Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1994-11-04
1997-06-03
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324318, G01R 3328
Patent
active
056358393
ABSTRACT:
A subject receiving bore (12) of a magnetic resonance apparatus has an axial length to diameter ratio of less than 1.75:1 and preferably about 1:1. The temporally constant magnetic field generated by superconducting magnets (10) surrounding the bore has various magnetic field harmonic distortions including a Z12 harmonic distortion which is described generally by the equation Z.sup.12. In long bore magnets with a length to diameter ratio of 2:1 or more, harmonic distortions above Z6 are not present, or if present, not measured. A magnetic field probe (80 ) measures the magnetic field in the bore at a sufficient number of axial locations to measure at least the Z12 harmonic, e.g., 24 axially displaced locations. The probes are sampled at a sufficient number of angular increments, e.g., 32-36, that any present transverse spherical harmonics are sampled. Ferrous shims (62) are mounted in the bore in the pockets (58) of shim trays (44) to compensate for the Z12 and other sampled harmonics above Z6. The shim trays have a sufficient number of pockets axially along the bore to compensate for the Z12 harmonic, e.g., 24 pockets. Optionally, segmented ferrous rings (92) are mounted in the bore at locations theoretically calculated to minimize higher order harmonic distortion and the shim trays are used to adjust the correction. In the preferred embodiment, the shim trays and the segmented rings are mounted to a cylindrical former (34) that supports a primary gradient coil assembly (32) to position the ferrous material close to the imaging volume.
REFERENCES:
patent: 4587504 (1986-05-01), Brown et al.
patent: 4698611 (1987-10-01), Vermilyea
patent: 4733189 (1988-03-01), Punchard et al.
patent: 4737716 (1988-04-01), Roemer et al.
patent: 4771243 (1988-09-01), Vreugdehil et al.
patent: 4853663 (1989-08-01), Vermilyea
patent: 5003266 (1991-03-01), Palkovich et al.
patent: 5045794 (1991-09-01), Dorri et al.
patent: 5168211 (1992-12-01), Laukien et al.
patent: 5179338 (1993-01-01), Laskaris et al.
patent: 5235282 (1993-08-01), Overweg
patent: 5235284 (1993-08-01), Tahara et al.
patent: 5296812 (1994-03-01), Kitamura et al.
patent: 5345208 (1994-09-01), Dorri et al.
patent: 5349297 (1994-09-01), DeMeester et al.
patent: 5361054 (1994-11-01), Knuttel
patent: 5400786 (1995-03-01), Allis
DeMeester Gordon D.
McGinley John V. M.
Srivastava Vishnu C.
Mah Raymond Y.
O'Shea Sandra L.
Picker International Inc.
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