Thermal shield for a magnetic resonance imaging magnet for limiting the magnetic gradient interaction

Abstract

A system for minimizing MGI in a superconducting magnet system (58) of an MRI system (10) includes a thermal shield (60) having a bimetallic material. The thermal shield (60) is configured to be disposed about a cold mass (66) of the superconducting magnet system (58), wherein the bimetallic material is configured to minimize MGI.

Description

[0001] Statement on Federal Government Funding for Research and Development

[0002] This invention was made with the support of the U.S. government under Contract No. U01EB026979, granted by the National Institutes of Health, Department of Health and Human Services. The government owns certain rights to the invention. Background Technology

[0003] The subject matter disclosed herein relates to a superconducting magnet system for magnetic resonance imaging (MRI) systems, and more specifically, to a thermal shield for a superconducting magnet system for limiting magnet gradient interaction (MGI).

[0004] Non-invasive imaging techniques allow for the acquisition of images of a patient's / subject's internal structure or features without the need for invasive procedures. Specifically, such non-invasive imaging techniques rely on various physical principles (such as differential transmission of X-rays through a target volume, sound wave reflection within the volume, paramagnetism of different tissues and materials within the volume, and the disintegration of the target radionuclide within the body) to acquire data and construct images or otherwise represent the observed internal features of a patient / subject.

[0005] During MRI, when material such as human tissue is subjected to a uniform magnetic field (polarization field B0), the individual magnetic moments of the spins within the tissue attempt to align with this polarization field, but precess around it in a random order at their characteristic Larmor frequencies. If the material or tissue is subjected to a magnetic field (excitation field B1) located in the xy-plane and close to the Larmor frequency, the net alignment torque, or "longitudinal magnetization," M... z It can be rotated or "tilted" into the xy plane to produce a net transverse magnetic moment M. t After the excitation signal B1 is terminated, a signal is emitted by the excitation spin, and this signal can be received and processed to form an image.

[0006] When these signals are used to generate images, the magnetic field gradient (G) is employed. x G y and G z Typically, the area to be imaged is scanned by a series of measurement cycles, where these gradient fields vary depending on the specific localization method used. The resulting set of received nuclear magnetic resonance (NMR) signals is digitized and processed to reconstruct the image using one of the well-known reconstruction techniques.

[0007] MRI systems can utilize superconducting magnets. MGI (Magnet Gradient Interaction, i.e., the electromagnetic and electromechanical interaction between the magnetic gradient field and the main magnet) presents challenges when utilizing high-field (3 Tesla (T) or greater) MRI magnets. During normal MRI operation, gradient coil pulses and the leakage magnetic field generated by the gradient coils at the location of the thermal shield induce eddy currents within the shield. This is because the thermal shield is typically made of a good thermally conductive material (e.g., aluminum), which is also a good electrical conductor. The eddy currents interact with the magnetic field at the location of the thermal shield and cause mechanical vibrations. The vibrations of the conductive thermal shield will cut through the magnetic flux of the strong main magnet and further induce dynamic eddy currents. The vibrating (dynamic) current element in the thermal shield irradiates the cold mass with a time-varying electromagnetic (EM) field. The time-varying EM field causes eddy current heating in the cold mass, which is typically made of a conductive material (e.g., copper, superconductor, aluminum, etc.). Heating can become excessive (exceeding the heat dissipation capacity of the cryogenic system) and may cause magnet quenching. The higher the magnetic field, the more pronounced this MGI effect. Therefore, it becomes a major technical problem when designing high-field (e.g., 3T) or ultra-high-field (e.g., 7T or greater) MRI magnets. Summary of the Invention

[0008] The following provides an overview of some embodiments disclosed herein. It should be understood that these aspects are provided merely to give the reader a brief overview of these particular embodiments and are not intended to limit the scope of this disclosure. In fact, this disclosure may cover aspects that may not be shown below.

[0009] In one embodiment, a system is provided for minimizing MGI in a superconducting magnet system of an MRI system. The system includes a thermal shield having a bimetallic material and configured to surround the cold mass of the superconducting magnet system, wherein the bimetallic material is configured to minimize MGI.

[0010] In another embodiment, a superconducting magnet system for an MRI system is provided. The system includes a cold mass. The cold mass includes a coil support structure and a superconducting magnet, the coil support structure having a body, and the superconducting magnet having a superconducting coil disposed around the body of the coil support structure. The system also includes a thermal shield containing the cold mass, wherein the thermal shield includes a bimetallic material configured to minimize MGI (Mean Gain of Influence).

