Assessment of glutamate and glutamine contribution to in vivo N-acetylaspartate quantification in human brain by 1H-magnetic resonance spectroscopy

N-Acetylaspartate (NAA) is one of the most important metabolites detectable by brain H-1-MRS being considered an index of neuronal integrity. At the low magnetic field used in most clinical settings beta,gamma-glutamate/glutamine (GIx) resonances are very close and partially overlap the methyl-NAA resonance interfering with NAA quantification especially at low TE and in the presence of increased GIx signals. NAA overestimation due to Glx on a set of model solutions containing NAA, glutamate, and glutamine in variable amounts was evaluated and the result tested in vivo in six healthy controls and five age- and sex-matched patients with hepatic encephalopathy (HE), the latter having an increased GIx content. A method to assess in vivo the NAA overestimation caused by GIx is proposed. A perfect match was obtained between the assessment of GIx contamination on the NAA of healthy controls and that obtained on the model solutions. However, a substantial difference in NAA overestimation was found between controls and HE patients that cannot be explained by our model. An interpretative hypothesis is provided. Magn Reson Med 54:1333-1339, 2005. (c) 2005 Wiley-Liss, Inc.