Measurement of Absolute CMRO2 in the Human Brain with Calibrated FMRI

Richard G. Wise¹, Ashley D. Harris¹, Kevin Murphy¹

We present a method for measuring absolute cerebral metabolic oxygen consumption (CMRO₂). ASL and BOLD FMRI were combined with hypercapnic and hyperoxic respiratory challenges. Under an assumption of iso-metabolism, the BOLD signal calibration parameter (M) established in hypercapnia was used with the hyperoxic BOLD signal changes to estimate the resting venous deoxyhaemoglobin concentration and therefore oxygen extraction fraction and CMRO₂, on a regional basis. This was performed at rest and with continuous visual stimulation. The proposed method may offer a useful marker of cerebral metabolism in health and disease given its non-invasiveness compared to radiotracer methods.