[0011] In another embodiment, an MRI system is provided. The system includes a plurality of gradient coils. The system also includes a cold mass and a thermal shield containing the cold mass, wherein the thermal shield comprises a bimetallic material configured to minimize the MGI using the gradient coils. Attached Figure Description

[0012] These and other features, aspects, and advantages of this disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, in which the same symbols denote the same parts throughout the drawings, wherein:

[0013] Figure 1 An embodiment of a magnetic resonance imaging (MRI) system suitable for use with the techniques disclosed in this invention is shown;

[0014] Figure 2 This is a schematic diagram (e.g., cross-section) of a superconducting magnet system with a bimetallic thermal shield according to various aspects of this disclosure;

[0015] Figure 3 Based on all aspects of this disclosure Figure 2 A schematic diagram of a portion of a bimetallic heat shield (e.g., having two layers);

[0016] Figure 4 Based on all aspects of this disclosure Figure 2 A schematic diagram of a portion of a bimetallic heat shield (e.g., having three layers in a first arrangement);

[0017] Figure 5 Based on all aspects of this disclosure Figure 2 A schematic diagram of a portion of a bimetallic heat shield (e.g., having three layers in a second arrangement);

[0018] Figure 6 It is a representation of the thermal generation of a conventional heat shield relative to a bimetallic heat shield in the frequency range, according to various aspects of this disclosure;

[0019] Figure 7 Based on the various aspects shown in this disclosure Figure 6 The graph in the figure represents the average power of heat generated by a conventional heat shield relative to a bimetallic heat shield in different frequency ranges.

[0020] Figure 8 It is a perspective view of a portion of a bimetallic heat shield according to various aspects of this disclosure (e.g., a tube portion having a flared flange);

[0021] Figure 9 It is connected to the heat shield flange according to various aspects of this disclosure. Figure 8 A perspective view of a portion of the bimetallic heat shield (e.g., inside the flared flange);

[0022] Figure 10 It is connected to the heat shield flange according to various aspects of this disclosure. Figure 8 A perspective view of a portion of the bimetallic heat shield (e.g., outside the flared flange);

[0023] Figure 11 It is a perspective view of a portion of a bimetallic heat shield according to various aspects of this disclosure (e.g., a tube with no flared flange);

[0024] Figure 12 Based on all aspects of this disclosure Figure 11 A perspective view of a portion of a bimetallic heat shield (e.g., a connector with a heat shield flange extending to the outside of the tube);

[0025] Figure 13 Based on all aspects of this disclosure Figure 11 A perspective view of a portion of a bimetallic heat shield (e.g., a connector with a heat shield flange extending into the interior of the tube);

[0026] Figure 14 This is a front view of an adapter ring for connecting a tube to a heat shield flange, according to various aspects of this disclosure;

[0027] Figure 15 Based on all aspects of this disclosure Figure 14 A perspective side view of the adapter ring;

[0028] Figure 16 It is based on the various aspects of this disclosure and the connection to Figure 14 A perspective view of the heat shield flange of the adapter ring;

[0029] Figure 17 This is a perspective side view of a heat shield flange having a welded adapter ring in a horizontal orientation, according to various aspects of this disclosure.

[0030] Figure 18 It is in a vertical orientation according to various aspects of this disclosure. Figure 17 A perspective side view of the heat shield flange; and

[0031] Figure 19 Based on all aspects of this disclosure Figure 17 A perspective view of the tube and the flange of the heat shield. Detailed Implementation

[0032] One or more specific implementations will be described below. To provide a concise description of these implementations, not all features of an actual implementation will be described in this specification. It should be understood that in the development of any such actual implementation, as in any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific objectives, such as complying with system-related and business-related constraints that may differ from implementation to implementation. Furthermore, it should be understood that such development efforts may be complex and time-consuming, but remain routine tasks of design, fabrication, and manufacturing for those skilled in the art who benefit from this disclosure.

[0033] When describing the elements of various embodiments of the subject matter of this invention, the articles “a,” “an,” “the,” and “the” are intended to indicate the presence of one or more of the stated elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and therefore the additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0034] While the various aspects discussed below are provided in the context of medical imaging, it should be understood that the techniques disclosed in this invention are not limited to such medical contexts. In fact, the examples and explanations provided in such medical contexts are merely for the purpose of facilitating explanation by providing examples of real-world implementations and applications. However, the techniques disclosed in this invention can also be used in other contexts, such as image reconstruction for non-destructive inspection of manufactured parts or goods (i.e., quality control or quality inspection applications) and / or non-invasive inspection of packages, boxes, suitcases, etc. (i.e., security screening or screening applications). Generally speaking, the techniques disclosed in this invention can be used in any imaging or screening context or in image processing or photography field, where a set or class of acquired data undergoes a reconstruction process to generate an image or volume.

