Neuroimaging. Brain imaging studies will be interpreted by more than one neuro-radiologist at each center without any knowledge of the clinical information. Standardized magnetic resonance image (MRI) sequences will be recommended to all participating centers. The minimal requirements for brain imaging studies are diffusion-weighted images, FLAIR images, T2-weighted images, and gradient echo images. All participants will undergo additional vascular imaging studies such as CT angiography, MR angiography or digital subtraction angiography. Based on the neuroimaging, ischemic stroke location, size and vascular territories will be noted. The diagnosis and treatment of stroke will follow the standard guidelines of each coordinating center.