Combining Acoustic Trapping with Plane Wave Imaging for Localized Microbubble Accumulation in Large Vessels

The capability of accumulating microbubbles using ultrasound, could be beneficial for enhancing targeted drug delivery. When microbubbles are used to deliver a therapeutic payload, there is a need to track them, for a localized release of the payload. In this study, a method for localizing microbubble accumulation with fast image guidance is presented. A linear array transducer performed trapping of microbubble populations interleaved with plane wave imaging, through the use of a composite pulse sequence. The acoustic trap in the pressure field was created parallel with the direction of flow in a model of a vessel section. The acoustic trapping force resultant from the large gradients in the acoustic field was engendered to directly oppose the flowing microbubbles. This was demonstrated numerically with field simulations, and experimentally using an Ultrasound Array Research Platform II (UARP II). SonoVue microbubbles at clinically relevant concentrations were pumped through a tissue-mimicking flow phantom and exposed to either the acoustic trap or a control ultrasonic field composed of a single-peak acoustic radiation force beam. Under the flow condition at a shear rate of 433 s-1, the use of the acoustic trap led to lower speed estimations (p< 0.05) in the center of the acoustic field, and an enhancement of 71 ± 28% (p< 0.05) in microbubble image brightness.