Measurement of the tricarboxylic acid cycle rate in human grey and white matter in vivo by H-1-[C-13] magnetic resonance spectroscopy at 4.1T

C-13 isotopic labeling data were obtained by H-1-observed/C-13-edited magne tic resonance spectroscopy in the human brain in vivo and analyzed using a mathematical model to determine metabolic rates in human,grey matter and wh ite matter. 22.5-cc and 56-cc voxels were examined for grey matter and whit e matter, respectively. When partial volume effects were ignored, the measu red tricarboxylic acid cycle rate was 0.72 +/- 0.22 (mean +/- SD) and 0.29 +/- 0.09 mu mol min(-1) g(-1) (mean +/- SD) in voxels of -70% grey and -70% white matter, respectively. After correction for partial volume effects us ing a model with two tissue compartments, the tricarboxylic acid cycle rate in pure grey matter was higher (0.80 +/- 0.10 mol min(-1) g(-1); mean +/- SD) and in white matter was significantly lower (0.17 +/- 0.01 mu mol min(- 1) g(-1); mean +/- SD). In H-1-observed/C-13-edited magnetic resonance spec troscopy labeling studies, the larger concentrations of labeled metabolites and faster metabolic rates in grey matter biased the measurements heavily toward grey matter, with labeling time courses in 70% grey matter appearing nearly identical to labeling in pure grey matter.