A constant gradient experiment for chemical-shift imaging

Following the rapid development of medical imaging, there has been in recent
years a growing interest in obtaining spatially resolved NMR spectra. This was
achieved by shaping either the constant magnetic field, & (I), or the rf field (2)
using surface coils, in such a way that the resonance conditions are obeyed only
within a small region of the sample. In another method, a selective rf pulse may be
applied in the presence of a field gradient, exciting only a certain chemically shifted
signal. Bendel et al. (4) have obtained a spatial distribution of 31P metabolites using a projection reconstruction on separate resonance lines. A similar procedure was used for ‘H and 13C imaging (5).