Characterization of a multi-element clinical HIFU system using acoustic holography and nonlinear modeling

TLDR

High‑intensity focused ultrasound delivers acoustic energy to remote tissue for thermal or mechanical ablation, but its field characterization is hindered by nonlinear propagation and phased‑array complexity. The study aims to establish a standard method for accurately characterizing the acoustic pressures of clinical HIFU sources to ensure safety and efficacy, extending prior measurement‑modeling approaches to a clinical phased‑array transducer. Low‑amplitude hydrophone measurements in water were used to holographically reconstruct the transducer surface vibrations, set boundary conditions for a 3‑D acoustic propagation model, and run nonlinear simulations across a range of source powers. Comparisons with hydrophone‑measured pressure waveforms at low and high power confirmed that the simulations quantitatively predict the acoustic field, including shock formation.

Abstract

High-intensity focused ultrasound (HIFU) is a treatment modality that relies on the delivery of acoustic energy to remote tissue sites to induce thermal and/or mechanical tissue ablation. To ensure the safety and efficacy of this medical technology, standard approaches are needed for accurately characterizing the acoustic pressures generated by clinical ultrasound sources under operating conditions. Characterization of HIFU fields is complicated by nonlinear wave propagation and the complexity of phased-array transducers. Previous work has described aspects of an approach that combines measurements and modeling, and here we demonstrate this approach for a clinical phased-array transducer. First, low amplitude hydrophone measurements were performed in water over a scan plane between the array and the focus. Second, these measurements were used to holographically reconstruct the surface vibrations of the transducer and to set a boundary condition for a 3-D acoustic propagation model. Finally, nonlinear simulations of the acoustic field were carried out over a range of source power levels. Simulation results were compared with pressure waveforms measured directly by hydrophone at both low and high power levels, demonstrating that details of the acoustic field, including shock formation, are quantitatively predicted.