Measurement of Broadband Temperature-Dependent Dielectric Properties of Liver Tissue

Characterization of changes in dielectric properties of tissue at elevated temperatures is essential for accurate modeling of microwave thermal therapy devices and systems. Available temperature-dependent dielectric properties are limited to the single frequency of 2.45 GHz, or wideband data temperatures less than -65°C. Here, we comparatively assess two configurations for placing a coaxial dielectric measurement probe relative to a microwave ablation antenna for measuring broadband temperature-dependent dielectric properties of liver tissue. Simulation and experimental measurements show that 10 to 20°C higher temperatures are observed when placing the dielectric measurement probe parallel to the ablation antenna, compared to perpendicular placement. The measured dielectric data of ex vivo bovine liver at 915 MHz and 2.45 GHz are in agreement with prior reports. It is further shown that dielectric measurement during low power and long duration (30 W, 10 min) ablation enables measurement of dielectric properties more uniformly scattered across the temperature range of interest.