阅读说明：本技术 具有旋转中心部件的***磁体 (Split magnet with rotating center part ) 是由 M·马利特 于 2020-03-06 设计创作，主要内容包括：本公开涉及具有旋转中心部件的分裂磁体。一种磁共振成像(MRI)系统包括：两个分离的静磁场生成单元(10),两个分离的静磁场生成单元(10)均是柱形并且在轴向上对齐,并且由旋转式负载承载结构(20)分离,该旋转式负载承载结构(20)被布置成绕由静磁场生成单元(10)生成的静磁场的轴线(A-A)自由旋转。旋转式负载承载结构被安装在推力轴承(22)上,该推力轴承(22)承担静磁场生成单元(10)之间的轴向负载。(The present disclosure relates to a split magnet having a rotational center member. A Magnetic Resonance Imaging (MRI) system comprising: two separate static magnetic field generating units (10), the two separate static magnetic field generating units (10) each being cylindrical and axially aligned and being separated by a rotary load carrying structure (20), the rotary load carrying structure (20) being arranged to rotate freely about an axis (A-A) of the static magnetic field generated by the static magnetic field generating units (10). The rotary load bearing structure is mounted on thrust bearings (22), the thrust bearings (22) taking up axial loads between the static magnetic field generating units (10).)

1. A Magnetic Resonance Imaging (MRI) system comprising:

two separate static magnetic field generating units (10), the two separate static magnetic field generating units (10) each being cylindrical and axially aligned, and the two separate static magnetic field generating units (10) being separated by a rotary load carrying structure (20), the rotary load carrying structure (20) being arranged to rotate freely about an axis (A-A) of the static magnetic field, the static magnetic field generating units (10) generating the static magnetic field, the rotary load carrying structure being mounted on thrust bearings (22), the thrust bearings (22) taking axial loads between the static magnetic field generating units (10).

2. The magnetic resonance imaging system of claim 1,

further comprising a radiant beam source mounted to the rotary load carrying structure (20) such that the radiant beam source is rotatable with the rotary load carrying structure (20) about the axis a-a.

3. The magnetic resonance imaging system of claim 1 or claim 2,

further comprising a surgical intervention device mounted to the rotary load carrying structure (20) such that the surgical intervention device is rotatable with the rotary load carrying structure (20) about the axis a-a.

4. The magnetic resonance imaging system of any one of the preceding claims, wherein the two separate static magnetic field generating units (10) define an imaging volume that is axially between the two separate static magnetic field generating units (10) and that is axially aligned with the two separate static magnetic field generating units (10).

5. The magnetic resonance imaging system of any one of the preceding claims, further comprising a cylindrical gradient coil assembly (14), the cylindrical gradient coil assembly (14) being axially aligned with the rotary load carrying structure (20) and the static magnetic field generating unit (10) and being located within a bore of the static magnetic field generating unit (10).

6. The magnetic resonance imaging system of claim 5 when dependent on claim 4, wherein the gradient coil assembly (14) extends axially into the bore of both static magnetic field generating units (10) and is provided with an aperture (17) axially between the static magnetic field generating units (10) to provide access to the imaging volume.

7. The magnetic resonance imaging system of claim 5, wherein the gradient coil assembly (14) is provided in two parts that are axially separated such that one part extends into the bore of one of the static magnetic field generating units (10), respectively.

8. The magnetic resonance imaging system of any one of claims 5 to 7, wherein the gradient coil assembly is mounted on bearings other than the thrust bearing (22).

9. The magnetic resonance imaging system of any one of the preceding claims, further comprising an RF body coil mounted to the rotary load carrying structure (20) and arranged to rotate with the rotary load carrying structure (20).

10. The magnetic resonance imaging system of claim 9, wherein the RF body coil is provided with apertures axially between the static magnetic field generating units (10) to provide access to the imaging volume.

11. The magnetic resonance imaging system of any one of the preceding claims, further comprising a further load bearing member arranged to resist vertical weight loading of the rotary load bearing structure (20).

Technical Field

The present invention relates to superconducting magnets, in particular to split-pair superconducting magnets for Magnetic Resonance Imaging (MRI) systems which are combined with radiotherapy apparatus and/or apparatus for surgical intervention during MRI imaging.

