Quantitative proton MR spectroscopic imaging of normal human cerebellum and brain stem

Quantitative, multislice proton MR spectroscopic imaging (MRSI) was used to investigate regional metabolite levels and ratios in the normal adult human posterior fossa. Six normal volunteers (36 ± 3 years, five male, one female) were scanned on a 1.5 T scanner using multislice MRSI at long echo time (TE 280 msec). The entire cerebellum was covered using three oblique-axial slice locations, which also included the pons, midbrain, insular cortex, and parieto-occipital lobe. Concentrations of N-acetylaspartate (NAA), choline (Cho), and creatine (Cr) were estimated using the phantom replacement technique. Regional variations of the concentrations were assessed using ANOVA (P < 0.05). High-resolution MRSI data was obtained in all subjects and brain regions examined. Metabolite concentrations (mM) (mean ± SD) were as follows: cerebellar vermis: 2.3 ± 0.4, 8.8 ± 1.7 and 7.6 ± 1.0 for Cho, Cr, and NAA respectively; cerebellar hemisphere: 2.2 ± 0.6, 8.9 ± 2.1, 7.5 ± 0.8; pons 2.2 ± 0.5, 4.3 ± 1.1, 8.3 ± 0.9; insular cortex, 1.8 ± 0.5, 7.8 ± 2, 8.0 ± 1.1, parieto-occipital gray matter, 1.3 ± 0.3, 5.7 ± 1.1, 7.2 ± 0.9, and occipital white matter, 1.4 ± 0.3, 5.3 ± 1.3, 7.5 ± 0.8. Consistent with previous reports, significantly higher levels of Cr were found in the cerebellum compared to parietooccipital gray and occipital white matter, and pons (P < 0.0001). NAA was essentially uniformly distributed within the regions chosen for analysis, with the highest level in the pons (P < 0.04). Cho was significantly higher in the cerebellum and pons than parieto-occipital gray and occipital white matter (P < 0.002) and was also higher in the pons than in the insular cortex (P < 0.05). Quantitative multislice MRSI of the posterior fossa is feasible and significant regional differences in metabolite concentrations were found.