Many biological tissues contain cylindrical microstructures, including teeth, muscles and skin. Therefore, the detailed understanding of light propagation in these structures is of great importance for biomedical optics. The transport theory is often used for the numerical calculation of light propagation in biological tissue. The ILM uses the Monte Carlo method to make these calculations.
The directed structure of cylindrical scatterers leads to anisotropic light propagation. These effects, caused by the microstructure of the tissue, have been the object of detailed investigations at the ILM over the last few years. In order to facilitate the investigations, the Monte Carlo methods were expanded to enable the anisotropic propagation of light to be described.
The transport theory is only an approximation of the Maxwell theory, which is exact in the classical sense. Neglecting effects in the transport theory that are determined by the wave nature of light, for example diffraction or interference, can lead to differences. The coupling of these two theories was investigated in greater detail in order enable statements to be made on the validity of the transport theory.
Based on simple models of parallel, infinitely long cylinders, analytical solutions from the Maxwell theory were compared with results from Monte Carlo simulations. Taking into account model-related differences - the results from the Maxwell theory were for example superimposed by diffraction effects caused by the necessary restriction to finite simulation volumes - the two approaches could be directly compared.
This approach enables the assessment of the accuracy of the Monte Carlo method independently of various parameters such as cylinder diameter, concentration of scatterers or refraction indices.