A study of methodology and technology for wireless monitoring of blood pressure inside a stent

This thesis presents research on systems for wirelessly monitoring blood pressure inside a vascular stent. Such systems are of interest because changes in the blood pressure gradient across a stent are indicative of a blockage caused by growth of scar tissue (restenosis). No cheap and non-invasive method for detecting the onset of restenosis currently exists, and in-stent wireless blood pressure monitoring may provide a solution. In this work, several monitoring methods are explored. The first utilizes a specially designed stent integrated with a capacitive pressure sensor to form a pressure sensitive inductor-capacitor (LC) resonant circuit (tank) with wireless sensing capability. This approach follows previous work successful in producing a proof-of-principle prototype, but makes several modifications directed at achieving clinical relevance. A custom designed inductive stent and capacitive pressure sensor are developed, and new integration techniques are explored. In vitro resonant frequency responses of integrated devices with applied pressure are measured in the range of 50 - 200 ppm/mmHg. Device characterization reveals reader-device communication range, sensor performance variation, and stent mechanical reliability as areas of concern. Therefore, a dedicated study of the wireless range achievable with inductive stent monitoring and related monitoring approaches is undertaken, finding a maximum read range of 2.75 cm for an inductive stent in air. A surface micromachined capacitive pressure sensor is developed to improve upon the original sensor, and a miniaturized monitoring device formed by integrating this sensor with a micro-inductor is proposed as a means of avoiding wiring problems and expansion non-uniformities encountered when utilizing inductive stents. Finally, as an alternative route to increasing wireless sensing range and resolution, a third system design approach employing a complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC) is explored An IC is designed to mount on a stent to read and transmit pressure information from a micro-electro-mechanical systems (MEMS) pressure sensor. The IC may be driven by using the stent as an antenna to harvest power from an external radio frequency (RF) transmitter. Characteristics of the antenna-IC interface are studied by electromagnetic modeling and circuit simulation.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat