Modeling and simulation of dual-frequency phase-difference ultrasound thermometry for multilayer tissue in HIFU

In high-intensity focused ultrasound (HIFU) therapy, the differing signs of the acoustic velocity-temperature coefficients in multilayered heterogeneous tissues (such as fat-muscle) lead to inherent systematic errors in traditional single-frequency ultrasound thermometry methods and make them susceptible to motion artifacts. Therefore, this study proposes a non-invasive temperature reconstruction theory based on the relative phase difference of dual-frequency ultrasound. By establishing a multiphysics model coupling nonlinear acoustic wave propagation and the Pennes bioheat transfer equation, and using the finite-difference time-domain (FDTD) method for simulation, the performance of this method was systematically evaluated in a three-layer tissue (skin-fat-muscle) model. Simulation results show that under 20 seconds of HIFU irradiation, the focal temperature rise reached 35.3 °C; the root-mean-square error of the temperature reconstructed by the dual-frequency phase difference method was only 0.076 °C, while the error of the traditional single-frequency time-of-flight method was as high as 8.531 °C, representing an accuracy improvement of approximately 99.1 %. Furthermore, the sensitivity of the dual-frequency method to overall axial tissue displacement was only 22.2 % of that of the single-frequency method, demonstrating excellent resistance to motion artifacts. This study provides a theoretical basis and a new design paradigm for developing high-precision and robust non-invasive thermometry systems for HIFU.