Near infrared spectroscopy and imaging have been used in measurements of brain activity. The scatter of light in biological tissue which causes ambiguity in the volume of tissue interrogated with near infrared instruments is a serious problem for near infrared spectroscopy and imaging. The heterogeneity of superficial tissue of the head, especially the presence of non-scattering clear cerebrospinal fluid, affects the light propagation in the brain. In this paper the theoretical results of the effect of superficial tissue on the spatial sensitivity profile in the head for near infrared spectroscopy and imaging are reviewed. Simplified homogeneous and heterogeneous models are used to investigate the effect of the non-scattering clear layer on the spatial sensitivity profile in the head. Time resolved spatial sensitivity profiles reveal the effect of this layer on the early and late detected light. Finally, the author presents the spatial sensitivity profiles in the sophisticated adult and neonate head models to discuss the effect of superficial tissue on the near infrared measurement of brain activity in the two heads.
ASJC Scopus subject areas