NMR Measurement of Brain Oxidative Metabolism in Monkeys Using 13C-Labeled Glucose Without a 13C

We detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U-13C6]glucose, using a simple 1H PRESS sequence without 13C editing or decoupling. Point-resolved spec-troscopy (PRESS) spectra revealed decreases in 12C-bonded pro-tons, and increases in 13C-bonded protons of glutamate. To take full advantage of the simultaneous detection of 12C- and 13C-bonded protons, we implemented a quantitation procedure to properly measure both glutamate C4 and C3 enrichments. This procedure relies on LCModel analysis with a basis set to account for simultaneous signal changes of protons bound to 12C and 13C. Signal changes were mainly attributed to 12C- and 13C-bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm3 voxel centered in the monkey brain on a whole-body 3 Tesla system (VTCA 0.55 0.04 mol.g1.min1, N 4). This work demonstrates that oxida-tive metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a 13C radiofrequenc