Magnetic resonance magnet assembly and radiation shield assembly

Abstract

This specification discloses a magnetic resonance imaging (MRI) magnet assembly. The magnet assembly comprises a two-stage cryogenic cooling system, a main coil, and a radiation shield assembly. The cryogenic cooling system comprises a high-temperature stage and a low-temperature stage. The high-temperature stage is configured to provide an upper operating temperature. The main coil is thermally coupled to the low-temperature stage. The radiation shield assembly is thermally coupled to the high-temperature stage and comprises a shim coil and a radiation shield supporting the shim coil. The radiation shield is positioned within a cryostat to shield the main coil from thermal radiation. When the shield assembly is in thermal equilibrium with the high-temperature stage, the radiation shield has an upper operating temperature and therefore shields the main coil from thermal radiation originating from temperatures higher than the upper operating temperature.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of magnetic resonance imaging systems. In particular, the present invention relates to the field of generating a uniform main magnetic field in a magnetic resonance imaging system. BACKGROUND ART

[0002] Modern magnetic resonance imaging (MRI) scanners use superconducting main magnets to generate a substantially uniform magnetic field (B0) to provide magnetic polarization to the sample being imaged. The quality of MRI scans strongly depends on the uniformity of B0. Since slight manufacturing tolerances, asymmetries, and disturbances of the magnet assembly are unavoidable, the magnetic field generated by the superconducting magnet must be shimmed, which means applying corrections that result in a uniform magnetic field. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0003] B0 shimming can be achieved using static and / or dynamic corrections. In the case of static or passive shimming, shims, that is, components made of materials that locally affect the strength and / or direction of the magnetic field when exposed to the magnetic field (e.g., small shims of ferromagnetic material such as iron), are fixed at different positions near the superconducting magnet. Although placing shim steel is an established process, there are several problems associated with it. Placing all shims in place is a time-consuming iterative procedure. Shim steel is prone to thermal drift during scanning. Steel shims are static. Shims occupy space. The last point can be serious when there is little room to incorporate them, for example in or near the gradient coils.

[0004] All of these problems can be overcome, at least to some extent, by adding a dynamic shim coil to the cryostat. When supplied with the appropriate current, the shim coil generates a magnetic field that eliminates the non-uniformity of B0 by superposition. Thus, the shim coil can be fine-tuned to facilitate the response to temporal variations in magnetic field uniformity and / or to cancel out residual non-uniformity of existing static corrections. Typically, the shim coil is a resistive coil, usually at room temperature, and can generate magnetic field corrections distributed as several orders of spherical harmonics. Dynamic magnetic field corrections can be automatically calibrated by iterating through observing a free induction decay (FID) signal in the absence of a magnetic field gradient and varying the supply current to the shim coil.

[0005] The paper "Persistent-mode high-temperature superconductor shim coils: A design concept and experimental results of a prototype Z1 high-temperature superconductor shim," Applied Physics Letters 103, 052607 (2013) by Y. Iwasa et al. discloses a superconducting shim coil cut from superconducting yttrium barium copper oxide (YBCO) tape placed inside a magnet assembly.

[0006] U.S. Patent Application Publication No. 2022 / 171004A1 describes a room-temperature permanent magnet assembly. [Means for solving the problem]

[0007] The present invention provides, in an independent claim, an MRI magnet assembly, an MRI scanner, a radiation shield assembly, and a method for assembling an MRI magnet assembly. Embodiments are described in the dependent claims.

[0008] In one embodiment, the present invention provides a magnetic resonance imaging (MRI) magnet assembly. The magnet assembly has a two-stage cryostat. The cryostat has a high-temperature stage and a low-temperature stage. The high-temperature stage is configured to provide an upper operating temperature.

[0009] The magnet assembly further comprises a main coil thermally coupled to a low-temperature stage.

[0010] The magnet assembly further comprises a radiation shield assembly thermally coupled to the high-temperature stage. The radiation shield assembly comprises a shim coil and a radiation shield supporting the shim coil. The radiation shield is located within the cryostat to shield the main coil from thermal radiation. When the shield assembly is in thermal equilibrium with the high-temperature stage, the radiation shield has an upper operating temperature and therefore shields the main coil from thermal radiation originating from temperatures above the upper operating temperature.

