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Nonlinear response of Sonazoid. Numerical simulations of pulse-inversion and subharmonics

The oscillation of Sonazoid contrast agent bubbles has been simulated numerically, using a modified Rayleigh-Plesset model including the effect of a shell. Pulse-inversion simulations showed how the echoes changed from inverted to time-shifted versions of each other as the driving amplitude increased. Simulations of subharmonic oscillations showed that the subharmonic mode was only present for some diameter-frequency combinations, and only above an amplitude threshold. This threshold was about 500 kPa, which is higher than values published for bubbles without a shell. For large bubbles, a chaotic oscillation pattern was found. A subharmonic mode was not always achieved for a finite-length pulse, even if it was predicted by CW results.