Identification of Stroke Patients ≤ 3 and ≤ 4.5 Hours of Symptom Onset by Fluid Attenuated Inversion Recovery (FLAIR) Imaging and Diffusion Weighted Imaging (DWI)

The aim of the study is to evaluate the use of combined fluid attenuated inversion recovery (FLAIR) imaging and diffusion weighted imaging (DWI) as surrogate marker of lesion age within the first 6 hours of ischemic stroke in order to identify patients ≤ 3 or ≤ 4.5 hours of symptom onset in a large multicenter study hours of ischemic stroke. The investigators hypothesize that the pattern of a visible lesion on DWI together with a negative FLAIR ("DWI-FLAIR mismatch") will identify patients ≤ 3 hours of symptom onset with \>80% specificity and positive predictive value.