[0011] In another embodiment, the present invention provides an MRI scanner having an MRI magnet assembly.

[0012] In another embodiment, the present invention provides a radiation shielding assembly. The shielding assembly is configured to be installed within a cryostat of an MRI magnet assembly. More specifically, the shielding assembly is configured to be installed within a cryostat having a high-temperature stage and a low-temperature stage. The high-temperature stage of the two-stage cryostat is configured to provide an upper operating temperature.

[0013] The MRI magnet assembly further comprises a main coil, which is thermally coupled to the low-temperature stage of the cryostat.

[0014] The radiation shield assembly comprises a shim coil and a radiation shield supporting the shim coil. The radiation shield is configured to be placed within the cryostat to shield the main coil from thermal radiation. When the shield assembly is in thermal equilibrium with the high-temperature stage, the radiation shield has an upper operating temperature and therefore shields the main coil from thermal radiation originating from temperatures above the upper operating temperature.

[0015] In another embodiment, the present invention provides a method, which includes providing a two-stage cryostat having a high-temperature stage and a low-temperature stage. The high-temperature stage is configured to provide an upper operating temperature.

[0016] This method further includes providing a main coil that is thermally coupled to a low-temperature stage.

[0017] The method further includes attaching a thermally coupled radiation shielding assembly to the high-temperature stage. The radiation shielding assembly comprises a shim coil and a radiation shield supporting the shim coil. The radiation shield is configured to be placed within the cryostat to shield the main coil from thermal radiation. When the shielding assembly is in thermal equilibrium with the high-temperature stage, the radiation shield has an upper operating temperature and therefore shields the main coil from thermal radiation originating from temperatures above the upper operating temperature. [Brief explanation of the drawing]

[0018] [Figure 1] Cross-sectional view of a medical system. [Figure 2] Another cross-section of the medical system. [Figure 3] A diagram showing a two-stage cryogenic cooling setup. [Figure 4] A diagram showing a radiation shield supporting a shim coil. [Modes for carrying out the invention]

[0019] Hereinafter, embodiments of the invention will be described illustratively with reference to the drawings.

[0020] In Figures 1 to 4, components denoted by the same reference numeral are equivalent components or perform the same function. Where functions are equivalent, components that have been previously described are not necessarily described in subsequent drawings.

[0021] Embodiments may be advantageous because the shim coils are carried by the radiation shield. Thus, the shim coils cannot consume valuable space from the bore, i.e., the volume enclosed by the magnet assembly in which the patient to be imaged is positioned. Likewise, the dynamic shim coils cannot occupy space within the gradient encoding coils. By disposing the shim coils within the magnet assembly without reducing the bore diameter of the magnet, the total shim volume can be effectively increased. If the channels for placing the iron shims in the room temperature region remain the same size, larger inhomogeneities can be removed by shimming, or the shim channels can be made smaller, which may allow for the construction of thinner gradient coils.

[0022] Furthermore, since the radiation shield carries the shim coils, the shim coils can be thermally coupled to the radiation shield, and the heat generated by the shim coils can be received by the radiation shield and transported to the warm stage of the cryostat. In this way, the shim coils can be efficiently cooled, and the thermal drift of the dynamic shim coils can be counteracted.

[0023] In one example, the radiation shield has an inner wall that carries the shim coils and is surrounded by the main coils. The inner wall of the radiation shield is relatively close to the field of view. Accordingly, to obtain a specific corrective magnetic field, the shim coils can be operated with a smaller current as compared to placing the shim coils at a greater distance from the field of view (FOV). Typically, the radiation shield may be the cold surface closest to the patient.

[0024] In another example, the radiation shield has an inner surface facing the main coil and carrying the shim coil. To obtain more free space on and immediately adjacent to the outside of the radiation shield, it may be beneficial to mount the shim coil or a portion thereof on the inner surface of the radiation shield. This free space can be made available for other components of the magnet assembly or MRI system, and can support a more compact design of the magnet assembly.

