CN118311066A

CN118311066A - CT apparatus

Info

Publication number: CN118311066A
Application number: CN202211742840.6A
Authority: CN
Inventors: 张丽; 陈志强; 李元景; 黄清萍; 张立国; 李桂培; 洪明志; 冯博
Original assignee: Tsinghua University; Nuctech Co Ltd
Current assignee: Tsinghua University; Nuctech Co Ltd
Priority date: 2022-12-30
Filing date: 2022-12-30
Publication date: 2024-07-09

Abstract

The present disclosure provides a CT apparatus, comprising: a frame; a plurality of support devices disposed on the frame, each support device comprising a plurality of rotatable wheels, wherein at least one rotatable wheel of at least one support device acts as a drive wheel; a rotatable portion rotatable about a rotation axis by the driving of the driving wheel, the rotatable portion being commonly supported by a plurality of supporting devices during rotation of the rotatable portion; the scanning device comprises a ray source and a detector, the ray source and the detector are arranged on the rotatable part, and the ray source and the detector are oppositely arranged along the radial direction of the rotatable part; the first axial limiting mechanism is used for limiting the movement of the rotatable part along the first direction; and a second axial limiting mechanism for limiting movement of the rotatable portion in a second direction, wherein the first direction and the second direction are both parallel to the rotational axis and the first direction and the second direction are opposite.

Description

CT apparatus

Technical Field

The present disclosure relates to the field of radiation inspection technology, and more particularly, to a CT apparatus.

Background

CT technology plays an important role in security inspection because it can eliminate the effects of object overlapping. CT equipment is also widely used in technical fields such as article detection, and CT equipment not only can detect smaller articles such as traveling bags and aviation containers, but also can detect larger articles such as containers and vehicles.

In the related art, a CT apparatus acquires projection data at different angles by rotation of an X-ray machine and a detector using a slip ring device, acquires tomographic images by a reconstruction method, and thus acquires internal information of a baggage item to be detected. The existing baggage item inspection equipment can reconstruct the atomic number and electron density of the inspected substance by matching with a dual-energy or multi-energy imaging technology, thereby realizing the identification of the substance type and playing a good role in the detection of explosives, dangerous goods and the like.

For example, in the related art, when a rotatable portion of a CT apparatus is supported by a supporting device, the rotatable portion generates displacement in a rotation axis direction when rotating, and when the displacement is large and the rotation speed of the rotatable portion is fast, the CT apparatus is caused to vibrate, which affects the imaging accuracy of the CT apparatus.

The above information disclosed in this section is only for understanding the background of the technical idea of the present disclosure, and thus, the above information may contain information that does not constitute prior art.

Disclosure of Invention

In order to solve the above-mentioned problem in the prior art, the embodiment of the present disclosure provides a CT apparatus, which has the characteristics of simple structure, accurate imaging in the operation process, and small vibration.

One aspect of the present disclosure provides a CT apparatus comprising: a frame; a plurality of support devices disposed on the frame, each of the support devices including a plurality of rotatable wheels, wherein at least one rotatable wheel of at least one support device acts as a drive wheel; a rotatable portion rotatable about a rotation axis by the drive wheel, the rotatable portion being commonly supported by the plurality of support devices during rotation of the rotatable portion; the scanning device comprises a ray source and a detector, wherein the ray source and the detector are arranged on the rotatable part and are oppositely arranged along the radial direction of the rotatable part; a first axial limiting mechanism for limiting movement of the rotatable portion in a first direction; and a second axial stop mechanism for limiting movement of the rotatable portion in a second direction, wherein the first direction and the second direction are both parallel to the rotational axis and the first direction and the second direction are opposite.

In some exemplary embodiments of the present disclosure, the rotatable portion includes a rotatable body and at least one rotatable track, the scanning device is disposed on the rotatable body, and the first axial limit mechanism and the second axial limit mechanism are disposed on both sides of the at least one rotatable track, respectively, in a direction parallel to the rotation axis.

