On the interaction between ultrasound and contrast agents during Doppler investigations

Knowledge of interaction mechanisms between ultrasound (US) and contrast ag ents (CA) suspended in blood is important for a correct interpretation of c linical investigation results. Experiments performed in different laborator ies have shown that, as a consequence of primary radiation force, CA tend t o move away from the US transducer. Accordingly, Doppler spectra produced b y particles suspended in moving water turn out to be significantly altered from what is theoretically expected. The purpose of this paper is twofold. First, an original model describing the bubble dynamics as the outcome of t he balance between US radiation force and fluid drag force is validated for the case in which bubbles are suspended in blood. The high fluid viscosity is shown to prevent significant bubble deviations from the unperturbed flu id streamlines so that, in large vessels, a residual spectral distortion ma y exist only at the highest intensity levels permitted by current regulatio ns. Finally, the relative importance and differences between the effect of primary radiation force and streaming mechanisms that, in principle, could lead to similar effects, are discussed.