| The goal of this work was to design and develop an integrated balloon ultrasound catheter to measure mechanical properties of vascular tissues and guide cardiovascular interventions. Initial work studied the mechanical properties of atherosclerotic plaques of low and high cholesterol fed rabbits using an atherosclerotic plaque rupture model. Young's modulus estimates were computed from pressure-volume data acquired during plaque rupture. Histological and Young's modulus estimates showed statistically significant differences in elastic properties between the two rabbit groups. After the initial plaque rupture study, an integrated compliant balloon ultrasound catheter was developed to allow greater deformations in strain imaging with intravascular ultrasound. Strains over 40% could be applied to normal arterial wall tissue with intracatheter pressures as low as 200 kPa (2 atm). Strain images of a hard-soft rubber phantom, thrombus in a rabbit aorta, and human fibrotic plaque were produced from ex vivo experiments with the integrated balloon ultrasound catheter. Results show that pathologies with different elastic modulus can be detected with this catheter. A second integrated balloon ultrasound catheter prototype was designed to image from inside the balloon for real-time guidance of stent deployment. A commercial stent, nominally 4.4 mm in diameter and 12 mm in length, was successfully deployed in a rubber phantom. The slope of the area-pressure ratio was compared to a reference measure of the balloon and stent expanded in water to determine a measure for optimal stent deployment. Using this metric, the results clearly indicate stent deployment at 1.1 MPa (11.1 atm), about 150 kPa (1.5 atm) less than the maximum allowed pressure for this balloon/stent combination. The APR slope measure could serve as a quantitative feedback measure for guiding stent deployment and ultimately reducing arterial injury and subsequent restenosis. After stent deployment, rf data were captured as the balloon catheter was moved along the length of the stent in pullback mode to confirm success. The integrated balloon ultrasound catheters developed as a part of this dissertation could serve as a single catheter device for pre-procedure diagnosis, real-time image guidance and quantitative feedback during stent deployment, and post-procedure validation. |
