Modeling of ultrasound contrast agents

In this study the authors modified the Rayleigh-Plesset equation to calculate the linear and nonlinear scattering of shell encapsulated gas bubbles. The bubbles can acoustically be described by two parameters: the effective compressibility and friction. These parameters were estimated by fitting the calculated transmission spectrum to the measured transmission spectrum. The proposed model is in good agreement for the contrast agent Quantison (Andaris Ltd., Nottingham, UK) for applied acoustic pressures lower than 200 kPa. The nonlinear properties are low for this agent. Above a value of the applied acoustic pressure of 200 kPa the scattering of Quantison becomes transient and is called Power Enhanced Scattering (PES). Measurements of the persistence of this transient signal together with the analyses of the spectrum of the scattered signal support the hypothesis that small (2 μm) free air bubbles are generated