Background

A typical split-pair superconducting magnet consists of two separate magnet components with mechanical support between them to ensure that the magnetic load between them is adequately resisted (act). Thermal and electrical interconnections are typically provided to ensure continuity of drive current and thermal behavior. The present invention relates to a split pair superconducting magnet which may be composed of two magnet components in close proximity to a magnetic force carrying component located between the two magnet components.

Fig. 1 shows a conventional split pair superconducting magnet arrangement for a combined MRI and radiation therapy system. As illustrated in fig. 1 in a cross section through the magnet axis a-a, two static magnetic field generating units 10, such as cryostats, are provided. Each of the cryostats will contain a magnet coil and between them the magnet coils will generate a static magnetic field in an imaging region centered on axis a-a and located between the two cryostats. The specific arrangement of the magnet coils does not form part of the present invention, and therefore the other contents of the magnet coils and the static magnetic field generating unit 10 are not shown in the drawings. The imaging zone centered on the axis a-a and located between the two cryostats corresponds to the treatment zone to be treated by the radiation therapy device and/or the device for surgical intervention during MRI imaging.

The static magnetic field is typically very strong and current MRI systems use magnetic fields with strengths in the range of 1.5T-3T. Two magnetic field generating units, such as the cryostat 10, will experience strong mutual attraction forces. In order to keep the cryostat in the desired respective position, a mechanical support 12 is provided. These mechanical supports are mechanically robust and mechanically attached to both cryostats 10. Depending on the magnet design, the mechanical support may be placed in mechanical compression in terms of the size and layout of the respective magnet coils. The mechanical support 12 is typically placed intermittently around the cylindrical cryostat and carries the forces typically in a direction parallel to the magnet axis a-a.

In a combined MRI/radiation therapy device, it is conventional per se to provide access to the imaging region in the magnet arrangement center for the radiation therapy beam and possibly also for devices for surgical intervention of the housing, such as a treatment robot. By intermittently placing the mechanical support 12 around the cryostat, access points for the radiation therapy beam and the equipment for surgical intervention may be provided.

However, disadvantages of this arrangement include: the presence of the mechanical support 12 means that certain positions of the mechanical support 12 are not available for the guidance of the radiation therapy beam or for the equipment used for surgical interventions. It is necessary to provide some kind of gantry on which the radiation therapy beam apparatus or the apparatus for surgical intervention is to be mounted. This requires extensive structural assembly outside the cryostat.

Some conventional arrangements have attempted to alleviate these difficulties by: limiting the amount of azimuthal access to the patient to exclude any position where a load bearing support is present; limiting the passage for the radiation beam or limiting the physical passage for surgical intervention.

In an attempt to provide an omni-directional angular channel, some conventional systems allow increased beam intensity to be directed to the support element so that sufficient beam intensity passes through the support structure to the processing region. However, this method must tolerate much higher particle beam intensities, diffractive absorption and scattering of the therapeutic beam, and in no way improve access to the patient for surgical intervention.

In an alternative approach, certain conventional arrangements have provided a load bearing structure that is outside the volume occupied by the cryostat. This arrangement provides complete access to the patient, but requires a much larger magnet structure with a large load bearing structure at a greater distance from the magnet axis a-a. The complexity and physical size of the system thus increases.

Prior art documents relating to similar subject matter include EP3047292, US6466018, WO1998/012964, US 5786694.

Disclosure of Invention

The present invention provides an arrangement which seeks to mitigate these and other disadvantages.

Accordingly, the present invention provides an arrangement as defined in the appended claims.

Drawings

The above and further objects, features and advantages of the present invention will become more apparent upon consideration of the following description of certain embodiments, given by way of example only, in which:

figure 1 shows an axial cross-section through a conventional split pair superconducting magnet arrangement for a combined MRI and radiation therapy system;

figure 2 shows an axial cross-section of a combined MRI and radiation therapy device according to a first embodiment of the present invention;

figure 3 illustrates the arrangement of figure 2 in use, in a configuration displaced from that of figure 2;

FIGS. 4 and 5 illustrate exemplary types of bearings that may be employed in embodiments of the present invention;

figure 6 shows an axial cross-section through a combined MRI and radiation therapy device according to a second embodiment of the present invention;

FIG. 7 illustrates the component of FIG. 6 in use, in a configuration displaced from that of FIG. 6;

FIG. 8 schematically illustrates an embodiment of the present invention;

FIG. 9 schematically illustrates one embodiment of the present invention including a radiant beam source; and

figure 10 schematically represents an embodiment of the invention comprising a treatment robot.

