Phase-Aberration Correction for HIFU Therapy Using a Multielement Array and Backscattering of Nonlinear Pulses

Area of Science:

• Medical Physics
• Biomedical Engineering
• Acoustic Imaging

Background:

• Tissue heterogeneities cause phase aberrations, degrading high-intensity focused ultrasound (HIFU) focus and intensity.
• These aberrations critically impair HIFU therapies like boiling histotripsy (BH) that depend on shock formation.
• Accurate focusing is essential for effective and safe HIFU treatments.

Purpose of the Study:

• To propose and evaluate a novel aberration correction method for HIFU using backscattered nonlinear ultrasound pulses.
• To assess the method's efficacy in restoring focal intensity and shock formation in the presence of tissue-mimicking aberrating layers.
• To demonstrate the feasibility of using HIFU phased-array transducers for real-time aberration correction.

Main Methods:

• Developed a custom boiling histotripsy (BH) system with a 1.5-MHz 256-element array for pulse/echo measurements.
• Implemented pulse inversion imaging to detect the second harmonic of backscattered signals from the focus.
• Adapted an ultrasound imaging aberration correction algorithm (beamsum and nearest neighbor correlation) for the HIFU array configuration.

Main Results:

• The proposed method successfully corrected phase aberrations caused by tissue-mimicking layers.
• Phase correction compensated for most intensity losses, enabling the generation of fully developed shocks.
• Results were validated using a fiber-optic hydrophone, confirming shock amplitude recovery.

Conclusions:

• A HIFU phased-array transducer can function as a pulse-echo probe in harmonic imaging mode for aberration correction.
• This method effectively compensates for phase distortions, enhancing HIFU focal precision and therapeutic efficacy.
• The technique holds promise for improving the safety and effectiveness of HIFU treatments in heterogeneous tissues.