Simulations for modeling the photothermal response of nerve tissue

Optical nerve stimulation (ONS) using infrared laser radiation is a technique developing as a potential alternative to electrical stimulation of nerve tissue. This preliminary study proposes and explores a computer simulation tool for numerically optimizing laser and surface scanning parameters including laser power and surface scanning speed to be used in laser scanning subsurface ONS. This tool consisted of three parts, including the Monte Carlo simulations for generating laser energy distribution in the tissue sample, the laser-scanning model by moving the heat source at the surface, and the thermal transfer simulations to calculate the tissue temperature. In the simulations, the laser wavelength of 1490 nm was used and the surface scan was performed on both x and y axes. In addition, the tissue model was constructed in such a way that the nerve tissue extends over the y-axis. As a result of calculations, the nerve tissue temperature map was produced as a function of laser power and surface scanning speed. According to the temperature map, the optimal laser power to reach the nerve temperature at 43 degrees C was estimated to be 15 mW at the scanning speeds of 1.2 mm/s in the x-axis and 1.0 mm/s in the y-axis. With further development this simulation tool may hold promise in the development of an optical stimulus device.