Examining cerebral hemodynamics in a two-layer model of the human head using broadband near-infrared spectroscopy

The development of a continuous-wave method is presented, to quantify accurately the optical properties of a two-layer model of the human head using a broadband spectral approach. In particular, focus is put on the reconstruction of the absolute absorption and scattering properties of a two-layered phantom model of the human head with steady-state multi-distance measurements by performing differential fit analysis of the near-infrared (NIR) reflectance spectrum between 700 nm and 1000 nm. The two-layer model approximation was fitted to experimental broadband absorbance measurements obtained from two-layered phantoms with known optical properties. Results demonstrated that the suggested method was able to determine the optical properties of the lower layer with minimal error at specific source-detector distances. Preliminary results on the non-invasive measurement of the optical properties of the adult human brain in a two-layer approximation are presented. Finally, a mobile wireless NIR device is used to measure changes in the temporal characteristics of cerebral hemodynamic responses to functional brain activity, in particulaur the effect of smoking. Results suggest that assuming homogeneous medium for the adult human head severely underestimates the changes in cerebral hemodynamics. Hence, it is important to take surrounding layers into consideration when performing cerebral measurements using NIR spectroscopy.