WAKE-UP is an investigator initiated European multicenter randomized controlled clinical trial of MRI based thrombolysis in acute stroke patients with unknown time of symptom onset, e.g. due to recognition of stroke symptoms on awakening. Objective of WAKE-UP is to prove efficacy and safety of MRI-based intravenous thrombolysis with Alteplase in patients waking up with stroke symptoms or patients with otherwise unknown symptom onset.