Histotripsy of Blood Clots within Hollow Cylindrical Transducers for Aspiration Thrombectomy Applications

Thrombotic occlusions in the setting of stroke, pulmonary embolism and the peripheral vasculature are increasingly being treated with catheter-based aspiration approaches. Unfortunately, aspiration is frequently unsuccessful in extracting more challenging blood clots, which can become corked in the distal tip. In this study, we investigated the feasibility of using histotripsy to mechanically degrade thrombus within the lumen of a hollow cylindrical transducer (HCT), with a view to ultimately using this approach to improve aspiration thrombectomy procedures.

Retracted porcine blood clots were situated within the lumen of a radially polarized HCT (2.5/3.3 mm inner/outer diameter, 2.5 mm length, PZT). The HCT was stimulated in thickness mode (6.1 MHz) as a function of pulse length (10, 20 and 100 µs), pulse repetition frequency (100, 500 and 1000 Hz) and treatment time (0.1-10.0 seconds). High-frequency ultrasound examination was used to monitor bubble clouds and lesion formation during treatments (2-D) and quantify post-treatment lesion volumes (3-D).

Bisected 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 with increasing treatment time. The lesion volume was highly dependent on the exposure scheme (n = 5/group), with the largest volume associated with the 10 µs pulse length 1000 Hz pulse repetition frequency scheme.

Collectively, these results support the feasibility of performing histotripsy on clots situated within an HCT compatible with mounting in the tip of an aspiration format catheter.