Focus Control in HIFU Therapy Assisted by Time-Reversal Simulation with an Iterative Procedure for Hot Spot Elimination

Abstract

Both focus control and hot spot elimination applied to the High Intensity Focused Ultrasound (HIFU) treatment are addressed using three-dimensional numerical simulations, which can faithfully capture the pressure field in the HIFU system involving strong heterogeneity in material properties. The hot spot corresponds to the superficial secondary pressure peak, which originates in the reflection and refraction of the ultrasonic waves. As an extension of the Time Reversal theory (Fink, 1992, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 39, 555), which is based on the reversibility of the linear wave equation, a heuristic, iterative and self-adaptive process is proposed to make the HIFU system mounting array piezotransducers dynamically controllable. The amplitude and phase of the driving pressure on each transducer are determined from the temporal change in the monitored pressure of diverging acoustic waves emitted from virtual acoustic sources at the hot spot as well as the target point. The primary peak is found to be strengthened through the process, while the secondary peaks are to be obliterated. The present method is applied to a transskull HIFU simulation using human body voxel data, and its effectiveness is discussed.

Keywords

• hifu
• time reversal
• grating lobes
• secondary hot spots