Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1986-12-03
1988-09-13
Tokar, Michael J.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
G01R 3320
Patent
active
047712449
ABSTRACT:
A method of predicting the locations and strengths of passive shims in the bore of a magnetic resonance magnet, necessary to attain imaging quality homogeneity in the bore of the magnet is provided. Electromagnetic coils are not needed to provide any shimming. The magnetic field effect of an arc of magnetized steel as a function of its position in the magnetized bore is determined. The locations at which an arc provides the most beneficial shimming effect are next determined. The most promising locations are used as a starting point for an iterative routine which attempts to identify a group of shim locations which will provide a prediction of inhomogeneity within the specified limit. The shims are placed in the magnet bore, the field measured and the result compared to prediction. If improvement is predicted by another iteration with the shim locations fixed, the determined thickness changes are implemented.
REFERENCES:
patent: 4425547 (1984-01-01), Sugimoto
patent: 4631481 (1986-12-01), Young et al.
"Aspects of Shimming a Superconductive Whole-Body MRI-Magnet", G. Frese, G. Pausch, G. Ries, Siemens AG, D-8520 Eriangen, Federal Republic of Germany, Proc. of 9th Intl. Conf. on Magnet Tech., 1985, pp. 249-251.
"Magnetic Field Homogeneity Correction Algorithm Using Pseudoinversion Formula for NMR Imaging", CB Ahn et al., Rev. Sci, Instrum, vol. 57, No. 4, Apr. 1986, pp. 683-688.
"Passive Shimming for Solenoidal Magnets", JH Coupland, Science and Engineering Research Council, Aug. 1986.
Davis Jr. James C.
General Electric Company
O'Shea Kevin D.
Steinberg William H.
Tokar Michael J.
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