Shielding arrangement and magnetic resonance device

Abstract

To provide a shielding arrangement for a magnetic resonance device.SOLUTION: The invention relates to a shielding arrangement (30) comprising a main magnet (17) including at least one solenoid coil, a shield structure (33) formed as a double-walled hollow cylinder comprising an outer wall and an inner wall, and a shield tube (34) enclosed between the at least one solenoid coil and the inner wall of the shield structure, wherein the main magnet is arranged between the outer wall and the inner wall of the shield structure and wherein the shield tube is mechanically supported by the shield structure. The invention also relates to a magnetic resonance device (11) comprising the shielding arrangement according to the present invention.SELECTED DRAWING: Figure 2

Description

[Background technology]

[0001] Regardless of grammatical usage, individuals of male, female, or other gender identity are included within the term.

[0002] Magnetic resonance devices typically use gradient systems for spatial encoding of magnetic resonance signals acquired in magnetic resonance measurements. Gradient systems usually include multiple gradient coils configured to generate rapidly varying gradient magnetic fields in an imaging volume surrounded by the gradient coils. Naturally, the gradient coils also generate rapidly varying stray magnetic fields outside the gradient coils. The stray magnetic fields can interact with the main magnet of the magnetic resonance device, which is usually arranged around the gradient coils.

[0003] The shielding structures surrounding the main magnet, such as the cryogen vessel or heat shields, are typically made from conductive metals (e.g., aluminum or stainless steel). When the rapidly changing stray magnetic fields from the gradient coils pass through the conductive material, eddy currents are generated. These eddy currents cause ohmic heating in the conductive surfaces of the shielding structures, increasing the demand for cooling provided by the cryogenic refrigeration system. Although the eddy currents protect the main magnet from the rapidly changing stray magnetic fields of the gradient coils, the magneto-mechanical interaction of the eddy currents with the conductive surfaces of the cryogen vessel creates secondary magnetic fields that result in high levels of heating in the main magnet and other cold surfaces of the magnetic resonance device.

[0004] Conventional magnetic resonance devices include a cryocooler with two separate cooling stages: a first cooling stage at about 50 K for cooling the thermal shield, and a second cooling stage at about 4 K for cooling the cryogen contained in the cryogen vessel and / or for maintaining the main magnet at superconducting temperature. The second cooling stage of the cryocooler typically provides a very low cooling capacity, e.g., 1 W to 2 W. Since it may be difficult to maintain the superconducting temperature, an increase in the heat load in the second cooling stage can be significant. Even a small deviation from the superconducting temperature can cause a quench of the magnet, especially in a "dry" system that does not contain a significant amount of cryogen to act as a thermal buffer. On the other hand, in a "wet" system, an increase in the heat load can lead to a high level of cryogen boil-off, which is also undesirable.

[0005] Therefore, the thermal load associated with eddy currents can limit acceptable gradient performance. Eddy currents in conductive surfaces can also generate magnetic fields (i.e., secondary magnetic fields) within the imaging volume of a magnetic resonance device. These secondary magnetic fields can disrupt the homogeneity of the main magnetic field and impair the quality of the acquired magnetic resonance images. Summary of the Invention

[0006] The invention aims to reduce the heat load of the cryogenic cooling elements of a magnetic resonance device without compromising image quality.

[0007] This object is achieved by a shielding arrangement and a magnetic resonance device according to the invention. Further advantageous embodiments are set forth in the dependent claims.

[0008] The shielding apparatus for a magnetic resonance device according to the present invention includes a main magnet including at least one solenoid coil, a shielding structure formed as a double-walled hollow cylinder including an outer wall and an inner wall, and a shielding tube encased between the at least one solenoid coil of the main magnet and the inner wall of the shielding structure.

[0009] The main magnet includes one or more superconducting magnets. In a preferred embodiment, the main magnet includes one or more solenoidal or cylindrical superconducting coils. The one or more solenoidal or cylindrical superconducting coils are rotationally symmetric or include a rotationally symmetric body. According to one embodiment, each of the solenoidal or cylindrical superconducting coils has an axis of rotational symmetry that is disposed on the axis of rotational symmetry of the main magnet. The main magnet includes a dedicated support structure configured to carry and / or provide support to the main magnet. As used herein, the term "main magnet" may include a dedicated support structure along with one or more solenoidal superconducting coils.

[0010] The shielding structure is configured to shield the main magnet from stray magnetic fields generated by the gradient system. The shielding structure is also configured to reduce transfer of thermal energy to the main magnet. Transfer of thermal energy may be characterized by heat transfer mechanisms such as thermal radiation, thermal conduction, and even thermal convection. The shielding structure, and in particular the outer wall of the shielding structure, for example, circumferentially surrounds the main magnet.

[0011] The shield structure forms a vessel surrounding the main magnet and the shield tube. In a preferred embodiment, the heat shield includes an outer wall, an inner wall, and an annular end wall connecting the outer and inner walls. Specifically, the heat shield forms a double-walled hollow cylinder that encases the main magnet and the shield tube within the outer wall, the inner wall, and the annular end wall. The shield structure includes an axis of rotational symmetry that is oriented parallel to or coincident with an axis of rotational symmetry defined by at least one solenoid coil of the main magnet.

[0012] Preferably, the shielding structure includes or is constructed from a material having high electrical and / or thermal conductivity. For example, the shielding structure may be constructed from copper or aluminum, particularly high purity aluminum. The shielding structure may also include gold, platinum, silver, or other metals having high electrical conductivity. In one aspect, the shielding structure is coated or plated with a material having high electrical and / or thermal conductivity.

[0013] The shielding structure is configured to shield the main magnet from magnetic fields (electromagnetic fields), in particular from the electromagnetic fields generated by the gradient system. For example, the shielding structure is configured to allow the generation of eddy currents or screening currents along the conductive surface of the shielding structure in response to the electromagnetic fields. In particular, the shielding structure includes a conductive layer that allows the generation of eddy currents in response to a primary electromagnetic field, e.g., a gradient magnetic field, in particular a stray field of the gradient magnetic field. The generated eddy currents generate a secondary magnetic field (electromagnetic field) that is opposite to the first electromagnetic field. More specifically, the first electromagnetic field and the secondary electromagnetic field cancel each other to a certain extent, resulting in a shielding effect.

[0014] The outer and inner walls of the shielding structure each include a continuous or coherent surface. In another aspect, the outer and / or inner walls of the shielding structure include or consist of a plurality of spaced apart shielding elements or rings. The shielding structure may further include one or more sections of coiled wire.

[0015] In a preferred embodiment, the shield structure is shaped to match the shape of the main magnet, e.g., the surface contour of the shield structure mimics or matches the surface contour of the main magnet.

[0016] According to one aspect, a shielding apparatus according to the present invention includes an outer vacuum chamber, which is an example of a vessel that is substantially impermeable to fluids, such as liquid or gaseous cryogens, that encloses other components of the shielding apparatus, such as the cryogen vessel, the shielding structure, the shield tube, and the main magnet.

