In acute ischaemic stroke, every minute of delay costs brain tissue. Imaging is the gate to treatment, so the goal is a single, fast protocol that answers three questions: is there bleeding, is there a large vessel occlusion, and how much brain can still be saved?
Non-contrast CT
The first scan excludes intracranial haemorrhage, which rules out thrombolysis. Early ischaemic signs — loss of grey–white differentiation, sulcal effacement and a hyperdense vessel — can be subtle. The ASPECTS score gives a structured estimate of early ischaemic change in the middle cerebral artery territory.
CT angiography
CT angiography from the aortic arch to the vertex identifies large vessel occlusion, the target for mechanical thrombectomy. It also shows the collateral circulation and the access route for the interventional team.
Perfusion imaging
CT or MR perfusion estimates the ischaemic core and the surrounding penumbra. In selected patients, a favourable mismatch extends thrombectomy eligibility well beyond the traditional six-hour window — up to 24 hours from last known well in trial populations.
The first-hour pathway:
- Pre-alert from the ambulance service
- Direct transfer to the scanner
- Non-contrast CT, then CTA and perfusion in one session
- Thrombolysis decision while imaging is completed
“The best stroke imaging protocol is the one that never waits for a phone call.”
Thrombolysis is generally given within 4.5 hours of onset in eligible patients. Imaging should never delay it unnecessarily.
This article is for education only and does not replace clinical judgement or local guidelines.
