Dynamic interactions between contrast agent microbubbles: High speed camera observations and simulation results

The efficacy of coated microbubbles as contrast agents for ultrasound imaging has been well established over the past two decades. More recently, their use as carriers for targeted drug delivery has also become an active area of research. However, the behaviour of microbubbles in an ultrasound field is by no means fully understood. For example, the dynamic interactions between microbubbles have frequently been neglected when considering contrast agent suspensions. In this investigation, high speed camera observations of a commercial contrast agent (SonoVue (R)) were made under controlled and calibrated acoustic exposure conditions (single 4 cycle (FWHM) Gaussian pulse with 0.5 MHz centre frequency and peak negative pressure <100 kPa). These were compared with numerical simulations of both single and pairs of coated microbubbles corresponding to the experiments. Both the theoretical and experimental results indicate that the dynamic behaviour of a microbubble may be substantially affected by the presence of neighbouring bubbles under certain conditions. This, in turn, may affect the microbubble's acoustic response and its destruction threshold, which has potentially significant implications for both diagnostic and therapeutic applications.