Optical characterization of two-layered tissue-like phantoms using multi-distance, frequency domain near-infrared spectroscopy

Abstract

We present a near-infrared spectroscopy (NIRS) approach for the optical characterization of two-layered tissuemimicking phantoms. For the data acquisition, we employed a multi-distance frequency-domain system. For the data analysis, we implemented an inversion routine based on a two-layered solution of the frequency-domain diffusion equation as the forward model. Measured quantities were the absorption and reduced scattering coefficients of the first layer (μ a1 , μ’ s1 ) and the second layer (μ a2 , μ’ s2 ), and the thickness of the first layer ( L ). We report measurements on three two-layered liquid phantoms featuring absorption coefficients in the range 0.009-0.017 mm -1 , reduced scattering coefficients in the range 0.69-0.92 mm -1 , and first layer thickness in the range 8-15 mm. Our method yielded measured values of the optical coefficients and first layer thickness (μ a1 , μ’ s1 , μ a2 , μ’ s2 , and L ) that are within 10% of the true values (optical properties measured in the infinite geometry; and the true first layer thickness). These are promising results toward exploring the potential of this two-layered medium approach in the human head, where the two layers would represent extracerebral and cerebral tissue, respectively.