[0025] In another example, the radiation shield has an outer surface facing away from the main coil and carrying the shim coil. To obtain more free space between the radiation shield and the main coil, it may be beneficial to mount the shim coil or a portion thereof on the outer surface of the radiation shield. This can also support a more compact design of the magnet assembly. Furthermore, the portion of the shim coil mounted on the outer surface of the radiation shield can have a greater tolerance for heat generation, since thermal radiation emitted by the shim coil in a warm state (i.e., having a temperature above the upper operating temperature or the actual temperature of the radiation shield) can be captured by the radiation shield. In this way, additional heat load on the main coil can be reduced or avoided.

[0026] In another example, the radiation shield has grooves for supporting shim coils. For example, the grooves can be formed by milling or another structuring technique. The grooves can define the specific structure expected of the shim coils. This can support the assembly of the shim coils into the radiation shield with higher precision. The grooves can also enable higher structural stability of the shim coils, thereby reducing the likelihood of unintended changes to the shim coil structure due to thermal or mechanical movement of the MRI scanner, for example, during the assembly of the magnet assembly or MRI scanner. The high structural precision of the shim coils can further support high quality MR images by ensuring that the magnetic field generated by the shim coils actually corresponds to the corrective magnetic field that the shim coils are intended to generate. Furthermore, the grooves can be useful for spatially constraining tapes that form the shim coils but cannot be laid flat on the surface because they can only be bent in one direction.

[0027] In another example, the radiation shield has an inner wall, an outer wall, and a flange. The outer wall surrounds the main coil. The flange connects the inner wall to the outer wall and supports the shim coil. This provides a greater degree of freedom in selecting the structure of the shim coil. For example, the inner wall, outer wall, and flange can form a cavity in which the main coil is placed. The flange can shield the main coil from thermal radiation from directions not covered by either the inner or outer wall. Thus, a shim coil or part thereof attached to the flange can be used to generate a magnetic field with orientations that cannot be generated by a shim coil supported only by the inner wall and / or the outer wall. Such a shim coil attached to the flange can be used, for example, to generate a magnetic field component related to spherical harmonics that is different from the component generated by (partial) shim coils attached to the inner wall and / or the outer wall. Thus, greater flexibility and precision in corrections can be achieved.

[0028] In another example, the shim coil is made of a high-temperature superconductor (HTS). Below, it is assumed that the HTS used to form the shim coil is superconducting at the upper operating temperature. Thus, a superconducting shim coil can be obtained. A superconducting shim coil may generate no heat during operation, or may generate a significantly reduced amount of heat due to local residual ohmic resistance. Compared to the typical current used to operate the main coil, the current required to drive the shim coil can be small, for example, on the order of 10A. Any available size of HTS conductor can easily maintain these currents at the upper operating temperature. A superconducting shim coil does not need to dissipate heat to the radiation shield (and cold mass). Therefore, the shim coil does not need to add an additional thermal load to the cryostat.

[0029] Superconducting shim coils can be operated in persistent current mode or drive mode. As a result, the superconductivity requirements for junctions and connections to, from, and between superconducting shim coils can be relaxed because these junctions can have residual ohmic resistance. The ohmic resistors forming the shim coils can have significantly lower resistance at upper operating temperatures (e.g., 40K), thus generating less heat than when operating at room temperature, but superconducting shim coils can further reduce the amount of heat generated to the small amount of heat generated by such potential residual ohmic resistance.

[0030] In other examples, high-temperature superconductors are MgB2, Bi2Sr2Ca2Cu3O 10These materials include (BSCCO) and one of the rare earth barium copper oxides (ReBCO). These materials can be more suitable for forming shim coils from strands on radiation shields and for forming stable strands with processing properties that support the operation of shim coils under cryogenic conditions. MgB2, with a critical temperature of 39K, can be suitable for relatively low upper operating temperatures below 39K (e.g., 30K) when operated at relatively low currents.

