High-speed optical observations of asymmetric pulsations of microbubbles released from tablet matrix

Microbubbles with a negligible shell are of utmost importance in the study of harmonic ultrasound contrast agents. The purpose of this study was to collect and quantify experimental pulsation footage of gas microbubbles released from tablet matrix under sonication. Radii were measured as a function of time of 50 microbubbles that had been released from tablet matrix and were subjected to 3-cycle pulses of 1-MHz ultrasound with a 0.3-MPa peak-negative pressure. The size distribution was measured, as well as pre- and postsonication radii. The experimental footage showed proof of asymmetric buckling, but also of excursion-only behaviour. The former phenomenon has been attributed to a surplus of material accumulated on the microbubble-liquid interfaces, whilst the latter phenomenon has been associated with the presence of incompressible material inside the microbubbles. The postsonication resting radii of 41 microbubbles had become less compared to the corresponding pre-sonication radii. The opposite effect was observed with eight microbubbles in the same size range. This feasibility study confirmed that the gas microbubbles released from tablet matrix may pulsate asymmetrically. Thus, they might be suitable tracers for harmonic imaging.