Inducing cavitation within hollow cylindrical radially polarized transducers for intravascular applications

• Published in: Ultrasonics 2024-03, Vol.138, p.107223-107223, Article 107223
• Main Authors: Gong, Li, Wright, Alex R., Hynynen, Kullervo, Goertz, David E.
• Format: Article
• Language: English
• Subjects: Aspiration; High intensity focused ultrasound; Histotripsy; Mechanical thrombectomy; Sonothrombolysis
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2023.107223

•The first demonstration of the generation of cavitation clouds within an intravascular scale hollow cylindrical transducer.•Peak internal pressures are dependant on element length and resonant mode.•Highest pressures are achieved in thickness mode and are impacted by internal reflections and the eventual development of a standing wave pattern.•Cavitation investigated as a function of pulsing scheme using a combination of hydrophone and imaging based methods.•This approach has potential use for enhancing aspiration based mechanical thrombectomy. Thrombotic occlusions of large blood vessels are increasingly treated with catheter based mechanical approaches, one of the most prominent being to employ aspiration to extract clots through a hollow catheter lumen. A central technical challenge for aspiration catheters is to achieve sufficient suction force to overcome the resistance of clot material entering into the distal tip. In this study, we examine the feasibility of inducing cavitation within hollow cylindrical transducers with a view to ultimately using them to degrade the mechanical integrity of thrombus within the tip of an aspiration catheter. Hollow cylindrical radially polarized PZT transducers with 3.3/2.5 mm outer/inner diameters were assessed. Finite element simulations and hydrophone experiments were used to investigate the pressure field distribution as a function of element length and resonant mode (thickness, length). Operating in thickness mode (∼5 MHz) was found to be associated with the highest internal pressures, estimated to exceed 23 MPa. Cavitation was demonstrated to be achievable within the transducer under degassed water (10 %) conditions using hydrophone detection and high-frequency ultrasound imaging (40 MHz). Cavitation clouds occupied a substantial portion of the transducer lumen, in a manner that was dependent on the pulsing scheme employed (10 and 100 μs pulse lengths; 1.1, 11, and 110 ms pulse intervals). Collectively the results support the feasibility of achieving cavitation within a transducer compatible with mounting in the tip of an aspiration format catheter.