In vivo detection and quantification of scalar coupled H-1 NMR resonances

In vivo H-1 nuclear magnetic resonance (NMR) spectroscopy is an important t ool in characterizing the metabolic status of brain tissue. Changes in abso lute concentrations of individual metabolites, like lactate and gamma -amin obutyric acid (GABA), are important markers associated with specific brain diseases. The absolute quantification of metabolites by in vivo H-1 NMR is not a straightforward task, because a large number of metabolites are reson ating in a small spectral region leading to severe spectral overlap. Furthe rmore, in vivo H-1 NMR is complicated by the need for complete three-dimens ional spatial localization and excellent water suppression. The response of scalar-coupled spin systems to typically employed in vivo H-1 NMR sequence s can be especially complicated. This article will review the complications of detecting and quantifying scalar-coupled spin-systems by in vivo H-1 NM R. The characteristics and consequences of scalar coupling will be describe d. The scalar coupling can be intelligently used to discriminate scalar-cou pled resonances from overlapping (uncoupled) resonances by spectral editing . However, in many cases, the scalar coupling introduces complications aris ing from spatial localization and water suppression. The effect of typical in vivo H-1 NMR sequences on scaler-coupled resonances will be analyzed in detail. Finally, examples of spectral editing of GABA, lactate, and glucose will be given to describe some of the practical considerations involved wi th in vivo H-1 NMR. (C) 2001 John Wiley & Sons, Inc.