Method and apparatus for producing homogeneous magnetic fields
First Claim
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1. A method for shimming a magnetic field in which there is an inhomogeneity having more than one functional component, the magnetic field being produced by a magnet assembly having two opposed and mutually distanced assembly ends and an assembly axis, the method comprising:
- providing a plurality of commonly oriented shim paths, said shim paths disposed on a common surface having two opposed and mutually distanced ends, each of said surface ends having at least one associated electrical connector;
applying a plurality of coordinately modulated single electronic shim currents along corresponding ones of the plurality of shim paths, each of said electronic shim currents entering said electrical connector at one said surface end, flowing from said electrical connector at said one said surface end to said electrical connector at the other said surface end, and exiting said electrical connector at the other said surface end; and
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suppressing the more than one functional component of the inhomogeneity in the magnetic field using the plurality of electronic shim currents;
wherein each of said surface ends is proximate a corresponding one of said assembly ends so that at least a portion of said shim currents flows from one said assembly end towards the other said assembly end.
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Abstract
A method for shimming a magnetic field is disclosed. The method uses a single shim current to contribute to suppression of more than one geometrical component of an inhomogeneity in the magnetic field without changing the geometry of the shim path. Apparatuses to implement the method are also disclosed. In embodiments the apparatuses comprise substantially commonly oriented shim paths.
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Citations
22 Claims
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1. A method for shimming a magnetic field in which there is an inhomogeneity having more than one functional component, the magnetic field being produced by a magnet assembly having two opposed and mutually distanced assembly ends and an assembly axis, the method comprising:
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providing a plurality of commonly oriented shim paths, said shim paths disposed on a common surface having two opposed and mutually distanced ends, each of said surface ends having at least one associated electrical connector; applying a plurality of coordinately modulated single electronic shim currents along corresponding ones of the plurality of shim paths, each of said electronic shim currents entering said electrical connector at one said surface end, flowing from said electrical connector at said one said surface end to said electrical connector at the other said surface end, and exiting said electrical connector at the other said surface end; and
;suppressing the more than one functional component of the inhomogeneity in the magnetic field using the plurality of electronic shim currents; wherein each of said surface ends is proximate a corresponding one of said assembly ends so that at least a portion of said shim currents flows from one said assembly end towards the other said assembly end. - View Dependent Claims (2, 3, 10, 11, 16, 17)
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4. A detector for detecting magnetic resonance in a sample exposed to a main magnetic field, the detector comprising:
a substantially flat shim panel having two opposed and mutually distanced panel ends and a panel axis, each of said two ends having one or more associated electrical connectors, the shim panel comprising a plurality of shim paths having a substantially common orientation extending between said two panel ends, the shim paths for applying electronic shim currents thereon, each of said currents entering an electrical connector at one said panel end, flowing from said electrical connector at said one said panel end to an electrical connector at the other said panel end, and exiting said electrical connector at the other said panel end. - View Dependent Claims (5, 6, 7, 8, 18, 22)
- 9. A shim panel comprising a printed circuit board having first and second substantially distanced and mutually opposed panel ends and a substantially flat portion comprising a plurality of electrical current conducting shim paths extending between and terminating at said panel ends, wherein individual ones of the shim paths have a substantially common orientation, wherein said electrical current enters each of said shim paths at one said panel end and is conducted along each of said shim paths and exits each of said shim paths at the other of said panel ends.
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12. A method for constructing a set of desired magnetic field configurations within a magnetic resonance apparatus comprising a plurality of shim paths, the method comprising the steps of:
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(a) providing a shim panel having first and second substantially distanced panel ends and a substantially flat portion, said shim panel adapted to comprise at least a subset of said shim paths such that individual ones of said subset of said shim paths each substantially extend between said panel ends, wherein individual ones of the shim paths have a substantially common overall orientation, and wherein said subset of said shim paths are configured for applying electronic shim currents thereon, each of said currents entering a shim path at one said panel end, flowing along said shim path from said one said panel end and exiting said shim path at the other said panel end; (b) estimating a representation of the magnetic field as a function of spatial coordinate variables produced by a known electronic shim current in a first one of said shim paths by integrating the Biot-Savart equation; (c) computing a scalar product of (i) a desired magnetic field configuration, and (ii) a magnetic field function estimated according to step (b); (d) repeating step (b) and step (c) for a plurality of pairs of said desired magnetic field configurations and estimated shimming field functions produced by known electronic shim currents; (e) arranging the scalar product values of step (d) into a matrix; (f) computing the pseudoinverse matrix values of said matrix; and (g) using said pseudoinverse matrix values to determine the electronic currents required to construct said set of desired magnetic field configurations. - View Dependent Claims (13, 14, 15)
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21. A method for constructing a set of desired magnetic field configurations within a magnetic resonance apparatus comprising a plurality of shim paths, the method comprising the steps of:
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(a) providing a shim panel having first and second substantially distanced panel ends and a substantially flat portion, said shim panel adapted to comprise at least a subset of said shim paths such that individual ones of said subset of said shim paths each substantially extend between said panel ends, wherein individual ones of the shim paths have a substantially common overall orientation, and wherein said subset of said shim paths are configured for applying electronic shim currents thereon, each of said currents entering a shim path at one said panel end, flowing along said shim path from said one said panel end and exiting said shim path at the other said panel end; (b) estimating a representation of the magnetic field as a function of spatial coordinate variables produced by a known electronic shim current in a first one of said shim paths by applying said current to said shim path and collecting a spatial map of magnetic field values using a magnetometer probe; (c) computing a scalar product of (i) a desired magnetic field configuration, and (ii) a magnetic field function estimated according to step (b); (d) repeating step (b) and step (c) for a plurality of pairs of said desired magnetic field configurations and estimated shimming field functions produced by known electronic shim currents; (e) arranging the scalar product values of step (d) into a matrix; (f) computing the pseudoinverse matrix values of said matrix; and (g) using said pseudoinverse matrix values to determine the electronic currents required to construct said set of desired magnetic field configurations.
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Specification