Influences of blood flow changes in cerebrospinal fluid and skin layers on optical mapping

In optical mapping for imaging brain activity, the effect of blood flow changes in superficial tissues such as the cerebrospinal fluid (CSF) and skin layers should be considered. However, it is difficult to know those changes in in vivo experiments. To investigate the influence of blood flow changes in CSF and skin layers on optical mapping, we perform numerical simulations of optical mapping by solving the photon diffusion equation for layered-models simulating human heads using the finite element method (FEM). The results show that mapping images of activated region in the gray matter layer are affected by the existence of blood vessels in CSF layer and by the blood flow changes in the skin layer. The increases in both the vessel size and vessel absorption coefficient reduce the sensitivity of the mapping images to the brain activity in the gray matter. On the other hand, the increase in the vessel volume fraction in the skin layer increases the sensitivity of the mapping images.