PARENT SESSION
3:45 PM to 5:15 PM
Monday, April 23, 2001
NAHS Mini-Symposium 09 Treatment Planning and Biothermal Modeling
Salon San Cristobal FG
Chair: M. Sherar, Co-Chair: E. MorosL. Chin, M. Sherar, E. Moros, O. Craciunescu
(MS09-1) Changes in Tissue Dielectric Properties Due to Heating at 915 MHz.
Chin, Lee1, Sherar, Michael1,2, 1 2
ABSTRACT-
Tissue dielectric properties determine the propagation and absorption of microwave energy. Knowledge of these properties is important in the planning and delivery of microwave thermal therapy. However, changes in tissue dielectric properties related to high temperature structural changes in tissue may result in errors in the mathematical models. We have implemented a coaxial sensor for the measurement of temporal changes in dielectric properties of bovine liver and rat prostate at 915 MHz during heating for temperatures between 45 - 75 °C. Our measurements demonstrate that, for treatment temperatures of greater than 60 °C, changes of up to 100 % in conductivity and 5 % in permittivity can occur. Both a reversible temperature dependent change and a time-temperature dependent permanent change were observed in the dielectric of bovine liver during heating. In rat prostate, only a reversible temperature dependent change was observed. Temperature coefficients were calculated to describe the reversible changes while rate parameters pertaining to the permanent changes were calculated using an Arrhenius analysis. The dielectric dispersions for tissue at 915 MHZ indicate that the permanent changes were possibly due to denaturation and coagulation of tissue proteins and that the temperature reversible changes were likely related to tissue water content. Differences in the dielectric behaviour between bovine liver and rat prostate might be attributed to variation in organ or species tissue structure. These results suggest that changing dielectric properties should be taken into account when planning thermal therapy treatments.
KEYWORDS: microwave dielectric properties, Arrhenius, temperature coefficient, coagulative thermal therapy