In some exemplary embodiments of the present disclosure, the rotatable portion includes two rotatable rails between which the rotatable body is sandwiched in a direction parallel to a rotation axis of the rotatable portion, and the first axial limit mechanism is disposed on a side of one of the two rotatable rails away from the rotatable body in a direction parallel to the rotation axis, and the second axial limit mechanism is disposed on a side of the other of the two rotatable rails away from the rotatable body.

In some exemplary embodiments of the present disclosure, the rotatable portion includes two rotatable rails between which the rotatable body is interposed in a direction parallel to a rotation axis of the rotatable portion, and the first axial limit mechanism and the second axial limit mechanism are disposed on both sides of the same one of the two rotatable rails, respectively, in a direction parallel to the rotation axis.

In some exemplary embodiments of the present disclosure, the first axial stop mechanism includes an axial pinch roller disposed proximate an end face of one of the rotatable tracks facing in the first direction.

In some exemplary embodiments of the present disclosure, the second axial stop mechanism includes an axial eccentric pinch roller disposed proximate an end face of the other rotatable track facing in the second direction.

In some exemplary embodiments of the present disclosure, the first axial stop mechanism includes an axial pinch roller, and the second axial stop mechanism includes an axial eccentric pinch roller, the axial pinch roller and the axial eccentric pinch roller being disposed proximate to an end face of the same rotatable track facing in the first direction and an end face facing in the second direction, respectively.

In some exemplary embodiments of the present disclosure, a minimum distance in the first direction between an outer circumferential surface of the axial pinch roller and an end surface of the rotatable rail facing the first direction remains unchanged during rotation of the axial pinch roller.

In some exemplary embodiments of the present disclosure, a minimum distance between an outer circumferential surface of the axial eccentric pinch roller and an end surface of the rotatable rail facing the second direction is varied along the second direction during rotation of the axial eccentric pinch roller.

In some exemplary embodiments of the present disclosure, the axial pinch roller includes a wheel seat fixedly connected to the frame, a wheel shaft provided on the wheel seat, a wheel bearing provided on the wheel shaft through the wheel bearing, and a first pinch roller element having a central axis coincident with a central axis of the wheel shaft, the first pinch roller element being rotatable on the wheel shaft, at least a portion of an outer peripheral surface of the first pinch roller element facing an end surface of the rotatable rail facing a first direction.

In some exemplary embodiments of the present disclosure, the axial eccentric pinch roller includes a wheel seat fixedly connected to the frame, a wheel shaft provided on the wheel seat, a wheel bearing provided on the wheel shaft through the wheel bearing, and a second pinch roller element having an eccentric amount between a central axis of the second pinch roller element and a central axis of the wheel shaft, the second pinch roller element being eccentrically rotatable on the wheel shaft, at least a portion of an outer circumferential surface of the second pinch roller element facing an end surface of the rotatable rail toward a second direction.

In some exemplary embodiments of the present disclosure, the axial pinch roller and the axial eccentric pinch roller share a wheel seat such that the axial pinch roller and the axial eccentric pinch roller constitute a pinch roller set.

In some exemplary embodiments of the present disclosure, the axial puck further includes a first baffle disposed on a side of the axle remote from the first puck element and a second baffle disposed on a side of the wheel bearing remote from the first baffle, the first baffle and the second baffle together restricting movement of the first puck element in a radial direction of the rotatable track; and/or, the axial eccentric pinch roller further comprises a first baffle and a second baffle, wherein the first baffle is arranged on one side of the wheel shaft away from the second pinch roller element, the second baffle is arranged on one side of the wheel bearing away from the first baffle, and the first baffle and the second baffle limit the second pinch roller element to move along the radial direction of the rotatable track together.

In some exemplary embodiments of the present disclosure, the CT apparatus further comprises a magnetic device disposed on the gantry for providing a magnetic attraction force to the rotatable portion when the rotatable portion rotates.