[0035] This disclosure provides a thermal shield for a superconducting magnet system of an MRI system made of a bimetallic material (having at least two different metallic materials, but may also refer to having more than two layers of metallic materials) to minimize MGI (and thus rapidly switching (time-varying) magnetic gradient fields). Specifically, the thermal shield is configured to surround or contain the cold mass of the superconducting magnet system (e.g., coil support, superconducting magnet or magnet coil, helium container, etc.). The thermal shield includes a first metal layer and a second metal layer made of different metallic materials, wherein the first metal layer (e.g., aluminum or copper) is more thermally conductive than the second metal layer, and the second metal layer (e.g., stainless steel or titanium) is more mechanically rigid than the first metal layer. The second metal layer is configured to minimize mechanical vibrations in the thermal shield caused by eddy current induction and to minimize heat generated in the cold mass of the superconducting magnet system. Therefore, magnet overheating and quenching (especially for high-field MRI magnets (3T or above)) are avoided. The disclosed embodiments minimize MGI in a more cost-effective manner (i.e., without increasing the thickness of conventional heat shields and the coil diameter of superconducting wires, which would increase costs). It should be noted that the disclosed technology does not exclude the presence of multiple metal layers, with at least two layers having different materials and electrical properties. Therefore, the heat shield may also have multiple different metal layers, each with different materials and electrical properties.

[0036] Now turn to the attached diagram, and refer to it first. Figure 1The magnetic resonance imaging (MRI) system 10 is schematically shown as including a scanner 12, scanner control circuitry 14, and system control circuitry 16. While the MRI system 10 may include any suitable MRI scanner or detector, in the illustrated embodiment, the system includes a whole-body scanner including a patient port 18 in which a stage 20 can be positioned to place a patient 22 in a desired position for scanning.

[0037] Scanner 12 includes a series of associated coils for generating a controlled magnetic field, for generating radio frequency excitation pulses, and for detecting radiation from gyromagnetic material within the patient's body in response to such pulses. Figure 1 In the schematic diagram, a primary magnet coil 24 (e.g., a superconducting magnet coil) is provided for generating a primary magnetic field B0 generally aligned with the patient aperture 18. In some embodiments, a B0 field of approximately 3 T to 7 T is considered, but fields higher than 7 T and as low as less than one Tesla are also possible. A series of gradient coils 26, 28, and 30 (e.g., magnetic gradient field coils) are grouped in the coil assembly for generating a controlled magnetic gradient field during the examination sequence described more fully below. A radio frequency coil 32 is provided for generating radio frequency pulses for exciting the gyromagnetic material. Figure 1 In the illustrated embodiment, coil 32 also functions as a receiving coil. Therefore, the radio frequency (RF) coil 32 can be coupled to the driving and receiving circuitry in both passive and active modes to receive rays from the gyromagnetic material and apply RF excitation pulses, respectively. Alternatively, various configurations of the receiving coil can be provided separately from the RF coil 32. Such coils may include structures particularly suited to the target anatomical structure, such as head coil assemblies. Furthermore, the receiving coil can be provided in any suitable physical configuration, including phased array coils, etc.

[0038] In the current configuration, the magnet gradient field coils 26, 28, and 30 have different physical configurations suitable for their function in the imaging system 10. As those skilled in the art will understand, the coils are constructed from wound or cut conductive wires, strips, or plates, and the winding or cutting is intended to form a coil structure that generates a gradient field when a control pulse, as described below, is applied. The placement of the coils within the gradient coil assembly can be accomplished in several different sequences, but in this embodiment, the Z-axis coil is positioned at the innermost location and is generally formed as a solenoid structure with relatively little influence on the RF magnetic field. Thus, in the illustrated embodiment, gradient coil 30 is a Z-axis solenoid coil, while coils 26 and 28 are transverse Y-axis and X-axis coils, respectively.

[0039] The coil of scanner 12 is controlled by external circuitry to generate the desired field and pulses in a controlled manner and to read signals. As those skilled in the art will understand, when material typically bound to a patient's tissue is subjected to a primary field, the magnetic moment of the nucleus in the tissue partially aligns with the field. Although a net magnetic moment is generated in the direction of the polarization field, the random orientation components of the moment in the perpendicular plane largely cancel each other out. During the examination sequence, RF frequency pulses are generated at or near the Larmor frequency of the material of interest, resulting in a rotation of the net alignment torque that generates a net transverse magnetic moment. This transverse magnetic moment precesses about the direction of the main magnetic field, emitting RF signals that are detected by the scanner and processed to reconstruct the desired image.

[0040] Gradient coils 26, 28, and 30 are used to generate a precisely controlled magnetic field whose intensity varies over a predetermined field of view, typically exhibiting both positive and negative polarities. When each coil is energized with a known current, the resulting magnetic field gradient is superimposed on the primary field, producing a desired linear variation of the Z-axis component of the magnetic field intensity over the field of view. The gradient coils on each axis produce a linear magnetic field gradient in the direction of that axis. Therefore, the spatially varying z-axis magnetic field varies linearly along the direction of the gradient coil axis. The three coils have mutually orthogonal axes with respect to their direction of variation, allowing a linear field gradient to be applied in any direction, provided the three gradient coils are appropriately combined.

