Monte Carlo simulation of light transport through inhomogeneous tissue

摘要

Abstract: Quantitation of near infrared spectroscopic (NIRS) data requires an accurate knowledge of the effective optical pathlengths within the various components of an inhomogeneous scattering medium. For instance, in the monitoring of cerebral oxygenation by NIRS, the contribution of the overlying tissues such as the skin and the skull to the total optical pathlength must be known. To elucidate this problem a Monte Carlo model of light transport through a heterogeneous scattering and absorbing medium has been developed in which the boundaries of the heterogeneous media are concentric spheres. The inside medium represents brain tissue and the outside medium represent skin and skull. The Monte Carlo model uses an anisotropic scattering phase function and values for absorption coefficient ($mu$-a$/) and scattering coefficient ($mu$-s$/) in each medium that are based upon experimentally measured data. The model follows paths of photons from an input point to their exit on the medium boundary and calculates the total optical pathlength (the differential pathlength DP) and the pathlength in each medium. An analytical proof of the applicability of the Modified Beer-Lambert Law in a heterogeneous medium is also presented and the possible contribution of the overlying tissues of the head to the total NIRS signal is discussed. !40