 The purpose of this study is to use an iatrogenic model of stroke, meaning those strokes inadvertently caused by endovascular coiling of elective aneurysms, to study the biology of stroke in humans. Clinical evidence suggests that simple catheterization of cerebral vasculature causes small, usually clinically silent, embolic strokes. These strokes are evident on MRI scans. Additionally, since the practitioner knows the onset of an interventional procedure, he by default knows the timing of injury. This simple model allows one to study stroke in real-time with knowledge of the time of onset. Magnetic resonance imaging MRI evaluation allows the practitioner to identify the volume of stroke caused by the intervention. Alternatively, patients who present to the emergency room with large ischemic infarcts provide a natural control population for this study. These patients present with large, usually devastating strokes. In most cases the timing of the onset of deficit is known. The investigators propose to use the simple model of ischemia from endovascular interventions with the more obvious devastating cases of ischemic stroke who present to the emergency room to better understand the molecular pathways involved in stroke. 