[0017] According to one aspect, the outer shell vacuum chamber includes an outer shell, an inner shell, and an annular end wall connecting the outer shell and the inner shell. Specifically, the outer shell vacuum chamber forms a double-walled hollow cylinder that encases the main magnet and shield structure within the outer shell, the inner shell, and the annular end wall. The outer shell vacuum chamber includes an axis of rotational symmetry oriented parallel to or coincident with an axis of rotational symmetry defined by at least one solenoid coil of the main magnet. The inner shell of the outer shell vacuum chamber corresponds to a patient bore of a magnetic resonance device.

[0018] In a preferred embodiment, the outer shell vacuum chamber is configured to provide mechanical support to the shielding structure and / or the main magnet, e.g., the main magnet and / or the shielding structure are suspended in or carried by the outer shell vacuum chamber.

[0019] The shield structure is configured to block thermal radiation from the direction of the outer shell, the inner shell, and the annular end wall of the outer vacuum chamber.

[0020] The shield tube has a tubular or cylindrical shape. For example, the shield tube is in the shape of a hollow cylinder. Preferably, the shield tube does not form a vessel or container surrounding the main magnet.

[0021] The shielding tube includes or is made of a material having an intermediate electrical conductivity at a temperature of 300 K. According to one embodiment, the shielding tube includes or is made of a material having a thermal conductivity of less than 120 W / (m·K), 100 W / (m·K), or 80 W / (m·K) at a temperature of 300 K. For example, the shielding tube is made of steel or stainless steel. Alternatively, the shielding tube can include or be made of other materials, particularly metals having high electrical conductivity such as copper or aluminum.

[0022] Providing a shielding tube that includes or is made of a material with intermediate electrical conductivity advantageously reduces the manufacturing costs of the shielding device and advantageously avoids the generation of eddy currents with long time constants that may affect image quality.

[0023] In a preferred embodiment, the shield tube is disposed between the main magnet and the inner wall of the shield structure. Alternatively, the shield tube may be disposed between the inner wall of the cryogen vessel and the inner wall of the shield structure.

[0024] According to the invention, the primary magnet is disposed between the outer and inner walls of the shield structure. For example, the primary magnet is enclosed within a vessel formed by the outer and inner walls and the annular end wall of the shield structure. Alternatively, the primary magnet may be enclosed within a cryogen vessel that is enclosed between the outer and inner walls of the shield structure.

[0025] The shield tube is mechanically supported by the shield structure. Preferably, the shield tube is mechanically supported by an inner wall of the shield structure.

[0026] According to one aspect, a shielding apparatus according to the present invention includes at least one spacer mechanically connected to a shielding structure and a shielding tube, the at least one spacer being configured to maintain a predetermined spacing between an inner wall of the shielding structure and the shielding tube.

[0027] At least one spacer is disposed between the inner wall of the shielding structure and the shielding tube, preferably configured to fix the shielding tube in a predetermined relative position with respect to the shielding structure.

[0028] The at least one spacer circumferentially surrounds the inner wall or tube of the shield structure over at least a portion of the circumference of the inner tube or wall, for example, the at least one spacer is embodied as a ring, multiple rings, a hollow cylinder, multiple hollow cylinders, or a whole piece of ring or hollow cylinder.

[0029] According to one embodiment, a radially outer surface of the at least one spacer is connected to the shield tube, while a radially inner surface of the at least one spacer is connected to an inner tube or wall of the shield structure.

[0030] The at least one spacer is configured to provide a pressure-locking mechanical connection between the shield tube and the shield structure. For example, the radial dimension of the at least one spacer can be oversized relative to the inner diameter of the shield tube. That is, the at least one spacer exerts a force on the shield structure and the shield tube, fixing the shield tube in a predetermined relative position with respect to the shield structure. Alternatively, the at least one spacer may include a recess or notch configured to receive a section of the shield tube and provide a form-locking connection with the shield tube. It is also contemplated that the at least one spacer is materially coupled to the shield tube and / or the shield structure by an adhesive, preferably a thermally conductive adhesive. Alternatively, the shield structure, the at least one spacer, and the shield tube may be mechanically connected by any suitable form-locking, pressure-locking, and / or material connection.

[0031] In a preferred embodiment, the at least one spacer includes or is composed of a thermally conductive material, and in particular, the at least one spacer is configured to transfer thermal energy between the shield tube and the shield structure by thermal conduction.

[0032] At least one spacer arranged between the shielding tube and the shielding structure is advantageous because it allows for adjustment of the mechanical resonance behavior or mechanical resonance profile of the shielding device, in particular of the shielding structure. For example, the at least one spacer is configured to enhance or attenuate the transfer of mechanical energy between the shielding tube and the shielding structure. That is, it is advantageous to be able to adjust the resonant frequency of the shielding structure as required, independently of the design of the shielding structure.

[0033] Furthermore, the at least one spacer is advantageous since it allows for the regulation of the exchange of thermal energy between the shield tube and the shield structure. In particular, the at least one spacer is configured to provide a thermal and mechanical connection between the shield tube and the shield structure. That is, it is advantageous since it is possible to avoid adding components to provide a mechanical support for the shield tube and / or a thermal contact between the shield structure and the shield tube.

[0034] In a preferred embodiment, the shield tube is configured to reduce heat loading in at least one solenoid coil of the main magnet.

[0035] Although the shielding tube preferably includes or is made of a material having an intermediate electrical conductivity, the shielding tube still allows for the generation of eddy currents (or shielding currents) along the conductive surfaces of the shielding tube in response to the primary magnetic (electromagnetic) fields, particularly the stray fields of the gradient fields. The shielding currents generated in the shielding tube can advantageously replace eddy currents generated in the conductive surfaces of the main magnet and / or the cryogen vessel, thus reducing the cooling requirements to temperature levels approaching superconducting temperatures.

[0036] According to one embodiment, the shielded tube has a wall thickness of less than 5 mm, 4 mm, or 3 mm. The wall thickness of the shielded tube may be greater than 1 mm. Preferably, the shielded tube has a wall thickness of about 2 mm.

[0037] The shielding tube is configured to act as a secondary shield, shielding the main magnet and / or the cryogen vessel from magnetic fields (electromagnetic fields), in particular from stray fields of the gradient magnetic fields, as well as from thermal radiation. Thus, the heat load of the main magnet and / or the cryogen vessel can be reduced, which is advantageous since it reduces the cooling requirements at very low temperature levels (i.e., temperature levels close to the superconducting temperature), where the efficiency of cooling is particularly low. As a result, the energy efficiency of a magnetic resonance device including the shielding arrangement according to the invention is advantageously increased compared to conventional magnetic resonance devices.

[0038] In providing a shielding tube constructed of a material having an intermediate electrical conductivity, the shielding current at the conductive surface of the shielding tube is lower or reduced compared to a material having a high electrical conductivity. Thus, secondary magnetic fields reaching or interacting with the main magnet and / or the main magnetic field in the imaging volume are reduced or attenuated. As a result, imaging artifacts due to secondary magnetic fields in the imaging volume are advantageously reduced or avoided.

[0039] According to one aspect, the shielding structure of the present invention includes a plurality of shielding tubes. The plurality of shielding tubes are mechanically supported by utilizing the shielding structure. It is also conceivable that a first shielding tube of the plurality of shielding tubes provides mechanical support for a second shielding tube of the plurality of shielding tubes. For example, a second shielding tube having a second diameter is mechanically supported by a first shielding tube having a first diameter smaller than the second diameter. Preferably, the plurality of shielding tubes are used in a shielding device including a magnet having a high magnetic field strength, for example, a magnetic field strength exceeding 3T.

