This study reports the first measurement of the relative cerebral metabolic rate of oxygen utilization (rCMRO(2)) during functional brain activation with sufficient temporal resolution to address the dynamics of blood oxygen level-dependent (BOLD) MRI signal. During rat forepaw stimulation, rCMRO(2) was determined in somatosensory cortex at 3-sec intervals, using a model of BOLD signal and measurements of the change in BOLD transverse relaxation rate, the resting state BOLD transverse relaxation rate, relative cerebral blood flow (rCBF), and relative cerebral blood volume (rCBV). Average percentage changes from 10 to 30 sec after onset of forepaw stimulation for rCBF, rCBV, rCMRO(2), and BOLD relaxation rate were 62 +/- 16, 17 +/- 2, 19 +/- 17, and -26 +/- 12, respectively. A poststimulus undershoot in BOLD signal was quantitatively attributed to the temporal mismatch between changes in blood flow and volume, and not to the role of oxygen metabolism. Magn Reson Med 42:944-951, 1999.
Copyright 1999 Wiley-Liss, Inc.