Finite Element Method (FEM) Modeling of Laser-Tissue Interaction during Hair Removal

Abstract

In this study, a comprehensive and realistic model of laser light interaction with skin and hair was constructed. The model was applied to study the characteristics of laser-tissue interaction for the deeply penetrating Nd:YAG laser. Three types of finite element method (FEM) models were developed. In the first model, the hair shaft grew straight out of the follicle; in the second model, it grew at a variable angle; and in the third model, an array of hair was considered. The transport equation and heat diffusion equation were solved with the mesh-based Monte Carlo method and partial differential equations, respectively. The results of the simulations indicated that the area of necrosis increased with increasing fluence; cooling had a limited effect on the extent of necrosis, particularly at a fluence of 80 J/cm2. The thermal damage to hair follicles on the periphery of an irradiated array of hair may be insufficient for achieving necrosis. The pulse itself and the short cooling-down period after the pulse contributed the most to the final thermal damage to the hair follicle. The FEM modeling of laser-tissue interaction has proven to be a useful tool for studying the influence of different therapeutic parameters on the resulting hair and skin damage.

GPU Adding-Doubling Algorithm for Analysis of Optical Spectral Images

“…Our approach has an obvious limitation in that it operates under assumptions outlined by Prahl et al [13], including the absence of time dependence, a geometric model comprising uniform layers of finite thickness extended infinitely parallel to the surface, uniform scattering and absorbing properties within tissue layers, and uniform illumination by collimated or diffuse light. While these assumptions do not contradict the application of GPU AD to HSI, it may be necessary to resort to the MC method in more complex cases when, for example, a beam would be spreading from a finite source [32].…”

“…In the situation where the bottom layer is the same as the external medium, the boundary conditions are identical on the upper and bottom boundaries; thus, we have R 01 = R 32 , R 10 = R 23 , T 01 = T 32 , and T 10 = T 23 . If the bottom layer is specular or Lambertian, then R 23 = R L , and only matrix R 03 is relevant, as all other matrices R 30 , T 03 , and T 30 are 0.…”

Investigation of Radial and Tangential Stresses Occurring in Epoxy (T300) Material Disc with Different Methods

“…For example, in one study, the effect of transition thickness shear (TTS) stress on the prediction of forming boundary diagrams (FLDS) was studied [13] . In a different study, the stresses occurring in the hair were investigated by the finite element method [14] .…”