Determination of the optical properties of turbid media by measurements of the spatially resolved reflectance considering the point-spread function of the camera system.

The radial dependence of the diffuse reflectance from a turbid medium that is due to a point source is basically influenced by the absorption and reduced scattering coefficients. A system consisting of a HeNe laser source and a CCD camera is described for making remote measurements of the spatially resolved diffuse reflectance. Liquid tissue phantoms were made of Intralipid and trypan blue to validate the experimental setup. We show that for the correct determination of the optical properties of the tissue phantoms, the point-spread function (PSF) of the camera system has to be considered. Convolving the PSF with a solution of the diffusion equation, the absorption and reduced scattering coefficients of the tissue phantoms could be determined with an average error of 8% in the absorption coefficient and 4% in the reduced scattering coefficient, whereas without convolution, the errors were considerably larger, especially for large optical parameters.