Monte-Carlo simulation of light transport for NIRS measurements in tumors of elliptic geometry.

Propagation of light in a highly scattering medium such as biological tissue is difficult to study. For complex geometry and multilayer structures computer simulation has to be used for light transport analysis. A Monte Carlo model of light propagation in tissue has been applied for the purpose of better understanding of the results of near-infrared spectroscopy (NIRS) measurements in experimental tumors. The major objective was to determine the percentage and location of the illuminated area in tumor and to estimate fraction of NIRS signal originating from the underlying tissues. Values of optical parameters used in the model were taken from literature. Tumor shape was approximated with a rotational ellipsoid. Computer simulations were made for two positions of optodes: reflectance and transmittance mode. Results of simulations indicate that in both configurations the majority of signal originates from tumor and not from surrounding tissue. In reflectance mode collected light comes from limited area near the optode whereas in transmittance mode the collected light illuminate almost whole tumor. This difference between the two modes is valid for all tissue parameters.