# US 2016/0252598 A1 · System for magnetic field distortion compensation and method of making same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0252598 A1 - Document ID: US20160252598A1 - Status: Published application - Kind: A1 - Application number: 14/962,345 - Filed: 2015-12-08 - Published: 2016-09-01 - Earliest claimed: 2011-12-20 - Assignees: General Electric Company - Applicants: General Electric Company - Inventors: Weijun Shen; Timothy John Havens; Longzhi Jiang; Saikat Saha; Benjamin Jacob Gronemeyer; Venkata Kishore Mogatadakala - Web page: https://patentgrep.com/patent/US20160252598A1 ## CPC - G01R 33/56518: {due to eddy currents, e.g. caused by switching of the gradient magnetic field} - G01R 33/34023: {Superconducting RF coils} - G01R 33/3804: {Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly} - G01R 33/3815: with superconducting coils, e.g. power supply therefor - G01R 33/3875: using correction coil assemblies, e.g. active shimming - H01F 6/04: Cooling - H01F 6/06: Coils, e.g. winding, insulating, terminating or casing arrangements therefor - Y10T 29/49014: Superconductor - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A system and method for magnetic field distortion compensation includes a cryostat for a magnetic resonance imaging (MRI) system. The cryostat includes a vacuum casing having a vacuum therein. A cryogen vessel is disposed within the casing, the vessel having a coolant therein. A thermal shield is disposed between the vacuum casing and the cryogen vessel. An eddy current compensation assembly is disposed within the casing. The eddy current compensation assembly includes a plurality of electrically conductive loops formed on one of the vacuum casing, the cryogen vessel, and the thermal shield and constructed to mitigate vibration-induced eddy currents in the MRI system. ## Claims ### Claim 1 A cryostat for a magnetic resonance imaging (MM) system, the cryostat comprising: a vacuum casing having a vacuum therein; a cryogen vessel disposed within the casing, the cryogen vessel having a coolant therein; a thermal shield disposed between the vacuum casing and the cryogen vessel; and an eddy current compensation assembly disposed within the vacuum casing, the eddy current compensation assembly comprising a plurality of symmetrical compensation coils formed on one of the vacuum casing, the cryogen vessel, and the thermal shield. ### Claim 2 (depends on 1) The cryostat of claim 1 wherein the plurality of symmetrical compensation coils are arranged as a plurality of independent sub-assemblies; wherein one of the plurality of independent sub-assemblies is positioned on a first surface of one of the vacuum casing, the cryogen vessel, and the thermal shield; and wherein another of the plurality of independent sub-assemblies is positioned on a second surface of one of the vacuum casing, the cryogen vessel, and the thermal shield, the second surface oriented perpendicular to the first surface. ### Claim 3 (depends on 1) The cryostat of claim 1 wherein the plurality of symmetrical compensation coils comprise a non-superconducting material. ### Claim 4 (depends on 3) The cryostat of claim 3 wherein the eddy current compensation assembly further comprises one of aluminum, copper, and silver. ### Claim 5 (depends on 4) The cryostat of claim 4 wherein the eddy current compensation assembly further comprises copper tape. ### Claim 6 (depends on 1) The cryostat of claim 1 wherein at least one surface of the one of the vacuum casing, the cryogen vessel, and the thermal shield has a first portion having the plurality of electrically conductive loops formed therein and a second portion free of the plurality of electrically conductive loops; and wherein the first portion has a thickness that is greater than a thickness of the second portion. ### Claim 7 (depends on 1) The cryostat of claim 1 further comprising an adhesive affixing the eddy current compensation assembly to at least one surface of the one of the vacuum casing, the cryogen vessel, and the thermal shield. ### Claim 8 (depends on 1) The cryostat of claim 1 wherein the eddy current compensation assembly further comprises: a first set of symmetrical compensation coils constructed to mitigate eddy currents induced in an axial direction; and a second set of symmetrical compensation coils constructed to mitigate eddy currents induced in at least one direction transverse to the axial direction. ### Claim 9 (depends on 8) The cryostat of claim 8 wherein the second set of symmetrical compensation coils comprises: a set of x-direction compensation coils; and a set of y-direction compensation coils. ### Claim 10 A method of manufacturing a magnetic resonance imaging (MRI) apparatus comprising: providing a helium vessel; forming a thermal shield around the helium vessel; disposing the helium vessel and the thermal shield within a vacuum vessel; forming an eddy current compensation assembly comprising a matrix of symmetrical pairs of closed loops on at least one surface of one of the vacuum vessel, the helium vessel, and the thermal shield; and assembling the vacuum vessel, the helium vessel, and the thermal shield to form a cryostat to house a superconducting magnet. ### Claim 11 (depends on 10) The method of claim 10 further comprising: arranging a first pair of the matrix of symmetrical pairs of closed loops on a first surface of one of the vacuum vessel, the helium vessel, and the thermal shield; and arranging a second pair of the matrix of symmetrical pairs of closed loops on a second surface of one of the vacuum vessel, the helium vessel, and the thermal shield, the second surface substantially orthogonal to the first surface. ### Claim 12 (depends on 10) The method of claim 10 further comprising: forming the eddy current compensation assembly from an electrically conductive material; and affixing the eddy current compensation assembly to the at least one surface of the cryostat using an adhesive. ### Claim 13 (depends on 10) The method of claim 10 further comprising machining the eddy current compensation assembly into a bulk material of the cryostat. ### Claim 14 (depends on 13) The method of claim 13 wherein machining the eddy current compensation assembly comprises modifying a thickness of the cryostat in a portion of the cryostat that includes the eddy current compensation assembly such that a thickness of the portion of the cryostat that includes the eddy current compensation assembly is greater than a thickness of a portion of the cryostat adjacent to the eddy current compensation assembly. ### Claim 15 (depends on 10) The method of claim 10 further comprising forming the eddy current compensation assembly on an internal surface of one of the vacuum vessel and the thermal shield. ### Claim 16 (depends on 10) The method of claim 10 further comprising forming the eddy current compensation assembly on an external surface of one of the helium vessel and the thermal shield. ### Claim 17 A magnetic resonance imaging (MRI) apparatus comprising: a plurality of superconducting coils having a bore therethrough; a plurality of bucking coils positioned about the bore; a cryostat comprising: a helium vessel sized to surrounding the plurality of superconducting coils and the plurality of bucking coils; a thermal shield surrounding the helium vessel; and a vacuum vessel surrounding the thermal shield; a coldhead extending through the vacuum vessel and the thermal shield; and an eddy current compensation assembly coupled to the cryostat, the eddy current compensation assembly comprising a matrix of closed loops arranged to passively generate compensation currents that substantially mitigate positive and negative eddy currents induced within the cryostat from mechanical vibrations generated by the coldhead. ### Claim 18 (depends on 17) The MRI apparatus of claim 17 wherein the eddy current compensation assembly comprises a plurality of symmetrical compensation coils coupled to a surface of one of the vacuum vessel, the helium vessel, and the thermal shield. ### Claim 19 (depends on 17) The MRI apparatus of claim 17 wherein the eddy current compensation assembly comprises raised, closed loops machined onto a surface of one of the vacuum vessel, the helium vessel, and the thermal shield. ### Claim 20 (depends on 17) The MRI apparatus of claim 17 wherein the eddy current compensation assembly comprises: a symmetrical pair of electrically conductive loops constructed to mitigate positive and negative eddy currents induced in the x-direction; a symmetrical pair of electrically conductive loops constructed to mitigate positive and negative eddy currents induced in the y-direction; and a symmetrical pair of electrically conductive loops constructed to mitigate positive and negative eddy currents induced in the z-direction.