Image formation by nuclear magnetic resonance: The sensitive-point method

TLDR

The method uses time‑varying magnetic‑field gradients and continuous phase‑alternated RF pulses to confine and monitor spatial sensitivity in a standard pulsed NMR spectrometer, then directly plots the phase‑detected resonance signal on an xy plotter as the sensitive region scans the sample, with analysis based on Bloch equations. The technique yields a spatial resolution of approximately 0.3 mm and delivers direct, detailed interior images of heterogeneous samples.

Abstract

An image formation method, using nuclear magnetic resonance techniques, has been developed which provides direct and detailed information on the interior details of heterogeneous samples. Time-dependent magnetic field gradients are used to limit and control the region of spatial sensitivity of a standard pulsed NMR spectrometer. A continuous string of intense phase-alternated rf pulses is used to provide a continuous monitor of the nuclear magnetization. The image is produced by directly plotting the phase-detected resonance signal on a xy plotter as the limited region of spectrometer sensitivity is scanned through the sample. An analysis of the method in terms of the phenomenological Bloch equations, a description of the experimental method, and a representative selection of images are presented. A spatial resolution of about 0.3 mm has been achieved.