Adrien POIZAT : Temporal control of ultrasound cavitation : application to extracorporeal ultrasound thrombolysis

Abstract:

Focused ultrasound can be used for therapeutic applications in the human body. In cardiovascular applications, they can destroy blood clots formed in the vascular system. In this case, thrombolysis mechanisms are related to ultrasonic cavitation, but the complex dynamics remains an obstacle to the development of a therapeutic device. In this thesis, a system for the temporal control of the pulsed cavitation activity has been developed and characterized. This device uses a focused transducer and a hydrophone with a feedback loop for regulating the cavitation activity. While cavitation activity has a random behaviour in non-regulated conditions, the control system developed achieves a desired level of cavitation with very reproducibly and with good temporal stability. The application of this device to the ultrasound thrombolysis was tested in vitro on human blood clots. In the previous device was added a system for moving the blood clot at the focal point, and a tube for counting the number of fragments released by the destruction of the clot. In comparison to uncontrolled regime, tests showed an excellent thrombolytic efficacy and a very good reproducibility, with reduced acoustic intensities. In parallel to the in vitro tests, ultrasound thrombolysis was tested in vivo on an animal model of acute limb ischemia. An extracorporeal ultrasound device, guided by ultrasound and mounted on a robotic arm, has been developed for in vivo investigation. An ovine model of arterial thrombosis has also been developed. Tests were used to validate the feasibility of the model of arterial clots and to validate in vivo the concept of purely ultrasonic extracorporeal thrombolysis based on inertial cavitation regulation system.