Localized proton MRS of the human hippocampus: metabolite concentrations and relaxation times.

Absolute concentrations and proton relaxation times of major metabolites in the human hippocampus were determined with use of fully relaxed, short-echo time STEAM localization sequences at 2.0 T (20 normal adults). Mean metabolite concentrations were 7.6+/-0.9 mM for total Nacetylaspartate (tNAA), 6.9+/-0.8 mM for total creatine (tCr), 2.1+/-0.3 mM for choline-containing compounds (Cho), and 6.2+/-0.9 mM for myo-inositol (Ins). The observation of relatively low tNAA and high Cho and Ins levels compared with cortical gray and white matter corresponds to a lower neuronal density and higher glial density than in the neocortex, in agreement with histologic findings. The data do not support a lateralization of metabolites. T1 and T2 relaxation times were in the range of 1400-1730 and 140-330 msec, respectively, similar to those in other brain regions.