Abstract

The time-resolved spatial sensitivity profiles on the brain surface and in the plane perpendicular to the brain surface are predicted by Monte Carlo simulation to discuss the volume of tissue sampled by multi-channel near infrared instruments. The adult head model consists of five types of tissue. The temporal point spread function of the detected light is divided into five parts and the trajectories of photons detected during each gate are accumulated to obtain the time-resolved spatial sensitivity profiles. Early photons only graze the cortex surface around the middle of the source and detector whilst late photons tend to penetrate into white matter. The spatial sensitivity profiles for the late photons widely spread on the cortex surface. These results suggest that the detected signal mainly reflects the absorption change in the grey matter.

© 2001 OSA/SPIE