[0031] In other embodiments, the shim coil is a wire or tape. The wire may have a greater thickness than the tape, which may allow it to carry a given current at a lower current density. Furthermore, the wire may have a smaller width than the tape, which may allow it to define the correction magnetic field with greater precision. The wire may have the further advantage of being bendable in any direction, which may allow it to be structured into a shim coil with high precision, which may be difficult when using tape. A useful wire material may be Bi2212 (Bi2Sr2CaCu2O8), which may be formed, for example, into a round wire and reacted after winding, which may increase the designer's freedom in structuring the shim coil. On the other hand, for certain materials, it may be easier to process them into tape than into wire. Tape may be useful to allow for stronger adhesion between the radiation shield and the shim coil. It may be possible to cut the tape into smaller widths to improve its flexibility in the lateral direction (parallel to the shield surface).

[0032] In other embodiments, the radiation shield assembly further includes retaining straps for securing shim coils to the radiation shield. The retaining straps can provide improved structural stability to the shim coils. The retaining straps may also form an interface layer between the shim coils and the radiation shield. The retaining straps may restrict the movement of the shim coils relative to the radiation shield, for example, by orienting an adhesive or rough surface toward the shim coils. Additionally or alternatively, the retaining straps may have an adhesive surface facing the radiation shield and / or be secured to the radiation shield in other ways. Furthermore, the retaining straps can improve thermal contact between the radiation shield and the shim coils.

[0033] In other embodiments, the radiation shield assembly further includes a mold for receiving shim coils on the radiation shield. The mold can mechanically guide the shim coils on the radiation shield and secure the shim coils to a particular structure. Compared to the grooves described above, the mold can be provided as a separate component of the radiation shield assembly. Similar to retaining straps, the mold may have an adhesive surface facing the radiation shield and / or can be secured to the radiation shield in other ways. The mold can form local or continuous fasteners for the shim coils, such as one or more retaining clips and / or support rails.

[0034] Figure 1 is a cross-sectional view of medical system 100. As with other drawings disclosed herein, Figure 1 is for illustrative purposes only and should be understood to include various simplifications and omissions compared to actual medical systems. Components not shown in Figure 1 may include, but are not limited to, gradient coils, transmitting coils, receiving coils, power supply components, cryogenic components, and the like.

[0035] In the non-limiting embodiment of Figure 1, the components of the medical imaging system 101 have a cylindrical shape. The diagram in Figure 1 is a cross-section of the medical system 100 in a plane containing the central axis of the cylindrical shape. Due to the cylindrical shape, the components similarly numbered in the upper and lower parts of Figure 1 can represent the same components of the medical imaging system 101, as can be seen more clearly in Figure 2. It will be understood that actual medical systems may include local or overall deviations from the cylindrical shape shown in Figure 1.

[0036] The medical system 100 may include a medical imaging system 101 and a control unit 150. The control unit 150 may be connected to the medical imaging system 101 (for example, via a bus) and may be configured to control the parameters and functions of the medical imaging system 101. In one embodiment, the control unit 150 may be a computer having a processor and a memory that stores a set of computer-executable instructions that, when executed by the processor, cause the control unit 150 to use the medical imaging system 101 to acquire medical images.

[0037] The medical imaging system 101 may have a housing 110 surrounding a free volume called a bore 102, and a target support 108 configured to support and position the target 106 within the bore 102 such that a portion of the target 106 is located within the imaging zone 104. When the medical imaging system 101 is used to acquire medical images as described above, the resulting medical images may include information representing a portion of the tissue of the target 106 within the imaging zone 104.

[0038] The housing 110 can accommodate an MRI magnet assembly 111 surrounding the bore 102. The magnet assembly 111 may have a main coil 114 housed by a radiation shield assembly, which is integrated by a cryostat 112, and the cryostat 112 may be referred to as a two-stage cryostat because it includes different components that are thermally connected to various stages of a cryogenic cooling system 140 as illustrated in relation to Figures 1 and 3. The main coil 114 can be supplied with current to operate as a superconducting magnet. While operating, the main coil 114 can generate a strong magnetic field with a typical intensity of about 1 Tesla (T) or more, which is substantially uniform at least within the imaging zone 104. The main coil 114 may include a superconducting material, which is typically a cryogenic superconductor (LTS), such as niobium-titanium (Nb-Ti, NbTi).