[0041] The pulsed gradient field performs various functions integrated with the imaging process. Some of these functions are slice selection, frequency encoding, and phase encoding. These functions can be applied along the X, Y, and Z axes of the original coordinate system or along other axes determined by a combination of pulsed currents applied to individual field coils.

[0042] The slice selection gradient determines the section or cross-section of tissue or anatomical structure to be imaged within the patient. The slice selection gradient field can be applied simultaneously with a frequency-selective RF pulse to excite a known spin volume within the desired slice precessing at a frequency equal to the excitation bandwidth of the RF pulse. The slice thickness is determined by the bandwidth of the RF pulse and the gradient intensity across the entire field of view.

[0043] Frequency-coded gradients, also known as readout gradients, are typically applied in a direction perpendicular to the slice selection gradient. Frequency-coded gradients encode the spin position information of a plane excited by an RF pulse. Generally, the frequency of the encoded gradient waveform includes a phase-shifting lobe and a readout gradient lobe. The phase-shifting lobe phases the spins, and the readout gradient lobe rephases the spins at the center of the readout gradient waveform to form an echo. The spins with nuclear magnetic moments are encoded with spatially varying phases based on their spatial position along the gradient field (because they precess at different frequencies). The acquired signal can be analyzed using a Fourier transform to identify its position in the selected slice by means of frequency coding.

[0044] Finally, a phase-encoded gradient is applied substantially before the readout gradient and after the slice selection gradient. The spin localization in the phase-encoded direction in the gyromagnetic material is achieved by sequentially inducing phase changes in the precessing protons of the material using slightly different gradient amplitudes applied sequentially during the data acquisition sequence. The phase-encoded gradient allows for a phase difference in the material's spins based on its position in the phase-encoded direction, in principle analogous to the phase accumulated from the spins in the readout gradient waveforms at different time points.

[0045] As those skilled in the art will understand, numerous variations can be designed for pulse sequences employing the exemplary gradient pulse function described above, as well as other gradient pulse functions not explicitly described herein. Furthermore, pulse sequence adjustments can be made to appropriately orient the selected slices and both frequency and phase encodings to excite the desired material and acquire the resulting MR signal for processing.

[0046] The coil of scanner 12 is controlled by scanner control circuitry 14 to generate the desired magnetic field and radio frequency pulses. Figure 1 In the schematic diagram, control circuit 14 therefore includes control circuit 36 ​​for commanding the pulse sequence employed during inspection and for processing the received signals. Control circuit 36 ​​may include any suitable programmable logic device, such as a CPU or digital signal processor of a general-purpose or special-purpose computer. Control circuit 36 ​​also includes memory circuitry 38 used during the inspection sequence performed by the scanner, such as volatile and non-volatile memory devices for storing physical and logical axis configuration parameters, inspection pulse sequence descriptions, acquired image data, programming routines, etc.

[0047] The interface between the control circuit 36 ​​and the coils of the scanner 12 is managed via the amplification and control circuit 40 and via the transmit and receive interface circuit 42. Circuit 40 includes amplifiers for each gradient field coil to supply drive current to the field coil in response to a control signal from the control circuit 36. Interface circuit 42 includes additional amplification circuitry for driving the RF coil 32. Furthermore, when the RF coil is used both to transmit RF excitation pulses and receive MR signals, circuit 42 will typically include a switching device for switching the RF coil between active or transmit mode and passive or receive mode. This is provided through... Figure 1 The power source, indicated by reference numeral 34 in the accompanying drawings, is used to energize the primary magnet 24. Finally, circuit 14 includes an interface component 44 for exchanging configuration and image data with the system control circuit 16. It should be noted that although a horizontal cylindrical aperture imaging system employing a superconducting primary magnet assembly is referenced in this specification, this technology can be applied to various other configurations, such as scanners employing a vertical field generated by a superconducting magnet, permanent magnet, electromagnet, or a combination of these devices.

[0048] System control circuitry 16 may include a wide range of devices for facilitating an interface between the operator or radiologist and scanner 12 via scanner control circuitry 14. In an illustrated embodiment, for example, operator controller 46 is provided in the form of a computer workstation employing a general-purpose or special-purpose computer. This station also typically includes memory circuitry for storing examination pulse sequence descriptions, examination protocols, user and patient data, image data (both raw and processed), etc. The station may also include various interfaces and peripheral drivers for receiving and exchanging data with local and remote devices. In an illustrated embodiment, such devices include a conventional computer keyboard 50 and alternative input devices such as a mouse 52. A printer 54 is provided for producing hard copy outputs of images and documents reconstructed from the acquired data. A computer monitor 48 is provided to facilitate the operator interface. Furthermore, system 10 may include various local and remote image access and examination control devices, typically provided by… Figure 1 Reference numeral 56 is used in the accompanying drawings. Such devices may include image archiving and communication systems, remote radiation systems, etc.

