Highly accurate scattering spectra of strongly absorbing samples obtained using an integrating sphere system by considering the angular distribution of diffusely reflected light.

An integrating sphere system has been used to investigate the estimation error in the scattering coefficient for biological tissues. Since the angular distribution of diffusely reflected light from a sample may depend on the sample absorbance, leakage at the entrance port may affect estimates of the scattering coefficient based on measurement of diffuse reflectance. In the present study, the dependence of the angular distribution of the diffusely reflected light on the hemoglobin (Hb) concentration in a sample was investigated. Subsequently, the effect of the entrance port diameter on the error in the scattering coefficient estimated based on diffuse reflectance measurements was evaluated. For a biological tissue phantom, the angular reflectance distribution at a wavelength of 405 nm, at which strong absorption occurred, showed an increasing bias toward specular reflection as the Hb concentration was increased. No such concentration dependence was found at a wavelength of 664 nm, where the absorbance was low. In addition, it was found that the estimation error in the scattering coefficient was reduced for smaller entrance port diameters. Therefore, when attempting to determine the scattering coefficient for strongly absorbing samples, it is necessary to consider both the angular distribution of the diffusely reflected light and the optimal entrance port diameter.