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

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.