Acoustic fields and ultrasound contrast agents

Abstract

Ultrasound contrast agents are encapsulated gas bubbles which oscillate nonlinearly upon acoustic excitation. Recent developments include targeted agents for molecular imaging applications and ultrasound contrast agents such those with polymer shells specifically designed for high frequency ultrasound applications. Though a variety of models have been proposed since the early development of the agents, many outstanding questions exist on the specifications of the shell and most appropriate model for the different materials. Moreover, only recently have independent mechanical measurements been attempted to advance and facilitate modeling efforts. The various shell models are reviewed and discussed. Validation of models of polymer shell agents are given with respect high frequency acoustic microscopy quantification of the shell elastic properties. Recent work on the modeling and design of agents for high frequency subharmonic excitation based on adaptive signal processing and nonlinear time series methodologies is overviewed. Novel analytical method for treating hydrodynamic interactions with respect to unsteady drag and secondary acoustic radiation forces are outlined with respect to drug delivery and sonoporation applications. The direction and magnitude of coupled oscillations are investigated with respect evolution of the amplitude and phase and the transfer entropy.