[0040] The shielding device according to the present invention is advantageous in that it can simplify the structure and / or reduce the manufacturing cost compared to a shielding device including multiple enclosures as a shielding structure. For example, the shielding tube occupies less radial space than a conventional cryogen vessel or similar enclosure, and is also easier to manufacture and / or install in the shielding device. Furthermore, the shielding tube according to the above-mentioned embodiment has only a small effect on the mechanical resonance behavior of the shielding structure. That is, the shielding tube can be advantageously installed in the shielding device for various magnets without requiring modification of the shielding structure.

[0041] Advantageously, the shielding device according to the invention allows for the optimization or adjustment of the provided shielding effect with respect to the occurrence of undesired secondary magnetic fields.

[0042] As a further advantage, the shielding arrangement according to the invention allows the use of high performance gradient systems without increasing the risk of cryogen boil-off or quenching of the main magnet.

[0043] According to one aspect, a shielding apparatus according to the present invention includes a flexible heat conductor thermally connected to a shielding tube and a shielding structure.

[0044] The flexible heat conductor can be plastically or elastically deformable. In particular, the flexible heat conductor can be manually deformable. In a preferred embodiment, the flexible heat conductor comprises a flexible metal fabric, such as a metal braid, a metal mesh, or a metal weave. The flexible metal fabric comprises or is made of a metal having a high thermal conductivity, such as copper, gold, aluminum, platinum, silver, etc. Alternatively, the flexible heat conductor can comprise a flexible carbon fabric or a fabric comprising other highly conductive materials. In a preferred embodiment, the flexible heat conductor comprises a copper braid.

[0045] A flexible heat conductor allows for simple and / or cost-effective implementation of thermal contact between the shield tube and the shield structure.

[0046] According to one embodiment of the shielding device according to the invention, the at least one spacer occupies the entire volume between the inner wall of the shielding structure and the shielding tube.

[0047] The at least one spacer can fill a gap or free volume between the shielding structure and the shielding tube. For example, the shape of the at least one spacer corresponds to the shape of the gap or free volume between the shielding structure and the shielding tube. Alternatively, the shielding device can include a plurality of spacers that together fill the gap or free volume between the shielding structure and the shielding tube.

[0048] In a preferred embodiment, at least one spacer or spacers correspond in shape to a hollow cylinder.

[0049] When at least one spacer is provided that occupies the entire volume between the shielding structure and the shielding tube, the shielding tube is mechanically supported over the entire axial dimension of the shielding tube. In this case, relative movement between the shielding structure and the shielding tube can be advantageously reduced or avoided. Furthermore, the transfer of mechanical energy from the shielding tube to the shielding structure is advantageously improved.

[0050] In a preferred embodiment, the shielding apparatus of the present invention includes at least two spacers spaced apart along an axial direction defined by at least one solenoid coil of the main magnet, providing a gap between the inner wall of the shielding structure and the shielding tube.

[0051] The shielding device may include at least two spacers, a first spacer of which may be located at a first end region of the shielded tube and a second spacer of which may be located at a second end region of the shielded tube, or the shielded tube may be supported by an additional spacer located at or near a central region of the shielded tube or a plane of symmetry of the shielded tube oriented perpendicular to the cylindrical axis.

[0052] At least two spacers are spaced apart along an axial direction defined by at least one solenoid coil of the main magnet. For example, the first spacer is spaced apart or separate from the second spacer along the axial direction of the main magnet. Alternatively, the first spacer and the second spacer are arranged at different rotation angles relative to the cylindrical axis of the main magnet. For example, the first spacer and the second spacer are arranged at different positions along the circumference of the shield tube.

[0053] The distance between the at least two spacers may affect the mechanical coupling between the shielding structure and the shielding tube. The shielding device according to the present invention is advantageous in that it is possible to adjust the transfer of mechanical energy between the shielding structure and the shielding tube depending on the size of the distance and / or the size of the at least two spacers.

[0054] According to a preferred embodiment of the shielding device according to the invention, at least one spacer and / or shielding tube comprises a plurality of layers.

[0055] The layers are disposed between the inner wall of the shielding structure and the shielding tube, or at least one layer of the shielding tube is disposed on a surface of the shielding tube facing away from the inner wall of the shielding structure.

[0056] The plurality of layers includes or consists of two or more layers, for example a first layer and a second layer. The material composition of the first layer can be different from the material composition of the second layer. At least one spacer and / or shielding tube includes one or more further layers having a material composition different from the material composition of the first layer and / or the material composition of the second layer. For example, a layer of the plurality of layers can be composed of a metal, a metal coating, a glass reinforced plastic (GRP), an epoxy resin, a vibration damping material, a ceramic, a metal alloy, or a composite material. Suitable metals are stainless steel, steel, aluminum, copper, etc. Examples of suitable metal coatings are aluminum, copper, silver, gold, and platinum.

[0057] Preferably, the layers of the plurality of layers are stacked in the radial direction of the shielding device. For example, the layers can form a sandwich structure with multiple layers stacked alternately in the radial direction of the shielding tube. Alternatively, the layers of at least one spacer and / or the shielding tube can be distributed along the axial direction of the shielding tube. In this way, the mechanical support of the shielding tube as well as the mechanical coupling between the shielding tube and the shielding structure can be adjusted locally, for example at a specific point along the axial direction of the shielding tube.

[0058] When at least one spacer and / or shielding tube comprising multiple layers is provided, it is advantageous that not only the mechanical coupling between the shielding tube and the shielding structure but also the mechanical resonance behavior of the shielding structure can be adjusted without requiring modifications to the design of the shielding structure.

[0059] In a preferred embodiment of the shielding device according to the invention, at least one of the layers consists of a metal coating.

[0060] The metal coating is comprised of any of the metals mentioned above. Preferably, the metal coating is comprised of a metal having high electrical conductivity, such as copper, aluminum, gold, silver, or platinum. The thickness of the metal coating is less than 1.5 mm, 1 mm, 0.5 mm, or 0.25 mm.

[0061] In a preferred embodiment, at least one surface of the shield tube comprises a metal coating. Alternatively, it is also conceivable that at least one layer of at least one spacer consists of a metal coating.

[0062] Advantageously, when a shielding tube and / or at least one spacer is provided that includes a metallic coating, the shielding effect of the shielding arrangement can be improved. In particular, the metallic coating can facilitate the generation of shielding currents and thus reduce the heat load of the main magnet and / or the cryogen vessel as well as the cooling requirements at temperature levels close to the superconducting temperature. Furthermore, the thickness of the metallic coating can be advantageously adjusted to limit the time constant of the eddy currents induced in the metallic coating.

[0063] According to one aspect of the shielding arrangement according to the invention, at least one spacer and / or the shielding tube comprises a damping element. Alternatively or additionally, the at least one spacer is arranged to reduce the transfer of mechanical energy between the shielding structure and the shielding tube.

[0064] Reducing the transfer of mechanical energy between the shielding structure and the shielding tube includes reducing or reducing the mechanical coupling between the shielding structure and the shielding tube.

