment and the subsequent embodiments, the same components as those described in the first embodiment are denoted by the same reference numerals, and redundant descriptions are omitted.

  The basic configuration of the X-ray CT apparatus of the second embodiment is the same as that of the first embodiment, and the second embodiment is different from the first embodiment in that the first embodiment. The brake device 41 is provided in place of the brake device 8 described in the embodiment.

  The brake device 41 is a device that fixes the tilt portion 13 rotated at an arbitrary angle to the base 25 at a predetermined angle with a predetermined gripping force, and includes a magnetic body 42 and a magnet 43.

  The magnetic body 42 is a semicircular iron plate disposed around the support shaft 27, and is fixed to one side plate 13 a of the tilt portion 13 so as to be rotatable integrally with the tilt portion 13. The semicircular range is a range in which the magnet 43 can maintain the state of facing the magnetic body 42 when the tilt portion 13 is rotated around the support shaft 27 in the maximum range. The magnetic body 42 only needs to have a function of being attracted to the magnet 43, and a magnet may be used as the magnetic body 42.

  An electromagnet can be used as the magnet 43. The adsorption state with respect to the magnetic body 42 can be adjusted by changing the energization amount of the electromagnet.

  In such a configuration, in the X-ray CT apparatus of the present embodiment, the tilt unit 13 can be rotated around the support shaft 27 by the tilt drive unit 7, and the tilt unit 13 rotated at an arbitrary angle is provided. The brake device 41 can be fixed to the base 25 with a predetermined gripping force.

  Accordingly, it is possible to prevent the rotating unit 12 from vibrating around the support shaft 27 together with the tilt unit 13 when the rotating unit 12 rotates. Thereby, the error of the image data reconstructed based on the X-ray projection data detected by the X-ray detector 10, the position information of the X-ray tube 9, the X-ray detector 10, etc. is reduced, and the reconstructed image The quality will be higher.

  In this embodiment, the case where the magnetic body 42 is attached to the tilt portion 13 and the magnet 43 is attached to the base 25 has been described as an example. However, the magnetic body is attached to the base 25 and the magnet is attached to the tilt portion. 13 may be attached.

[Example 3]
An X-ray CT apparatus according to a third embodiment of the present invention will be described with reference to FIG.

  The basic configuration of the X-ray CT apparatus of the third embodiment is the same as that of the first embodiment, and the third embodiment is different from the first embodiment in that the first embodiment. The brake device 51 is provided in place of the brake device 8 described in the embodiment.

  The brake device 51 is a device that fixes the tilt portion 13 rotated at an arbitrary angle to the base 25 at the angle, and includes a frictional resistance receiving portion 52 and a frictional resistance applying portion 53.

  The frictional resistance receiving portion 52 is a part provided as a part of the tilt portion 13. In the third embodiment, a support shaft that rotatably supports the tilt portion 13 is fixed to the tilt portion 13. The support shaft is provided as a frictional resistance receiving portion 52. The support shaft that functions as the frictional resistance receiving portion 52 has a larger outer diameter than the support shaft 27 described in the above-described embodiment.

The frictional resistance applying unit 53 is attached to the base 25, and the application position for applying the frictional resistance to the frictional resistance receiving part 52 by sandwiching the frictional resistance receiving part 52 from the outer peripheral side and the outer peripheral side of the frictional resistance receiving part 52. It is provided so as to be movable to a release position where the application of the frictional resistance to the frictional resistance receiving portion 52 is released by separation. As the frictional resistance applying portion 53, a member that is disposed at a position surrounding the periphery of the frictional resistance receiving portion 52 and is pressed against the outer peripheral surface of the frictional resistance receiving portion 52 so as to be able to contact and separate can be used. As a means for moving the frictional resistance application unit 53 between the application position and the release position, for example, a pressing device using a solenoid, hydraulic pressure, air pressure, or the like can be used. The frictional resistance applying unit 53 can be moved to the release position by turning on the solenoid or the like, and the frictional resistance applying unit 53 can be moved to the friction position by turning off the solenoid or the like.
In this embodiment, the resonance determination unit 16 adjusts the energization amount, hydraulic pressure, and air pressure to the solenoid of the pressing device.

  In this configuration, in this X-ray CT apparatus, the tilt drive unit 7 can rotate the tilt unit 13 around the support shaft 27, and the tilt unit 13 rotated to an arbitrary angle can be rotated by the brake device 51. It can be fixed to the base 25.

  Therefore, the rotating unit 12 can be prevented from rotating while vibrating around the frictional resistance receiving unit 52 that is a support shaft together with the tilting unit 13 when the rotating unit 12 rotates. Thereby, the error of the image data reconstructed based on the X-ray projection data detected by the X-ray detector 10, the position information of the X-ray tube 9 and the X-ray detector 10 is reduced, and the reconstructed image The quality becomes high.

  In the present embodiment, the case where the frictional resistance receiving part 52 is provided in the tilt part 13 and the frictional resistance applying part 53 is attached to the base 25 has been described as an example. The frictional resistance applying unit 53 may be provided in the tilt unit 13.

