Based on the results of recent randomized controlled trials, current international guidelines recommend the initiation of endovascular treatment within 6 hours of symptom onset for acute ischemic stroke. Endovascular treatment may be beneficial in selected patients beyond 6 hour time window. In particular, treatment response to endovascular therapy may be greatly influenced by pretreatment collateral status. The aim of this study is to evaluate whether MRI-based collateral imaging (the Fast Analysis SysTem for COLLaterals, 'FAST-COLL') is feasible and can predict the response to endovascular treatment in a wide range of patients with acute ischemic stroke .

Inclusion Criteria:

• Acute ischemic stroke
• Age 20 years and older
• Disabling stroke defined as a baseline NIHSS > 5 at the time of arrival
• Onset (last-seen-well) time to endovascular treatment time < 12 hours
• Confirmed symptomatic intracranial occlusion, based on CT or MR angiography, at one or more of the following locations: Carotid T/L, M1 MCA, or M1-MCA equivalent (2 or more M2-MCAs)
• Signed informed consent or appropriate signed deferral of consent where approved

Exclusion Criteria:

• Baseline non-contrast CT reveals a moderate/large core defined as extensive early ischemic changes of ASPECTS 0-5 in the territory of symptomatic intracranial occlusion.
• Clinical history, past imaging or clinical judgment suggests that the intracranial occlusion is chronic
• Unable to undergo MRI (contraindicated or poor cooperation)
• Patient has a severe or fatal comorbid illness that will prevent improvement or follow-up or that will render the procedure unlikely to benefit the patient
• Pregnant females as determined by positive urine hCG test or lactating females

Acute ischemic stroke, eligible for endovascular treatment within 12 hours of symptom onset