In some exemplary embodiments of the present disclosure, the magnetic force device includes a plurality of permanent magnets or electromagnets arranged on the frame in a spaced manner from each other in a rotation direction of the rotatable portion.

In some exemplary embodiments of the present disclosure, the plurality of permanent magnets or electromagnets are arranged on the frame at uniform intervals in a rotation direction of the rotatable portion.

In some exemplary embodiments of the present disclosure, the rotatable portion includes a rotatable body on which the scanning device is disposed, and at least one rotatable rail including a magnetic material, or on an outer circumferential surface of which a magnetic portion composed of a magnetic material is mounted.

Additional aspects and advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure.

Drawings

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

fig. 1A is a front view of a CT apparatus according to some exemplary embodiments of the present disclosure;

FIG. 1B is a side view of a CT apparatus according to some exemplary embodiments of the present disclosure;

Fig. 2A is a front view of a rotatable portion of a CT apparatus according to some exemplary embodiments of the present disclosure;

Fig. 2B is a front view of a rotatable portion of a CT apparatus according to some exemplary embodiments of the present disclosure;

FIG. 3A is a schematic structural view of an axial puck of a CT apparatus according to some exemplary embodiments of the present disclosure;

FIG. 3B is a schematic structural view of an axially eccentric puck of a CT apparatus according to some exemplary embodiments of the present disclosure;

FIG. 4A is a diagram of an arrangement of a first axial stop structure and a second axial stop structure of a CT apparatus according to an exemplary embodiment of the present disclosure;

Fig. 4B is a setup view of a first axial limit structure and a second axial limit structure of a CT apparatus according to another exemplary embodiment of the present disclosure;

Fig. 5 is a schematic structural view of a magnetic device of a CT apparatus according to another exemplary embodiment of the present disclosure.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the concepts of the present disclosure. In addition, the various embodiments provided below of the present disclosure and technical features in the embodiments may be combined with each other in any manner.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. Furthermore, the terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components. All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.

In the description of the present disclosure, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present disclosure. Furthermore, features defining "first", "second" may include one or more such features, either explicitly or implicitly. In the description of the present disclosure, unless otherwise indicated, the meaning of "a plurality" is two or more.

In the description of the present disclosure, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this disclosure will be understood by those of ordinary skill in the art in the specific context.

Fig. 1A is a front view of a CT apparatus according to some exemplary embodiments of the present disclosure. Fig. 1B is a side view of a CT apparatus according to some example embodiments of the present disclosure. Fig. 2A is a front view of a rotatable portion of a CT apparatus according to some exemplary embodiments of the present disclosure. Fig. 2B is a front view of a rotatable portion of a CT apparatus according to some exemplary embodiments of the present disclosure.

The CT apparatus according to the embodiment of the present disclosure will be described in detail with reference to fig. 1A to 2B.

As shown in fig. 1A to 2B, the CT apparatus 100 includes a gantry 110, a supporting device 1, a rotatable portion 2, a scanning device 3, a first axial stopper mechanism 4, and a second axial stopper mechanism 5.

The gantry 110 is used to support the CT apparatus 100. The supporting device 1 is disposed on the frame 110, and the supporting device 1 may be disposed in plural, for example, two opposite to a first side near the lower side of the frame and two opposite to a second side near the lower side of the frame opposite to the first side. The support device 1 is used for supporting the rotatable part 2.

The support device 1 comprises a plurality of rotatable wheels 11, wherein at least one rotatable wheel of at least one support device 1 acts as a driving wheel. For example, one rotatable wheel of the support device 1 as in 1B is connected to the drive motor 12, which rotatable wheel serves as a drive wheel.

The rotatable part 2 is rotatable about the rotation axis AX1 under the drive of the drive wheel, and the rotatable part 2 is supported in common by the plurality of support devices 1 during rotation of the rotatable part 2.

