Surface wave phenomena on ultrasound contrast agents

A variety of materials have been used in the construction of ultrasound contrast agent shells. These include protein, lipid, polymer and fluid. The shell material and thickness influence the magnitude and type of resonance response produced by the agent. Previously, we reported on a novel dipole response using modal scattering solutions for thick shell agents >25 nm) whose shell material properties approximate albumin. These resonance responses are thought to in part originate from Lamb wave propagation within the shell. In this work, we extend our solutions to investigate the role of the interior gas on the dipole resonance responses. Novel oil-shelled agents do not support Lamb waves, but these shells undergo violent shape oscillations. As an initial step to understanding this phenomenon, we characterize their nonlinear, radial oscillations as a function of the shell thickness and viscosity. Finally, corresponding issues of contrast agent design and optimization are addressed.