Finite-difference modeling of laser ablation of tissue

Finite-difference modeling offers a flexible approach toward modeling tissue ablation. The model presented here considers optical penetration of the laser, thermal diffusion, water diffusion, surface evaporation, carbonization, and subsurface explosive vaporization. An example simulation considers near-infrared diode laser heating and ablation of a low-absorption nonscattering tissue which has been superficially stained with an absorbing dye (indocyanine green, ICG). Computer simulation illustrates 5 distinct phases of the process: (1) initial heating due to ICG absorption, (2) evaporation with surface clamped at 100°C which desiccates surface layer, (3) heating of surface after desiccation has slowed evaporation, (4) rapid heating after onset of carbonization due to combination of desiccation and heating, and (5) subsurface explosive vaporization which removes a superficial tissue layer and exposes a fresh surface which repeats the above cycle.