Detailed Description

The present invention provides a rotary load bearing structure between two cryostats. The rotary load bearing structure is mounted on thrust bearings that bear the axial magnetic load between the two cryostats. The bearings also serve to accurately position the rotary load bearing structure and allow the rotary load bearing structure to rotate freely about the axis a-a of the magnet and magnetic field. The radiation beam source and/or the surgical intervention device mounted to the rotary load carrying structure may be rotated to any circumferential position around the magnet axis a-a to allow passage at any angle for the surgical intervention device or the electromagnetic or particle radiation beam source without risk of diffraction, absorption or attenuation of the electromagnetic or particle radiation beam. The gantry rotates around the central magnet axis, but the gantry does not move in any radial direction.

One embodiment of the present invention is illustrated in fig. 2. As described with respect to fig. 1, two cryostats 10 are provided, spaced apart. However, instead of being axially constrained in the desired relative position by the mechanical support 12 against axial magnetic forces, the two cryostats 10 in the embodiment of fig. 2 are axially constrained by a rotary load bearing structure 20 mounted on a thrust bearing 22.

The rotary load bearing structure 20 is free to rotate about the axis a-a of the static magnetic field independently of the two cryostats 10.

In the illustrated embodiment, the thrust bearings 22 are located at the axially and radially inner edges of the respective cryostats 10. In the illustrated embodiment, the rotary load bearing structure 20 extends between thrust bearings 22. In this embodiment, the rotary load bearing structure is axially aligned with the magnet structure and rotates about the magnet axis a-a. Also illustrated in FIG. 2 is a radiant beam source 16 and a gradient coil assembly 14. The radiant beam source 16 is mounted to the rotary load bearing structure 20 and is rotatable with the rotary load bearing structure 20 about the magnet axis a-a.

In the illustrated embodiment, the gradient coil assembly 14 includes two apertures 17 aligned with a radiation beam 18 generated by the radiation beam source 14. Corresponding apertures are provided in the rotary load bearing structure 20 to provide an unobstructed path for the radiation beam 18 through an imaging region coincident with the processing region. In the illustrated embodiment, the gradient coil assembly 14 is also arranged to rotate with the rotary load carrying structure 20. The radiation beam source 16 can be correspondingly rotated about axis a-a while maintaining alignment of the radiation beam 18 with the aperture 17. The gradient coil assembly 14 may be mounted to a rotary load bearing structure, which in turn is mounted to a thrust bearing 22; or the gradient coil assembly 14 may be mounted on a separate set of bearings (not shown in fig. 2) and may be controlled to rotate in synchronization with the rotary load bearing structure 20. In another embodiment, the rotary load bearing structure 20 and the gradient coil assembly 14 may be controlled separately, but the user must then ensure that: prior to use of the radiation beam, the aperture on the rotary load bearing structure 20 and the aperture in the gradient coil assembly are both aligned with the radiation beam 18. The thrust bearing 22 and the rotary load bearing structure 20 carry the compressive magnetic force between the two cryostats 10.

As schematically represented in fig. 8, the rotating central part is generally composed of a tubular cylindrical structure with thrust bearings 22 on either end of the tubular cylindrical structure connected to the magnetic field generating unit 10. The tubular cylindrical structure 20 will typically have one or more apertures 17 near the centre line to allow an unobstructed passage for the particle beam. The use of such apertures in the tubular structure 20 ensures that no degradation, reflection or modulation of the particle beam will occur, or that free access to the treatment area is available to other devices, for example robotic treatment devices.

To ensure that there is a full circumferential path to the imaging region, the gradient coil assembly 14 and any RF body coils (not shown in the drawings) may also preferably be mounted to and rotate with the rotary load bearing structure 20. Any such RF body coil may have a similar aperture 17 near its centerline to ensure that physical or particle beam passage to the processing region is not obstructed. Each aperture 17 should be transparent to the radiation beam 18. If a surgical intervention device is provided, the aperture 17 should allow physical access to the treatment area.

