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Background and Purpose: Intravenous rt-PA is associated with risk of hemorrhagic transformation. We sought to determine if the degree of white matter hyperintensity on Fluid Attenuated Inversion Recovery (FLAIR) and the presence of cerebral microbleeds (MB) on Gradient Recalled Echo (GRE) sequences on MRI was associated with increased risk of hemorrhagic transformation following intravenous rt-PA.Methods: Acute ischemic stroke patients admitted to University of Iowa Hospitals and Clinics between 1/1/2009 and 12/31/2013 were included in the study if - i) received intravenous rt-PA ii) had MRI brain with Diffusion Weighted Imaging (DWI), GRE and FLAIR sequence within the first 48 hours of stroke onset, and iii) had CT head or MRI at 20-36hr post rt-PA to evaluate for hemorrhagic transformation. White matter hyperintensity on FLAIR was evaluated based on Fazekas scale from 0-4. A score of 0 and 1 on Fazekas scale was combined to form group 1 and a score 3 and 4 was combined to form group 2 for analysis. MB were evaluated on GRE. Presence of MB was categorized as group 1 (1-5 MB) and 2 (6 or more MB). CT or MRI head performed at 20-36 hours after rt-PA was evaluated for hemorrhagic transformation. If present it was classified as group 1 (HI 1 and 2) and 2 (PH 1 and 2).Results: A total of 402 patients met the study criteria among 607 patients. Mean age was 67±14 years. Among them 45% were women and 88% whites. FLAIR deep white matter hyperintensity was graded on Fazekas as 0 - 26%, 1-51%, 2-12% and 3-11%. FLAIR periventricular white matter hyperintensity was graded as 0 - 10%, 1-49%, 2-25% and 3- 16%. MB were present in 26% of the study population with only 3 patients in group 2. Hemorrhagic transformation was seen in 24% of the patients with 66% of these having petechial hemorrhage. Deep white matter (p=0.47) and periventricular (p=0.73) white matter hyperintensity was not significantly associated with hemorrhagic transformation. However, presence of MB was significantly associated with hemorrhagic transformation (p=0.006, OR = 2.03, CI 1.215-3.392).Conclusion: Microbleeds increases the risk of hemorrhagic transformation following administration of intravenous rt-PA. However, white matter hyperintensity did not result in increased risk of hemorrhagic transformation after rt-PA.