Microbubble radiation force-induced translation in plane-wave versus focused transmission modes

Microbubble displacement due to the primary radiation force has been observed previously in the focal region of single-element and array ultrasound probes. This effect has been harnessed to increase the contact between microbubbles and targeted endothelium for drug delivery and ultrasound molecular imaging. In this study, microbubble displacements associated with plane-wave (PW) transmission are thoroughly investigated and compared to those obtained in focused-wave (FW) transmission over a range of pulse repetition frequencies, burst lengths, peak negative pressures and transmission frequencies. In PW mode, the displacements, depending on the experimental conditions, are in some cases consistently higher (e.g. by 28%, when the longest burst length was used at PRF = 4 kHz), and the axial displacements are spatially more uniform compared to FW mode. Statistical analysis on the measured displacements reveals a slightly different frequency dependence of statistical quantities compared to transient peak microbubble displacements, which may suggest the need to consider the size range within the tested microbubble population.