Intravenous thrombolysis is recommended within 4.5 hours of stroke onset. The aim of the study is to evaluate whether a hypodensity on native CT within the virtually entire area of hypoperfusion on perfusion CT, i.e. hypoperfusion-hypodensity mismatch, identifies patients within the time window of thrombolysis in a multicenter cohort. The investigators hypothesize hypoperfusion-hypodensity mismatch will identify patients ≤ 4,5 hours of symptom onset with >70% specificity and >85% positive predictive value.

Inclusion Criteria:

• acute ischemic stroke
• evidence of acute intracranial vessel occlusion (any supratentorial proximal or peripheral artery of the anterior cerebral artery, middle cerebral artery or posterior cerebral artery territory) by CT hyper dense thrombus and/or CTangiography vessel occlusion and/or by ischemic perfusion deficit
• evidence for acute ischemic perfusion deficit, i.e. acute symptoms attributable to ischemic CT perfusion lesion
• complete native CT and CTperfusion performed on admission
• sufficient CT and CTperfusion quality for judgement of acute ischemic hypodensity
• known time of symptom onset.

Exclusion Criteria:

• None

Patients with acute ischemic stroke and known time of symptom onset.