Subharmonic Plane Wave Imaging of Liposome-Loaded Microbubbles

A key component of targeted drug delivery using liposome-loaded microbubbles and ultrasound is the ability to track these drug vehicles in real time to guide payload release locally. As a uniquely identifiable emission from microbubbles, the subharmonic signal is of interest for this purpose. Acoustic characterization of liposome-loaded microbubble populations confirmed the decreased pressure threshold for subharmonic emissions (50 kPa vs. 200 kPa for normal microbubbles). This study proved the feasibility of subharmonic plane wave imaging of liposome-loaded microbubbles with improved subharmonic sensitivity especially at depth compared to their counterpart of bare (unloaded) microbubbles.