WET, A T-1-INSENSITIVE AND B-1-INSENSITIVE WATER-SUPPRESSION METHOD FOR IN-VIVO LOCALIZED H-1-NMR SPECTROSCOPY

Suppression of the water signal during H-1 magnetic resonance spectroscopy by repeated sequences of a frequency-selective radiofrequency pulse and a gradient dephasing pulse requires nulling of the longitudinal component of the water magnetization and is therefore affected by T-1 relaxation, RE-pulse flip angles (which depend on B-1), and sequence timing. In in vivo applications, T-1 and B-1 inhomogeneity within the sample may cause spatially inhomogeneous water suppression. An improved water-suppression technique called WET (water suppression enhanced through T-1 effects), developed from a Bloch equation analysis of the longitudinal magnetization over the T-1 and B-1 ranges of interest, achieves T-1- and B-1-insensitive suppression with four RF pulses, each having a numerically optimized flip angle. Once flip angles have been optimized for a given sequence, time-consuming flip-angle adjustments during clinical examinations are eliminated. This water-suppression technique was characterized with respect to T-1 variations, B-1 variations, off-resonance effects, and partial saturation effects and was compared to similar techniques. Effective water suppression has been achieved with this new technique in single-voxel spectroscopy examinations of more than 50 brain tumor patients at 1.5 T. (C) 1994 Academic Press, Inc.