[0039] The two-stage cryostat 110 may have a high-temperature stage and a low-temperature stage, the high-temperature stage may be configured to provide an upper operating temperature (e.g., 40-50 Kelvin (K)), and the low-temperature stage may be configured to provide a lower operating temperature (e.g., 4 K to allow liquid helium cooling). The main coil 114 may be thermally coupled to the low-temperature stage, and the radiant shielding assembly may be thermally coupled to the high-temperature stage. During operation, if the radiant shielding assembly is in thermal equilibrium with the high-temperature stage, the radiant shielding assembly may have an upper operating temperature and thus can shield the main coil 114 from thermal radiation originating from temperatures above the upper operating temperature.

[0040] A radiation shield assembly may have a radiation shield 120 and one or more shim coils 130 supported by the radiation shield 120. The radiation shield 120 can house a main coil 114 with multiple walls, such as an inner wall 122, an outer wall 124, and one or more flanges 126 connecting the inner wall 122 and the outer wall 124. The surfaces of the outer wall 124, inner wall 122, and flanges 126 facing the main coil 114 are referred to as the inner surface 402 of the radiation shield 120, and the surfaces of the outer wall 124, inner wall 122, and flanges 126 facing away from the main coil 114 are referred to as the outer surface 404 of the radiation shield 120. These surfaces are depicted in alternative diagrams in Figure 4.

[0041] The shim coil 130 can be formed, for example, by a wire or tape wound around one or more walls of the radiation shield 120. The structure of the shim coil 130 can be stabilized and / or fixed to the radiation shield 120 using, for example, grooves, retaining straps, molds, adhesives, solder, welding, or a combination thereof. For example, the shim coil 130 can be bonded to retaining straps that adhere to the radiation shield 120. Similarly, the shim coil 130 may be fixed to the radiation screen 120 by a mold, or laid in grooves formed on the surface of the radiation screen 120 (so that the radiation screen itself can effectively function as a mold). In the example of Figure 1, one or more shim coils 130 are supported by the inner surface 402 of the inner wall 122 and by the outer surface 404 of the flange 126.

[0042] In addition to mechanical contact, the shim coil 130 can be in thermal contact with the radiation shield 120. Thus, the shim coil 130 can be cooled by the radiation shield 120, which may be a radiation screen. In particular, the shim coil 130 can be formed using a superconducting material, more specifically, using a high-temperature superconductor (HTS) that is superconducting at its upper operating temperature. Exemplary HTS materials that appear suitable for forming the shim coil 130, but are not limited to, include MgB2, Bi2Sr2Ca2Cu3O 10It may contain ("BSCCO") or YBa2Cu3O7 ("YBCO").

[0043] Figure 2 is another cross-sectional view of the medical system 100. The diagram in Figure 2 is a cross-section of the medical system 100 in a plane perpendicular to the plane of view in Figure 1 and indicated by the line labeled "II" in Figure 1. In the non-limiting example of Figure 2, the housing 110, the walls of the cryostat 112, the outer walls 124 and inner walls 122 of the radiation shield 120, and the main coil 114 are arranged concentrically around the bore 102. It is understood that actual medical systems may include local or global deviations from the concentric arrangement shown in Figure 2. Again, the object 106 and object support 108 can be located within the bore 102 and surrounded by components housed by the housing 110, with a portion of the object 106 located within the imaging zone 104.

[0044] Figure 3 is a schematic diagram of a two-stage cryogenic cooling system 140 in which two cooling stages 302, 306 can be used to cool corresponding stages (regions, volumes) of a cryostat 112. The first cooling stage 302 may have a cooling device configured to provide an upper operating temperature T1 (e.g., 40K). The heat outlet of the first stage 302 is thermally coupled to a heat exchanger 304, each of which has a lower end (not shown) that is thermally coupled to a corresponding thermal coupling point of a radiant shield 120 installed in the first stage of the two-stage cryostat 112. The second stage 306 may have another cooling device configured to provide a lower operating temperature T2 (e.g., 4K). The heat outlet of the second stage 306 is thermally coupled to a heat exchanger 308, each of which has a lower end that is thermally coupled to a corresponding thermal coupling point of a main coil 114 installed in the second stage of the two-stage cryostat 112. Heat exchange between the cooling stages 302, 306 and the main coil 114 or radiant shield 120 can be carried out by heat conduction through heat exchangers 304, 308, by gaseous refrigerants and / or working gases (e.g., helium, hydrogen, nitrogen vapor), by liquid refrigerants (e.g., liquid helium, hydrogen, nitrogen), or by a combination thereof. Once the cryogenic cooling system 140 is operated until thermal equilibrium is reached, the radiant shield 120 can be heated at an upper operating temperature T1 and the main coil 114 can be heated at a lower operating temperature T2.

