Monte carlo investigation of the effect of skull optical properties on optical pathlength in the brain

Appropriate modelling of light propagation in the adult head is important to deduce the partial optical pathlength for quantitative measurement of brain oxygenation using near infrared spectroscopy. It is known that the clear CSF layer significantly affects the light propagation in the brain and it is likely that the optical properties of the skull adjoining the CSF will also affect the light propagation, especially in the case of a layered (i.e. cortical/trabecular/cortical) bone. In this study a Monte Carlo simulation has been used to investigate the influence of the optical properties of the skull on the partial optical pathlength of light in the adult head. Results show that where the absorption coefficient of the trabecular bone is higher than that of outer cortical bone, the partial optical pathlength in the brain decreases and the detected light has not propagated through the trabecular bone. In this case the outer border of the intensity PMDF tends to be confined to the inner skull boundary with the CSF layer.