Shear strain from irrotational tissue displacements near bubbles
Edwin Carstensen1, Sheryl M Gracewski, Diane Dalecki
1Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627-0126, USA.
The Journal of the Acoustical Society of America
|November 18, 2011
Summary
Acoustic waves near bubbles cause large shear strains, potentially leading to tissue damage. These high strains occur even at low acoustic pressures, suggesting a new mechanism for bioeffects.
Area of Science:
- Acoustics
- Biophysics
- Medical Ultrasound
Background:
- Acoustic waves in homogeneous media produce strains of similar magnitude.
- Bubbles in a medium significantly alter particle displacement under acoustic exposure.
Purpose of the Study:
- To investigate the magnitude of shear strain near oscillating bubbles exposed to acoustic waves.
- To explore the potential link between bubble-induced shear strain and biological effects.
Main Methods:
- Analysis of particle displacement and strain fields around oscillating bubbles.
- Comparison of shear and bulk strain magnitudes near resonance frequencies.
Main Results:
- Shear strain near resonating bubbles is approximately four orders of magnitude greater than bulk strain.
- Significant shear strains (a few percent) are achieved at acoustic pressures below inertial cavitation thresholds.
- Observed tissue hemorrhages (lung, liver, kidney) at ~1% shear strain following audio frequency acoustic exposure.
Conclusions:
- Oscillating bubbles dramatically amplify shear strain in the surrounding medium.
- High shear strains near bubbles present a plausible mechanism for acoustic bioeffects at non-cavitating pressures.
- This finding has implications for ultrasound safety and therapeutic applications.
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