Experimental assessment of the CSF contribution to light propagation in the adult head

Summary form only given. The deep penetrability of NIR photons through scalp and skull has provoked much interest in utilizing this form of radiation as a non-invasive investigative tool for cognitive processes, and diagnostic tools for diseased states of the brain, such as hematomas, cerebral hypoxia, and brain edema. The success of the proposed techniques is significantly dependent on their ability to quantify the optical response of head tissues, including scalp, skull, grey matter, white matter, and cerebral spinal fluid (CSF). Recent studies have shown that minimally scattering tissues, such as the CSF layer surrounding the brain, should have a profound effect on photon diffusion through the surrounding tissues. Such regions may behave as "light-pipes" that facilitate the transport of photons from an emitter to a detector, leading to a smaller attenuation and shorter transient times through the tissues. We report on time-resolved and continuous-wave measurements performed on the foreheads of adult human volunteers, with the aim of assessing experimentally the effect of the CSF layer on the signals produced by cerebral diagnostic devices based on photon transport in head tissues.