HOMONUCLEAR J-COUPLING EFFECTS IN VOLUME LOCALIZED NMR-SPECTROSCOPY -PITFALLS AND SOLUTIONS

It has been observed that the signal amplitude of multiplet resonances such as the 1H doublet resonance of lactate varies with pulse sequenc e timing when echo-driven volume selective methods such as point resol ved spectroscopy are used. Herein a standard vectorial description is presented for the mechanism of this artifact, which results from the c hemical shift between homonuclear scalar-coupled (i.e., J coupled) nuc lei. The chemical shift causes the extent of a signal phase modulation to vary for different spatial regions of the excited voxel. This vari ation results in spatial interference effects that can lead to marked loss of signal intensity as well as corruption of the size and shape o f the voxel from which signal is obtained. The phenomenon is substanti al at an imaging field of 1.5 T and becomes especially pronounced at h igher field strengths. Several strategies to avoid the artifact are pr ovided.