[0049] As described more fully below, this technology includes providing a bimetallic thermal shield for a superconducting magnet system for an MRI system to minimize MGI. Figure 2 This is a schematic diagram (e.g., cross-section) of a superconducting magnet system 58 with a bimetallic thermal shield 60. As depicted, the superconducting magnet system 58 is disposed adjacent to gradient coils 62 and imaging volume 64. The superconducting magnet system 58 includes a cold mass 66. The cold mass 66 includes a magnet coil support structure 68 (having a body 70) and a superconducting magnet 72 comprising a plurality of superconducting magnet coils 74 disposed (e.g., wound) around the body 70 of the magnet coil support structure 68. The cold mass 66 also includes a helium container 76 disposed around (e.g., enclosed or sealed) the magnet coil support structure 68 and the superconducting magnet 72. As those skilled in the art will understand, the liquid helium contained in the helium container 76 provides cooling for the superconducting magnet 72 at cryogenic temperatures for superconducting operation. Specifically, the liquid helium maintains the superconducting magnet 72 at approximately and / or substantially at a liquid helium temperature of about 4.2 Kelvin (K). In some embodiments, a conventional helium container is not required, and the superconducting magnet 72 is cooled by conductive cooling or thermosiphonic cooling. A vacuum container 78 is disposed around (e.g., enclosed or sealed) both the heat shield 60 and the cold mass 66. The vacuum container 78 provides a vacuum environment to reduce convective heat loads to the superconducting coil. The heat shield 60 is disposed between the helium container 76 and the vacuum container 78. In some embodiments, as described in more detail below, the heat shield 60 may comprise a tube (e.g., an inner tube) with a pair of flanges on its sides.

[0050] As described above, the heat shield 60 is made of a bimetallic material that minimizes the MGI between the superconducting magnet system 58 and the gradient coil 62. Specifically, as Figure 3 As shown, the heat shield 60 includes a first metal layer 80 and a second metal layer 82 made of different metallic materials, wherein the first metal layer 80 is more thermally conductive than the second metal layer 82, and the second metal layer 82 is more mechanically rigid than the first metal layer 82. In some embodiments, the first metal layer 80 may be made of aluminum or copper. In some embodiments, the second metal layer 82 may be made of stainless steel or titanium. The thermally conductive material of the first metal layer 80 is used as a conventional heat shield. The second metal layer 82 hardens the heat shield 60 to resist or minimize mechanical vibrations caused by eddy current induction. Minimizing mechanical vibrations also minimizes the heat generated in the cold mass 66 of the superconducting magnet system 58. In some embodiments, the thickness 84 of the first metal layer 80 and the thickness 86 of the second metal layer 82 may be the same. In some embodiments, the thickness 84 of the first metal layer 80 may be greater than the thickness 86 of the second metal layer 82. In some embodiments, the thickness 86 of the second metal layer 82 may be greater than the thickness 84 of the first metal layer 80.

[0051] Utilizing a second metal layer 82 made of a material with higher mechanical hardness avoids the need to increase the thickness of a conventional heat shield made solely of thermally conductive material to the required hardness level. Increasing the thickness of a conventional heat shield would occupy valuable radial space between the vacuum container and the cold mass. Furthermore, a thicker conventional heat shield would result in a larger diameter superconductor coil, and thus increase the cost of the superconducting wire. Therefore, utilizing a second metal layer 82 made of a material with higher mechanical hardness provides a more cost-effective technique for minimizing MGI.

[0052] In some implementations, the heat shield 60 may be made of more than two metal layers. Figure 4 and Figure 5 A heat shield 60 with three metal layers arranged in different configurations is depicted. For example... Figure 4 As depicted, the heat shield 60 includes, for example, Figure 3 The first metal layer 80 and the second metal layer 82 described herein. Furthermore... Figure 4 The heat shield 60 includes a third metal layer 87. The third metal layer 87 is made of the same thermally conductive material (e.g., aluminum or copper) as the first metal layer 80. Figure 4 As depicted, the second metal layer 82 is disposed (e.g., sandwiched) between the first metal layer 80 and the third metal layer 87. This configuration can enhance thermal conductivity.

[0053] like Figure 5 As depicted, the heat shield 60 includes, for example, Figure 3The first metal layer 80 and the second metal layer 82 described herein. Furthermore... Figure 5 The heat shield 60 includes a third metal layer 88. The third metal layer 88 is made of a material with the same mechanical hardness as the second metal layer 82 (e.g., stainless steel or titanium). Figure 5 As depicted, the first metal layer 80 is disposed (e.g., sandwiched) between the second metal layer 82 and the third metal layer 88. This configuration can enhance mechanical stiffness.

