In Vivo Diffuse Optical Spectroscopy and Imaging of Blood Dynamics in Brain

In this paper we provide a cursory review on diffuse optical probes and their relevance to the investigation of human tissues. Then we describe a recent instrument we have built and used to study variations of blood flow, hemoglobin concentration, and blood oxygen saturation in the functioning rat brain. The instrument combines two novel optical methodologies. Diffuse correlation spectroscopy monitors changes in the cerebral blood flow by measuring the optical phase-shifts caused by moving blood cells. Diffuse near-infrared absorption spectroscopy concurrently measures tissue absorption at two wavelengths to determine hemoglobin concentration and blood oxygen saturation in the same tissue volume. The optical probe is non-invasive and was employed through the intact skull. The utility of the technique is demonstrated in vivo by measuring the temporal changes in the regional vascular dynamics of rat brain during hypercapnia and hypoxia.