Changes in Arterial Oxygen Tension with Evoked Stimulation in the Rat Somato-sensory Cortex: Implications for Quantitative fMRI

Introduction It is accepted that the BOLD fMRI signal results from changes in the amount and saturation of hemoglobin in a voxel that stem from neurophysiological changes in CBF, CBV and CMRO2 with brain activation. This sensitivity of BOLD fMRI to CMRO2 has been used to quantify the changes in CMRO2 with brain activation (1,2,3). In general, this physiological parameter has been of interest because it is inherent from tissue and, therefore, closer to the activation site, but its quantification relies mostly on the calculation of the venous oxygen saturation under the assumption of a constant and highly saturated arterial oxygenation (~100%). In this work, our goal was to investigate the changes in arterial, tissue and venous oxygen tension and saturation with evoked somato-sensory stimulation in the anesthetized rat using oxygen microelectrodes and deoxy-hemoglobin sensitive optical imaging as a BOLD fMRI surrogate. This data was then used to investigate the impact of these measurements on the quantification of CMRO2 from blood oxygenation data (i.e. BOLD fMRI).