Method for determining shim placement on tubular magnet

Details Method for determining shim placement on tubular magnet Method for determining shim placement on tubular magnet

1994-05-02

1995-05-23

Arana, Louis

Electricity: measuring and testing

Particle precession resonance

Spectrometer components

324319, G01V 300

Patent

active

054184622

ABSTRACT:
A method for using ferromagnetic shims to reduce the inhomogeneity of the magnetic field in a Diameter Spherical Volume (DSV) in the bore of a Magnetic Resonance Imaging (MRI) device is provided. More specifically, a magnetic field is established within the bore of the MRI device. An operator defines the DSV. The strength of the magnetic field is measured at the surface of the DSV. A Legendre polynomial is derived to model the inhomogeneity in the magnetic field in the DSV. A set of coefficients for the harmonic terms of the polynomial is calculated from the field strength measurements and segregated into three separate groups for evaluation. Each group of terms expresses field inhomogeneity in a unique set of spatial dimensions. Ferromagnetic shims are attached to the surface of the bore in individual dipole, linear bar, and ring arrangements to separately reduce the first, second, and third groups of harmonic coefficients to acceptable levels corresponding to a predetermined peak-to-peak inhomogeneity range.

REFERENCES:
patent: 4498048 (1985-02-01), Lee et al.
patent: 4656449 (1987-04-01), Mallard et al.
patent: 4672346 (1987-06-01), Miyamoto et al.
patent: 5045794 (1991-09-01), Dorri et al.
patent: 5343151 (1994-08-01), Cory et al.
patent: 5343183 (1994-08-01), Shimada et al.

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