Method for in-vivo shimming

Details Method for in-vivo shimming Method for in-vivo shimming

1989-11-27

1991-01-22

Tokar, Michael J.

Electricity: measuring and testing

Particle precession resonance

Spectrometer components

324307, G01R 3320

Patent

active

049873717

ABSTRACT:
In-vivo shimming is performed by acquiring two NMR images with evolution times differing by ##EQU1## where .omega..sub.1, .omega..sub.2, are the Larmor frequencies of the dominant proton species of the imaged object. A pixel by pixel division of the image yields a third image whose phase is proportional to magnetic field inhomogeneity. The phase of the third image set has periodic discontinuities as a result of the periodicity of the arctangent function used to extract the phase from the image. These discontinuities are removed by taking the derivative of the phase and integrating the product of that derivative and a weighting function where the weighting function has zero weight at the points of discontinuity. Off-center quadratic terms in the inhomogeneity are removed prior to fitting the linear shimming gradients.

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patent: 4733189 (1988-03-01), Punchard
patent: 4749948 (1988-06-01), Duby
patent: 4761614 (1988-08-01), Prammer
patent: 4899109 (1990-02-01), Tropp
patent: 4949044 (1990-08-01), Statewicz

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