Analysis of light propagation in adult head model by direct hybrid Monte Carlo-diffusion method

The development of a model to calculate light propagation in the head is essential for brain function measurement by near-infrared spectroscopy and imaging. The light propagation in the head is affected by low-scattering cerebrospinal fluid layer surrounding the brain although the diffusion equation is no longer valid in non- or low-scattering regions. In this study, the light propagation in a circle model and realistic head model is calculated by the direct hybrid Monte Carlo-diffusion method (DHMDM). The light propagation in the highly scattering medium is calculated by the diffusion theory and that in the low-scattering CSF is predicted by Monte Carlo method. The results by the DHMDM are validated by those by Monte Carlo simulation. The results for the circle and realistic head models suggest that non-smoothness of the CSF boundary affects the light propagation in the brain.