[0065] At least one spacer is configured to limit the area or surface that contacts the shield tube. For example, the radially outer area of ​​the at least one spacer that contacts the shield tube may include a ridge that tapers toward the shield tube. It is also contemplated that the at least one spacer may include one or more pins, knobs, or buttons that mechanically support the shield tube at discrete locations along the outer surface or circumference of the shield tube. Furthermore, the at least two spacers are spaced apart such that one or more gaps are formed between the at least two spacers. The one or more gaps are an example of an area in which the shield tube can vibrate without transmitting mechanical variations, particularly undesirable mechanical vibrations, to the shield structure.

[0066] According to one embodiment, at least one spacer and / or shielding tube includes a damping element configured to absorb or dissipate mechanical energy. For example, at least one spacer includes a damping material, multiple layers of damping material, an elastic element, or multiple elastic elements configured to absorb mechanical fluctuations. In one embodiment, at least one spacer includes a spring and / or an elastic material (e.g., an elastomer and / or an elastic foam material) configured to convert mechanical fluctuations into elastic deformation and / or thermal energy. Any thermal energy released by the elastic deformation of the at least one spacer is advantageously transferred to a cold source connected to the shielding structure at a temperature level well above the superconducting temperature.

[0067] The shielded tube may include a vibration damping element according to the above aspects.

[0068] Advantageously, when a shielding tube and / or at least one spacer is provided that is configured to reduce the transfer of mechanical energy between the shielding tube and the shielding structure, the influence of the shielding tube on the mechanical resonance behavior of the shielding structure can be reduced or avoided.

[0069] According to one aspect of the shielding device according to the invention, the at least one spacer and / or the shielding tube comprises a rigid material. Alternatively or additionally, the at least one spacer is arranged to improve the transfer of mechanical energy between the shielding structure and the shielding tube.

[0070] At least one spacer and / or shield tube are configured to transmit mechanical fluctuations from the shield tube to the shield structure. At least one spacer is made of a rigid or inelastic material, such as steel, stainless steel, or glass-reinforced plastic. The rigid material of the at least one spacer is in mechanical contact with the shield tube and the shield structure. The shield tube is made of a rigid material, such as steel or stainless steel. In a preferred embodiment, one layer of the at least one spacer and / or one layer of the shield tube is made of a rigid material.

[0071] The at least one spacer is positioned to improve the transfer of mechanical energy between the shield structure and the shield tube. According to one embodiment, a majority of the outer surface of the shield tube is in contact with the at least one spacer. For example, more than 50%, 60%, 70%, or 80% of the outer surface or circumference of the shield tube is in contact with the at least one spacer.

[0072] In a preferred embodiment, the at least one spacer is configured to transmit mechanical fluctuations of a selected mechanical frequency and / or selected mechanical vibrations from the shielded tube to the shielded structure. For example, the at least one spacer is disposed at one or more selected nodes along the circumference of the shielded tube. The one or more selected nodes are characterized by a specific vibration frequency and / or vibration amplitude of a section of the wall of the shielded tube caused by the mechanical fluctuations of the shielded tube. When the at least one spacer is disposed at one or more selected nodes along the circumference of the shielded tube, it is advantageous because the selected mechanical fluctuations and / or selected mechanical frequencies are transmitted from the shielded tube to the shielded structure.

[0073] Advantageously, mechanical variations of the shielding tube can be used to tune the mechanical resonance behavior of the shielding structure, e.g., to modify or reduce the peak mechanical resonance of the shielding structure. Furthermore, advantageously, undesirable resonance frequencies of the shielding tube can be attenuated if the mechanical coupling between the shielding tube and the shielding structure is improved or strengthened.

[0074] In one aspect of the shielding device of the present invention, the shielding structure includes a plurality of layers, and at least one of the plurality of layers is configured to modify the mechanical resonance behavior of the shielding structure in response to the mechanical resonance behavior of the shielding tube.

[0075] The inner wall of the shielding structure is an example of a layer of the shielding structure. According to one embodiment, at least one layer of the shielding structure is mechanically coupled to the shielding tube via at least one spacer and / or the inner wall of the shielding structure. Preferably, the at least one layer of the shielding structure exhibits a layer of additional material mechanically connected to a surface of the shielding structure, for example, the inner surface and / or the outer surface of the inner wall of the shielding structure. The material of the at least one layer of the shielding structure is different from the material of the shielding structure. For example, the shielding structure is made of a highly conductive material such as aluminum, copper, etc. The at least one layer is made of a material with high rigidity such as steel or stainless steel.

[0076] According to one embodiment, at least one layer of the shielding structure may form part of at least one spacer mechanically connected to the shielding structure, or alternatively, at least one layer of the shielding structure may also be mechanically connected to a surface of the inner wall of the shielding structure, in particular a surface of the inner wall of the shielding structure facing away from the shielding tube.

[0077] Preferably, at least one layer of the shielding structure is configured to mitigate or compensate for the mechanical resonance behavior of the shielding tube, for example, according to at least one spacer configured to improve the transfer of mechanical energy between the shielding structure and the shielding tube and / or to transfer mechanical fluctuations of a selected mechanical frequency and / or selected mechanical vibrations from the shielding tube to the shielding structure, as in the above-mentioned embodiment.

[0078] At least one layer of the shielding structure is configured to increase the stiffness of the shielding structure. Specifically, at least one layer of the shielding structure is configured to increase the stiffness of an inner wall or inner tube of the shielding structure. The stiffness of the shielding structure is characterized by the degree to which the shielding structure resists deformation in response to an applied force, such as a mechanical disturbance caused by the shielding tube. Preferably, at least one layer of the shielding structure includes or is composed of steel or stainless steel.

[0079] The mechanical resonance behavior of the shielding structure and / or the shielding tube is characterized by the resonant frequency of the shielding structure and / or the shielding tube under specific operating conditions, e.g., under magnetic resonance measurements performed using a magnetic resonance device including a shielding apparatus according to the present invention. In a preferred embodiment, the thickness and / or material of at least one layer of the shielding structure is selected to compensate for one or more peak mechanical resonance frequencies of the shielding tube.

[0080] Providing a shielding structure including at least one layer configured to increase the stiffness of the shielding structure is advantageous since it allows for damping of mechanical variations introduced or caused by the shielding tube. Furthermore, increasing the stiffness of the shielding structure is advantageous since it allows for a reduction in the wall thickness of the shielding structure, which allows the shielding structure to occupy less space in the radial direction of the shielding device.

[0081] According to one embodiment, at least one layer of the shielding structure includes a vibration-damping material configured to dissipate mechanical energy. For example, at least one layer of the shielding structure can include a resilient material according to the embodiment described above.

[0082] It is advantageous to provide a shielding structure that includes at least one layer configured to modify the mechanical resonance behavior of the shielding structure, thereby balancing or compensating for mechanical variations introduced or caused by the shielding tube.

[0083] According to one aspect, a shielding apparatus according to the present invention includes a gradient system including at least one gradient coil configured to generate a gradient magnetic field in a volume circumferentially enclosed by an inner wall of a shielding structure, a shielding tube being positioned away from the gradient coil so as to reduce shielding currents induced in the shielding tube by stray fields of the gradient magnetic field.

