Ultrasonic Atomization: A Mechanism of Tissue Fractionation.

Area of Science:

• Biomedical Engineering
• Acoustics
• Tissue Mechanics

Background:

• High intensity focused ultrasound (HIFU) is known to atomize liquids.
• The cavitation-wave hypothesis explains liquid atomization via capillary waves and subsurface cavitation.
• The application of HIFU to biological tissues requires understanding its mechanical effects.

Purpose of the Study:

• To investigate the atomization of free tissue surfaces using HIFU.
• To characterize the resulting tissue erosion and jet velocities.
• To explore the implications of tissue atomization for procedures like boiling histotripsy.

Main Methods:

• Experimentally applied a 2-MHz spherically focused HIFU transducer to ex vivo bovine liver and in vivo porcine liver tissue surfaces.
• Utilized in situ intensities up to 14,000 W/cm².
• Analyzed tissue erosion volume and jet velocities.

Main Results:

• HIFU successfully atomized both ex vivo and in vivo liver tissue surfaces, leading to measurable erosion.
• Maximum erosion volume in bovine liver was 25.7±10.9 mm³ with 300 pulses.
• Observed jet velocities were approximately 10 m/s.

Conclusions:

• Tissue surface atomization is a novel mechanical effect of HIFU.
• This atomization mechanism provides insight into how HIFU disrupts tissue.
• Atomization may be the underlying process for tissue fractionation observed in boiling histotripsy.