The determination of optical properties of turbid, absorbing media is of increasing interest in both reseach and industry. In order to estimate the optical properties from steady-state diffuse reflectance measurements sophisticaed analytical models have been introduced. These models, which are based on diffusion approximation, properly explain the diffuse reflectance of low absorbing media in the so-called asymptotic region, which means some mean free paths away from strong sources. It should be noted however, the nearer the sourcea nd the stronger the medium absorbs, the accuracy of these models decrease rapidly. For high spatial resolution, i.e. the use of a small oprical probe, the restriction on the asymptotic region becomes crucial. This restriction can be overcome by means of Monte Carlo simulations, which are not confined to low absorption and the asymptotic region. Given an experimental set-up, i.e. given the radius and the direction of the incident pencil beam and the shape of the collection area, the reflectance can be simulated. Thus a numerical model can be established relating the input parameters - anisotrophy factor, absorption and scattering coefficient - to the diffuse reflectance according to the Monte Carlo simulations.
The advantages of this numerical model are a large area of validity in respect of anisotrophy factor, amount of absorption and source distance, and the possibility to adapt the model easily to an even more complex experimental set-up.