[0084] The gradient system includes one or more gradient coils. The gradient coils are configured to generate a gradient magnetic field in an imaging region surrounded in a circumferential direction by the shielding device, in particular the inner wall of the shielding structure and / or the gradient coil. In a preferred embodiment, the gradient system includes at least a first gradient coil and a second gradient coil. The first gradient coil is configured to generate a first gradient magnetic field in the imaging region. Similarly, the second gradient coil is configured to generate a second gradient magnetic field in the imaging region. The first gradient magnetic field is oriented essentially orthogonal to the second gradient magnetic field. The gradient system may further include a third gradient coil configured to generate a third gradient magnetic field in the imaging region. It is conceivable that the third gradient magnetic field is oriented substantially orthogonal to the first gradient magnetic field and the second gradient magnetic field.

[0085] The shield tube circumferentially surrounds the gradient system. In a preferred embodiment, the gradient system is arranged in a tubular or cylindrical configuration. The diameter of the shield tube is greater than the diameter of the gradient system.

[0086] Preferably, the shielding tube is positioned relative to the gradient system to reduce the generation of shielding currents along the conductive surface of the shielding tube in response to the gradient magnetic fields. For example, the spacing between a point on the inner surface of the shielding tube and a point on the outer surface of the gradient system along a surface normal to the inner surface of the shielding tube is greater than 1 cm, 2 cm, 4 cm, 6 cm, 8 cm, or even 10 cm. Of course, the spacing between the shielding tube and the gradient system depends on the magnetic field strength of the gradient coils in addition to the magnetic field strength of the main magnet.

[0087] Locating the shielding tube away from the gradient system as in the above-described embodiment advantageously reduces or limits mechanical movement of the shielding tube. Furthermore, reducing shielding currents in the conductive surfaces of the shielding tube can also reduce or attenuate secondary magnetic fields reaching or interacting with the main magnet and / or the main magnetic field in the imaging volume. Thus, imaging artifacts due to secondary magnetic fields in the imaging volume are advantageously reduced or avoided.

[0088] According to one aspect, the shielding apparatus of the present invention includes a cryogen vessel containing a primary magnet, the cryogen vessel having an inner diameter greater than a diameter of a shield tube, the cryogen vessel circumferentially surrounding the shield tube.

[0089] A cryogen vessel is a liquid-tight container configured to contain a primary magnet and a fluid, specifically a cryogen. At least a portion of the primary magnet is immersed in the liquid portion of the fluid in the cryogen vessel. In a preferred embodiment, the cryogen vessel forms a double-walled hollow cylinder that contains the primary magnet between the outer and inner walls of the cryogen vessel. The outer and inner tubes are mechanically connected via an annular end wall. The cylindrical axis or axis of rotational symmetry of the cryogen vessel is oriented parallel to or coincides with the axis of rotational symmetry defined by the solenoid coil of the primary magnet.

[0090] The cryogen vessel is configured to provide a shielding effect. Preferably, the cryogen vessel is maintained at a temperature level close to the superconducting temperature of the main magnet. In one embodiment, the cryogen vessel and / or the cryogen contained therein is thermally connected to a second stage of a cryocooler. That is, the thermal energy absorbed from the cryogen vessel via the cryocooler must be absorbed at a very low temperature level with low efficiency.

[0091] The shield tube is disposed within a tubular space or cavity defined by the cryogen vessel, specifically the inner wall of the cryogen vessel. In a preferred embodiment, the shield tube is disposed between the inner wall of the cryogen vessel and the inner wall or inner tube of the shield structure.

[0092] Advantageously, the shielding effect of the shielding arrangement according to the invention according to the above-mentioned aspects exceeds or is better than that of a conventional shielding arrangement without a shielding tube. When a shielding tube is arranged between the inner wall of the cryogen vessel and the gradient system, the stray magnetic field of the gradient magnetic field is at least partially counteracted by eddy currents generated at the conductive surface of the shielding tube. Thus, mechanical fluctuations and / or thermal loads associated with eddy currents are at least partially shifted to the shielding tube, which can be cooled to higher temperatures compared to the cryogen vessel. Advantageously, the shielding tube allows for lower cooling requirements at the level of superconducting temperatures and reduced power requirements of the cryocooler, since the cooling efficiency of the cryocooler usually increases with increasing temperature levels.

[0093] A magnetic resonance device according to the invention is configured to perform magnetic resonance measurements of an object located in an imaging region of the magnetic resonance device, the magnetic resonance device having a gradient system including at least one gradient coil and a shielding device according to the above-mentioned aspects.

[0094] The magnetic resonance device according to the invention is configured for acquiring magnetic resonance data from a subject located within an imaging region of the magnetic resonance device. Preferably, the magnetic resonance device is configured for acquiring magnetic resonance image data, in particular diagnostic magnetic resonance image data, from a subject located within the imaging region. The subject is a patient, in particular a human or an animal.

[0095] Preferably, the magnetic resonance device according to the present invention is a closed bore scanner. The closed bore scanner comprises a substantially cylindrical bore that circumferentially surrounds the imaging region. The main magnet of the closed bore scanner comprises one or more solenoid coils that circumferentially surround the imaging region along the axial or rotational symmetry axis of the cylindrical bore. The one or more solenoid coils comprise a wire that has negligible electrical resistance at (or below) the superconducting temperature. The direction of the main magnetic field provided by the main magnet is oriented substantially parallel to the direction of the subject's access to the imaging region and / or the axial direction of the cylindrical bore.

[0096] The magnetic resonance device includes at least one cryocooler configured to cool components of the magnetic resonance device, such as a main magnet, a shield structure, a shield tube, a cryogen vessel, etc.

[0097] The at least one cryocooler is configured to provide a temperature at or below a temperature approaching a superconducting temperature of a superconducting material of the main magnet, for example, the superconducting temperature of the main magnet is in a range of 3 K to 100 K, preferably in a range of 3 K to 6 K, 5 K to 10 K, 30 K to 60 K, or 60 K to 90 K. The at least one cryocooler may be implemented by a pulse tube refrigerator, a Gifford-McMahon refrigerator, a Stirling cryocooler, a Joule-Thomson cryocooler, or the like.

[0098] In a preferred embodiment, at least one cryocooler is thermally and mechanically connected to the main magnet, the shield structure, and the shield tube, and is configured to maintain the main magnet and the shield structure, as well as the shield tube, at different temperature levels.

[0099] At least one cryocooler includes a cold head having one or more cooling stages. When the cold head includes multiple cooling stages, each of the cooling stages may have a different temperature level. Alternatively, the magnetic resonance device according to the present invention includes a first cryocooler configured to cool the main magnet and a second cryocooler configured to cool the shield structure and / or the shield tube. Preferably, the temperature level provided by the second cryocooler is higher than the temperature level provided by the first cryocooler.

[0100] According to one embodiment, at least one cryocooler includes at least a first cooling stage and a second cooling stage. The first cooling stage is thermally and mechanically connected to the shield structure and the shield tube. The second cooling stage is thermally and mechanically connected to the main magnet. Preferably, the temperature level of the first cooling stage is higher than the temperature level of the second cooling stage. For example, the first cooling stage is configured to provide a temperature in the range of 40K to 180K, preferably in the range of 40K to 60K, 60K to 100K, or 100K to 180K. The second cooling stage is configured to provide a temperature level close to the superconducting temperature of the main magnet.

