Monte-Carlo based simulations of photothermal response of nerve tissue for laser wavelengths of 1455 nm, 1490 nm, 1550 nm

Electrical nerve stimulation (ENS) technique has been tested on nerve mapping devices, which are intraoperative diagnostic tools. However, these technologies suffer from general limitations. Optical Nerve Stimulation (ONS) has been a developing technique as a potential alternative to ENS. This new technique using infrared laser radiation can offer many advantages, including a non-contact stimulation mode, improved spatial selectivity, and elimination of stimulation artifacts. However, the stimulation parameters, including laser power, beam diameter, and surface scanning speed, provide a large variable matrix that must be optimized for consistent and reliable nerve mapping using ONS. This preliminary study explores a computational tool to provide a guiding map for determining optimal stimulation parameters for laser-scanning subsurface ONS. It consisted of three parts: (1) Monte Carlo simulations for generating laser energy distribution in the tissue sample, (2) laser-scanning model by moving the heat source at the surface, and (3) thermal transfer simulations to calculate the tissue temperature. The tool was tested on laser wavelengths of 1455 nm, 1490 nm, and 1550 nm. According to the results of calculations, nerve temperature maps were generated for those wavelengths. Each map demonstrated specific optimal parameter values to reach the nerve activation temperature. Additionally, the results of laser power densities at the lowest scanning speeds of 0.4 mm/s in x-axis and 0.5 mm/s in yaxis showed proximate results with our previous study about ONS on rat model. With further development, this tool may hold promise in the development of an intraoperative optical stimulus device for surgical applications.