Automatic eddy current correction

Details Automatic eddy current correction Automatic eddy current correction

1989-05-10

1990-05-22

Williams, Hezron E.

Electricity: measuring and testing

Particle precession resonance

Using a nuclear resonance spectrometer system

324320, G01R 3320

Patent

active

049280635

ABSTRACT:
A gradient field controller (30) generates current pulses with a preselected profile. Eddy current compensation circuits (42) alter the current pulse profile by adding additional components of selectable frequencies with selectable amplitudes or gains. A power amplifier (32) amplifies the modified current pulse and applies them to gradient field coils (34) of a magnetic resonance imager. A probe or coil (50) monitors the induced gradient response which is integrated (52) to provide an electronic representation of the induced gradient profile. A least squares analysis routine (72) determines the time constant and amplitude of a component attributable to a first eddy current which degrades the induced gradient profile. A filter frequency correction factor calculating routine (76) calculates appropriate filter frequency settings and a gain calibration factor calculating routine (78) calculates the gain settings for the compensation circuits (42). In operation, a repetitive correction sequence is implemented in which a current pulse is applied, the induced gradient field monitored, the longest time constant and the corresponding amplitude are determined, and appropriate adjustments to the calibration circuits are determined. The correction sequence is repeated, each time monitoring a shorter time constant eddy current until the profile of the induced gradient substantially conforms to a preselected profile.

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"Noise Pulse Generator for Nuclear Magnetic Resonance (NMR) Measurements of Self Diffusion According to the Pulsed Gradient Method" by Skirda, et al., Instruments and Experimental Techniques, vol. 19, No. 3, pp. 750-752, May-Jun., 1976.

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