[0045] The shim coil 130 can be placed on the inner surface 402 and / or outer surface 404 of any wall of the radiation shield 120.

[0046] Figure 4 shows an example where an exemplary shim coil 130 is wound around a cylindrical inner wall 122. Since the inner and outer surfaces of the radiant shield 120 wall are defined as described above with respect to the main coil 114, it can be seen that the surface called the "inner surface" 402 of the inner wall 122 is located on the radially outer surface of the inner wall 122, and the surface called the "outer surface" 404 is located on the radially inner surface of the inner wall 122.

[0047] As already stated in the background art section of the present invention, U.S. Patent Application Publication No. 2022 / 171004A1 discloses a room-temperature permanent magnet assembly that does not include a cryostat. While this housing facilitates precise temperature control, the absence of a cryostat means that a structure with good thermal conductivity to which shims are attached simply functions as a heat sink.

[0048] It is understood that the above examples or one or more embodiments of the present invention may be combined, provided that the combined embodiments are not mutually exclusive.

[0049] As those skilled in the art will understand, aspects of the present invention may be embodied as apparatus, methods, or computer program products. Accordingly, aspects of the present invention may take the form of entirely hardware embodiments, entirely software embodiments (including firmware, resident software, microcode, etc.), or embodiments combining software and hardware embodiments, all of which may be commonly referred to herein as “circuits,” “modules,” or “systems.” Furthermore, aspects of the present invention may take the form of computer program products embodied in one or more computer-readable media in which computer executable code is embodied.

[0050] Any combination of one or more computer-readable media may be used. Computer-readable media may be computer-readable signal media or computer-readable storage media. As used herein, “computer-readable storage media” encompasses any tangible storage media capable of storing instructions executable by the processor or computing system of a computing device. Computer-readable storage media may also be referred to as computer-readable non-temporary storage media. Computer-readable storage media may also be referred to as tangible computer-readable media. In some embodiments, computer-readable storage media may also store data accessible by the computing system of a computing device. Examples of computer-readable storage media include, but are not limited to, floppy disks, magnetic hard disk drives, solid-state hard disks, flash memory, USB thumb drives, random access memory (RAM), read-only memory (ROM), optical discs, magneto-optical disks, and computer system register files. Examples of optical discs include compact discs (CDs) and digital multi-purpose discs (DVDs), such as CD-ROMs, CD-RWs, CD-Rs, DVD-ROMs, DVD-RWs, or DVD-R discs. The term "computer-readable storage medium" also refers to various types of recording media accessible by computer devices via a network or communication link. For example, data may be obtained via a modem, the Internet, or a local area network. Computer executable code embodied on a computer-readable medium can be transmitted using any suitable medium, including but not limited to wireless, wired, fiber optic cable, RF, or any suitable combination thereof.

[0051] A computer-readable signal medium may include, for example, a propagating data signal in which computer-executable code is embodied, either in the baseband or as part of a carrier wave. Such a propagating signal may take any of a variety of forms, including but not limited to electromagnetic, optical, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium, rather than a computer-readable storage medium, that can communicate, propagate, or transfer programs for use by or in connection with an instruction execution system, apparatus, or device.

[0052] "Computer memory" or "memory" is an example of a computer-readable storage medium. Computer memory is any memory that is directly accessible by a computing system. "Computer storage" or "storage" is another example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. In some embodiments, computer storage may be computer memory, and vice versa.

[0053] As used herein, “computational system” includes electronic components capable of executing programs, machine-executable instructions, or computer-executable code. References to computational systems, including examples of “computational systems,” should be interpreted as potentially including multiple computational systems or processing cores. A computational system may, for example, be a multi-core processor. A computational system may also refer to a collection of computational systems within a single computer system, or a collection of computational systems distributed across multiple computer systems. The term “computational system” should be interpreted as potentially referring to a collection or network of computing devices, each containing a processor or computational system. Machine-executable code or instructions may be executed by multiple computational systems or processors, either within the same computing device or distributed across multiple computing devices.

