Acoustic Nonlinearity Parameter B/A in the Suspension of Ultrasound Contrast Agents Part I: A Thermodynamic Approach

TL;DR

This paper introduces a thermodynamic approach to estimate the acoustic nonlinearity parameter B/A in ultrasound contrast agent suspensions, revealing wide variability and thermodynamic differences in bubbly liquids.

Contribution

It develops a new thermodynamic-based equation for B/A estimation in bubbly liquids, incorporating bubble dynamics and phase velocity, with validation against existing methods.

Findings

Maximum B/A reaches up to 10^5

Minimum B/A can be as low as -10^5

Negative B/A indicates distinct thermodynamic properties

Abstract

The acoustic nonlinearity parameter B/A plays a significant role in the characterization of acoustic properties of various biomaterials and biological tissues. It has the potential to be a favorable imaging modality in contrast ultrasound imaging with coated microbubbles. However, the development of effective means for evaluating the nonlinearity parameter of suspensions of ultrasound contrast agents (UCAs, also known as bubbly liquids) remains open. The present paper formulates a new equation based on the thermodynamic method that correlates both attenuation and phase velocity of linear ultrasound. The simplicity of the present method makes the B/A estimation possible with a relatively rigorous mathematical derivation. The calculated nonlinearity parameter contains the contribution of dynamic effects of bubbles, and its low-frequency limit agrees with B/A estimated by the method of mixture law when the volume fraction is below 10-4. Furthermore, the maximum B/A in bubbly liquids can reach up to105, while the minimum can be as low as -105. The negative nonlinearity parameter indicates significantly different thermodynamic properties of bubbly liquids.