Microbubble translation in plane-wave ultrasound transmission

Primary radiation force is capable of translating microbubbles in the focal region of single-element and array ultrasound probes. This effect can be harnessed to enhance the contact between ligand-bearing microbubbles and targeted endothelium for applications in targeted drug delivery and ultrasound molecular imaging. In this study, displacements of lipid-coated microbubbles associated with plane-wave transmission are investigated using the multi-gate Doppler approach, and compared with focused-wave transmission at equivalent peak negative pressures. In plane wave transmission, the radiation force is nearly uniform over the field of view and therefore allows for a more uniform translation of microbubbles compared to focused wave. Statistically determined median displacements are in good agreement with the axial and lateral ultrasound beamplots both in plane-wave and focused-wave transmissions, while peak microbubble displacements reveal a number of discrepancies. Distinct size-isolated microbubble populations (diameters 1–2 μm, 3–4 μm, 4–5 μm, 5–8 μm, and polydisperse) were tested, showing important differences in their displacements and a strong driving frequency dependence thereof. These findings help tune the ultrasound transmission parameters for uniform and size-selective microbubble translations.