Real-time tracking of brain oxygen gradients and blood flow during functional activation

Abstract

SIGNIFICANCE Cerebral metabolic rate of oxygen ( CMRO 2 ) consumption is a key physiological variable that characterizes brain metabolism in a steady state and during functional activation. AIM We aim to develop a minimally invasive optical technique for real-time measurement of CMRO 2 concurrently with cerebral blood flow (CBF). APPROACH We used a pair of macromolecular phosphorescent probes with nonoverlapping optical spectra, which were localized in the intra- and extravascular compartments of the brain tissue, thus providing a readout of oxygen gradients between these two compartments. In parallel, we measured CBF using laser speckle contrast imaging. RESULTS The method enables computation and tracking of CMRO 2 during functional activation with high temporal resolution ( ∼ 7    Hz ). In contrast to other approaches, our assessment of CMRO 2 does not require measurements of CBF or hemoglobin oxygen saturation. CONCLUSIONS The independent records of intravascular and extravascular partial pressures of oxygen, CBF, and CMRO 2 provide information about the physiological events that accompany neuronal activation, creating opportunities for dynamic quantification of brain metabolism.