[Example 4]
An X-ray CT apparatus according to a fourth embodiment of the present invention will be described with reference to FIG.

  The basic configuration of the X-ray CT apparatus of the fourth embodiment is the same as that of the first embodiment, and the fourth embodiment is different from the first embodiment in that the first embodiment. Instead of the brake device 8 described in the embodiment, a brake cylinder is provided.

  As shown in FIGS. 8A and 8B, the brake cylinder 80 is attached so as to connect the base plate 25 and the side plate 13a on the side opposite to the tilt drive unit 7. The brake cylinder 80 has a structure in which an electromagnetic brake is attached to the tip of the ball screw, and the holding force can be changed by controlling the current applied to the electromagnetic brake.

[Example 5]
A fifth embodiment of the present invention will be described.
In the present embodiment, when the X-ray CT apparatus is installed or shipped, the natural frequency of the gantry is calculated in advance, and the gripping force of the brake device described above is adjusted based on the data.
The present invention can also be applied to an X-ray CT apparatus having no tilt unit.

DESCRIPTION OF SYMBOLS 1 Base 2 Operation console part 3 Vibration parameter change means 4 Base control part 5 High voltage generation part 6 Rotation drive part 7 Tilt drive part 8 Brake device 9 X-ray tube 10 X-ray detector 11 Data collection part 12 Rotation part 13 Tilt part 13a Side plate 13b Frame 14 Natural vibration parameter calculation means 15 Vibration parameter detection means 16 Resonance judgment section 19 Preprocessing section 20 X-ray projection data storage section 21 Reconstruction processing section 23 Image processing section 24 Display section 25 Base 25a Base section 25b Column Part 26 Exterior case 27 Support shaft 28 Frame 29 Power supply unit 30 Mechanical control unit 31 First gear 31a Tooth part 32 Second gear 33 Movable piece 33a Support shaft 41 Brake device 42 Magnetic body 43 Magnet 51 Brake device 52 Friction resistance receiving portion 53 Friction resistance application section

Claims (8)

An X-ray CT apparatus comprising a gantry, an X-ray tube and an X-ray detector facing each other, rotatably attached to the gantry, and a rotating unit that rotates around the subject,
Storage means for storing a natural vibration parameter relating to the natural vibration of the gantry in a stopped state of the rotating unit;
Vibration parameter detecting means for detecting a vibration parameter relating to vibration of the gantry generated along with rotation of the rotating part;
Resonance determination means for comparing the stored natural vibration parameter with the vibration parameter detected by the vibration parameter detection means to determine whether resonance is present;
A braking device to change the rack base rigidity with the rotation of the rotating part,
An X-ray CT apparatus comprising: a brake control unit that controls a brake device so as to change the gantry rigidity based on a result of the resonance determination unit. A tilt portion supported by the gantry so as to be rotatable around a support shaft;
A tilt drive unit that rotates the tilt unit around the support shaft at an arbitrary angle;
The X-ray CT apparatus according to claim 1, comprising: The brake device is
A first gear fixed to the tilt portion and having a plurality of tooth portions located in an arc portion centered on the support shaft;
A second gear that is provided on the pedestal so as to restrict rotation, and is movable to a meshing position that meshes with the first gear and a mesh release position that releases meshing with the first gear;
The X-ray CT apparatus according to claim 2, comprising: The brake device is
A magnetic body provided on one of the tilt part and the mount;
A magnet provided on the other of the tilt part and the gantry and capable of switching between an attracting state and an attracting release state with respect to the magnetic body, wherein the brake control unit adjusts the attracting state. The X-ray CT apparatus according to claim 2 or 3. The brake device is
A frictional resistance receiving part that is provided on any one of the tilt part and the frame and to which a frictional resistance is applied;
Provided on the other of the tilt part and the gantry and moved to an application position for applying frictional resistance to the frictional resistance receiving part and a release position for releasing application of frictional resistance to the frictional resistance receiving part The X-ray CT apparatus according to claim 2, further comprising a frictional resistance applying unit, wherein the brake control unit adjusts the value of the frictional resistance. Means for releasing the fixing of the tilt part to the gantry by the brake device;
Means for rotating the tilt unit by the tilt drive unit when the fixing of the tilt unit by the brake device is released;
Means for fixing the tilt part to the gantry by the brake device when the tilt part is turned by the tilt drive part;
The X-ray CT apparatus according to claim 2, comprising: The brake device is
A first gear fixed to the tilt portion and having a plurality of tooth portions located in an arc portion centered on the support shaft;
A second gear that is provided on the pedestal so as to restrict rotation, and is movable to a meshing position that meshes with the first gear and a mesh release position that releases meshing with the first gear;
The X-ray CT apparatus according to claim 2, comprising:   The X-ray CT apparatus according to claim 2, wherein the brake device is a brake cylinder provided on a side opposite to the tilt drive unit.

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