[0101] The magnetic resonance device of the present invention may be configured as a "dry" system. A "dry" system includes little or no cryogen. For example, the magnetic resonance system of the present invention may include one or more small cryogen vessels thermally connected to the main magnet via a solid thermal conductor. The small cryogen vessels include volumes of cryogen less than 10 L, 5 L, or 1 L. In one embodiment, the cryogen vessel is omitted. That is, the main magnet is cooled entirely by thermal conduction.

[0102] In an alternative embodiment, the magnetic resonance device of the present invention is configured as a "wet" system. A "wet" system includes a cryogen vessel containing a fluid or cryogen with a low boiling point, such as argon, nitrogen, neon, helium, etc. The predetermined temperature level corresponds substantially to the superconducting temperature of the main magnet.

[0103] It is contemplated that components of the magnetic resonance device, such as the main magnet, the cryogen vessel, the shielding structure, the shielding tube, etc., may be thermally connected to the cryocooler. Preferably, the components of the magnetic resonance device are thermally connected to the cryocooler via solid thermal conductors, convection loops, and / or heat pipes.

[0104] The magnetic resonance device according to the invention shares the advantages of the shielding arrangement according to the invention.

[0105] Further advantages and details of the invention can be seen from the embodiments and drawings described below. [Brief description of the drawings]

[0106] [Figure 1] 1 is a schematic diagram showing an embodiment of a magnetic resonance device according to the present invention; [Diagram 2] 1 is a schematic diagram showing an embodiment of a magnetic resonance device according to the present invention; [Diagram 3] 1 is a schematic diagram showing an embodiment of a shield device according to the present invention. [Figure 4]1 is a schematic diagram showing an embodiment of a shield device according to the present invention. [Diagram 5] 1 is a schematic diagram showing a portion of an embodiment of a shield device according to the present invention. [Figure 6] 1 is a schematic diagram showing a shield tube and a spacer in an embodiment of a shield device according to the present invention. [Figure 7] 1 is a schematic diagram showing a portion of an embodiment of a shield device according to the present invention. [Figure 8] 1 is a schematic diagram showing an embodiment of a shield device according to the present invention. [Figure 9] 1 is a schematic diagram showing an embodiment of a shield device according to the present invention. [Figure 10] Comparison of the mechanical resonance behavior of each embodiment of the shielding device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0107] 1 shows an embodiment of a magnetic resonance device 11 according to the present invention. In the illustrated example, the magnetic resonance device 11 includes a static magnetic field magnet 17 (main magnet) configured to provide a uniform static magnetic field 18 (B0 field) containing an imaging volume 38. The static magnetic field 18 passes through an imaging region 36 configured to receive an imaging subject, such as a patient 15. The imaging region 36 corresponds to a patient bore configured to accommodate the patient during magnetic resonance measurements. The imaging region 36 is surrounded in a circumferential direction by a shielding arrangement 30.

[0108] In the illustrated example, the magnetic resonance device 11 includes a patient support 16 configured to transport a patient 15 into an imaging region 36. In particular, the patient support 16 is configured to transport a diagnostic body region of the patient 15 into an imaging volume 38 or isocenter of the magnetic resonance device 11. Typically, a shielding arrangement 30 of the magnetic resonance device 11 is concealed within a housing 41.

[0109] The magnetic resonance device 11 includes a gradient system 19 configured to provide gradient magnetic fields used for spatial encoding of magnetic resonance signals acquired during magnetic resonance measurements. The gradient system 19 is operated or controlled by a gradient controller 28 using appropriate current signals. It is contemplated that the gradient system 19 includes one or more gradient coils configured to generate gradient magnetic fields in different, preferably orthogonally oriented, spatial directions.

[0110] The magnetic resonance device 11 may include an integrated radio frequency antenna 20 (i.e., a body coil). The radio frequency antenna 20 is operated by a radio frequency controller 29 that controls the radio frequency antenna 20 to generate a high frequency magnetic field and emit radio frequency excitation pulses into the imaging region 36. The magnetic resonance device 11 further includes a local coil 21. The local coil 21 may be positioned at or near a region of interest of the patient 15. The local coil 21 is configured to emit radio frequency excitation pulses to and / or receive magnetic resonance signals from the patient 15. The local coil 21 may be controlled by the radio frequency controller 29.

[0111] Preferably, the magnetic resonance device 11 comprises a control unit 23 configured to control the magnetic resonance device 11. The control unit 23 comprises a processing unit 24 configured to process the magnetic resonance signals and to reconstruct the magnetic resonance image. The processing unit 24 is configured to process inputs by a user of the magnetic resonance device 11 and / or to provide an output to the user. For this purpose, the processing unit 24 and / or the control unit 23 may be connected to a display unit 25 and an input unit 26 via suitable signal connections. In preparation for the magnetic resonance measurement, preparatory information such as imaging parameters and patient information is provided to the user via the display unit 25. The input unit 26 is configured to receive information and / or imaging parameters from the user.

[0112] Needless to say, the magnetic resonance device 11 may include further components that a magnetic resonance device typically provides. The overall operation of the magnetic resonance device 11 is well known to those skilled in the art, and will not be described in detail.

[0113] FIG. 2 shows a cross-sectional view of the magnetic resonance device 11 according to the present invention shown in FIG. 1. In the illustrated example, the shielding apparatus 30 includes an outer shell vacuum chamber 42 that provides an enclosure for the components of the shielding apparatus 30. The outer shell vacuum chamber 42 separates the ambient environment 70 from a vacuum region 71 enclosed by the outer shell vacuum chamber 42. In a preferred embodiment, the outer shell vacuum chamber 42 forms a double-walled hollow cylinder including an outer shell and an inner shell. The components of the shielding apparatus 30 are housed within or surrounded by the outer and inner shells of the outer shell vacuum chamber 42. The inner shell of the outer shell vacuum chamber 42 forms a patient bore 37 that circumferentially surrounds the imaging region 36.

[0114] In the illustrated embodiment, the shielding device 30 includes a shielding structure 33 and a shielding tube 34. The shielding structure 33 is implemented as a double-walled hollow cylinder, and the shielding tube 34 is implemented as a single tube or hollow cylinder. The shielding tube 34 and the primary magnet 17 are encased between an outer wall and an inner wall of the shielding structure 33. The primary magnet 17 is thereby confined by the outer wall of the shielding structure 33 and the shielding tube 34.

[0115] Preferably, the shielding apparatus 30 includes one or more suspension rods 12 mechanically connected to the outer shell of the outer hull vacuum chamber 42 and the main magnet 17. The suspension rods 12 extend through passages or holes in the shielding structure 33 to provide a mechanical connection between the outer shell of the outer hull vacuum chamber 42 and the main magnet 17.

[0116] The magnetic resonance device 11 further includes a cryocooler 32 mounted in the outer shell vacuum chamber 42. The cryocooler 32 is configured to cool the main magnet 17, the shielding structure 33, the shielding tube 34, as well as other components of the shielding apparatus 30, such as the cryogen vessel 31 (see FIG. 4).

