Optical properties of brain tissue

A rigorous technique using a Monte Carlo model has been developed to determine the optical properties of biological tissue from goniometer and integrating sphere measurements. Using these techniques, the wavelength dependence of the phase function, g-value, absorption coefficient, scattering and reduced scattering coefficient were determined for postmortem neonate and adult human brain tissue over the wavelength range of 500 to 1000 nm. Single scattering phase functions as a function of wavelength have been measured using a goniometer system and optically thin tissue slices. Spectra for the absorption and scattering coefficients have been determined from a set of integrating sphere measurements, using a white light source and a CCD spectrometer. The integrating sphere data were analyzed using a novel Monte Carlo inversion technique, which makes use of the measured phase functions and which takes into account the effects of sample geometry and the angular dependence of specular reflection. This method overcomes some of the problems and shortfalls of the analytical techniques which employ Kubelka Munk or diffusion theory. The reduced scattering coefficients for all types of brain tissue showed a linear decrease with increasing wavelength. The wavelength dependence of the scattering coefficient and the phase function is shown to be considerable, and cannot be neglected.