In vivoestimation of light scattering and absorption properties of rat brain using single reflectance fiber probe during cortical spreading depression

Izumi Nishidate,Keiichiro Yoshida,Satoko Kawauchi,Manabu Sato,Shunichi Sato,Chiharu Mizushima

doi:10.1117/12.2003049

Abstract

Diffuse reflectance spectroscopy using fiber optic probe is one of most promising technique for evaluating optical properties of biological tissue. We present a method determining the reduced scattering coefficients μs’, the absorption coefficients μa, and tissue oxygen saturation StO2 of in vivo brain tissue using single reflectance fiber probe with two source-collector geometries. In this study, we performed in vivo recordings of diffuse reflectance spectra and the electrophysiological signals for exposed brain of rats during the cortical spreading depression (CSD) evoked by the topical application of KCl. The time courses of μa in the range from 500 to 584 nm and StO2 indicated the hemodynamic change in cerebral cortex. Time courses of μs’ are well correlated with those of μa in the range from 530 to 570 nm, which also reflect the scattering by red blood cells. On the other hand, increases in μs’ at 500 and 584 nm were observed before the profound increase in μa and they synchronized with the negative DC shift of the local field potential. It is said that the DC shift coincident with a rise in extracellular potassium and can evoke cell deformation generated by water movement between intracellular and extracellular compartments, and hence the light scattering by tissue. Therefore, the increase in μs’ at 500 and 584 nm before the profound increase in μa are indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological conditions of in vivo brain.

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