Use of Monte Carlo simulations for propagation of light in biomedical tissues.

In problems relating to light propagation in biomedical tissues, the tissue is generally modeled as a turbid medium and Monte Carlo (MC) simulation is employed to compute quantities such as diffuse reflectance, fluence, and transmittance. Two prescriptions are available in the literature for MC simulations. The first prescription considers all input quantities, including phase function, as an average over the particle size distribution, and the second prescription considers the phase function of each scatterer individually. The two prescriptions have been compared and contrasted in this paper for a given soft tissue model. It is demonstrated that, in general, the two recipes do not yield identical results. The source of this disagreement has been traced.

Volume concentration and size dependence of diffuse reflectance in a fractal soft tissue model.

Employing a fractal model for the particle size distribution, we examine the possibility of relating the size/volume concentration changes in the tissue to its diffuse reflectance. It is noted that for the practically interesting range of fractal dimension values alpha, the curves depicting the variation of diffuse reflectance (the ratio of diffuse reflectance at two suitably chosen source detector separations) with alpha at fixed volume concentration Tv, are single valued. The same is true if alpha is fixed and Tv is varied. This crucial observation shows that it should be possible to identify changes in the size/volume concentration of the tissue from the diffuse reflectance measurement at two source detector separations when either alpha or Tv is a priori known. Similar results have been obtained for ratio of fluence measured at two suitably chosen depths within the tissue.