Changes in dielectric properties of ex vivo bovine liver at 915 MHz during heating.

We have developed a coaxial measurement system for determining the time and temperature dependence of the dielectric properties of bovine liver at 915 MHz during heating. Our data suggest that changes in dielectric properties due to heating are dominated by the relaxation response of two tissue components: tissue water and proteins. At temperatures above 60 degrees C, the effects of these two components contribute to increases of up to 100% and 5% in the values of conductivity and permittivity respectively. Changes due to tissue water content were found to be reversible with temperature, while changes due to protein denaturation were found to be permanent. The temperature coefficients for reversible changes were found to be 1.82 +/- 0.28% degrees C(-1) and -0.130 +/- (5.9 x 10(-2))% degrees C(-1) for conductivity and permittivity respectively. The critical temperatures and activation energies leading to irreversible changes in conductivity and permittivity were determined using Arrhenius analysis. Frequency factors of (1.14 +/- 0.27) x 10(43) s(-1) and (1.95 +/- 0.49) x 10(36) s(-1) were determined for permittivity and conductivity respectively. The activation energies were calculated to be 70.7 +/- 15.8 kcal mol(-1) for permittivity and 60.1 +/- 14.0 kcal mol(-1) for conductivity.