Steady-state reflectance spectroscopy in the P-3 approximation

The Green's function of the steady-state radiative-transport equation is de rived in the P-3 approximation for isotropic sources. It is demonstrated th at the P-3 approximation models the radiance in highly absorbing media or c lose to sources more accurately than does diffusion theory. Boundary condit ions consistent with the P-3 approximation are also developed for semi-infi nite media bounded by a nonscattering medium. Expressions for the reflectan ce remitted from media interrogated by a normally incident pencil beam are derived and fitted to simulated and experimental reflectance data from medi a having optical properties typical of biological tissue. The reconstructed optical properties are accurate to within +/-10% in absorption and scatter ing for source-detector separations as small as 0.43 mm and albedos as low as 0.59. Methods for simplifying these expressions given some a priori know ledge of the scattering phase function are discussed. (C) 2001 Optical Soci ety of America.