Continuous and Longitudinal Monitoring of Cerebral Blood Flow and Metabolism in Freely Moving Rodents

ABSTRACT Continuous and longitudinal measurements of cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMRO2) in response to brain activity allows investigation of underlying excitatory and inhibitory neural responses and holds the key to optimizing novel therapies for neurological disorders and cerebrovascular diseases. Rodents (mice and rats) make up 95% of the animal models to help scientists investigate human diseases. One major challenge in translating animal model findings to humans is the experimental setup difference, particularly anesthesia routinely used in animal studies. Anesthesia impacts neurovascular coupling and cerebral hemodynamics profoundly and interferes with many neurological studies such as behavioral neuroscience, cognitive function, and sleep disorders. A few wearable methods available for cerebral monitoring in conscious rodents require invasive craniotomy and/or implantation of probes on the cortex due to limited penetration/detection depths. Supported by NIH (R21), we have recently developed an innovative, noninvasive, low-cost, fiber-free, near-infrared diffuse speckle contrast flowmetry (DSCF) probe, which affixes on the heads of animals and humans for continuous CBF monitoring. The goal of this proposal is to extend, optimize, and validate this novel technology toward a dual-wavelength diffuse speckle contrast flow-oximetry (DSCFO) system with wearable head probes/stages for simultaneous imaging of CBF, cerebral oxygenation, and CMRO2 in conscious, freely moving rodents. DSCFO uses small near-infrared laser diodes at different wavelengths as focused point sources for deep tissue penetration and a tiny CMOS camera as a 2D detector array to detect spatial dynamic light scattering by intrinsic motions of red blood cells (i.e., CBF) and light attenuations by oxy- and deoxy-hemoglobin absorptions ([HbO2] and [Hb]). Combination of CBF, [HbO2], and [Hb] enables derivation of CMRO2 based on established models. The 2D camera array enables high-density imaging of cerebral responses over two hemispheres and at different depths of the rodent head. Importantly, connections between the DSCFO probe and a control device are electrical wires/cables (i.e., fiber-free), thereby offering the promise for continuous cerebral monitoring in freely behaving subjects. After optimizing the DSCFO system using head- simulating phantoms and calibrating it in anesthetized rodents against established techniques, we will evaluate its performance for continuous and longitudinal cerebral monitoring in conscious, freely behaving rodents with or without ischemic stroke insult. While we explore stroke-induced cerebral outcomes in this project, the DSCFO technology is applicable for studying many other neurological disorders and cerebrovascular diseases. In combination with our ongoing R21 studies in humans, completion of this study in rodents will generate a unique noninvasive, low-cost, fast, multiscale, and multimodal brain imaging tool for both neuroscience research and clinical applications. Ultimately, the levels/variations and combinations of CBF, [HbO2], [Hb], and CMRO2 may serve as biomarkers for evaluating outcomes of cerebral pathological conditions and interventions.