In vivo cerebrovascular measurement combining diffuse near-infrared absorption and correlation spectroscopies

We combine two near-infrared diffuse optical techniques to study variations of blood flow, haemoglobin concentration, and blood oxygen saturation in t he functioning rat brain. Diffuse correlation spectroscopy (or flowmetry) m onitors changes in the cerebral blood flow, without the use of the principl es of tracer clearance, by measuring the optical phase-shifts caused by mov ing blood cells. Near-infrared absorption spectroscopy concurrently measure s tissue absorption at two wavelengths to determine haemoglobin concentrati on and blood oxygen saturation in this same tissue volume. This optical pro be is non-invasive and was employed through the intact skull. The utility o f the technique is demonstrated in vivo by measuring the temporal changes i n the regional vascular dynamics of rat brain during hypercapnia. Temporal and spatial variations of cerebral blood flow, haemoglobin concentration an d blood oxygen saturation during hypercapnia are compared with other measur ements in the literature, and a quantitative analysis demonstrating the sel f-consistency of our combined observations of vascular response is presente d.