Background and Purpose- Computed tomography (CT) perfusion (
CTP) provides potentially valuable information to guide treatment decisions in
acute stroke. Assessment of interobserver reliability of
CTP has, however, been limited to small, mostly single center studies. We performed a large, internet-based study to assess observer reliability of
CTP interpretation in
acute stroke. Methods- We selected 24 cases from the IST-3 (Third International
Stroke Trial), ATTEST (
Alteplase Versus
Tenecteplase for Thrombolysis After
Ischaemic Stroke), and POSH (Post
Stroke Hyperglycaemia) studies to illustrate various perfusion abnormalities. For each case, observers were presented with noncontrast CT, maps of cerebral blood volume, cerebral blood flow, mean transit time, delay time, and thresholded penumbra maps (dichotomized into penumbra and core), together with a short clinical vignette. Observers used a structured questionnaire to record presence of perfusion deficit, its extent compared with ischemic changes on noncontrast CT, and an Alberta
Stroke Program Early CT Score for noncontrast CT and
CTP. All images were viewed, and responses were collected online. We assessed observer agreement with Krippendorff-α. Intraobserver agreement was assessed by inviting observers who reviewed all scans for a repeat review of 6 scans. Results- Fifty seven observers contributed to the study, with 27 observers reviewing all 24 scans and 17 observers contributing repeat readings. Interobserver agreement was good to excellent for all
CTP. Agreement was higher for perfusion maps compared with noncontrast CT and was higher for mean transit time, delay time, and penumbra map (Krippendorff-α =0.77, 0.79, and 0.81, respectively) compared with cerebral blood volume and cerebral blood flow (Krippendorff-α =0.69 and 0.62, respectively). Intraobserver agreement was fair to substantial in the majority of readers (Krippendorff-α ranged from 0.29 to 0.80). Conclusions- There are high levels of interobserver and intraobserver agreement for the interpretation of
CTP in
acute stroke, particularly of mean transit time, delay time, and penumbra maps.