Histotripsy of blood clots within a hollow cylindrical transducer for aspiration thrombectomy applications

Abstract: Thrombolytic occlusions in stroke, pulmonary embolism and the peripheral vasculature are increasingly treated with aspiration, a catheter-based approach that employs suction to extract clots through a hollow catheter lumen. Unfortunately, aspiration is frequently unsuccessful in extracting more challenging clots, which can become corked in the distal tip. We hypothesize that clot extraction can be enhanced by using histotripsy to degrade the mechanical integrity of clot material within the lumen of a hollow cylindrical transducer which can be situated at the tip of an aspiration catheter. To demonstrate the feasibility of degrading clot material within the lumen of a hollow cylindrical transducer, the effect of pulsing schemes on lesion generation within clots was assessed using a retracted clot model. A radially polarized cylindrical transducer (2.5 mm and 3.3 mm for inner and outer diameter, 2.5 mm length, PZT) working at 6.1 MHz was used to degrade retracted porcine clots with pulse lengths of 10, 20, and 100 us, pulse repetition frequencies (PRF) of 100, 500, and 1000 Hz, using treatment times from 0.1 to 10 seconds (n = 5 clots per condition). 3D ultrasound scans and bisected optical examinations of treated clots confirmed the formation of liquified zones. Lesions could form within 0.1 seconds along the central axis of the transducer and then grow in diameter and length over time. The lesion volume was found to be highly dependent on the exposure scheme, with the largest lesion volume associated with the 10 us pulse length 1000 kHz PRF case. Collectively these results demonstrate the feasibility of degrading blood clots within hollow cylindrical transducers, which suggests their potential for enhancing aspiration based mechanical thrombectomy.