Imaging systems

Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system

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324309, G01N 2700

Patent

active

043330533

ABSTRACT:
In known NMR imaging apparatuses it has been the practice to arrange the G.sub.R field gradient, which rotates in the plane of the examined slice, with a zero crossing substantially in the center of the slice and to demodulate at the Larmor frequency at the zero crossing. It is now proposed to demodulate the detected resonance signals at a frequency which, in the presence of the field gradient, is for a part of the plane lying outside the body slice. This may be by arranging the zero-crossing to be outside the slice. In that case it is preferable that the zero-crossing of G.sub.R lies on a straight line (27) maintained tangential to a circle (28) lying outside the body (23) about an axis (24) through the slice. Control may then be by precalculated coil currents or by precalculating fields at probe positions and adjusting the coil currents to give the expected fields.
Alternatively the zero-crossing may be maintained at the center and demodulation may be at a different frequency. It is then desirable also to measure the resonance frequency in the absence of the field gradient across the slice. The resonance signals are then effectively further demodulated at that measured frequency. The effective demodulation is preferably achieved by complex multiplication of the two signals.

REFERENCES:
patent: 4015196 (1977-03-01), Moore
patent: 4021726 (1977-05-01), Garroway
patent: 4070611 (1978-01-01), Ernst
patent: 4115730 (1978-09-01), Mansfield

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