[0054] As mentioned above, the bimetallic material of the heat shield reduces the heat generated in the cold mass of the superconducting magnet system. Figure 6 This is a representation of Figure 90 used to illustrate the heat generation of a conventional heat shield relative to a bimetallic heat shield over a frequency range (e.g., approximately 0 Hz to 2000 Hz). Figure 90 includes an X-axis 92 (which represents frequency (e.g., in Hz)) and a Y-axis 94 (which represents thermal power (e.g., in watts (W))). Curve 96 (shown as a solid line) represents the thermal power generated over the frequency range when using a bimetallic heat shield as described above. Curve 98 (shown as a dashed line) represents the thermal power generated over the frequency range when using a conventional (e.g., all-aluminum) heat shield. The results in Figure 90 are summarized in... Figure 7 In the bar chart 100, the average power of heat from different frequency ranges (e.g., 0Hz to 1000Hz and 1000Hz to 2000Hz) is shown. The Y-axis 102 represents the average thermal power (e.g., in W), and the X-axis 104 includes the frequency range (e.g., in Hz). Solid bars 106 and 108 represent conventional (e.g., all-aluminum) heat shields, and shaded bars 110 and 112 represent bimetallic heat shields. As depicted in Figures 90 and 100, bimetallic heat shields minimize heat generation in the 0Hz to 2000Hz frequency range compared to conventional heat shields.

[0055] Figures 8 to 19 Different views depict the ways in which the bimetallic heat shield 60 can be constructed or manufactured. Figure 8 This is a perspective view of the bimetallic heat shield 60. (See image.) Figure 8As depicted, the bimetallic heat shield 60 includes a tube 114 (e.g., an inner tube) having a pair of flanges 116, 118 (e.g., flared flanges) at its longitudinal ends 120, 122. The tube 114 is configured to surround a cold mass surrounding a superconducting magnet. The flanges 116, 118 are configured to engage with corresponding heat shield flanges. In some embodiments, during the construction of the heat shield 60, the tube 114 may initially consist of two portions 124, 126. When the flanges 116, 118 are engaged with the corresponding heat shield flanges, the ends 128 and 130 of the portions 124, 126 of the tube 114 are joined (e.g., welded) together. The weld joint may be covered with an aluminum tapered surface for thermal conductivity and emissivity. Figure 8 and Figure 9 As depicted, the innermost surface 132 of the tube 114 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The tube 114 is made of a metal layer 82, and the outermost surface 134 of the tube 114 is made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The flanges 116 and 118 are made of a bimetallic material and are circumferentially spaced (e.g., relative to the longitudinal axis of the tube 114). Each portion 136 includes a first surface 138 facing away from the tube 114 and a second surface 140 opposite to the first surface 138 and facing the tube 114. As depicted, the first surface 138 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The metal layer 82 is made of the metal layer, and the second surface 140 is made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 It is made of a metal layer (80).

[0056] Parts 124 and 126 can be connected to the heat shield flange in a pair with different arrangements. For example... Figure 9 As depicted, a heat shield flange 142 (e.g., made of a thermally conductive material such as aluminum) is disposed around the inner tube 114 of a portion 124 of the heat shield 60, such that the surface 140 of a portion 136 of the flange 116 directly intersects with the heat shield flange 142 (i.e., is attached to the interior of the flared flange 116). The portion 136 is attached to the heat shield flange 142 via rivets or other fasteners 144 having a Stycast 2850FT epoxy (or other thermally conductive epoxy) or indium interface for thermal contact. Similarly, a portion 126 of the inner tube 114 may be attached to the heat shield flange. Figure 10As depicted, a heat shield flange 146 (e.g., made of a thermally conductive material such as aluminum) is disposed around the inner tube 114 of a portion 126 of the heat shield 60, such that the surface 138 of a portion 136 of the flange 118 directly intersects with the heat shield flange 146 (i.e., is attached to the outside of the flared flange 118). The portion 136 is attached to the heat shield flange 146 via rivets or other fasteners 144 having a Stycast2850FT epoxy or indium interface for thermal contact. Similarly, a portion 124 of the inner tube 114 may be attached to the heat shield flange. Figure 10 As depicted, surfaces 134 and 140 may be made of layers with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The metal layer 82 is made of the metal layer, and surfaces 132 and 138 may be made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 It is made of a metal layer (80).

[0057] Figure 11 This is a perspective view of a portion of a bimetallic heat shield 60 (e.g., a tube 114 without a flared flange). Figure 11 and Figure 12 As depicted, the bimetallic heat shield 60 includes a single tube 114 (e.g., an inner tube) configured to be coupled to a pair of heat shield flanges 150 at the longitudinal ends 120, 122 of the tube 114 (e.g., only a single flange 150 at...). Figure 11 (As shown in the figure). The tube 114 is configured to be arranged with a cold mass around the superconducting magnet. As depicted, the innermost surface 132 of the tube 114 is made of a layer with greater mechanical rigidity (e.g., made of stainless steel or titanium). Figure 3 The tube 114 is made of a metal layer 82, and the outermost surface 134 of the tube 114 is made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The heat shield flange 160 is made of a metal layer 80. The heat shield flange 160 includes circumferentially spaced axial fins 162 (e.g., relative to the longitudinal axis of the tube 114), which form a connector 164 to attach the heat shield flange 160 to the tube 114. The heat shield flange 160 and the axial fins 162 of the connector 164 are made of a thermally conductive material such as aluminum.

