THEORETICAL AND EXPERIMENTAL INVESTIGATION OF NEAR-INFRARED LIGHT-PROPAGATION IN A MODEL OF THE ADULT HEAD

Near-infrared light propagation in various models of the adult head is analyzed by both time-of-flight measurements and mathematical predict ion. The models consist of three- or four-layered slabs, the latter in corporating a clear cerebrospinal fluid (CSF) layer. The most sophisti cated model also incorporates slots that imitate sulci on the brain su rface. For each model, the experimentally measured mean optical path l ength as a function of source-detector spacing agrees well with predic tions from either a Monte Carlo model or a finite-element method based on diffusion theory or a hybrid radiosity-diffusion theory. Light pro pagation in the adult head is shown to be highly affected by the prese nce of the clear CSF layer, and both the optical path length and the s patial sensitivity profile of the models with a CSF layer are quite di fferent from those without the CSF layer. However, the geometry of the sulci and the boundary between the gray and the white matter have lit tle effect on the detected light distribution. (C) 1991 Optical Societ y of America