Phase-contrast imaging of tissue using near-infrared diffusing light

We describe a new model-based image reconstruction method that can extract the spatial variation of tissue refractive index with near-infrared diffusing light. The model of light propagation is a diffusion approximation to the radiative transfer equation for highly scattering media with spatially varying refractive index. The spatial map of refractive index is recovered using a finite element-based Newton-type reconstruction algorithm. The imaging method is validated using several tissue-like phantom experiments. Initial in vivo imaging of breast tissue is also presented, demonstrating the ability of this new imaging method for tumor detection. (C) 2003 American Association of Physicists in Medicine.