FEA modeling of temperature elevation in neural tissue illuminated by a laser: Transient effects

The primary effect of light penetration into neural tissue is the heat generated inside the volume as a result of photons being absorbed. The spatio-temporal distribution of the temperature increase in the tissue is not very intuitive since it depends on many parameters including the optical properties of the medium and the thermal time constant that depends on the size of the volume being illuminated. The main objective of this study was to take advantage of finite element analysis method to gain some insights into the spatio-temporal variations in the temperature distribution inside the tissue while being illuminated by a train of laser pulses. The simulation results suggest that the transient temperature changes can be significantly large especially near the surface of laser beam entry at low pulse frequencies. Considering the time constants indicated by the simulations, the critical pulse frequencies above which extreme temperature oscillations, especially near the surface, can be avoided is in the order of hundreds of Hertz.