Phase-Inverted Multifrequency HIFU Transducer for Lesion Expansion: A Simulation Study.

Area of Science:

• Medical Imaging and Ultrasound Technology
• Biomedical Engineering
• Acoustic Physics

Background:

• High-intensity focused ultrasound (HIFU) surgery aims to reduce treatment time by increasing the focal area per sonication.
• Previous dual-concentric transducers extended focal area but suffered from a deep notch point between focal lobes.

Purpose of the Study:

• To propose an improved HIFU transducer using dual-concentric aperture driven by phase-inverted multifrequency signals.
• To generate an expanded focal zone with a significantly reduced notch point in the axial direction.
• To enhance coagulated lesion size and reduce overall HIFU surgery treatment time.

Main Methods:

• Utilized finite element analysis simulation to investigate transducer performance.
• Simulated electrical impedance, one-way impulse response, and acoustic field.
• Employed heat transfer simulation to investigate lesion volume.

Main Results:

• The improved transducer generated an expanded focal zone with a notch point level above -6 dB.
• Achieved a 141% increase in -6-dB depth of field related to necrotic lesion size compared to conventional transducers.
• Phase interactions between fundamental/harmonic and inverted/noninverted frequencies mitigated the notch point.

Conclusions:

• The proposed dual-concentric HIFU transducer effectively enlarges the coagulated lesion size.
• This advancement offers a potential method for reducing overall HIFU surgery treatment time.
• The inversion layer technique with multifrequency signals successfully addresses limitations of previous designs.