Less than 10% of all ischemic stroke patients are treated by intravenous thrombolysis (IVT) as most present later than the accepted 3 hour time window. Intra-arterial thrombolysis (IAT) is possible 3-6 hours post ictus, but is infrequently used. Mechanical thrombectomy (MT) with a MERCI device is a new intervention possibility but lacks large randomized studies. Although it is desirable to treat more stroke patients, clinical information and plain CT alone are insufficient to discriminate which patients are most likely to benefit or be harmed from treatment. Advanced imaging techniques can help predict patient outcome and provide the necessary information to weigh expected benefit against associated risk of treatment. Visualizing the penumbra, the hypoperfused tissue at risk of infarction around the irreversible infarct core, is one way of identifying patients most likely to benefit from intervention. Magnetic resonance imaging (MRI) based selection of patients with sufficient penumbra for thrombolysis is possible, however, MR has less 24-hour availability than CT in the acute setting. Plain CT is mostly used to exclude intracerebral hemorrhage, and can easily be extended with CT perfusion (CTP) and CT angiography (CTA). CTP compares well to MRI for imaging penumbra and infarct core, and it is faster and more feasible than MRI. Other image findings such as infarct core size and leakage of the blood-brain-barrier (permeability) on CTP, and site and extent of the occlusion and collateral circulation on CTA also influence stroke outcome but have not been combined in one study to assess their combined predictive value.

Hypothesis:

The investigators hypothesize that combined CTP and CTA parameters can predict patient outcome in acute ischemic stroke.

Inclusion Criteria:

• Acute neurological deficit caused by cerebral ischaemia
• Admission < 9 hours after onset of neurological deficit
• NIH Stroke Scale (NIHSS) of at least 2
• No absolute contraindications against intravenous contrast
• Informed consent from patient or family after admission scan
• Patients who awaken with stroke symptoms can only be included if they went to sleep without any stroke symptoms and the time from going to sleep until imaging is less than 9 hours

Exclusion Criteria:

• Neurological deficit caused by another diagnosis than cerebral ischaemia (such as intracerebral hemorrhage, subarachnoid hemorrhage or tumor)
• Patients with known contrast allergy or kidney failure
• Patients with the known combination of renal insufficiency and heart failure (New York Heart Association (NYHA) IV) will be excluded for the CTP and CTA scan at 3 days; they will have a non-contrast CT (NCCT) at that time.

Patients 18 years or older with acute stroke symptoms who present in the hospital within 9 hours of onset of symptoms.