Comparing the Marmottant model for ultrasound contrast agents with experimental postexcitation signals.

Abstract

When insonified with sufficiently large rarefactional pressures, single unconstrained ultrasound contrast agents undergo inertial collapse with postexcitation emissions. Experimental measurements of postexcitation signal data for Definity microbubbles are compared with the Marmottant theoretical model for large amplitude oscillations of ultrasound contrast agents (UCAs). After taking into account the insonifying pulse characteristics, microbubble properties, and size distribution of the population of UCAs, a good comparison between simulated results and experimental data is obtained by determining a threshold maximum radial expansion (Rmax) to indicate the onset of postexcitation activity. Though this threshold Rmax is found to vary depending on insonification frequency, the values obtained are well above the typical free bubble inertial cavitation threshold commonly chosen at 2R0. The close agreement between the experiment and models suggests that lipid shelled UCAs behave as unshelled bubbles during most of a large amplitude cavitation cycle, as proposed in the Marmottant equation. [NIH Grant No. R37EB002641.]