High-speed quantitative optical imaging of absolute metabolism in the rat cortex

Abstract

Quantitative measures of blood flow and metabolism are essential for improved assessment of brain health and response to ischemic injury. In this report, we demonstrate a multimodal technique for measuring the cerebral metabolic rate of oxygen (CMRO2) in the rodent brain on an absolute scale (M O2 / min). We use laser speckle imaging (LSI) at 809 nm and spatial frequency domain imaging (SFDI) at 655 nm, 730 nm, and 850 nm to obtain spatiotemporal maps of cerebral blood flow (CBF), tissue absorption (a), and tissue scattering (s). Knowledge of these three values enables calculation of a characteristic blood flow speed, which in turn is input to a mathematical model with a \"zero-flow\" boundary condition to calculate absolute CMRO2. We apply this method to a rat model of cardiac arrest (CA) and cardiopulmonary resuscitation. With this model, the zero-flow condition occurs during entry into CA. The CMRO2 values calculated with our method are in good agreement with those measured with magnetic resonance (MR) and positron emission tomography (PET) by other groups. Our technique provides a quantitative metric of cerebral metabolism that can potentially be used for comparison between animals and longitudinal monitoring of a single animal over multiple days, to assess differences in baseline metabolism and track recovery of metabolism in survival studies following ischemia and reperfusion.