Patent Description:
Certain conventional systems, methods and components are known, for example, from <CIT>, <CIT>, <CIT> and <CIT>.

Magnetic resonance imaging (MRI) systems used for obtaining images of intact biological systems of a human being typically include a primary superconducting magnet provided as a superconducting coil supported by a tubular former. The primary superconducting magnet is housed in a chamber cooled to around <NUM> Kelvin. A vacuum vessel is used to provide thermal insulation to the superconducting magnet.

The vacuum chamber bore tube has a large internal diameter to receive a human patient and for accommodating the gradient or pulse coils used for generating field gradients in three orthogonal directions relative to the principal magnetic field. As a result of the nature of the gradient coils, it is necessary to have substantial heat insulation between the primary superconducting magnet and the gradient coils so as to insulate the primary superconducting magnet both from higher environmental temperature of the gradient coils and from the heat generated during use of these coils.

In low cryogen magnet type MRI systems, a magnet is exposed to vacuum. The surface structure of such a magnet is made of different materials, resulting in different surface finish and roughness. In addition to the magnet, components mounted on the coil former have cavities with low thermal reflectivity that results in increased heat load to the cartridge.

In accordance with one embodiment outside the scope of the invention, a device is disclosed. The device includes a component operable at a temperature in a range of <NUM> to <NUM> Kelvin. The device further includes a thermal reflective sheet comprising a plurality of layers, wound around at least a portion of the component. The device also includes a coupling device for coupling the thermal reflective sheet to at least the portion of the component.

In accordance with an embodiment of the invention, a magnetic resonance imaging system is disclosed. The magnetic resonance imaging system includes a plurality of magnets operable at a temperature in a range of <NUM> to <NUM> Kelvin the magnets comprising a superconducting main coil. The main coil is supported by a cylindrical shell having an axis. The magnetic resonance imaging system further includes a thermal reflective sheet comprising a plurality of layers, wound around at least a portion of the main coil, so that when viewed in a cross section taken in a plane that coincides with the axis, the portion of the main coil is completely surrounded by the thermal reflective sheet. The magnetic resonance imaging system also includes a coupling device for coupling the thermal reflective sheet to at least the portion of the main coil.

In accordance with yet another embodiment outside the scope of the invention, a method is disclosed. The method involves winding a themial reflective sheet comprising a plurality of layers, around at least a portion of the component operable at a temperature in a range of <NUM> to <NUM> Kelvin. The method further involves coupling the thermal reflective sheet to at least the portion of the component via a coupling device.

Referring to <FIG>, a side schematic view of an exemplary magnetic resonance imaging system <NUM> in accordance with an exemplary embodiment is shown. The magnetic resonance imaging system <NUM> has a low cryogen magnet arrangement providing cryorefrigeration as described in detail herein. In the illustrated embodiment, the magnetic resonance imaging system <NUM> includes a superconducting magnet system <NUM> having a plurality of concentric superconducting main coils <NUM> and bucking coils <NUM> supported inside cylindrical shells namely a coil support shell <NUM> and a coil support shell <NUM> of high thermal conductivity. The superconducting magnet system <NUM> is cooled by a cryorefrigerator <NUM> using a helium thermosiphon system. A radial spacing is provided between the plurality of superconducting main coils <NUM> and the bucking coils <NUM>. In some embodiments, the coil support shells <NUM>, <NUM> are formed from metal. A plurality of cooling tubes <NUM> are thermally coupled (e.g., bonded) to an outside surface of the coil support shell <NUM>. In one embodiment, the coil support shells <NUM>, <NUM> may have circumferentially extending solid metal walls that define a bore therein.

The superconducting main coils <NUM> and bucking coils <NUM> in various embodiments are molded with epoxy resin. The superconducting main coils <NUM> and bucking coils <NUM> then may be bonded to the outer surface of the coil support shells <NUM>, <NUM>. The superconducting main coils <NUM> and bucking coils <NUM> are shrink fitted and bonded inside the coil support shells <NUM>, <NUM>, to provide good thermal contact. The superconducting main coils <NUM> and bucking coils <NUM> are sized to define a bore <NUM> there through which is used to image an object (e.g., a patient). For example, a field of view (FOV) <NUM> may be defined to image a particular portion of the object. A patient support device <NUM> is movable along a space within bore <NUM>.