As shown in fig. 2A and 2B, the scanning device 3 includes a radiation source 31 and a detector 32, both of which are disposed on the rotatable portion 2, and the radiation source 31 and the detector 32 are disposed opposite to each other in a radial direction of the rotatable portion 2. For example, the radiation source 31 is disposed on a circumferential side of the rotatable part, the detector 32 is disposed on a second side opposite to the first circumferential side, and the centers of gravity of the radiation source 31 and the detector 32 are located on the rotation axis AX1, thereby ensuring that no vibration occurs when the rotatable part rotates the radiation source 31 and the detector 32.

The first axial limiting mechanism 4 is used for limiting the movement of the rotatable part2 in the first direction D1. The second axial limiting mechanism 5 is used to limit the movement of the rotatable part2 in the second direction D2. As shown in fig. 1B, the first direction D1 and the second direction D2 are both parallel to the rotation axis AX1, and the first direction D1 and the second direction D2 are opposite.

As shown in fig. 1B, the rotatable portion 2 includes at least one rotatable rail 21 and a rotatable body 22, the scanning device 31 is provided on the rotatable body 22, and the first axial limit mechanism 4 and the second axial limit mechanism 5 are provided on both sides of the at least one rotatable rail 21, respectively, in a direction parallel to the rotation axis AX 1.

Fig. 3A is a schematic structural view of an axial pinch roller of a CT apparatus according to some exemplary embodiments of the present disclosure.

The axial pinch roller 20 shown in fig. 3A includes a wheel seat 221, an axle 222, a wheel bearing 223, and a first pinch roller element 224, the wheel seat 221 is fixedly connected to the frame 110, the axle 222 is provided on the wheel seat 221, the first pinch roller element 224 is provided on the axle 222 through the wheel bearing 223, the central axis of the first pinch roller element 224 coincides with the central axis of the axle, the first pinch roller element 224 is rotatable on the axle 222, and at least a portion of the outer peripheral surface of the first pinch roller element 224 faces the end surface of the rotatable rail in the first direction.

Fig. 3B is a schematic structural view of an axially eccentric puck of a CT apparatus according to some exemplary embodiments of the present disclosure.

The second axial limiting mechanism comprises an axial eccentric pressing wheel, and the axial eccentric pressing wheel is arranged close to the end face of the other rotatable track, which faces the second direction.

As shown in fig. 3B, the axial eccentric pinch roller 20' includes a wheel seat 221, an axle 222, a wheel bearing 223, and a second pinch roller element 224', wherein the wheel seat 221 is fixedly connected to the frame 110, the axle 222 is disposed on the wheel seat 221, the second pinch roller element 224' is disposed on the axle 222 through the wheel bearing 223, and an eccentric amount is provided between a central axis of the second pinch roller element 224' and a central axis of the axle 222, for example, as shown in fig. 3B, the eccentric amount of the second pinch roller element 224' and the central axis of the axle 222 is d. Second puck element 224 'is capable of eccentric rotation on axle 222, and at least a portion of an outer peripheral surface of second puck element 224' faces an end surface of the rotatable rail that faces in the second direction.

In some embodiments of the present disclosure, the rotatable portion includes two rotatable tracks, the rotatable body being sandwiched between the two rotatable tracks in a direction parallel to the rotational axis of the rotatable portion.

Illustratively, as shown in fig. 1B, the rotatable rail 21 includes two rotatable rails 21 disposed on both sides of the rotatable body 22 in a direction parallel to the rotation axis AX1, respectively, that is, the two rotatable rails 21 sandwich the rotatable body 22.

Fig. 4A is a diagram of an arrangement of a first axial limit structure and a second axial limit structure of a CT apparatus according to an exemplary embodiment of the present disclosure.

In a direction parallel to the rotation axis AX1, the first axial limit mechanism 4 is provided on one side of the two rotatable rails 21 away from the rotatable body 22, and the second axial limit mechanism 5 is provided on the other side of the two rotatable rails 21 away from the rotatable body 22.

