Excitation thresholds for subharmonic response of ultrasound contrast microbubbles.

Abstract

Nonlinear dynamics of encapsulated contrast microbubbles generates subharmonic response at stronger acoustic excitations. The response depends on environmental conditions such as ambient pressure. It has therefore been proposed that the subharmonic response could offer a novel means for non-invasive monitoring of organ-level blood pressure. For a free bubble, there exists a threshold excitation pressure for subharmonic response, the threshold being minimum at twice the resonance frequency of the free bubble. The stabilizing encapsulation of a contrast microbubble significantly alters the behavior of a bubble. Several models of encapsulation have been developed and their predictions compared with measured response from contrast microbubbles. Here, we use these models to study the threshold pressure for initiation of subharmonic scattered response. We will show that the encapsulation significantly affects the threshold and the variation of subharmonic response with other parameters such as ambient pressure, excitation, and bubble radius.