In the illustrated embodiment, the helium thermosiphon arrangement includes the plurality of the cooling tubes <NUM> thermally coupled to the coil support shells <NUM>, <NUM>, a recondenser <NUM> thermally coupled to the cryorefrigerator <NUM>, and helium storage vessels including a liquid helium storage system <NUM> and a helium gas storage system <NUM> contained inside a magnet vacuum vessel <NUM>. The fluid communication between the cooling tubes <NUM> and the liquid helium storage system <NUM> may be provided via one or more fluid passageways <NUM>. A motor <NUM> of the cryorefrigerator <NUM> is provided outside the vacuum vessel <NUM>.

The cooling tubes <NUM> are also in fluid communication with a vapor return manifold <NUM>, which is in fluid communication with a helium gas storage system <NUM> through the recondenser <NUM>. The fluid communication between the recondenser <NUM> and the liquid helium storage system <NUM> is provided via one or more passageways <NUM>.

In the illustrated embodiment, a thermal shield <NUM> is provided in thermal contact with the helium gas storage system <NUM>. The thermal shield <NUM> is thermally coupled to a plurality of cooling tubes <NUM> (e.g., pre-cooling tubes), which in various embodiments are different than and not in fluid communication with the cooling tubes <NUM>. For example, the cooling tubes <NUM> provide cooling using helium and the cooling tubes <NUM> may provide cooling, using liquid nitrogen.

In the illustrated embodiment, a thermal reflective sheet <NUM> is wound around each of the superconducting main coils <NUM> and bucking coils <NUM>, a coupling device (not shown in <FIG>) for coupling the thermal reflective sheet <NUM> to each of the superconducting main coils <NUM> and bucking coils <NUM>. The thermal reflective sheet <NUM> is wound around at least a portion or completely around the each of the superconducting main coils <NUM> and bucking coils <NUM>. In some other embodiments, the thermal reflective sheet <NUM> is wound around the liquid helium storage system <NUM>, fluid passageways <NUM>, and vapor return manifold <NUM>. The magnet system <NUM> is exposed to vacuum and requires a high thermal reflecting surface to minimize heat load by thermal radiation. The thermal reflective sheet <NUM> provides a low thermal emissivity coefficient that is required to minimize heat loads to the magnet system <NUM>. The magnet system <NUM> and the thermal reflective sheet <NUM> are explained in detail with reference to subsequent figures.

Although the magnet system <NUM> in the magnetic resonance imaging system <NUM> is discussed, the thermal reflective sheet is applicable to all surfaces that have a working temperature in a range of <NUM> to <NUM> Kelvin. The range of application may vary from simple cryostats, cryo-containers, superconducting magnet surfaces that are exposed to vacuum. For cryostats and cryo-containers, the exemplary thermal reflective sheet facilitates to reduce evaporation of liquid helium or the heat load to a magnet irrespective of a surface quality of a coil former or the magnet. In one embodiment, the exemplary thermal reflective sheet may be application for a G10 type surface or a stainless steel surface for reducing an emissivity coefficient.

Referring to <FIG>, a schematic sectional view of the exemplary thermal reflective sheet <NUM> wound around the superconducting main coil <NUM> in accordance with an exemplary embodiment is shown. In the illustrated embodiment, the thermal reflective sheet <NUM> includes a first aluminum layer <NUM> having a purity in a range of <NUM> percent to <NUM> percent disposed contacting the superconducting main coil <NUM>. The first aluminum layer <NUM> may be wound completely around the superconducting main coil <NUM> or at least a portion of the superconducting main coil <NUM>. The first aluminum layer <NUM> has a thickness in a range of <NUM> to <NUM> micrometers. A mesh layer <NUM> is disposed on the first aluminum layer <NUM>. The mesh layer <NUM> may be a glass fiber mesh layer, polyethylene mesh layer, polytetrafluoroethylene mesh layer, and the like. The mesh layer <NUM> has a thickness in a range of <NUM> to <NUM>. The smaller square portions of the mesh layer <NUM> confine and reduce the eddy current heating effect during gradient switching.

