摘要
Increasing the local concentration of microbubbles (MBs) within the blood flow plays a crucial role in several medical applications, but there are few imaging modalities available for volumetric tracking of the aggregated MBs in real time. Here we describe a device integrating acoustic vortex tweezers (AVT) and ultrasound plane-wave imaging to achieve the goal of controlling the spatial distribution of MBs in blood vessels and simultaneously monitoring this process using the same probe. Experiments were conducted using a 5-MHz 2D array ultrasound probe (with three cycles of excitation at an acoustic pressure of 2000 kPa) and 1.2-&null MBs at a flow rate of 20 mm/s. The AVT waveform was produced by modulating the repetition frequency of the transmitted pulse asymmetrically (4 and 8 kHz at the inflow and outflow ends, respectively). In order to simultaneously capture MBs and perform imaging with the same probe, the asymmetric AVT pulse signal and the ultrasound-imaging pulse signal were arranged in a staggered series, and the imaging was performed using plane-wave pulses at nine angles (-7&null to 7&null) in compounded plane-wave imaging (volume rate: 200 Hz). Microscopy observations showed that freely suspended MBs could indeed be gathered by the asymmetric AVT in the flow field to form an MBs cluster with a spot size of about 4022 &null, which could resist the flow to remain at a fixed location for about 22 s. After the asymmetric AVT signal and the ultrasound-imaging pulse signal was turned on for 1 s, the ultrasound 3D image showed that the signal intensity of the MB clusters increased by 13.1&null dB relative to the background area. These results show that the proposed strategy can be used to accumulate flowing MBs at a desired location and to simultaneously observe this phenomenon. This tool could be used in the future to improve the outcomes of MB-related treatments for various diseases.