Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1987-04-03
1988-08-02
Levy, Stewart J.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324322, G01R 3320
Patent
active
047616121
ABSTRACT:
In a magnetic resonance imaging apparatus, a gradient profile generator (30) generates gradient energization profiles or current pulses (32, 34, 36) each of which has a shape that corresponds to a profile of a preselected magnetic field gradient that is to be applied across an image region (10) by gradient coils (38). The applied gradient magnetic field profile inherently causes eddy currents which generate opposing magnetic field components and distort the gradient magnetic field profile. A series of calibration circuits (62) alters the gradient energization profiles to compensate for eddy current distortion. A profile amplifier (74) is connected with a first MDAC (80) in parallel with a capacitor (82) and a second MDAC (84) in a feedback loop. By digitally controlling the internal resistance of the MDACs, the magnitude of a feedback signal and its RC time constant are digitally adjusted. A magnetic field sensor (90) measures the resultant gradient magnetic field profile. An iterative adjustment computer (92) compares the measured and preselected gradient magnetic field profiles and iteratively adjusts the MDACs to optimize the conformity therebetween. The calibration circuits are enabled only during a radio frequency transmission or receipt. Between radio frequency transmissions and reception, bypass switches (114, 116) bypass the calibration circuits to conserve electrical power.
REFERENCES:
patent: 3792345 (1974-02-01), Hawkins et al.
patent: 4005358 (1977-01-01), Foner
patent: 4300096 (1981-11-01), Harrison et al.
patent: 4386318 (1983-05-01), Burbank et al.
patent: 4585995 (1986-04-01), Flugan
patent: 4670716 (1987-06-01), Kunz
patent: 4680547 (1987-07-01), Leue et al.
patent: 4698591 (1987-10-01), Glover et al.
"Noise Pulse Generator for Nuclear Magnetic Resonance (NMR) Measurements of Self Diffusion According to Pulse Gradient Method" by Skirda, et al., Inst. & Exp. Tech., vol. 19, No. 3, (1976).
"Simulator for Video Pulse Signals with Specified Envelope Form" by B. E. Ryshchar, Pribory Tekhnika Eksperimenta, No. 1, pp. 145-148, Jan.-Feb. 1981.
"NMR Imaging: Image Recovery Under Magnetic Fields with Large Non-Uniformities" by Hutchison, et al., The Institute of Physics, 1978, pp. 217-221.
Holland G. Neil
Stauber John R.
Levy Stewart J.
O'Shea Kevin D.
Picker International Inc.
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