Illustratively, as shown in fig. 4A, the first axial stop mechanism 4 includes a first axial stop mechanism 41 disposed on a first side of the rotational axis AX1 and a first axial stop mechanism 42 disposed on a second side of the rotational axis AX1, as viewed from the top of fig. 1B downward, wherein the first side and the second side are opposite.

The second axial stop mechanism 5 includes a second axial stop mechanism 51 provided on a first side of the rotation axis AX1 and a second axial stop mechanism 52 provided on a second side of the rotation axis AX 1.

Fig. 4B is a diagram illustrating an arrangement of a first axial limit structure and a second axial limit structure of a CT apparatus according to another exemplary embodiment of the present disclosure.

In some embodiments of the present disclosure, as shown in fig. 1A and 4B, the rotatable portion 2 includes two rotatable rails 21, the rotatable body 22 is sandwiched between the two rotatable rails 21 in a direction parallel to the rotation axis AX1 of the rotatable portion 2, and the first axial limit mechanism 4 and the second axial limit mechanism 5 are provided on both sides of the same one of the two rotatable rails 21, respectively, in the direction parallel to the rotation axis.

In some embodiments of the present disclosure, the first axial stop mechanism 4 and the second axial stop mechanism 5 may be, for example, one of an axial eccentric puck or an axial puck. For example, the first axial limiting mechanism 4 and the second axial limiting mechanism 5 are both axial eccentric pinch rollers. For example, the first axial limiting mechanism 4 and the second axial limiting mechanism 5 are both axial pinch rollers. For example, the first axial limiting mechanism 4 is an axial pinch roller, and the second axial limiting mechanism 5 is an axial eccentric pinch roller.

In some embodiments of the present disclosure, the first axial stop mechanism 4 includes an axial pinch roller 20, and the second axial stop mechanism 5 includes an axial eccentric pinch roller 20', the axial pinch roller 20 and the axial eccentric pinch roller 20' being disposed proximate to an end face of the same rotatable track facing in the first direction and an end face facing in the second direction, respectively.

During rotation of axial pinch roller 20, the minimum distance between the outer circumferential surface of the axial pinch roller and the end surface of the rotatable rail facing in the first direction D1 remains unchanged.

During rotation of the axially eccentric pinch roller 21, the minimum distance between the outer circumferential surface of the axially eccentric pinch roller and the end surface of the rotatable rail facing in the second direction D2 is varied. By providing the axial eccentric pressing wheel 21, the minimum distance of the rotatable part 2 in the second direction D2 can be adjusted, so that the rotatable part 2 can be effectively prevented from being greatly shifted or moved in the second direction.

In some embodiments of the present disclosure, axial pinch roller 20 and axial eccentric pinch roller 20' share a wheel mount such that the axial pinch roller and the axial eccentric pinch roller form a pinch roller set.

For example, as shown in fig. 4B, the axial pinch roller 20 and the axial eccentric pinch roller 20 'are disposed on the same wheel base 221, so that the axial pinch roller 20 and the axial eccentric pinch roller 20' constitute a pinch roller group that can hold one rotatable rail 21 of the rotatable portion 2.

As shown in FIG. 3A, axial puck 20 also includes a first stop 225 and a second stop 226, the first stop 225 being disposed on a side of axle 222 remote from the first puck element 224, the second stop 226 being disposed on a side of wheel bearing 223 remote from the first stop 225, the first and second stops together limiting movement of the first puck element in a radial direction of the rotatable track.

As shown in FIG. 3B, axially eccentric puck 20' further includes a first stop 225 and a second stop 226, first stop 225 being disposed on a side of axle 222 remote from second puck element 224', second stop 226 being disposed on a side of wheel bearing 223 remote from first stop 225, first stop 225 and second stop 226 together limiting movement of second puck element 224' in a radial direction of the rotatable track.