Figure 3 illustrates the embodiment of figure 2 wherein the rotary load bearing structure 20, the radiant beam source 16 and the gradient coil assembly 14 have been rotated about the a-a axis by about 30 °. Although only half of the cryostat 10, rotary load bearing structure 20 and gradient coil assembly 14 are shown in FIG. 3, this is for illustration purposes only. The half of the components shown in fig. 3 are the half shown in fig. 2 to illustrate the rotation imparted to some of the components. Of course, in practice, the rotary load bearing structure 20, the gradient coil assembly 14 and the cryostat 10 are completely cylindrical. In the embodiment of FIG. 3, the gradient coil assembly 14 is mounted to the rotary load bearing structure 20 and is not provided with its own bearings.

The thrust bearing 22 allows free rotation of the rotary load bearing structure 20. The bearings 22 may be roller bearings, ball bearings, slide bearings, or any other form of bearing that can resist magnetic loads and ensure accurate positioning of the cryostat 10 and rotary load bearing structure 20 with respect to each other. The thrust bearing 22 is preferably axisymmetrical in nature about the axis a-a, so that any iron content in the bearing 22 produces an axisymmetrical effect on the magnetic field and can therefore be relatively simply eliminated by appropriate shimming.

The bearings 22 may also resist the full vertical weight loading of the gradient coils, body coils, and other components connected to the rotary load bearing structure 20. In alternative embodiments, there may be separate load bearing members to resist these vertical weight loads.

Fig. 4 and 5 illustrate two types of bearings that may be used as the thrust bearing 22 in embodiments of the present invention. Both types of thrust bearings are conventional per se.

FIG. 4 schematically illustrates in cross-section one example of a roller bearing 30 that may be used as thrust bearing 22 in one embodiment of the invention. The roller bearing 30 includes: a first washer 32, the first washer 32 having an axially outer surface shaped to interface with a surface of a first one of the cryostats 10 and a radially inner surface shaped to interface with the rolling elements 34; a rolling element 34 in the form of a roller (roller) held within a cage 36; and a second washer 38, the second washer 38 having an axially outer surface shaped to interface with a surface of a second one of the cryostats 10, and a radially inner surface shaped to interface with the rolling elements 34. A suitable grease may be applied to the rolling elements 34.

Fig. 5 schematically shows in cross-section one example of a ball bearing 40 that may be used as bearing 22 in one embodiment of the invention. The ball bearing 40 includes: a first gasket 42, the first gasket 42 having an axially outer surface shaped to interface with a surface of a first one of the cryostats 10 and a radially inner surface shaped to interface with the rolling elements 44; rolling elements 44 in the form of balls retained within a cage 46; and a second washer 48, the second washer 48 having an axially outer surface shaped to interface with a surface of a second one of the cryostats 10, and a radially inner surface shaped to interface with the rolling elements 44. A suitable grease may be applied to the rolling elements 44.

The thrust bearing 22 should provide consistent, reproducible behavior in the axial direction to ensure repeatable magnetic uniformity of the static magnetic field. The thrust bearing 22 should provide repeatable behavior under static loading conditions, but need not provide such repeatable behavior during dynamic rotation, as MRI imaging may only be performed when the rotary load bearing structure 20 is in a static state. The thrust bearing 22 should also provide repeatable behavior under these conditions if MRI measurements are required during dynamic rotation of the rotary load bearing structure 20.

The typical level of repeatable accuracy of the bearings in the axial direction must be sufficient to account for the typical 100PPM/mm field variation level of the axial separation motion of the two cryostats 10. The operating load condition is a condition in which the thrust bearing 22 is under a constant magnetic axial load. This load should be beneficial to eliminate any float in the bearing and take up any voids in the bearing in the uncompressed state.

Another embodiment of the present invention is illustrated in fig. 6. As described with respect to fig. 1, two cryostats 10 are provided, spaced apart. However, instead of being held in the required relative position by mechanical supports 12, the two cryostats 10 in the embodiment of fig. 6 are held apart by a rotary load bearing structure 20 mounted on bearings 22. In this embodiment, bearings 22 are positioned at the axially inner and radially outer edges of the respective cryostat 10. A rotary load bearing structure 20 extends between the bearings. In this embodiment, the rotary load bearing structure 20 is axially aligned with the magnet structure and rotates about the magnet axis A-A.