[0054] Machine-executable instructions or computer-executable code may include instructions or programs that cause a processor or other computing system to perform an aspect of the present invention. Computer-executable code for performing an action for an aspect of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as the C programming language or similar languages, and may be compiled into machine-executable instructions. In some examples, the computer-executable code may be in the form of a high-level language or a pre-compiled form and may be used in conjunction with an interpreter that generates machine-executable instructions on the fly. In other examples, the machine-executable instructions or computer-executable code may be in the form of programming for a programmable logic gate array.

[0055] Computer executable code can be fully executed on a user's computer, partially executed on a user's computer, executed as a standalone software package, partially executed on a user's computer and partially executed on a remote computer, or fully executed on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or wide area network (WAN), or it may not be connected to the external computer (for example, via the Internet using an Internet service provider).

[0056] Aspects of the present invention will be described with reference to flowcharts and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present invention. It will be understood that each block or part of a block in a flowchart, diagram, and / or block diagram can be implemented, where applicable, by computer program instructions in the form of computer executable code. It will be further understood that different combinations of blocks in flowcharts, diagrams, and / or block diagrams may be combined if they are not mutually exclusive. These computer program instructions can be provided to a computing system of a general-purpose computer, a dedicated computer, or other programmable data processing device to generate a machine, and the instructions executed via the computing system of the computer or other programmable data processing device create means for implementing the functions / operations specified in the blocks or groups of blocks in the flowchart and / or block diagram.

[0057] These machine-executable instructions or computer program instructions may be stored in a computer-readable medium that can enable a computer, other programmable data processing device, or other device to function in a particular way, and the instructions stored in the computer-readable medium generate a product that includes instructions that perform functions / operations specified by blocks or groups of blocks in a flowchart and / or block diagram.

[0058] Machine-executable instructions or computer program instructions can also be loaded into a computer, other programmable data processing device, or other device to execute a series of operational steps on the computer, other programmable device, or other device, thereby generating a computer-implemented process, where instructions executed on the computer or other programmable device provide a process for realizing the functions / operations specified by blocks or groups of blocks in a flowchart and / or block diagram.

[0059] As used herein, “user interface” refers to an interface that enables a user or operator to interact with a computer or computer system. A “user interface” may also be called a “human interface device.” A user interface can provide information or data to an operator and / or receive information or data from an operator. A user interface can enable a computer to receive input from an operator and provide output from the computer to a user. In other words, a user interface can enable an operator to control or operate a computer, and the interface can enable the computer to demonstrate the effects of the operator’s control or operation. Displaying data or information on a display or graphical user interface is an example of providing information to an operator. Receiving data through a keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, pedal, wired glove, remote control, and accelerometer are all examples of user interface components that enable the reception of information or data from an operator.

[0060] As used herein, “hardware interface” encompasses interfaces that enable a computer system’s computing system to interact with and / or control external computing devices and / or equipment. Hardware interfaces can enable a computing system to send control signals or commands to external computing devices and / or equipment. Hardware interfaces can also enable a computing system to exchange data with external computing devices and / or equipment. Examples of hardware interfaces include, but are not limited to, universal serial buses, IEEE 1394 ports, parallel ports, IEEE 1284 ports, serial ports, RS-232 ports, IEEE-488 ports, Bluetooth connections, wireless local area network connections, TCP / IP connections, Ethernet connections, control voltage interfaces, MIDI interfaces, analog input interfaces, and digital input interfaces.

[0061] As used herein, “display” or “display device” encompasses an output device or user interface configured to display images or data. A display may output visual, auditory, and / or tactile data. Examples of displays include, but are not limited to, computer monitors, television screens, touchscreens, tactile electronic displays, braille screens, cathode ray tubes (CRTs), storage tubes, bistable displays, electronic paper, vector displays, flat panel displays, fluorescent display tubes (VFs), light-emitting diode (LED) displays, electroluminescent displays (ELDs), plasma display panels (PDPs), liquid crystal displays (LCDs), organic light-emitting diode (OLED) displays, projectors, and head-mounted displays.

