High frequency nonlinear scattering from a micrometer to submicrometer sized lipid encapsulated contrast agent

Area of Science:

• Acoustic Imaging
• Biomedical Engineering
• Materials Science

Background:

• Contrast agents are crucial for enhancing ultrasound imaging resolution and diagnostic capabilities.
• Nonlinear acoustic phenomena offer potential for improved image quality and targeted imaging.
• Lipid-encapsulated microbubbles are a key class of ultrasound contrast agents.

Purpose of the Study:

• To evaluate an experimental lipid-encapsulated bubble contrast agent for nonlinear scattering.
• To investigate the agent's response to high transmit frequencies (20 and 30 MHz) and varying bandwidths.
• To assess the potential of these microbubbles for high-frequency nonlinear contrast imaging.

Main Methods:

• Characterization of lipid-encapsulated microbubbles using a broadband focused piezoelectric transducer.
• Experiments conducted at 20 and 30 MHz with 5%, 15%, and 25% bandwidths.
• Analysis of acoustic emissions, including subharmonic, ultraharmonic, and second harmonic energies, across a range of acoustic pressures.

Main Results:

• Subharmonic energy was detected across all bandwidths at various pressures for both 20 and 30 MHz.
• Distinct ultraharmonic signals were observed exclusively in the 5% bandwidth cases.
• Microbubble destruction was noted only at higher peak negative pressures (>2 MPa at 30 MHz, 5% bandwidth).

Conclusions:

• The experimental lipid-encapsulated bubbles exhibit significant nonlinear scattering properties.
• These microbubbles demonstrate potential for generating harmonic and subharmonic signals useful in advanced imaging.
• Small lipid bubble formulations are suitable for high-frequency nonlinear contrast-enhanced ultrasound imaging applications.