In Vitro Study of Thermal Changes in Optical Properties of Myocardium Tissue with Diffuse Reflectance Imaging

Optical properties of porcine myocardium tissue in the exposure temperature range of 37-80degC were determined for 700, 750, 800, 850, 900 nm wavelengths of a Ti: sapphire laser. A neural network were trained with diffuse reflectance data from Monte Carlo simulations based on the semi-infinite tissue model, and then it was used to assess the absorption coefficient and reduced scattering coefficient from the spatially resolved relative reflectance which derived from diffuse reflectance image. The result showed that there was slight change in the absorption coefficient; the average for fresh is 0.11 mm-¹, which increased to 0.17mm-¹ for 80degC. The average reduced scattering coefficient of the five wavelengths for fresh samples is 0.14 mm-¹, which increased obviously to 0.66 mm-¹ for 80degC, and the average for all samples is 0.13 mm-¹. The reduced scattering coefficient at the longer wavelength increased slowly compared with the shorter wavelength in the wavelength range of 700-900 nm. The average optical penetration depth of the five wavelengths for fresh samples is 3.37 mm, which reduced obviously to 1.54 mm for 80degC. In conclusion, thermal effect during photothermal treatment of tissue is an important factor altering optical properties of tissue.