Optical Ultrasound Imaging for Endovascular Repair of Abdominal Aortic Aneurysms: A Pilot Study

An abdominal aortic aneurysm (AAA) is a persistent localized dilatation of the aorta to more than 1.5 times the expected diameter, which may lead to rupture with resultant high mortality. Endovascular repair (EVAR) of AAAs is a minimally invasive procedure that involves the peripheral delivery of one or more covered endografts to the aneurysmal segment, via a catheter-based system. A particularly challenging group of patients to treat are those in which the aneurysmal sac extends proximally to include the origin of the renal arteries (15% of all AAAs). To maintain the patency of renal side branches in these "complex" cases, in situ fenestration (ISF) of endografts during AAA procedures has been proposed. The challenges addressed in this study were a) to develop an endovascular imaging system for visualizing side branches beyond deployed endografts and thereby to determine the locations for ISF; b) to obtain an initial assessment of the clinical utility of this system. Here, all-optical ultrasound (OpUS) imaging with a fiber optic transducer was used for real-time guidance, wherein ultrasonic pulses are generated in nanocomposite coatings via the photoacoustic effect and received optically using a Fabry-Perot cavity. These custom OpUS transducer components were integrated into a steerable sheath (6 Fr) that also included a separate optical fiber for delivering laser pulses for fenestrating the endograft. In an ex-vivo model, it was shown that OpUS imaging extended through the endograft and underlying aortic tissue, and permitted aortic side-branch visualization. During an EVAR procedure in a porcine model in vivo, an aortic side branch was visualized with OpUS imaging after the endograft was deployed and optical fenestration of the stent graft was successfully performed. This study showed that OpUS is a promising modality for guiding EVAR and could find particularly utility with identifying aortic side branches for ISF during treatment of complex AAAs.