Room: Exhibit Hall | Forum 9
Purpose: To simulate fluorescence detected at air-tissue and water-tissue interfaces from semi-infinite turbid media using Monte Carlo modeling and to investigate the effect of refractive index mismatch on the optical properties correction factors.
Methods: Monte Carlo simulations were performed for a semi-infinite medium with uniform optical properties (absorption coefficient, Î¼â‚?=0.1-1 cm^-1, and reduced scattering coefficient Î¼_sâ€™=5-40 cm^-1) and scattering anisotropy (g) of 0.9. The indices of refraction for air, water and tissue are 1, 1.33, and 1.4 respectively. Uniform circular light field with radius of 4 cm was used and incident normal to the air-tissue or water-tissue interfaces. 500,000 photons were launched in each simulation. Specular reflection at the surface, resulting from the refractive index mismatch, is calculated by the Fresnel reflectance for unpolarized light. Each photon is traced until it escapes the medium or completely absorbed. A new fluorescence photon is generated at each step and is followed by the same algorithm. The MC code records the diffuse components of the reflected light (R_d) and the fluorescence light at the surface (F_MC). F_MC is normalized to the total light fluence rate on the surface (1+2R_d). Correction factors, CF_MC, were computed for a range of tissue optical properties.
Results: CF_MC for both air-tissue and water-tissue interfaces can be fitted to CF=C_1 (Î¼â‚?_a^(b_1 ) Î¼_s^('b_2 )+C_2 ), a 4-parameter power function. Fluorescence tissue optical properties correction factors increase with Î¼a for a fixed Î¼_sâ€™.
Conclusion: The optical properties correction factors are within 15% for both air-water and tissue-water interfaces over Î¼â‚?=0.1-1 cm^-1 and Î¼sâ€™=10-40 cm^-1 with the exception of Î¼sâ€™= 5 cm^-1, which is within 25%.
Not Applicable / None Entered.