NUMERICAL SIMULATION OF THE REFLECTANCE SIGNAL FROM A SHORT-PULSE GAUSSIAN LASER BEAM INCIDENT ON HEALTHY AND MALIGNANT SKIN TISSUE

The application of short-pulse lasers in biomedical diagnosis and therapies has garnered significant attention in recent years. Specifically, for human skin, the reflected laser signal can provide valuable information about tissue health, as the optical properties of healthy and malignant tissues differ, leading to distinguishable signals. In this study, a short-pulse Gaussian laser beam is applied to diagnose cutaneous tumors using two-dimensional axisymmetric coordinates. This method extends previous studies that utilized one-dimensional approximations or top-flat laser beams. The transient radiative transfer equation is solved using the discrete ordinates method. Scattering is described by the Henyey-Greenstein phase function. A second-order Runge-Kutta method is used for time discretization, while spatial discretization is handled using the finite volume method and the CLAM scheme. The skin is modelled as a multi-layered medium with distinct optical properties for each layer. The temporal variation of the reflected signal from healthy skin tissue is compared to those from tissues with non-melanoma and melanoma carcinomas. Additionally, the variation of the signal with the size of the tumor is investigated. The results show that different skin carcinomas of the same size produce reflected signals of different magnitudes, allowing for their identification, although this becomes more challenging at early growth stages. The reflectance varies with tumor size and growth stage.