Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1985-12-31
1988-01-19
Levy, Stewart J.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324312, 324320, G01R 3320
Patent
active
047206799
ABSTRACT:
A shimming magnetic field control (22) causes shimming magnetic fields for improving uniformity of a main magnetic field generated by main magnets (10). A resonance excitation control (32) selectively applies a resonance excitation pulse (34) and inversion pulse (36) for inverting the spin magnetization of water and lipid dipoles. A phase sensitive detector (30) selectively receives resonance signal components which are transformed by a transform algorithm (70) into a real image (72) and an imaginary image (74). The inversion pulse (36) is shifted by a time such that the water and lipid spin magnetizations are out of phase by a predetermined amount. With a 90.degree. phase difference, the real image represents water and the imaginary represents lipid. A phase image (80) is derived from a reference image pair (76, 78). A phase unwrap circuit (82) removes ambiguities attributable to the spin magnetizations becoming dephased by multiples of 2.pi. to create a phase map (84). A shim adjustment circuit (94) measures uniformity of the phase map and causes the shim field control circuit (22) to adjust the shimming magnetic fields to optimize the measured uniformity. The phase map is inversely transformed (100) to generate a field map (102) indicative of geometric distortion. A geometric distortion correction circuit (106) selectively interpolates values in the real and imaginary images in accordance with the field map to correct the image for geometric distortion.
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Haacke E. Mark
Hahn Janice E.
Linga Nagarjuna R.
Patrick John L.
Levy Stewart J.
O'Shea Kevin D.
Picker International Inc.
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