Unraveling the Thermal Sting Effect in Microbubble-Enhanced High-Intensity Focused Ultrasound Ablation Through a Cross-Scale Dynamic Feedback Model

Abstract

This paper develops a cross-scale dual-heat-source coupled model to tackle the difficulty of forecasting nonlinear thermal effects in microbubble-enhanced high-intensity focused ultrasound, encompassing both microscopic single-bubble dynamics and macroscopic biological heat transfer. The model utilizes the Keller–Miksis equation, which includes liquid compressibility, to precisely measure the mechanical work produced by microbubble collapse. A novel approach is also developed to employ a dynamic nonlinear negative feedback mechanism that is triggered by tissue coagulative necrosis. This mechanism is called "acoustic attenuation jump" and "hardening-induced cavitation inhibition." The research indicates that the substantial mechanical work generated by extreme inertial collapse (temporary high temperature of around 5000 K) is the catalyst for the "thermal sting effect." The dynamic negative feedback quickly cuts off the cavitation heat source, keeping the peak temperature at about 81°C. This fixes the static model's serious error of overestimating the amount of damage caused by heat diffusion (by about 89.7%). Also, optimizing the parameters showed that the energy efficiency factor follows a nonlinear 'U-shaped' law, which means that the best duty cycle is about 42%. Two-dimensional acoustic field simulation validated that dynamic feedback efficiently mitigated hazardous axial thermal dispersion and target forward displacement. This study establishes a robust theoretical framework for accurate dose planning and the delineation of a safe operational range for microbubble-enhanced high-intensity focused ultrasound.