Anna Custo
LIRA-Lab, DIST, University of Genova (Italy)
Fast simulation of Diffuse Optical Imaging: determining an effective scattering coefficient of a void space in adult head models
There has been debate that the scattering coefficient within the supposed void space between the human brain and skull is small (e.g. musp <0.01 mm-1) as it is mostly filled with a clear liquid called cerebral spinal fluid (CSF). The diffusion equation can not be used for the forward photon migration problem when the scattering coefficient is small compared to the absorption coefficient or when the scattering length (inverse of the scattering coefficient) is large compared to the length scales of the medium. Both of these conditions are not satisfied if this CSF space has a small scattering coefficient. However, it is not obvious that this CSF space needs to be treated with a small scattering coefficient. There is connective tissue and vessels in the space, not just CSF. Also, even if the space was a void with no or little scattering, one could consider treating the void with an effective scattering coefficient equal to the inverse of the typical line of sight distance through the space (~3 mm in adult humans). The diffusion equation should provide reasonable solutions with a musp = 0.3 mm-1. We test this hypothesis of treating the scatter-less void as a region with scattering by running Monte Carlo simulations with increasing amounts of scattering in the void to quantify the changes in measured photon fluence and brain sensitivity and find that similar results are obtained with a 0.0001 mm-1 <= musp <= 0.3 mm-1.