Quantitative proton magnetic resonance spectroscopic imaging: Regional variations in the corpus callosum and cortical gray matter

Purpose: To evaluate regional variations of metabolite concentrations in normal adult brain cortical gray matter regions, and the genu and splenium of the corpus callosum, using proton magnetic resonance spectroscopic imaging (MRSI). Materials and Methods: Quantitative, multislice proton MRSI (TR/TE = 2000/280 msec) was performed in 12 normal human volunteers (age = 39 ± 6 years, 7 male). Metabolite concentrations in selected cortical gray matter regions and the corpus callosum were estimated using the phantom replacement methodology. Results: Frontal and parietal gray matter (PGM) showed strong differences in choline-containing compound (Cho) concentrations; in particular, Cho was higher in mesial frontal gray matter than in both dorsolateral prefrontal cortex (P < 0.0005) and PGM (P < 0.004). In contrast, both N-acetylaspartate (NAA) and creatine (Cr) were relatively uniformly distributed in the cortical gray matter regions evaluated. Significant metabolic differences were found between the genu and splenium of the corpus callosum. Cho concentrations were significantly higher in genu than splenium (P < 0.005). while Cr was lower (P < 0.004). NAA showed a trend to be higher in the splenium than the genu (P = 0.05). Conclusion: Metabolite concentrations, particularly Cho, showed strong regional variations both within cortical gray matter regions and between the genu and splenium of the corpus callosum. Mesial frontal regions showed the highest Cho signals. Differences in spectra presumably reflect underlying changes in structure and cellular composition. Normal spectral variations should always be considered when evaluating pathology within those brain regions.