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The goal of this clinical trial is to test whether perfusion CT can be used as a selection tool in stroke patients with a major anterior circulation occlusion, to exclude patients from thrombectomy because of a predicted non-beneficial outcome, when treated within 6 hours of symptom onset.

Researchers will compare the experimental group, where mechanical thrombectomy is only performed when prespecified perfusion CT criteria are fulfilled, with the standard of care treatment group, where all patients will receive mechanical thrombectomy, to see if functional independence at 90 days is non-inferior.

Ischemic stroke is a major cause of death or residual disability. It is caused by a blood clot blocking the brain arterial blood flow. Resolution of this blood clot can be achieved by intravenous injection of a blood clot resolving medication, if done within 4,5 h after the onset of complaints. Since about ten years, a supplementary treatment, known as mechanical thrombectomy, can be used to retrieve the blood clot from the brain circulation using a stent-retrieving system. This procedure requires an invasive transarterial approach and placement of tubes (catheter-systems) in the main brain supplying arteries to retrieve the clot by deploying stent-retrievers or by aspiration. After this maneuver, the blood supply of the brain is restored and the brain tissue that was at risk for infarction can recover. Mechanical thrombectomy has been proven to improve the functional independence of patients significantly, compared to best medical treatment alone, when performed within 6 hours of symptom onset (46% vs 26,5%).

Studies emerged on patients arriving late in the hospital, more than 6 h after onset, where mechanical thrombectomy was only performed on selected patients. Selection was based on perfusion CT scan results, which demonstrate infarction and surrounding tissue at risk (penumbra).

The functional independence was significantly better in patients who received mechanical thrombectomy versus those who only got best medical support.

In this trial the investigators aim to investigate whether the application of perfusion CT criteria to select or exclude patients from mechanical thrombectomy is non-inferior to mechanical thrombectomy without selection, with respect to functional independence at 90 days (mRS score of 0 to 2), in patients with an acute ischemic stroke caused by an occlusion of a major vessel in the anterior cerebral circulation, treated within 6 hours of symptom onset.

Inclusion Criteria:

• Major vessel occlusion of the anterior cerebral circulation (internal carotid artery tip, middle cerebral artery or both) on CTA
• Randomised within 6h of symptom onset
• Perfusion CT scan
• ASPECTS ≥ 5
• Age ≥18 years and ≤90 years
• Subjects capable of giving informed consent, or if appropriate, subjects having an acceptable individual capable of giving consent on the subject's behalf (e.g. parent or guardian of a child under 16 years of age) within 3 days after treatment.

Exclusion Criteria:

• Occlusion of a peripheral arterial segment (M3), anterior cerebral artery or posterior circulation
• Evidence of intracranial hemorrhage on initial CT scan
• Bad functional condition before stroke (mRS >2)

The performing interventional radiologist will be blinded for the result of the perfusion CT scan, except for the information where the occlusion of the major vessel is located.

The assessor of the mRS score at 90 days (primary outcome) will be blinded for the treatment allocation.