Ultrasound signal analysis applied to determine the optimal contrast dose for echographic examinations

In recent years the understanding of the behaviour of currently available ultrasound contrast agents (UCAs), in the form of gas-filled microbubbles encapsulated in elastic shells, has significantly improved thanks to "ad hoc" designed "in vitro" studies. However, in several studies there has been a tendency to use high UCA concentrations, potentially reducing the safety of microbubbles in clinical applications. In this study we investigated a possible strategy to improve microbubble safety by reducing the injection dose and employing low ultrasound intensities. We measured the achievable contrast enhancement insonifying microbubbles at different low concentrations (range 0.01-0.10 ¼L/mL) using a very low mechanical index (MI=0.08). Our results, based on the use of advanced techniques for signal processing and spectrum analysis, showed that UCA backscatter strongly depends on microbubble concentration also in the considered low range, providing useful indications towards the definition of an optimal low contrast dose, effectively employable at low MIs.