Computational modeling of 915 MHz microwave ablation: Comparative assessment of temperature‐dependent tissue dielectric models

Abstract

The inclusion of decreased electrical conductivity above 95 °C, implemented with model B as guided by our experimental measurements, may be a good approach for approximating the dynamic changes that occur during MWA at 915 MHz. Although a step toward more effectively modeling MWA at 915 MHz, further investigation of the transition in dielectric properties with temperature and tissue shrinkage, especially at high temperatures is needed for more accurate simulations.

Broadband lung dielectric properties over the ablative temperature range: Experimental measurements and parametric models

“…The transient temperature profiles at the measurement site were also independently measured and stored at a sampling rate of 1 Hz. Initially, the hot plate temperature was set to 130–152 C, in order to achieve a rate of heating similar to that achieved during MWA with cooled applicators at distances of 10 mm from the applicator; it is noted that rates of heating adjacent to the applicator may vary across systems as a function of operating frequency and antenna design . When the sample temperature reached ∼94 C, the hot plate surface temperature was set to 200 C (maximum setting) in order to overcome the latent heat of water vaporization, and raise the tissue temperatures above 100 C.…”

“…Computational models are widely used to guide the design and optimization of MWA applicators, to comparatively assess the impact of energy‐delivery strategies on ablation outcome, and for characterizing applicator performance in a variety of tissue types . Computational models are also being developed for use as treatment planning tools that may assist a physician in selecting treatment parameters that maximize the likelihood of achieving a favorable treatment outcome .…”

“…Tissue dielectric properties are known to be highly dependent on tissue type, and are a function of frequency, temperature, water content, and other physical variables . During an MWA procedure, tissue temperatures within the target zone can increase rapidly from physiologic temperatures up to > 100 C within a few minutes . Several studies have reported substantial changes in dielectric properties of liver tissue at 2.45 GHz over temperatures ranging from ∼20 to > 100 C .…”

“…2,3 Computational models are widely used to guide the design and optimization of MWA applicators, to comparatively assess the impact of energy-delivery strategies on ablation outcome, and for characterizing applicator performance in a variety of tissue types. 1,[4][5][6][7][8] Computational models are also being developed for use as treatment planning tools that may assist a physician in selecting treatment parameters that maximize the likelihood of achieving a favorable treatment outcome. 9 For all these applications, MWA models are implemented to predict the spatial distribution of electric fields radiated by the MWA applicator into surrounding tissue, the corresponding microwave power absorption and transient temperature profiles.…”

“…12 During an MWA procedure, tissue temperatures within the target zone can increase rapidly from physiologic temperatures up to > 100 C within a few minutes. 5,15 Several studies have reported substantial changes in dielectric properties of liver tissue at 2.45 GHz over temperatures ranging from $ 20 to > 100 C. 17,18 These changes have been most commonly related to the effects of tissue desiccation at elevated temperatures. In addition to characterizing the dielectric properties, these studies have provided parametric models for approximating dielectric properties as a function of temperature, which serve as an elegant means for expressing temperature dependence of dielectric properties in computational models.…”