As shown in fig. 5, the CT apparatus 100 further includes a magnetic device 6, the magnetic device 6 being disposed on the gantry 110 for providing a magnetic attraction force to the rotatable portion 2 when the rotatable portion 2 rotates, so as to apply an attraction force to the rotatable portion 2 toward the gantry 110.

The magnetic means 6 comprise, for example, a plurality of permanent magnets or electromagnets arranged on the frame at a distance from each other in the direction of rotation of the rotatable part 2.

Illustratively, a plurality of permanent magnets or electromagnets are arranged on the frame at uniform intervals in the rotational direction of the rotatable portion. For example, a plurality of permanent magnets are arranged on the frame along the outer circumference of the rotatable portion, may be arranged in the lower side region of the frame, or may be arranged in other regions of the frame.

As shown in fig. 2A and 2B, the rotatable part 2 comprises a rotatable body 22 and at least one rotatable track 21, the scanning device 31 being provided on the rotatable body 22, the rotatable track comprising a magnetic material in some embodiments. In some alternative embodiments, a magnetic portion composed of a magnetic material is mounted on the outer peripheral surface of the rotatable rail. The magnetic part can be attracted to the magnetic means, thereby exerting an attraction force on the rotatable part 2 towards the frame 110.

According to the embodiment of the disclosure, the movement of the rotatable part in the first direction and the second direction can be limited by arranging the first axial limiting mechanism and the second axial limiting mechanism, so that the imaging accuracy of the CT equipment is improved, and meanwhile, the vibration of the CT equipment in the running process is reduced.

In the description of the present specification, reference to the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the present disclosure have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined by the claims and their equivalents. Those skilled in the art will appreciate that the features recited in the various embodiments of the disclosure and/or in the claims may be provided in a variety of combinations and/or combinations, even if such combinations or combinations are not explicitly recited in the disclosure. In particular, the features recited in the various embodiments of the present disclosure and/or the claims may be variously combined and/or combined without departing from the spirit and teachings of the present disclosure. All such combinations and/or combinations fall within the scope of the present disclosure.

Claims

1. A CT apparatus, comprising:

A frame;

A plurality of support devices disposed on the frame, each of the support devices including a plurality of rotatable wheels, wherein at least one rotatable wheel of at least one support device acts as a drive wheel;

a rotatable portion rotatable about a rotation axis by the drive wheel, the rotatable portion being commonly supported by the plurality of support devices during rotation of the rotatable portion;

The scanning device comprises a ray source and a detector, wherein the ray source and the detector are arranged on the rotatable part and are oppositely arranged along the radial direction of the rotatable part;

A first axial limiting mechanism for limiting movement of the rotatable portion in a first direction; and

A second axial limiting mechanism for limiting movement of the rotatable portion in a second direction,

Wherein the first direction and the second direction are both parallel to the axis of rotation, and the first direction and the second direction are opposite.

2. The CT apparatus of claim 1, wherein the rotatable portion comprises a rotatable body and at least one rotatable track, the scanning device being disposed on the rotatable body,

The first axial stop mechanism and the second axial stop mechanism are disposed on either side of the at least one rotatable track in a direction parallel to the axis of rotation.

3. The CT apparatus according to claim 1, wherein the rotatable portion includes two rotatable rails, the rotatable body being sandwiched between the two rotatable rails in a direction parallel to a rotation axis of the rotatable portion,

The first axial limiting mechanism is disposed on a side of one of the two rotatable rails away from the rotatable body in a direction parallel to the rotational axis, and the second axial limiting mechanism is disposed on a side of the other of the two rotatable rails away from the rotatable body.

4. The CT apparatus according to claim 2, wherein the rotatable portion includes two rotatable rails, the rotatable body being sandwiched between the two rotatable rails in a direction parallel to a rotation axis of the rotatable portion,

The first axial limit mechanism and the second axial limit mechanism are disposed on both sides of the same one of the two rotatable rails, respectively, in a direction parallel to the rotation axis.

