Monte Carlo simulations to investigate light coupling with optical skin phantom

• Autor(a) principal: Fortunato, Thereza Cury
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/76/76132/tde-02092021-160416/
• topic: Distribuição de luz; Fotodiagnóstico; Fototerapias; Light distribution; Meios túrbidos; Monte Carlo eXtreme; Monte Carlo eXtreme; Monte Carlo simulations; Photodiagnosis; Phototherapies; Simulações de Monte Carlo; Turbid media

The effects observed during the light interaction with the most varied biological tissues make light an interesting tool for both diagnostic and therapeutic purposes. For a particular biomedical optical technique to be successful, it is essential to know and understand how the light interacts with the target tissue. Experimental measurements, theoretical modeling and computational simulations are widely used to improve the understanding of how light can interact with a tissue. The Monte Carlo simulations are considered important and reliable tools for detailed studies on the light propagation in tissue. It is known that to analyze the propagation of light in biological tissues we should take into account many factors, such as tissue optical properties, light source characteristics, interface roughness and illuminated tissue composition. In this context, in this thesis we used an optimized computational simulation method, Monte Carlo eXtreme (MCX), to predict the changes in the propagation of 630 nm light beam when a layer of a transparent material with different refraction indexes and thicknesses is added between the air and the surface of a homogeneous turbid medium (human dermis phantom) and a multi-layer (human skin phantom). We explored the effects caused by the transparent material when the light beam angle of incidence was varied and also when multiple sources are combined. Lastly, the material´s refractive index was extrapolated in order to obtain a mirror-like object on the skin phantom surface. The simulations demonstrated that the phantom structures and optical properties, as well as the incident light beam geometry (angle of incidence) highly influence the light propagation, and that using a transparent material between the air and the phantom we can create a more uniform field of illumination, however, the observed effects are also dependent on the material thickness and refractive index. A mirror-like object also led to a significant change in the photon flux. The observed results are due, in large part, to the phenomena of refraction and total internal reflection of the light scattered by the phantom. The presented results showed that MCX is a useful tool for more fundamental studies towards a better understanding on the light propagation in biological tissues according to different irradiation strategies. It can also help to path the way to the personalization of light dosimetry dosimetry in clinics.