Influence of the pressure-dependent resonance frequency on the bifurcation structure and backscattered pressure of ultrasound contrast agents: a numerical investigation

The bifurcation structure of the oscillations of ultrasound contrast agents (UCAs) was studied as a function of the driving pressure for excitation frequencies that were determined using the UCAs pressure-dependent resonances (f(s)). It was shown that when excited by the (f(s)), the UCA can undergo a saddlenode bifurcation (SNB) to higher amplitude oscillations. The driving pressure at which the SNB occurs is controllable and depends on the (f(s)) magnitude. Utilizing the appropriate (f(s)), the scattering cross section of the UCAs can significantly be enhanced (e.g., similar to ninefold) while at the same time avoiding potential UCAdestruction (by limiting the radial expansion ratio <2). This offers significant advantages for optimizing UCA-mediated imaging and therapeutic ultrasound applications.