[0117] The cryocooler 32 includes, by way of example, a compressor (not shown) that supplies pressurized gas to the cryocooler 32. According to the embodiment shown in FIG. 2, the cryocooler 32 includes a coldhead with one or more cooling stages 32a, 32b. Preferably, a first cooling stage 32a of the coldhead is thermally connected to the shield structure 33, while a second cooling stage 32b of the coldhead is thermally connected to the main magnet 17. In a preferred embodiment, the first cooling stage 32a provides a temperature level of about 50K and the second cooling stage 32b provides a temperature level of about 4K. In the case of a "dry" system, the cooling stages 32a, 32b of the cryocooler 32 are thermally connected to the components of the shield arrangement 30 via solid thermal conductors 39a, 39b. It is also contemplated that the magnetic resonance device 11 includes one or more small cryogen vessels (not shown) that are thermally connected to the cryocooler 32 via solid thermal conductors, heat pipes, and / or convection loops. One or more cryogen vessels may be thermally connected to the main magnet 17 via a heat exchanger and / or a solid thermal conductor 39 .

[0118] According to one embodiment, the shield tube 34 is thermally connected to the shield structure 33 via a solid thermal conductor, such as a copper braid (not shown). Alternatively, the shield tube 34 may be thermally connected to the first cooling stage 32a of the cryocooler 32 via a solid thermal conductor 39.

[0119] During operation of the magnetic resonance device 11, the shielding structure 33 is maintained at an intermediate temperature, for example, between 40 K and 60 K, preferably around 50 K. The shielding structure 33 includes a conductive material configured to shield the main magnet 17 not only from thermal radiation, but also from stray magnetic fields of the gradient magnetic fields generated by the gradient system 19.

[0120] In an alternative embodiment, the shield structure 33 and the main magnet 17 are thermally connected to the same stage of the cryocooler 32. It is also contemplated that the shield structure 33 and the main magnet 17 are connected to different or separate cryocoolers 32.

[0121] FIG. 3 shows a cross-sectional view of an embodiment of the shielding device 30 according to the present invention. In the illustrated example, the shielding device 30 includes an outer vacuum chamber 42, a main magnet 17, a shielding structure 33, and a shielding tube 34. The shielding tube 34 is mechanically supported via spacers 43a and 43b mounted on the shielding structure 33. The spacers 43a and 43b are spaced apart along the axial direction of the shielding device 30. For example, the spacer 43a is located away from the spacer 43b in an axial direction oriented parallel to the axis of rotational symmetry 80 of the shielding device 30. In the illustrated embodiment, the spacers 43a and 43b are implemented as rings or hollow cylinders circumferentially surrounding the inner wall of the shielding structure 33.

[0122] The shielding apparatus 30 shown in Figure 3 can be used in "dry" magnetic resonance devices that rely primarily on conductive cooling, but which may also include a small cryogen vessel that acts as a thermal buffer, the cryogen vessel being thermally connected to the main magnet 17 via a solid thermal conductor.

[0123] FIG. 4 shows a cross-sectional view of another embodiment of a shielding arrangement 30 according to the present invention. In the illustrated example, the shielding arrangement 30 includes a cryogen vessel 31 enclosing the main magnet 17. The cryogen vessel 31 forms a liquid-tight vessel containing the cryogen (not shown). A portion of the main magnet 17 is immersed in the liquid portion of the cryogen. The cryogen in the cryogen vessel 31 is in direct contact with the second cooling stage 32b of the cryocooler 32. Alternatively, the wall of the cryogen vessel 31 is thermally connected to the second cooling stage 32b of the cryocooler via a solid thermal conductor and / or a heat pipe. The cryogen vessel 31, the shielding tube 34, and the shielding structure 33 of the shielding arrangement 30 are configured to contribute to the shielding effect of the shielding arrangement 30. The shielding arrangement 30 shown in FIG. 4 is preferably used for a "wet" magnetic resonance device.

[0124] 5 shows a cross section of an embodiment of the shielding device 30 according to the invention, which includes a number of spacers 43. In the illustrated example, the spacer 43a is arranged in the end regions, in particular the axial ends, of the shielding tube 34. The spacer 43c is arranged in the central region of the shielding tube 34. The spacer 43a is arranged to support the ends of the shielding tube 34, and the spacer 43c is arranged to prevent sagging of the central region of the shielding tube 34. The spacer 43b, and possibly additional spacers 43 (not shown), are also arranged to provide additional support to the shielding tube 34. One or more spacers 43 may also be arranged to adjust the mechanical resonance behavior of the shielding tube 34 and / or the shielding structure 33.

[0125] The spacers 43 shown in Figs. 3-5 may be implemented as buttons or pins configured to mechanically decouple the shielding structure 33 from the shielding tube 34. The spacers 43 are arranged spaced apart from each other. Preferably, the spacers 43 are bolted or glued to the end spinning or annular end walls of the shielding structure 33 and / or to the end sections of the shielding tube 34. It is also conceivable that the spacers 43 are distributed in a regular or irregular pattern over the circumference of the shielding tube 34. Alternatively, the spacers 43 are implemented as rings, ring segments, plates, hollow cylinders, and / or hollow cylinder segments. According to one embodiment, the spacers 43 are arranged in a cross section of the shielding device 30 including the solenoid coil of the main magnet 17.

[0126] According to one embodiment, the spacer 43 includes or is comprised of glass reinforced plastic. Alternatively, one or more of the spacers 43 includes or is comprised of aluminum, steel, stainless steel, epoxy resin, vibration damping elements, and / or vibration damping materials. According to a preferred embodiment, one or more of the spacers 43 is comprised of multiple layers.

[0127] According to the embodiment shown in FIG. 6, the spacer 43 includes a recess or notch configured to receive a portion of the shield tube 34, thereby providing a form-locking mechanical connection between the spacer 43 and the shield tube 34.

[0128] FIG. 7 shows another embodiment of the shielding device 30 according to the present invention. In the illustrated example, the spacer 43 fills the entire gap or free volume between the shielding structure 33 and the shielding tube 34. The spacer 43 is composed of a single layer of material such as glass-reinforced plastic, aluminum, stainless steel, or epoxy resin. Alternatively, the spacer 43 can include multiple layers of different materials. For example, the spacer 43 shown in FIG. 7 is composed of a series of layers stacked in the radial direction of the shielding device 30. According to one embodiment, the shielding device 30 includes multiple spacers 43 that together fill the entire gap or free volume between the shielding structure 33 and the shielding tube 34.

[0129] 8 shows a radial cross section of an embodiment of a shielding device 30 according to the invention, including a cryogen vessel 31. In the illustrated example, the shielding structure 33 includes a layer 33a configured to increase the stiffness of an inner wall or inner tube of the shielding structure 33. Preferably, the shielding structure 33 is made of aluminum, in particular aluminum 5005, and the layer 33a of the shielding structure 33 is made of stainless steel. The shielding structure 33 and the layer 33a are thermally connected to a first cooling stage 32a of a cryocooler 32, which is maintained at a temperature level of about 50K.

