Fig 1.

Enhanced neuronal contrast through selective ¹³C enrichment. With noninvasive ¹³C MR spectroscopy, it is possible to separately evaluate glial metabolism by use of the precursor 1-¹³C acetate (left panel), which is selectively transported into astrocytes and metabolized to glutamate (Glu) and glutamine (Gln) enriched in carbon 5 (C5). Neuronal metabolism favors ¹³C glucose (GLc, right panel), which is also converted to glutamate and glutamine, enriched in carbon 2 (C2), as well as carbons 3 and 4 (C4) (not shown). Both acetate and glucose are metabolized to ¹³C bicarbonate (HCO₃, left panel), respectively quantifying glial and neuronal tricarboxylic acid (TCA) cycle rates of the intact human brain. Oral Ac indicates administered load of 1-¹³C enriched sodium acetate, followed 80-100 min later by enrichment of cerebral metabolites as indicated; mins, minutes; Gln, glutamine; Asp, aspartate; Cr, creatine; Cho, choline; NAA, N-acetylaspartate.