CT angiography (CTA) of the brain is acutely performed in AIS patients before or immediately after administering IV tissue plasminogen activator (tPA) The Alberta Stroke Program Early CT (ASPECTS) leptomeningeal collaterals score on CT-angiography helps in prognosticating functional outcome in acute ischemic stroke (AIS) patients treated with intravenous thrombolysis. Leptomeningeal collaterals in AIS are dynamic, especially during the first few hours or days of AIS.