[0130] The shielding tube 34 is supported via one or more spacers 43 according to the above-mentioned embodiment. Depending on a certain position of the radial cross section along the axis 80, the gap or free volume between the shielding tube 34 and the inner wall of the shielding structure 33 is filled by the spacers 43 according to the above-mentioned embodiment. However, the gap may be devoid of any structure or component of the shielding device 30. For example, there may be one or more vacuum regions between the shielding tube 34 and the inner wall of the shielding structure 33.

[0131] The shielding tube 34 is thermally connected to the shielding structure 33 via a separate heat conductor (not shown) and / or via one or more spacers 43. Thus, the shielding tube 34 is indirectly connected to the cryocooler and may exhibit a higher temperature compared to the shielding structure 33. For example, the shielding tube 34 is maintained at a temperature level of 60K to 70K during operation of the shielding apparatus 30 in the magnetic resonance device 11. Preferably, the shielding tube 34 is made of stainless steel having a thickness of about 2 mm.

[0132] 8, the cryogen vessel 31 surrounding the main magnet 17 is constructed from stainless steel. Preferably, the cryogen vessel 31 is thermally connected to the second cooling stage 32b of the cryocooler 32 and is maintained at a temperature of about 4K during operation of the shielding arrangement 30 for the magnetic resonance device 11.

[0133] The inner and outer shells of the outer vacuum chamber 42 are preferably constructed from steel, stainless steel, or another resilient metal.

[0134] Fig. 9 shows a radial cross section of another embodiment of the shielding device 30 according to the invention. In the embodiment shown, the spacer 43 is made up of three layers 43a, 43, 43c. Unlike the embodiment shown in Fig. 8, the layer 43c is mechanically connected to the outer surface of the inner wall of the shielding structure 33. The layer 43c is made of stainless steel and can increase the rigidity of the shielding structure 33. Preferably, the layer 43c is physically bonded to the inner tube of the shielding structure 33 using an adhesive, for example an epoxy resin.

[0135] The spacer 43 further comprises a layer 43b, which may comprise a continuous piece or a number of separate pieces of glass-reinforced plastic, or alternatively, the layer 43b may be implemented according to the embodiments described above.

[0136] The layer 43a is formed by a metal coating. The metal coating is preferably made of a metal having a high electrical conductivity at 300 K, such as copper, aluminum, gold, silver, or platinum. Preferably, the layer 43a is coated on the inner surface of the shield tube 34.

[0137] 9, the outer surface of the shield tube 34 includes another metal coating 34a, which may correspond to the metal coatings described above, except that the metal coating 34a does not form part of the spacer 43 since it is formed on the outer surface of the shield tube 34.

[0138] According to one embodiment of the shielding device 30, the spacer 43 (eg, layer 43a or layer 43b), the shielding tube 34 (eg, layer 34a), as well as one or more layers of the shielding structure 33 (eg, layer 33a) may be omitted.

[0139] FIG. 10 shows the results of a simulation of the mechanical resonance behavior of the shielding structure 33. On the X-axis in the figure, the frequency of the mechanical fluctuations is plotted. On the Y-axis, the power of the mechanical fluctuations is plotted. Plot S1 represents a conventional shielding device without a shielding tube 34. The simulated mechanical frequency behavior shows that the shielding structure 33 exhibits a significant resonance frequency at about 1800 Hz. Simulation S2 of the shielding device 30 according to the present invention suggests that the addition of the shielding tube 34 according to the present invention attenuates the main peak at 1800 Hz without introducing a new peak into the mechanical resonance behavior of the shielding structure 33.

[0140] Another simulation S3 of the shielding device 30 according to the invention suggests that the power deposition peaks are further reduced by adding a layer 33a configured to reinforce the inner tube of the shielding structure 33.

[0141] The above-described embodiments should be regarded as examples. It is to be understood that each embodiment may be enhanced by or combined with features of other embodiments, unless otherwise specified. The embodiments shown in Figures 1 to 9 are representations that are not necessarily drawn to scale.

Claims

1. A shielding device (30) for a magnetic resonance device (11), A main magnet (17) including at least one solenoid coil, A shield structure (33) formed as a double-walled hollow cylinder including an outer wall and an inner wall, The system includes the main magnet (17) and the shield tube (34) provided between the at least one solenoid coil and the inner wall of the shield structure (33), The main magnet (17) is positioned between the outer wall and the inner wall of the shield structure (33). The shielding device (30) is mechanically supported by the shielding structure (33) in the shielding tube (34).

2. The shielding device (30) according to claim 1, wherein the shielding tube (34) comprises a material having a thermal conductivity lower than 120 W / (m·K) at a temperature of 300 K.

3. The shielding device (30) according to claim 1, comprising a flexible heat conductor thermally connected to the shielding tube (34) and the shielding structure (33).

4. The shield structure (33) and the shield tube (34) include at least one spacer (43) mechanically connected to them. The at least one spacer (43) is configured to maintain a predetermined distance between the inner wall of the shield structure (33) and the shield pipe (34). The shielding device (30) according to claim 1.

5. The shielding device (30) according to claim 4, wherein the at least one spacer (43) occupies the entire volume between the inner wall of the shield structure (33) and the shield pipe (34).

6. The spacer (43) includes at least two spacers (43) spaced apart along the axial direction defined by the at least one solenoid coil of the main magnet (17), The shielding device (30) according to claim 4, wherein the at least two spacers provide a gap between the inner wall of the shield structure (33) and the shield pipe (34).

7. The shielding device (30) according to claim 4, wherein the at least one spacer (43) and / or the shielding tube (34) comprises a plurality of layers.

8. The shielding device (30) according to claim 7, wherein at least one of the plurality of layers is made of a metal coating.

9. The at least one spacer (43) and / or the shielding tube (34) includes a vibration damping element and / or The at least one spacer (43) is positioned to reduce the transfer of mechanical energy between the shield structure (33) and the shield tube (34). The shielding device (30) according to claim 4.

10. The at least one spacer (43) and / or the shield tube (34) include a rigid material and / or The at least one spacer (43) is arranged to improve the transfer of mechanical energy between the shield structure (33) and the shield tube (34). The shielding device (30) according to claim 4.

11. The shield structure (33) includes a plurality of layers, At least one of the multiple layers of this shield structure (33) is configured to modify the mechanical resonance behavior of the shield structure (33) in accordance with the mechanical resonance behavior of the shield tube (34). The shielding device (30) according to claim 4.

12. The shielding device (30) according to claim 11, wherein at least one layer of the shielding structure (33) is configured to increase the rigidity of the shielding structure (33).

13. The gradient system (19) includes at least one gradient coil configured to generate a gradient magnetic field within a volume circumferentially surrounded by the inner wall of the shield structure (33), The shield tube (34) is positioned away from the gradient coil so as to reduce the shielding current induced in the shield tube (34) via the stray magnetic field of the gradient magnetic field. The shielding device (30) according to claim 1.

14. The cryogen container (31) includes the main magnet (17), The inner diameter of the cryogen container (31) is larger than the diameter of the shield tube (34), The cryogen container (31) surrounds the shield tube (34) in the circumferential direction. The shielding device (30) according to claim 1.

15. A magnetic resonance device (11) configured to perform magnetic resonance measurements on an object located within the imaging region (36) of the magnetic resonance device (11), A magnetic resonance device (11) comprising a gradient system (19) including at least one gradient coil, and a shielding device (30) according to any one of claims 1 to 14.

Images