In vivo short echo time H-1-magnetic resonance spectroscopic imaging (MRSI) of the temporal lobes

Two different methodologies for obtaining PRESS-localized magnetic resonanc e spectroscopic imaging (MRSI) data from the mesial and lateral temporal lo bes were investigated. The study used short echo times (30 ms) and long rep etition times (3000 ms) to minimize relaxation effects. Inhomogeneity and s pectral distortions from the proximity of the temporal bones precluded the attainment of consistently good-quality data from both temporal lobes at on ce. Even when the right and left temporal lobes were studied separately, di stortions often disturbed spectra from the anterior lateral temporal lobe. Quantitative analysis using LCModel was therefore performed only on the pos terior lateral temporal lobe, and the posterior, middle, and anterior mesia l temporal lobe. No significant left-right differences in metabolite conten t were found in a series of 10 controls. Significantly higher concentration s of myoinositol and choline were found in the anterior mesial temporal lob e, even when grey matter content was included as a covariate. The concentra tion of N-acetyl aspartate plus N-acetyl aspartyl glutamate (NAc) was not f ound to vary significantly along the length of the hippocampus. The previou sly observed lower anterior ratios of NAA to creatine plus choline (NAA/(Cr + Cho) may instead have been due to higher anterior choline. Large differe nces in metabolite concentrations were seen between posterior lateral tempo ral lobe (predominantly subcortical white matter) and the posterior mesial temporal lobe, most notably lower creatine, glutamate/glutamine, and myo-in ositol, and higher NAA/(Cr + Cho) in the lateral than mesial temporal lobe. This pattern was similar to that previously seen for grey/white matter dif ferences in the frontal, parietal and occipital regions. (C) 2001 Academic Press.