Graham Collins
BME PhD Defense Presentation

Date:2022-04-25
Time: 4:00 pm
Location / Meeting Link: EBB CHOA Seminar Room and https://emory.zoom.us/j/93526062769

Committee Members:
Dr. Brooks Lindsey, PhD (Advisor) Zachary Bercu, MD Levent Degertekin, PhD Jaydev Desai, PhD Stanislav Emelianov, PhD


Title: Forward-viewing ultrasound guidance of a robotically-steered guidewire for peripheral interventions

Abstract: Peripheral artery disease affects more than 200 million people globally. When the blood supply fails to reach peripheral tissues, they can become critically ischemic. In addition to discomfort and mobility challenges, critical limb ischemia is followed by amputation within a year in approximately one third of cases. While revascularization procedures currently restore blood flow in some cases, nearly one quarter of cases with chronic total occlusions fail due to inability to navigate to the target vessel segment under fluoroscopy. To increase procedural success and salvage limbs, ultrasound imaging tools can be integrated with interventional devices to provide direct visualization of tortuous vessels, occlusions, and remaining channels that allow navigation. Designing, building, and characterizing such tools was the focus of this thesis. In the first phase, high-contrast power Doppler imaging was developed for intravascular ultrasound where a single element transducer is rotated to view cross sections. With adaptive filtering and angular compounding of correlated scanlines, slow blood flow in small channels was detected, showing underlying structures previously unseen by interventionalists. In the second phase, a forward-viewing, single-element transducer was designed, fabricated, and characterized. The transducer was integrated with a robotic guidewire, and an image formation strategy was developed with synthetic aperture beamforming from the expanded aperture formed while steering the guidewire. The developed system provides a highly functional, sub-mm guidewire that can directly visualize the path through an occlusion, informing navigation beyond the projection view from fluoroscopy. In the third phase, a novel dual-resonant, single-element transducer was designed with finite element modeling and fabricated with laser micromachining. Characterization reflected the design goal of producing a single transducer with a single cable that can provide simultaneous imaging with a 16 MHz band, allowing high penetration, and a 33 MHz band, giving high spatial resolution close to the transducer. In the final phase, using the developed system, a processing approach was created that provides simple and accurate images of viable avenues for guidewire advancement by segmenting ultrasound intensity data. Interpretation of B-mode images with small, low-contrast channels requires a high level of training as well as risk-associated trial-and-error, while following segmented images showing the path through the occlusion is expected to allow for high procedural success from more providers while reducing rates of iatrogenic injury. This thesis represents a collection of ultrasound tools that show promise for improving patient outcomes by revealing information that would otherwise be unavailable to the interventionalist.