Investigation into tendon histotripsy

Histotripsy uses cavitation bubble clouds or shock wave heating and millisecond boiling to fractionate soft tissues. While this modality has proven successful in debulking most soft tissues, highly collagenous tissues such as tendons have proven resistant to mechanical fractionation using histotripsy. In this study, ex vivo rat and bovine Achilles tendons were placed at the focus of a 1.5-MHz transducer and exposed to 1–20 ms pulses repeated at 1 Hz for 1 min over ranges of acoustic pressures up to p + = 88 MPa (peak positive), p = 20 MPa (peak negative). Simultaneous ultrasound imaging with the Verasonics® research ultrasound system and ATL L7-4 transducer monitored bubble activity, or hyperechogenicity, during the histotripsy exposure. Collected samples were stained with Hematoxylin and Eosin for histological analysis of tissue disruption. Preliminary results show hyperechogenicity within the tendon during the histotripsy exposure; however, thus far only thermal injury has been found histological. The threshold to detect hyperechogenicity in the tendon for 10-ms pulses were p + = 63 MPa, p = 19 MPa. Future work involves additional parameter testing to promote mechanical fractionation rather than thermal injury of tendons. [Work supported by Penn State College of Engineering Multidisciplinary Research Seed Grant]