Signal Selection in High-Resolution NMR by Pulsed Field Gradients: I. Geometrical Analysis

Abstract

A geometrical description for the selection of coherence transfer pathways in high resolution NMR by the application of pulsed field gradients along three orthogonal directions in space is presented. The response of the spin system is one point of the three-dimensional Fourier transform of the sample volume affected by a sequence of field gradients. The property that a pathway is retained (or suppressed) when a sequence of field gradients is applied is expressed by the property of vectors, representing the pathway and the sequence, respectively, to be orthogonal (or not orthogonal). Ignoring imperfections of RF pulses, and with the exception of sensitivity enhanced experiments and experiments where the relevant coherence order is zero while field gradients are applied, it is shown that at most only half of the relevant pathways, as compared to a phase cycled experiment, are retained when field gradients are used for signal selection.