Also illustrated in fig. 6 is the radiation beam source 16 and the gradient coil assembly 54. The gradient coil assembly 54 is provided in two parts, one part being mounted to one of the two cryostats 10. A gap 56 is provided between the two portions of the gradient coil assembly 54 to provide access for the radiation beam 18 to an imaging region, which coincides with the treatment region.

The radiant beam source 16 is mounted to the rotary load bearing structure 20 and is rotatable with the rotary load bearing structure 20 about the magnet axis a-a. In this embodiment, the radiation beam source 16 is mounted to the rotary load carrying structure 20 and generates the radiation beam 18 inside the rotary load carrying structure 20. Since the radiation beam 18 is generated inside the rotary load bearing structure, the rotary load bearing structure 20 does not obstruct the radiation beam 18 from reaching the processing region. As discussed above, the gradient coil assembly is provided in two portions 54 with a gap 56 therebetween. Thus, the radiation beam is able to pass through the gap 56 and is not obstructed by the gradient coil assembly.

The radiation beam source 16 can be correspondingly rotated about axis a-a while maintaining passage of the radiation beam 18 to the radiation processing volume. The thrust bearing 22 and the rotary load bearing structure 20 carry the compressive forces between the two cryostats 10.

Fig. 7 illustrates the embodiment of fig. 6 wherein the rotary load bearing structure 20 and the radiant beam source 16 have been rotated about the a-a axis by about 30 °. Although only half of the cryostat 10, rotary load bearing structure 20 and gradient coil assembly 14 are shown in FIG. 7, this is for illustration purposes only. The half of the components shown in fig. 7 are the half shown in fig. 6 to illustrate the rotation imparted to some of the components. Of course, in practice, the rotary load bearing structure 20, the gradient coil assembly 14 and the cryostat 10 are completely cylindrical. In the embodiment of FIG. 7, the gradient coil assembly 14 is mounted to the cryostat 10 and does not require rotation.

In certain embodiments of the present invention, various objects may be mounted to the rotary load bearing structure 20, which allows the object to rotate about the axis A-A of the magnetic field. Examples of such objects that may usefully be mounted in this manner include, but are not limited to, linear particle accelerators, angiography devices, therapeutic robots.

Figure 9 schematically shows an example of an embodiment in which the radiation beam source 16 is mounted for rotation with the rotary load carrying structure 20. As illustrated, the radiant beam source 16 may be mounted to the rotary load carrying structure 20 itself, or may be mounted directly to the thrust bearing 22.

Figure 10 schematically shows an example of an embodiment in which the treatment robot 58 is mounted to rotate with the rotary load carrying structure 20. As illustrated, the treatment robot 58 may be mounted to the rotary load bearing structure 20 itself, or may be mounted directly to the thrust bearing 22. In other embodiments (not shown), a treatment robot may be provided in addition to the radiation beam source, such that both are mounted to the rotary load carrying structure 20. It may be provided that the treatment robot and the radiation beam source are independently rotatable about the a-a axis.

While the invention has been described with respect to a limited number of specific embodiments, given by way of non-limiting example only, it will be apparent to those skilled in the art that the invention may be practiced with various modifications to the specific embodiments described above.

Although the above example illustrates the rotary load bearing structure 20 as a thin walled cylinder, it may take other forms such as a squirrel cage structure, as long as it supports the function of mechanically constraining the cryostat 10 against axial magnetic forces and supports the mounting of equipment such as therapeutic beam sources, linear particle accelerators, angiographic equipment, therapeutic robots.

The thrust bearing 22 may be, for example, a roller bearing, a ball bearing, a slide bearing, an oil bearing, or any other type of thrust bearing that provides accurate positioning of the two magnet units and the rotary load bearing structure 20 with respect to each other.

Accordingly, the present invention provides a Magnetic Resonance Imaging (MRI) system comprising two separate static magnetic field generating units, each of which is cylindrical and axially aligned, and separated by a rotary load carrying structure arranged to rotate freely about the axis of the static magnetic field generated by the static magnetic field generating units, the rotary load carrying structure being mounted on thrust bearings which bear axial loads between the static magnetic field generating units.

Various modifications and variations of this invention will be apparent to those skilled in the art, within the scope of this invention as defined in the appended claims.