Simulations of light propagation in biological tissues by considering the modeling of light sources and sensors

Simulations of light propagation in biological tissues are a useful method in detector development for tissue spectroscopy. In practice most attention is paid to the adequate description of tissue structures and the ray trace procedure. The surrounding light source geometry, such as output window, reflector and casing is neglected. Instead, the description of the light source is usually reduced to incident beam paths. This also applies to detectors and further surrounding tissue connected sensor geometry. This paper discusses the influence of a complex and realistic description of the light source and detector geometry with the ray tracing software ASAP (Breault Research Organization). Additionally simulations include the light distribution curve in respect to light propagation through the tissue model. It was observed that the implementation of the geometric elements of the light source and the detector have direct influence on the propagation paths, average photon penetration depth, average photon path length and detected photon energy. The results show the importance of the inclusion of realistic geometric structures for various light source, tissue and sensor scenarios, especially for reflectance measurements. In reality the tissue surrounding sensor geometry has a substantial impact on surface and subsurface reflectance and transmittance due to the fact that a certain amount of photons are prevented from leaving the tissue model. Further improvement allows a determination of optimal materials and geometry for the light source and sensors to increase the number of light-tissue-interactions by the incident photons.