Experimental approaches to image localized human31P NMR spectroscopy

Abstract

Experimental procedures for obtaining localized ³¹P NMR spectra of humans by means of the ISIS sequence are discussed in detail. The technique is optimized for use with volume coils and with surface coils in order to measure localized ³¹P NMR spectra ofdifferent tissues and organs. Selective frequency-modulated (FM) inversion and excitation pulses are applied for optimal inversion or excitation despite B1 inhomogeneity. Pulse imperfection may lead to spurious signal contributions from outside the selected volume; this contamination is reduced by using long pulse intervals, by properly ordering the ISIS acquisitions, and by using FM excitation pulses. Simultaneous measurement of multiple volumes was implemented by including an additional selective inversion pulse, and an extension of the ISIS addition/subtraction scheme. Localized T1 measurements with surface coils are implemented by using a B1-insensitive inversion pulse in the inversion recovery sequence. The quantitative reproducibility of localized ³¹P NMR spectra was verified. Absolute metabolite concentration can be determined after a suitable calibration of the ³¹P NMR spectrum. Localized shimming is required to obtain localized ³¹P NMR spectra of excellent spectral resolution. This is done by monitoring the ¹H NMR signal from water by a single-shot localization technique. The techniques discussed can be applied to obtain spectra of brain, liver, heart, and other organs. ³¹P NMR spectra of intracranial tumors demonstrate its applicability in the examination of patients. © 1989 Academic Press. Inc.