We conduct a simulation-based study to investigate the impact of a dynamic temperature environment on the characteristics of microwave-induced thermoacoustic signals. We investigate thermoacoustic signals that are generated using an interstitial microwave ablation antenna powered by a microsecond pulsed microwave source. Two temperature regimes are examined: first, a spatially uniform temperature throughout the medium to experimentally validate the simulation model, and second, the realistic, spatially nonuniform temperature profiles that arise during microwave ablation. We employ a multi-physics model that considers electromagnetics, heat transfer, and acoustic physics to simulate the coupled processes of microwave absorption and heating of the medium and thermoacoustic signal generation and propagation. An interstitial coaxial antenna is used to generate microsecond microwave pulses that simultaneously induce microwave heating and excite thermoacoustic signals via microwave pulse absorption. We find that thermoacoustic signal characteristics are highly temperature-dependent and thus change significantly within an environment where temperature varies through space and time. Furthermore, the temperature-dependent properties within the active region of the antenna drive the evolution of thermoacoustic signal characteristics. Temperature-dependent thermoacoustic signal characteristics can be exploited to track the progress of microwave ablation. Consequently, microwave-induced thermoacoustic imaging is a promising method for monitoring microwave ablation in real-time.
Microwave-induced thermoacoustic signals are generated when pulsed microwave energy is absorbed by tissue. Thermoacoustic signals contain information about the electromagnetic, thermal, and acoustic material properties of the tissue. Thus, we propose using microwave-induced thermoacoustic signals to monitor microwave ablation, a thermal therapy used to heat and kill malignant tissue, in real-time. Conventional microwave-induced thermoacoustic signals are excited using an external waveguide. Our approach excites thermoacoustic signals via pulsed microwave energy delivered by the already present interstitial microwave ablation antenna. In this talk, we will present the experimental investigation of the evolution of microwave-induced thermoacoustic signals generated during microwave ablation in bovine liver tissue. Pulsed microwave energy was delivered via a narrow-diameter coaxial ablation antenna to simultaneously ablate tissue and excite thermoacoustic signals. Trials were conducted in room-temperature fresh liver tissue as well as room-temperature boiled liver tissue to investigate the influence of ablative temperature rise and tissue coagulation on thermoacoustic signals. Our experimental results show thermoacoustic signal characteristics change throughout the course of microwave ablation that could potentially be used for monitoring the microwave ablation process.
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