Ultrasound-Based Post-Endovascular Aneurysm Repair (EVAR) Monitoring Device

Abstract

A diverse set of stimulators, transducers and data transceivers can be integrated into medically implantable devices using ultrasonic power. An application for such a device is postoperative monitoring of abdominal aortic aneurysm repair. Endoleaks are a potentially serious, but correctible, complication of aorta repair. A miniscule ultrasonic powered device incorporated into the stent-graft for endovascular delivery could provide on demand diagnostic information about the presence of endoleak by monitoring the dimensions of the aneurysm sack in real time. To power this device, a wireless ultrasonic power recovery scheme is demonstrated in oil using a single-element capacitive micromachined ultrasonic transducer, and a circuit made with commercially available discrete components. The 2mm diameter element, a diode rectifier bridge and inductor-based boost circuit form the power conversion circuit delivering over 1 mW to the load. Other aspects of the implantable device are a pulse echo measurement of the diameter of the vessel lumen, and a data transmission method that encodes clock, data and transmission framing information in biphasic ultrasonic pulses and takes advantage of the wideband characteristics of the CMUT. This proof of concept is guiding the design of an integrated circuit implementing the key elements of the implantable device.