A coupling device <NUM> is used for coupling the thermal reflective sheet <NUM> to the superconducting main coil <NUM>. In the illustrated embodiment, the coupling device <NUM> includes a plurality of adhesive tapes <NUM> for bonding the thermal reflective sheet <NUM> to the superconducting main coil <NUM>. The number of adhesives tapes <NUM> may vary depending on the application. In other embodiments, other types bonding or gluing or other clamping mechanisms may be used to couple the thermal reflective sheet <NUM> to the superconducting main coil <NUM>. The thermal reflective sheet <NUM> has a thickness in a range of <NUM> to <NUM> micrometers. The thermal reflective sheet <NUM> having a single aluminum layer <NUM> is easier to handle and for winding around tight curvature surfaces. Although one set of the first aluminum layer <NUM> and the mesh layer <NUM> is disclosed, in other embodiments, the number of sets of the first aluminum layer <NUM> and the mesh layer <NUM> in the thermal reflective sheet <NUM> may vary.

Referring to <FIG>, a schematic sectional view of the exemplary thermal reflective sheet <NUM> wound around the superconducting main coil <NUM> in accordance with an exemplary embodiment is shown. In the illustrated embodiment, the thermal reflective sheet <NUM> includes the first aluminum layer <NUM> having a purity in a range of <NUM> percent to <NUM> percent disposed contacting the superconducting main coil <NUM>. The mesh layer <NUM> is disposed on the first aluminum layer <NUM>. Additionally, the thermal reflective sheet <NUM> includes a second aluminum layer <NUM> having a purity in a range of <NUM> percent to <NUM> percent. Specifically, the mesh layer <NUM> is disposed between the first aluminum layer <NUM> and the second aluminum layer <NUM>. The provision of the mesh layer <NUM> ensures good contact with a metal mating surface of the former and reduces eddy current effects.

In the illustrated embodiment, the coupling device <NUM> includes a plurality of adhesive tapes <NUM> for bonding the thermal reflective sheet <NUM> to the superconducting main coil <NUM>. In other embodiments, other types bonding or gluing or other clamping mechanisms may be used to couple the thermal reflective sheet <NUM> to the superconducting main coil <NUM>. Although one set of the first aluminum layer <NUM>, the second aluminum layer <NUM>, and the mesh layer <NUM> is disclosed, in other embodiments, the number of sets of the first aluminum layer <NUM>, the second aluminum layer <NUM>, and the mesh layer <NUM> in the thermal reflective sheet <NUM> may vary.

In accordance with the embodiments discussed herein, the thermal reflective sheet <NUM> reduces the surface emissivity and does not fold, warp, and tear while being wrapped around components. Further, the sheet surface does not crease or shrink when cooled. The thermal reflective sheet <NUM> can be removed easily from the surface of the component and reapplied to the surface of the component.

In accordance with the embodiments discussed herein, the exemplary thermal reflective sheet reduces the surface emissivity when used as a cover for openings. The thermal reflective sheet does not move when subjected to higher fields, for example up to <NUM> Tesla, after quench, during warm-up or cool down. Further, no adhesive is required on a mating surface. The adhesive tape does not tear the thermal reflective sheet when applied.

Claim 1:
A magnetic resonance imaging system comprising:
a superconducting main coil (<NUM>) exposed to vacuum and operable at a temperature in a range of <NUM> to <NUM> Kelvin;
a cylindrical shell (<NUM>) having an axis and supporting the superconducting main coil (<NUM>);
a thermal reflective sheet (<NUM>) comprising a plurality of layers (<NUM>), wound around at least a portion of the superconducting main coil (<NUM>) so that, when viewed in a cross section taken in a plane that coincides with the axis, the portion of the superconducting main coil (<NUM>) is completely surrounded by the thermal reflective sheet (<NUM>); and
a coupling device (<NUM>) for coupling the thermal reflective sheet (<NUM>) to at least the portion of the superconducting main coil (<NUM>).