Determination of regional variations and reproducibility in in vivo (1) H NMR spectroscopy of the rat brain at 16.4 T

In vivo 1H NMR spectroscopy was used to obtain the neurochemical profile in the posterior parts of the brain, the cerebellum and the medulla oblongata in comparison to the hippocampus and the thalamus. Using small voxel sizes between 16 and 32 μl to avoid partial volume effects, most metabolites demonstrated significant regional differences except acetate, γ-aminobutyric acid, and phosphorylcholine. Noticeable regional differences in metabolite concentrations were the significant increase of total creatine in the cerebellum and the substantial decrease of taurine in thalamus and medulla oblongata. In particular, the glycine concentration in the medulla oblongata was determined to be 4.37 ± 0.68 μmol/g (Cramér-Rao lower bounds 7%) and thus significantly higher than in the other regions, consistent with findings reported in both in vivo 1H NMR spectroscopy and in vitro biochemical assays. Intraindividual reproducibility and interindividual variability were investigated by acquiring spectra from the thalamus of the same rats in two sessions. No prominent influence on measurement session was observed in metabolite concentrations with coefficients of variations being below 20% in 16 metabolites