Spatial mapping of the chemical shift in NMR



In many biological systems, nuclear magnetic resonance chemical-shift studies of 31P, 13C, and 1H can be of great value as a means of studying metabolic processes in vivo. This information is likely to be of great clinical value in the diagnosis of disease and in the study and monitoring of the effect of drug treatment. This paper discusses two new techniques, based on the echo-planar imaging (EPI) method. One is the echo-planar shift mapping (EPSM) technique and the other is a hybrid projection reconstruction-echo-planar (PREP) method. Both methods may be used to obtain complete chemical-shift spectra at each point of a specified grid in a chosen plane through the subject. A major attraction of the EPSM method is the very high speed at which this information is obtained. The major attraction of the PREP hybrid method is its simplicity. Both techniques have the advantage of speed and efficiency over both the point-by-point topical magnetic resonance (TMR) and 3D Fourier transform approaches. The new mapping techniques may also be used to measure magnetic field spatial inhomogeneities, caused by either the presence of magnetic material or simply nonalignment of the magnet.