5. A CT apparatus according to claim 3 wherein the first axial stop mechanism comprises an axial pinch roller disposed adjacent an end face of one of the rotatable tracks facing in the first direction.

6. A CT apparatus according to claim 3 wherein the second axial stop mechanism comprises an axially eccentric pinch roller disposed adjacent an end face of the other rotatable track facing in the second direction.

7. The CT apparatus of claim 4, wherein the first axial stop mechanism comprises an axial pinch roller and the second axial stop mechanism comprises an axial eccentric pinch roller, the axial pinch roller and the axial eccentric pinch roller being disposed proximate to an end face of the same rotatable track facing in the first direction and an end face facing in the second direction, respectively.

8. The CT apparatus of claim 5 or 7, wherein a minimum distance in the first direction between an outer circumferential surface of the axial pinch roller and an end surface of the rotatable rail facing the first direction remains unchanged during rotation of the axial pinch roller.

9. The CT apparatus of claim 6 or 7, wherein a minimum distance in the second direction between an outer circumferential surface of the axially eccentric pinch roller and an end surface of the rotatable rail facing the second direction is varied during rotation of the axially eccentric pinch roller.

10. The CT apparatus of claim 7 wherein the axial pinch roller comprises a wheel mount fixedly connected to the frame, an axle disposed on the wheel mount, a wheel bearing, and a first pinch roller element disposed on the axle through the wheel bearing, a central axis of the first pinch roller element coincident with a central axis of the axle, the first pinch roller element rotatable on the axle, at least a portion of an outer peripheral surface of the first pinch roller element facing an end face of the rotatable rail facing a first direction.

11. The CT apparatus of claim 10 wherein the axially eccentric puck comprises a wheel mount fixedly coupled to the frame, an axle disposed on the wheel mount, a wheel bearing disposed on the axle through the wheel bearing, and a second puck element having an amount of eccentricity between a central axis of the second puck element and a central axis of the axle, the second puck element being capable of eccentric rotation on the axle, at least a portion of an outer peripheral surface of the second puck element facing an end face of the rotatable rail in a second direction.

12. The CT apparatus of claim 7 wherein the axial pinch roller and the axial eccentric pinch roller share a wheel mount such that the axial pinch roller and the axial eccentric pinch roller form a pinch roller set.

13. The CT apparatus of claim 11, wherein the axial pinch roller further comprises a first baffle disposed on a side of the axle remote from the first pinch roller element and a second baffle disposed on a side of the wheel bearing remote from the first baffle, the first and second baffles together restricting movement of the first pinch roller element in a radial direction of the rotatable rail; and/or the number of the groups of groups,

The axial eccentric pinch roller further comprises a first baffle and a second baffle, the first baffle is arranged on one side, far away from the second pinch roller element, of the wheel shaft, the second baffle is arranged on one side, far away from the first baffle, of the wheel bearing, and the first baffle and the second baffle limit the second pinch roller element to move along the radial direction of the rotatable track jointly.

14. The CT apparatus of claim 1, further comprising a magnetic device disposed on the gantry for providing magnetic attraction to the rotatable portion when the rotatable portion is rotated.

15. The CT apparatus of claim 14, wherein the magnetic device comprises a plurality of permanent magnets or electromagnets arranged on the gantry in a spaced manner from each other in a rotational direction of the rotatable portion.

16. The CT apparatus of claim 15, wherein the plurality of permanent magnets or electromagnets are arranged on the gantry at uniform intervals in a rotation direction of the rotatable portion.

17. The CT apparatus according to claim 3, wherein said rotatable portion comprises a rotatable body and at least one rotatable track, said scanning device being disposed on said rotatable body,

The rotatable rail includes a magnetic material, or a magnetic portion composed of a magnetic material is mounted on an outer peripheral surface of the rotatable rail.