Optical tomographic reconstruction from diffuse remittance in scattering media using partial least squares estimation

The long-term goal of this research is to develop a method for quantitative, three-dimensional optical imaging in scattering media. Towards this end, a reconstruction technique for depth-resolved absorption determinations based on diffuse reflectance measurements was developed. The approach employs an array of radial measurements of intensity to obtain multi-perspective information through a specimen. Both Monte Carlo simulations and experimentally obtained reflectance measurements of known phantoms were used to evaluate the sensitivity of the method to changing sample absorption. Diffuse reflectance experiments were made using a collimated incident light source and layered absorbing/scattering samples. A fiber optic detection system measured radial responses for a series of different phantom compositions. Results demonstrate that a well defined ray path is obtained for light measured from each source and detector pair. For image reconstruction, a comparison to volume element estimation was made for classical back projection, inverse least squares and partial least squares methodologies. Overall, PLS gave significantly better results with a 50% reduction in the coefficient of variation compared to the back projection method. This depth resolved tomographic approach is a new tool to study spatial relationships of chromogenic constituents in scattering media.