In vivo estimation of light scattering and absorption properties of rat brain using single reflectance fiber probe during anoxic depolarization

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 mu(s)', the absorption coefficients mu(a), and tissue oxygen saturation StO(2) of in vivo brain tissue using single reflectance fiber probe with two source-collector geometries. In the present study, we performed in vivo recordings of diffuse reflectance spectra and the electrophysiological signals for exposed brain of rats during normoxia, hyperoxia, hypoxia, and anoxia. The time courses of mu(a) in the range from 500 to 584 nm and StO(2) indicated the hemodynamic change in cerebral cortex. Time courses of mu(s)', are well correlated with those of mu(a) in the range from 530 to 570 nm, which also reflect the scattering by red blood cells. On the other hand, a fast decrease in mu mu(s)' at 800 nm were observed after the respiratory arrest and it synchronized with the negative deflection of the extracellular DC 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 decrease in mu mu(s)' at 800 after the respiratory arrest is indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological and loss of tissue viability in brain tissue.