Subharmonic analysis using singular-value decomposition of ultrasound contrast agents

Area of Science:

• Biomedical Engineering
• Acoustics
• Materials Science

Background:

• Ultrasound contrast agents (UCAs) typically operate below 10 MHz.
• Growing interest in high-frequency ultrasound (HFU) for novel applications.
• Understanding UCA behavior at HFU is crucial for advanced imaging.

Purpose of the Study:

• To analyze the subharmonic response of polymer-shelled UCAs at 40 MHz.
• To compare conventional and singular-value-decomposition (SVD) methods for subharmonic analysis.
• To investigate the influence of acoustic pressure and pulse duration on subharmonic generation.

Main Methods:

• Polymer-shelled UCAs (1.1 µm diameter) were studied in a flow phantom.
• Excitation using 40 MHz tone-bursts (1-20 cycles) at varying peak-negative pressures (0.75-5.0 MPa).
• Subharmonic content at 20 MHz was analyzed using conventional and SVD methods, generating a subharmonic score (SHS).

Main Results:

• SHSs from conventional and SVD methods showed a linear relationship.
• Subharmonic likelihood increased with pulse duration and peaked near 2 MPa.
• The SVD method provided quantitative subharmonic data beyond the conventional approach.

Conclusions:

• Polymer-shelled UCAs exhibit measurable subharmonic responses at 40 MHz.
• Subharmonic generation is dependent on acoustic pressure and pulse duration.
• SVD offers a more comprehensive analysis of subharmonic emissions from UCAs.