Imaging vascular implants with optical coherence tomography

Vascular stents and grafts have many proven and promising clinical applications, but also a large number of complications. A focus of current research is the development of biocompatible implants. Evaluation of these devices generally requires a large number of animals due to the need for explantation and histological evaluation of the implant at several time intervals. It would be desirable to use instead a high resolution, in situ assessment method. An in vitro study was performed to determine if Optical Coherence Tomography (OCT) could image cell proliferation and thrombus formation on vascular stents and grafts. First, images were taken of explanted stents. The implants were located in peripheral vessels of a porcine model of atherosclerosis. The images clearly show the vessel response to initial damage (to induce atherosclerosis), the materials of the implant, extent of intimal cell hyperproliferation, and small platelet aggregates. Next, a tissue engineered graft, which had been sodded with smooth muscle cells and incubated in a bioreactor, was evaluated. Cross-section images showed the pores of the polymer material and the layer of smooth muscle cells beginning to invade the graft material. For comparison, in vitro 20 MHz IVUS images of the same grafts were obtained. The resolution of the OCT images was clearly superior. A catheter was designed for intravascular imaging. The 2.3 mm diameter catheter contains a fiber with GRIN lens and right angle prism, a monorail guidewire, and a novel positioning wire that can be protruded to push the catheter against the vessel wall, potentially eliminating the need for saline flush. Preliminary in vitro results with this catheter are encouraging.