OPTICAL COHERENCE TOMOGRAPHY IMAGING IN ACUTE ISCHEMIC STROKE: PRELIMINARY ANIMAL AND HUMAN RESULTS Christopher R. Pasarikovski (SSTP) 1 , Victor X.D. Yang 2 1 Neurosurgical Resident, Institute of Medical Sciences, Surgeon-Scientist Training Program, University of Toronto 2 Division of Neurosurgery, Sunnybrook Health Sciences Centre; Neurointerventional Surgeon, Division of Medical Imaging, Sunnybrook Health Sciences Centre; Senior Scientist, Brain Sciences Program/Imaging Research, Sunnybrook Research Institute; Associate Professor, Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, ON, Canada INTRODUCTION The cerebrovascular endothelium is known to play a pivotal role in regulating inflammatory pathways, permeability of the blood-brain barrier, and thrombosis. During endovascular thrombectomy (EVT) with second-generation stent retrievers, considerable outward radial force can be delivered to the vessel wall via the stent struts or thrombus. Studies evaluating for iatrogenic endothelial injury during EVT have been done by means of retrieved human thrombus, post-mortem histopathologic analysis, magnetic resonance vessel-wall (MRVW) imaging, and animal histopathologic studies 1,2 . Furthermore, damage to the endothelium may not strictly be due to the mechanical thrombectomy device alone. Prolonged vessel wall exposure to luminal thrombus can also cause endothelial damage. Reil et al. showed that ligated arteries with thrombus had increased endothelial damage compared to arteries with interrupted flow in the absence of thrombus 3 . Various components of the thrombus can affect endothelial function and morphology. Endovascular optical coherence tomography (OCT) imaging is the highest-resolution intravascular imaging modality currently available. This technology has traditionally been utilized in interventional cardiology, and more recently applied in neurointerventional surgery 4 . OCT utilizes near-infrared light with a wavelength of approximately 1.3μm and excellent intraluminal spatial resolution of 10-20 μm is achievable. Although studies have shown that some degree of iatrogenic endothelial injury likely occurs during EVT, whether this is clinically significant remains unknown. Before attempting to correlate vessel injury with clinical outcome, the degree of vessel wall injury should be adequately quantified, as it is likely endothelial denudation, intimal dissection, and edema of the tunica media will have varying clinical implications. Current techniques such as MRVW imaging have insufficient spatial resolution to directly visualize endothelial injury, and histopathologic examinations are ex-vivo, prone to processing artifacts, and unable to provide real-time patterns of injury. The purpose of this project is to assess the feasibility of endovascular OCT in quantifying vessel injury in real-time after EVT, correlate the OCT findings of vessel injury with histology, and lastly imaging after EVT at varying time intervals to assess the impact of prolonged direct vessel exposure to thrombus. The pre-clinical animal model and preliminary human model and results are described. METHODS Animal Model: All experiments were conducted in accordance with policies established by our institutional research ethics board committee. Nine vessels in three Yorkshire swine weighing 35-40kg were selected for the animal model, as they have well-developed superficial cervical