Sci‐PM Fri ‐ 02: Determination of optical properties of tissue in situ using four different frequency domain models

The following problem was investigated: implant an intensity modulated light source and two detectors in tissue. From a measurement of the ratio of fluences and relative phase at the two detectors, estimate the absorption (μ a ) and reduced scattering (μ s ′) coefficients of the tissue. An initial guess of these quantities is iteratively improved by comparison of forward calculations with measurements. The model used for forward calculation must be fast, yet accurate. Four models were compared on the basis of errors in recovered optical properties: standard diffusion approximation (SDA), single Monte Carlo (SMC), delta‐P 1 , and isotropic similarity model (ISM). For μ s ′/μ a >10, SDA recovered both coefficients within 5–10%, but for lower μ s ′/μ a the errors were as large as 25%. Although the delta‐P 1 model has been found to perform better under some conditions, we found no significant advantage in this application. The ISM was equivalent to SDA for μ s ′/μ a >10 and gave errors in μ a less than 7% and μ s ′ less than 17% for low albedo. The SMC model was the best; both coefficients were recovered to within 10% regardless of the albedo. In order to apply the SMC model, a restricted optical coefficient space must be used in the inverse problem solution.