Ultrasonically induced dynamics of a contrast agent microbubble between two parallel elastic walls

Area of Science:

• Acoustics
• Biomedical Engineering
• Fluid Dynamics

Background:

• Contrast agent microbubbles are crucial in medical ultrasound imaging.
• Understanding microbubble dynamics in confined spaces is essential for optimizing imaging.
• Existing models often simplify boundary conditions, neglecting wall interactions.

Purpose of the Study:

• To derive and apply a Rayleigh-Plesset-like equation for microbubble oscillations between two elastic walls.
• To investigate the impact of a second wall on microbubble resonance and scattered echo.
• To analyze the influence of wall confinement on the second harmonic generation.

Main Methods:

• Derivation of a modified Rayleigh-Plesset equation incorporating two elastic walls.
• Numerical simulations using the Marmottant shell model for encapsulated microbubbles.
• Comparison of microbubble behavior with and without the presence of a second wall, using OptiCell and blood vessel wall properties.

Main Results:

• The second wall increases the microbubble's resonance frequency.
• Radial oscillation amplitude and scattered echo intensity are reduced by the second wall.
• The second harmonic intensity is significantly affected, with increases or decreases possible based on driving frequency.

Conclusions:

• Confined microbubble dynamics differ significantly from free-field behavior.
• The presence of elastic boundaries alters key acoustic parameters relevant to ultrasound imaging.
• This model provides insights into microbubble behavior in physiologically relevant confined environments.