Changes in optical properties ofex vivorat prostate due to heating

Abstract

This study examines the effectiveness of a single, first-order Arrhenius process in accurately modelling the thermally induced changes in the optical properties, particularly the reduced scattering coefficient, µ'_s, and the absorption coefficient, µ_a, of ex vivo rat prostate. Recent work has shown that µ'_s can increase as much as five-fold due to thermal coagulation, and the observed change in µ'_s has been modelled well according to a first-order rate process in albumen. Conversely, optical property measurements conducted using pig liver suggest that this change in µ'_s cannot suitably be described using a single rate parameter. In canine prostate, measurements have indicated that while the absorption coefficient varies with temperature, it does not do so according to first-order kinetics. A double integrating sphere system was used to measure the reflectance and transmittance of light at 810 nm through a thin sample of prostate. Using prostate samples collected from Sprague-Dawley rats, optical properties were measured at a constant elevated temperature. Tissue samples were measured over the range 54-83 °C. The optical properties of the sample were determined through comparison with reflectance and transmittance values predicted by a Monte Carlo simulation of light propagation in turbid media. A first-order Arrhenius model was applied to the observed change in µ'_s and µ_a to determine the rate process parameters for thermal coagulation. The measured rate coefficients were E_a = (7.18±1.74)×10⁴ J mol^-1 and A_freq = 3.14×10⁸ s^-1 for µ'_s. It was determined that the change in µ'_s is well described by a single first-order rate process. Similar analysis performed on the changes in µ_a due to increased temperatures yielded E_a = (1.01±0.35)×10⁵ J mol^-1 and A_freq = 8.92×10¹² s^-1. The results for µ_a suggest that the Arrhenius model may be applicable to the changes in absorption.