A three-dimensional modular adaptable grid numerical model for light propagation during laser irradiation of skin tissue

Information regarding energy deposition during laser irradiation of structurally complex biological tissue is needed to understand and improve the results of clinical procedures. A modular adaptive geometry numerical model capable of simulating the propagation of laser light in a wide variety of multiple component tissues has been developed and tested. A material grid array is generated by assigning a value representing a tissue type to each of a large number of small voxels. The grid array is used to indicate optical properties in an existing variable step size, weighted-photon Monte Carlo algorithm that has been modified to account for voxels-to-voxels changes in optical properties. To test the model, simple geometric shapes and optical low coherence reflectometry images of rat skin have been used to create material grids consisting of epidermis, dermis, and blood. The model assumes 1-J/cm² irradiation of the tissue samples with a 1.0-mm diameter uniform beam at 585 nm. Computed results show good quantitative and qualitative agreement with published data. Various effects due to shading and scattering, similar to those suggested in the literature, are noted. This model provides a way to achieve more realistic representation of anatomical geometry as compared to other models, and produces accurate results