In vivo detection and quantification of scalar coupled1H NMR resonances

Abstract

In vivo1H nuclear magnetic resonance (NMR) spectroscopy is an important tool in characterizing the metabolic status of brain tissue. Changes in absolute concentrations of individual metabolites, like lactate and γ-aminobutyric acid (GABA), are important markers associated with specific brain diseases. The absolute quantification of metabolites by in vivo1H NMR is not a straightforward task, because a large number of metabolites are resonating in a small spectral region leading to severe spectral overlap. Furthermore, in vivo1H NMR is complicated by the need for complete three-dimensional spatial localization and excellent water suppression. The response of scalar-coupled spin systems to typically employed in vivo1H NMR sequences can be especially complicated. This article will review the complications of detecting and quantifying scalar-coupled spin-systems by in vivo1H NMR. The characteristics and consequences of scalar coupling will be described. The scalar coupling can be intelligently used to discriminate scalar-coupled resonances from overlapping (uncoupled) resonances by spectral editing. However, in many cases, the scalar coupling introduces complications arising from spatial localization and water suppression. The effect of typical in vivo1H NMR sequences on scalar-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 with in vivo1H NMR. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 32–76, 2001