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Background: Thrombi retrieved from patients with an acute ischemic stroke with Large Vessel Occlusion (LVO) and correlation with hyperdense vessel sign seen on non contrast CT and blooming artifact seen on gradient-echo(GRE) MRI have given relevant insights into the pathophysiology of thrombotic lesions (RBC-dominant vs Fibrin-dominant). This may facilitate the development of safer noninvasive reperfusion treatment approaches. Our goal was to evaluate the benefit of anticoagulation for posterior circulation strokes based on imaging characteristics in patients where endovascular therapy was not justified.Method: Comprehensive prospective evaluation of patients who presented with posterior circulation LVOs at a community based, university affiliated comprehensive stroke center during one year period (January 2015-December 2015) was done. The clot characteristics on thin-sliced reformatted CT, CT Angiogram and GRE MRI were noted. The clot size and characteristics were followed by sequential imaging while the patients were on anticoagulation for presumed embolic thrombus.Results: Total 749 patients presented with acute ischemic stroke during the pre-specified time period. Of those 78 were posterior circulation strokes; of which, 7 had LVO and 4 underwent endovascular treatment. Endovascular therapy was not justified in 3 patients due to clinically stable exam. These patients were thought to have embolic etiology of stroke and therefore were started on anticoagulation. Group A (RBC-dominant thrombus; n=2) mean clot length was 15.5mm, measured on CT, CTA, MRI. GRE MRI showed blooming artifact around the area of thrombus. Thrombus resolved on repeat CTA at 48-72hours. Group B (Fibrin-dominant; n=1) 5.5mm clot was visualized only on CTA (nothing on CT head and MRI) and it persisted on repeat CTA at 48-72hours. Mean initial NIHSS was 2 (SD +/-1 ). Mean discharge NIHSS was 0.33 (SD +/- 0.577). Mean discharge mRS was 0.67 (SD +/- 0.57).Conclusion: Hyperdense sign on reformatted thin-sliced CT head and blooming artifact on GRE MRI brain in patients with LVO can be used to characterize the composition of thrombus, which could be helpful in deciding medical therapy. A larger prospective randomized trial is needed to corroborate our findings.