El-Tawil S, Mair G, Huang X, et al. - A total of 24 cases from the IST-3 (Third International Stroke Trial), Alteplase Vs Tenecteplase for Thrombolysis After Ischaemic Stroke, and Post Stroke Hyperglycaemia studies were enrolled in order to evaluate observer reliability of CT perfusion (CTP) interpretation in acute stroke. Fifty-seven observers added to the study, with 27 observers analyzing all 24 scans and 17 observers providing repeat readings. For all CTP, the interobserver agreement was good to excellent. For perfusion maps vs noncontrast CT and for mean transit time, delay time, and penumbra map vs cerebral blood volume and cerebral blood flow, the agreement was higher. In the majority of readers, the intraobserver agreement was fair to ample. In summary, for the interpretation of CTP in acute stroke, there are high levels of interobserver and intraobserver agreement, especially of mean transit time, delay time, and penumbra maps.