Real time evaluation of tissue optical properties during thermal ablation of ex vivo liver tissues

Complete ablation of liver tumors is vital for minimizing the risk of local tumor recurrence. Accurately identifying the hallmarks of tissue necrosis during thermal ablative therapies may significantly increase the efficacy of ablation, while minimizing unnecessary damage to the surrounding normal tissues or critical structures. Light propagation in biological tissues is sensitive to the tissue microstructure and chromophore concentrations. In our previous studies, we found that the wavelength (λ) averaged liver tissue absorption coefficient (µ_a) and reduced scattering coefficient (µ_s') change significantly upon heating which may be used for assessment of tissue damage during thermal ablation of solid tumors. Here, we seek to demonstrate the use of an integrated fiber-optic probe for continuous monitoring of the local tissue temperature (T), µ_a(λ) and µ_s'(λ) during thermal ablation of ex vivo porcine livers. The wavelength-averaged (435-630 nm) tissue absorption and scattering (µ_a and µ_s' ) increased rapidly at 45 °C and plateaued at 67 °C. The mean µ_a and µ_s' for liver tissue at 37 °C (n = 10) were 8.5 ± 3.7 and 2.8 ± 1.1 cm^-1, respectively. The relative changes in µ_a and µ_s' at 37, 55, and 65 °C were significantly different (p < .02) from each other. A relationship between the relative changes in µ_a and µ_s' and the degree of tissue damage estimated using the temperature-based Arrhenius model for porcine liver tissues was established and studied.