Measurement of Absolute CMRO2 by Simultaneous Hypercapnic and Hyperoxic Calibration of fMRI Signal

Richard G. Wise¹, Ashley D. Harris¹, Alan J. Stone¹, Kevin Murphy¹

We present a method for measuring absolute cerebral metabolic oxygen consumption (CMRO₂). ASL and BOLD FMRI were combined with intermittent hyperoxia applied at four different levels of hypercapnia, facilitated by end-tidal forcing. A BOLD signal model permitted estimation of venous oxygenation which when combined with CBF gave estimates CMRO₂ in regions of interest and voxel-wise. The sensitivity of the hyperoxia induced BOLD signal changes to CBF induced changes in CBV reduced the need to assume vascular parameters in the BOLD signal model, potentially expanding the range of (patho)physiological conditions in which the method could be applied.