[0062] Although the present invention is illustrated and described in detail in the drawings and the above description, such illustrations and descriptions should be considered illustrative or descriptive and not limiting, and the present invention is not limited to the disclosed embodiments.

[0063] Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art in carrying out the claimed invention, based on a consideration of the drawings, this disclosure, and the appended claims. In the claims, the words “comprising” do not exclude other components or steps, and the indefinite articles “a” or “an” do not exclude plurals. A single processor or other unit can perform the functions of multiple items described in the claims. The mere fact that certain means are described in different dependent claims does not imply that combinations of these means cannot be used advantageously. Computer programs can be stored / distributed on suitable media such as optical storage media or solid-state media supplied with or as part of other hardware, but they can also be distributed in other forms, such as via the Internet or other wired or wireless communication systems. No reference numerals in the claims should be construed as limiting their scope.

Claims

1. A magnetic resonance imaging (MRI) magnet assembly, A two-stage cryogenic cooling system, Low temperature stage, A high-temperature stage configured to provide an upper operating temperature, A two-stage cryogenic cooling system having, It is a cryostat, A main coil thermally coupled to the low-temperature stage, A radiation shield assembly thermally coupled to the high-temperature stage, A cryostat having, An MRI magnet assembly having, wherein the radiation shield assembly has a radiation shield supporting at least one shim coil, and the radiation shield is positioned to shield the main coil from thermal radiation emanating from temperatures higher than the upper operating temperature when the radiation shield assembly is in thermal equilibrium with the high-temperature stage.

2. The MRI magnet assembly according to claim 1, wherein the radiation shield has an inner wall surrounded by the main coil, and the inner wall supports the shim coil.

3. The MRI magnet assembly according to claim 1 or 2, wherein the radiation shield faces the main coil and has an inner surface supporting the shim coil.

4. The MRI magnet assembly according to any one of claims 1 to 3, wherein the radiation shield is oriented away from the main coil and has an outer surface supporting the shim coil.

5. The MRI magnet assembly according to any one of claims 1 to 4, wherein the radiation shield has grooves for supporting the shim coil.

6. The MRI magnet assembly according to claim 1, wherein the radiation shield comprises an inner wall, an outer wall surrounding the main coil, and a flange connecting the inner wall to the outer wall and supporting the shim coil.

7. The MRI magnet assembly according to any one of claims 1 to 6, wherein the shim coil has a high-temperature superconductor.

8. The aforementioned high-temperature superconductor is MgB ２ , Bi ２ Sr ２ Ca ２ Cu ３ O １０ The MRI magnet assembly according to claim 7, wherein the material is one of the rare earth barium copper oxides.

9. The MRI magnet assembly according to any one of claims 1 to 8, wherein the shim coil is a wire or tape.

10. The MRI magnet assembly according to any one of claims 1 to 9, further comprising a retaining strap for securing the shim coil to the radiation shield.

11. The MRI magnet assembly according to any one of claims 1 to 10, wherein the radiation shield assembly further comprises a mold for receiving the shim coil on the radiation shield.

12. The MRI magnet assembly according to any one of claims 1 to 11, wherein the cryostat is a two-stage cryostat.

13. A magnetic resonance imaging scanner having an MRI magnet assembly according to any one of claims 1 to 12.

14. A radiation shielding assembly configured to be incorporated into an MRI magnet assembly according to any one of claims 1 to 13.

15. A method for assembling a magnetic resonance imaging magnet assembly, The step of providing a two-stage cryogenic cooling system having a low-temperature stage and a high-temperature stage configured to provide an upper operating temperature, The steps include providing a main coil thermally coupled to the low-temperature stage, The steps include attaching a thermally coupled radiation shield assembly to the high-temperature stage, A method comprising, wherein the radiation shield assembly has a radiation shield supporting at least one shim coil, and the radiation shield is positioned within the cryostat to shield the main coil from thermal radiation emanating from temperatures higher than the upper operating temperature when the radiation shield assembly is in thermal equilibrium with the high-temperature stage.

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