NMR measurement of brain oxidative metabolism in monkeys using 13C-labeled glucose without a 13C radiofrequency channel

We detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U-C-13(6)]glucose, using a simple H-1 PRESS sequence without C-13 editing or decoupling. Point-resolved spectroscopy (PRESS) spectra revealed decreases in C-12-bonded protons, and increases in C-13-bonded protons of glutamate. To take full advantage of the simultaneous detection of C-12- and C-13- 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 12 C and 13C. Signal changes were mainly attributed to C-12- and C-13-bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm(3) voxel centered in the monkey brain on a whole-body 3 Tesla system (VTCA = 0.55 0.04 mumol.g(-1).min(-1), N = 4). This work demonstrates that oxidative metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a C-13 radiofrequency (RF) channel. (C) 2004 WileyLiss, Inc.