The effect of acoustic parameters on the Non-Invasive Embolus Trap (NET) using a histotripsy-generated bubble cloud

Previous observations during histotripsy-mediated thrombolysis revealed that free-flowing clot fragments are attracted, trapped, and eroded simultaneously near the bubble cloud even with background flow. This feature may be used to develop a Noninvasive Embolus Trap (NET) that eliminates clot fragments during cardiovascular therapies. This study investigated the effect of histotripsy acoustic parameters on the trapping ability of NET in-vitro. A flow system was developed to circulate particles under a fixed mean background flow velocity. A 1-MHz, elliptical transducer (f# = 0.6) was used to generate a cavitation bubble cloud. Peak negative pressures ranging from 5 MPa to 20 MPa, PRFs from 30 Hz to 1000 Hz, and pulse durations from 5 to 50 cycles were used. The maximum trapping velocity was the performance metric used to assess the trapping ability of a particle for a given acoustic parameter set. The maximum trapping velocity increased linearly with increasing pressure after a bubble cloud was initiated, and nonlinearly with increasing PRF and pulse duration. At 20 MPa P-, 10 cycles, and 1000 Hz PRF, the maximum trapping velocity was 9.8cm/s. The size distribution of debris from blood clots exposed by NET showed that 93% of the sampled debris was less than 50 μm. These findings promote the idea that the NET could be a useful clinical tool to noninvasively eliminate emboli in many vascular applications, including ultrasound-mediated thrombolysis.