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

Significance: Quantitative measures of blood flow and metabolism are essential for improved assessment of brain health and response to ischemic injury. Aim: We demonstrate a multimodal technique for measuring the cerebral metabolic rate of oxygen (CMRO2) in the rodent brain on an absolute scale (mu MO2/min). Approach: We use laser speckle imaging at 809 nm and spatial frequency domain imaging at 655, 730, and 850 nm to obtain spatiotemporal maps of cerebral blood flow, tissue absorption (mu(a)), and tissue scattering (mu(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. Results: The CMRO2 values calculated with our method are in good agreement with those measured with magnetic resonance and positron emission tomography by other groups. Conclusions: Our technique provides a quantitative metric of absolute cerebral metabolism that can potentially be used for comparison between animals and longitudinal monitoring of a single animal over multiple days. Though this report focuses on metabolism in a model of ischemia and reperfusion, this technique can potentially be applied to far broader types of acute brain injury and whole-body pathological occurrences. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

Automated summary

This study demonstrates a multimodal technique for measuring absolute CMRO2 in the rodent brain. By using laser speckle imaging and spatial frequency domain imaging to obtain spatiotemporal maps of cerebral blood flow, tissue absorption, and tissue scattering, combined with a mathematical model, absolute CMRO2 values can be calculated. The results obtained with this method in a rat model of cardiac arrest are consistent with those obtained through magnetic resonance and positron emission tomography.