Quantitative proton magnetic resonance spectroscopy was performed in frontal, parietal and occipital white and gray matter of young adults with use of a fully relaxed, short-echo time stimulated echo acquisition mode localization sequence at 2.0 T. Separate concentrations of the neuronal compounds N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) were obtained by user-independent spectral analysis (LCModel). Except for occipital gray matter in which an NAA concentration of 10.1 +/- 1.0 mM correlated with enhanced neuronal density in visual cortex, NAA was found to be homogeneously distributed throughout cortical white and gray matter at a concentration of 8.0-8.9 mM. NAAG concentrations of 1.5-2.7 mM were higher in white matter than levels of 0.6-1.5 mM found in gray matter, contributing up to 25% of total N-acetyl-containing compounds. The frontal to parieto-occipital increase of both gray and white matter NAAG levels is also reflected in the distribution of total NAA.
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