[0058] The longitudinal ends 120 and 122 can be connected to the heat shield flange 160 in a pair with different arrangements. For example... Figure 12 As depicted, the axial fins 162 of connector 164 are disposed around and attached to the outermost surface 134 of tube 114 at its longitudinal end 122. Similarly, another heat shield flange 160 may be attached to the longitudinal end 120 of tube 114. Figure 13As depicted, the axial fins 162 of connector 164 are disposed within and connected to the innermost surface 132 of tube 114 at its longitudinal end 122. Similarly, another heat shield flange 160 may be connected to the longitudinal end 120 of tube 114. Figure 12 and Figure 13 In both cases, the axial fins 162 are connected to the tube 114 via rivets or other fasteners 144 with a Stycast2850FT epoxy or indium interface for thermal contact. Figure 13 As depicted, surface 134 is composed of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The metal layer 82 is made of metal, and the surface 132 is made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 It is made of a metal layer (80).

[0059] Figure 14 and Figure 15 These are different views of the adapter ring 166 (e.g., a pre-formed adapter ring) used to connect the tube 114 (e.g., a bimetallic tube) to the heat shield flange to form the bimetallic heat shield 60. Figure 16 This is a perspective view of the tube 114 and the heat shield flange 169 connected to the adapter ring 166. The adapter ring 166 may be made of a thermally conductive material such as aluminum or copper. The adapter ring 166 includes a head portion 168 and an axial connector portion 170. The axial connector portion 170 is configured to connect to the tube 114. In some embodiments, the axial connector portion 170 is configured to insert into the inner portion of the longitudinal end 122 of the tube 114, such that the outer surface 171 of the axial connector portion 170 intersects with the innermost surface 132 of the tube 114. In this case, the innermost surface 132 of the tube 114 and the adapter ring 166 are made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The tube 114 is made of a metal layer 80, and the outermost surface 134 of the tube 114 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The metal layer 82 is formed. In some embodiments, the inner surface 173 of the axial connector portion 170 is configured to surround and intersect with the outermost surface 134 of the longitudinal end 122 of the tube 114. In this case, as Figure 16 As depicted, the outermost surface 134 of tube 114 and adapter ring 166 are made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The innermost surface 132 of the tube 114 is made of a metal layer 80, and the innermost surface 132 of the tube 114 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3The diameter 172 of the axial connector portion 170 can vary depending on whether the axial connector portion 170 is configured to be disposed inside or around the outside of the tube 114.

[0060] Before the adapter ring 166 is coupled to the tube 114, the adapter ring 166 is coupled to the heat shield flange 169 by inserting the axial connector portion 170 into the bore of the heat shield flange 169. The axial connector portion 170 is disposed on the surface 174 of the heat shield flange 169 facing the tube 114, and the head portion 168 is disposed on the surface 176 of the heat shield flange 169 facing away from the tube 114. The outer diameter 178 of the head portion 169 is wider than the diameter 172 of the axial connector portion 170 and the bore of the heat shield flange 169 to hold the adapter ring 166 fixed to the heat shield flange 169. The heat shield flange 169 with the adapter ring 166 is coupled to both the longitudinal ends 120 and 122 of the tube 114.

[0061] Figure 17 and Figure 18 This is a different view of the heat shield flange 180 having a welded adapter ring 182 for connecting the tube 114 (e.g., a bimetallic tube) to the heat shield flange 180 to form a bimetallic heat shield 60. Figure 16 This is a perspective view of the tube 114 and the heat shield flange 180 with a welded adapter ring 182. The adapter ring 182 may be made of a thermally conductive material such as aluminum or copper. The adapter ring 182 includes an axial connector portion 184. The axial connector portion 184 is configured to engage with the tube 114. In some embodiments, the axial connector portion 184 is configured to insert into an inner portion of the longitudinal end 122 of the tube 114, such that the outer surface 186 of the axial connector portion 184 intersects with the innermost surface 132 of the tube 114. In this case, the innermost surface 132 of the tube 114 and the adapter ring 182 are made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The tube 114 is made of a metal layer 80, and the outermost surface 134 of the tube 114 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3 The metal layer 82 is formed. In some embodiments, the inner surface 188 of the axial connector portion 184 is configured to surround and intersect with the outermost surface 134 of the longitudinal end 122 of the tube 114. In this case, as Figure 19 As depicted, the outermost surface 134 of tube 114 and adapter ring 182 are made of a more thermally conductive layer (e.g., made of copper or aluminum). Figure 3 The innermost surface 132 of the tube 114 is made of a metal layer 80, and the innermost surface 132 of the tube 114 is made of a layer with greater mechanical hardness (e.g., made of stainless steel or titanium). Figure 3The metal layer 82 in the tube is made of the axial connector portion 184. The diameter 190 of the axial connector portion 184 can vary depending on whether the axial connector portion 184 is configured to be disposed inside or around the outside of the tube 114.

