DYNAMICS OF TEMPERATURE-DEPENDENT OPTICAL-PROPERTIES OF TISSUE - DEPENDENCE ON THERMALLY-INDUCED ALTERATION

Thermal damage in heated bovine myocardial tissue is assessed from mea sured changes in total reflection and transmission of light, Mathemati cal expressions, based on random walk analysis of light propagation wi thin tissue slabs, are used to relate the diffuse reflection and trans mittance to the absorption coefficient, mu(a), and effective scatterin g coefficient, mu(s)' for samples of myocardial tissue which were subj ected to rapid step changes in temperature, Time-dependent changes in mu(s)' indicate two processes, one with a fast and temperature-depende nt rate the other with a slow and apparently temperature-independent r ate. For final temperatures above 56.8 degrees C and for the first 500 s after the temperature change, the optical parameters are well fit b y exponential forms that exhibit temperature-dependent time constants as predicted by Arrhenius reaction rate theory of thermal damage, The scattering changes are associated with an apparent activation energy, Delta E, of 162 kJ/mole and a frequency constant, A, of 3 x 10(23) s(- 1). This method provides a means for estimating optical coefficients w hich are needed to assess laser tissue dosimetry.