SU-FF-T-307: Determination of Optical Properties in Semi-Infinite Media

Abstract

Purpose: To develop a method to quickly determine tissue optical properties(absorption coefficient μa and transportscattering coefficient μs') in a semi‐infinite medium. Method and material:Optical properties where determined by measuring the ratio of light fluence rate to source power along a linear channel at a fixed distance (4 mm) from an isotropic point source. The light detection system consists of two parallel light transmitting catheters placed 4mm apart. Diffuse light, from a 2mm cylindrical diffusing tip, is collected by an isotropic detector with a 0.5mm scattering bulb whose position is determined by a computer controlled step motor, with a positioning accuracy of better than 0.1 mm. The system automatically records and plots the light fluence rate per unit source power as a function of position. The result is fitted with a diffusion equation to extrapolate μa and μs'. Measurements where made in liquid tissue simulating phantoms, with known reduced scattering coefficient (μs') and absorption coefficient (μa). A theory based on light source on semi‐infinite medium has been developed to interpret the measured data. To test the ability of this algorithm to accurately recover the optical properties of the tissue, we made measurements in tissue simulating phantoms consisting of Liposyn concentration of 0.53% (μs' = 3.68cm−1) in the presence of Higgins black India ink at concentrations of 0.002, 0.012 and 0.023% (μa = 0.1 – 1 cm−1). For comparison, the optical properties of the phantom were determined independently using broad‐beam illumination. Results: We find that μa and μs' can be determined by this method with a standard (maximum) deviation of 24% (27%) and 29% (42%) for μa and μs', respectively. Conclusion: We developed a model for quick and accurate determination of tissue optical properties in semi‐infinite medium, which is theoretically suitable for determination of optical properties for esophagus PDT.