Effects of ambient pressure on the subharmonic response from encapsulated microbubbles

TL;DR

This study numerically investigates how ambient pressure affects the subharmonic response of encapsulated contrast microbubbles, revealing complex behaviors influenced by encapsulation that are relevant for noninvasive blood pressure estimation.

Contribution

It introduces a numerical analysis of subharmonic responses considering different encapsulation models, highlighting how encapsulation alters pressure response trends compared to free microbubbles.

Findings

Subharmonic response varies nonmonotonically with ambient pressure.

Encapsulation broadens the excitation range for subharmonic detection.

Different behaviors are explained by changes in threshold and resonance frequency.

Abstract

Subharmonic response from contrast microbubbles as a function of ambient overpressure is numerically investigated for subharmonic aided noninvasive estimation of local organ level blood pressure. Three different interfacial rheological models for the encapsulation is used with material parameters appropriate for a common lipid coated contrast agent Sonazoid. The subharmonic response is seen to either decrease, increase or vary nonmonotonically with increasing ambient pressure. Compared to a free microbubbles important differences arise due to the encapsulation. Specifically due to the enhanced damping due to encapsulation, the range of excitation over which subharmonic is seen is broader than that in free microbubbles. This results in different trends of subharmonic response at the same excitation frequency for different excitation pressures. The observed behaviors are explained by investigating subharmonic generation threshold and resonance frequency.