[0062] The technical effects of the disclosed subject matter include providing a bimetallic thermal shield configured to minimize quenching in the cold mass setting of a superconducting magnet in an MRI system. The bimetallic thermal shield comprises a first metal layer and a second metal layer made of different metallic materials, wherein the first metal layer (e.g., aluminum or copper) is more thermally conductive than the second metal layer, and the second metal layer (e.g., stainless steel or titanium) is more mechanically rigid than the first metal layer. The second metal layer is configured to minimize mechanical vibrations within the thermal shield caused by eddy current induction and to minimize heat generated in the cold mass of the superconducting magnet system. The disclosed bimetallic thermal shield prevents magnet overheating, thereby avoiding quenching (especially for high-field MRI magnets (3T or higher)).

[0063] Referring to the technology presented herein and protected by the claims, and applying it to physical objects and concrete examples of practical nature, which explicitly improves the present art, it is therefore not abstract, intangible, or purely theoretical. Furthermore, if any claim appended to the end of this specification contains one or more elements designated as “means for [performing]...the function” or “steps for [performing]...the function,” such elements are intended to be interpreted pursuant to Section 35, Section 112(f) of the USC. However, for any claim containing elements designated in any other manner, such elements are not intended to be interpreted pursuant to Section 35, Section 112(f) of the USC.

[0064] This written description uses examples to disclose the subject matter, including best practices, and also enables those skilled in the art to practice the subject matter, including making and using any device or system and performing any included methods. The patent scope of this subject matter is defined by the claims and may include other examples that would occur to those skilled in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that are not indistinguishable from the literal language of the claims, or if they include equivalent structural elements that have minor differences from the literal language of the claims.

Claims

1. A system for minimizing the magnetic gradient interaction (MGI) in a superconducting magnet system of a magnetic resonance imaging system, the system comprising: A heat shield having a bimetallic material and configured to surround the cold mass of the superconducting magnet system, wherein the bimetallic material is configured to minimize MGI, wherein the heat shield comprises a plurality of metal layers, wherein the plurality of metal layers include a first metal layer, a second metal layer and a third metal layer, and wherein the first metal layer is disposed between and in contact with both the second metal layer and the third metal layer, wherein the second metal layer and the third metal layer are made of the same metal material, and wherein the first metal layer is made of a different material from both the second metal layer and the third metal layer, wherein both the second metal layer and the third metal layer have greater mechanical hardness than the first metal layer, and wherein the first metal layer has greater thermal conductivity than both the second metal layer and the third metal layer.

2. The system of claim 1, wherein at least two of the plurality of metal layers comprise materials having different electrical properties.

3. The system of claim 1, wherein the first metal layer is made of aluminum or copper, and both the second metal layer and the third metal layer are made of stainless steel or titanium.

4. The system of claim 1, wherein the second metal layer and the third metal layer are configured to minimize mechanical vibrations in the heat shield caused by eddy current induction.

5. The system of claim 1, wherein the second metal layer and the third metal layer are configured to minimize the heat generated in the cold mass of the superconducting magnet system.

6. The system of claim 1, wherein the heat shield comprises a pair of flanges and a tube disposed between the pair of flanges, wherein the tube is configured to surround the cold mass.

7. A superconducting magnet system for a magnetic resonance imaging system, the superconducting magnet system comprising: Cold mass, the cold mass comprising: A coil support structure, the coil support structure having a main body; and A superconducting magnet having a superconducting coil disposed around the body of the coil support structure; and A heat shield encompassing the cold mass, wherein the heat shield comprises a bimetallic material configured to minimize magnetic gradient interactions, wherein the heat shield comprises a plurality of metal layers, wherein the plurality of metal layers include a first metal layer, a second metal layer, and a third metal layer, and wherein the first metal layer is disposed between and in contact with both the second metal layer and the third metal layer, wherein the second metal layer and the third metal layer are made of the same metal material, and wherein the first metal layer is made of a different material from both the second metal layer and the third metal layer, wherein both the second metal layer and the third metal layer have greater mechanical hardness than the first metal layer, and wherein the first metal layer has greater thermal conductivity than both the second metal layer and the third metal layer.

8. The superconducting magnet system of claim 7, wherein the superconducting magnet system includes a vacuum container containing the cold mass, wherein the heat shield is disposed between the vacuum container and the cold mass.

9. The superconducting magnet system of claim 7, wherein the second metal layer and the third metal layer are configured to minimize mechanical vibrations in the heat shield caused by eddy current induction.

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