Measurement of the optical properties of a two-layer model of the human head using broadband near-infrared spectroscopy.

We present the development of a continuous-wave method of quantifying the optical properties of a two-layered model of the human head using a broadband spectral approach. Absolute absorption and scattering properties of the upper and lower layers of phantoms with known optical properties were reconstructed from steady-state multi-distance measurements by performing differential fit analysis of the near-infrared reflectance spectrum between 700 and 1000 nm. From spectra acquired at 10, 20, and 30 mm, the concentration of a chromophore in the bottom layer was determined within an error of 10% in the presence of a 15 mm thick top layer. These results demonstrate that our method was able to determine the optical properties of the lower layer, which represents brain, with acceptable error at specific source-detector distances.