BACKGROUND AND PURPOSE: The use of intravenous thrombolysis is restricted to a minority of patients by the rigid 3-hour time window. This window may be extended by using modern imaging-based selection algorithms. We assessed safety and efficacy of MRI-based thrombolysis within and beyond 3 hours compared with standard CT-based thrombolysis. METHODS: Five European stroke centers pooled the core data of their CT- and MRI-based prospective thrombolysis databases. Safety outcomes were predefined as symptomatic intracranial hemorrhage and mortality. Primary efficacy outcome was a favorable outcome (modified Rankin Scale 0 to 1). We performed univariate and multivariate analyses for all end points, including age, National Institutes of Health Stroke Scale, treatment group (CT 3 hours), and onset to treatment time as variables. RESULTS: A total of 1210 patients were included (CT 3 hours: N=180). Median age, National Institutes of Health Stroke Scale, and onset to treatment time were 69, 67, and 68.5 years (P=0.66); 12, 13, and 14 points (P=0.019); and 130, 135, and 240 minutes (P
