• James E Siegler, Andrew Olsen, Johannes Pulst-Korenberg, Daniel Cristancho, Jon Rosenberg, Lindsay Raab, Brett Cucchiara, and Steven R Messé.
• Department of Neurology, Hospital of the University of Pennsylvania, Philadelphia, PA.
• J Neuroimaging. 2019 Sep 1; 29 (5): 573-579.

Background And PurposeAutomated computed tomography perfusion (CTP) is recommended to inform selection of stroke patients for thrombectomy >6 hours from last known normal (LKN). However, artifacts on automated perfusion output may overestimate the tissue at risk leading to misclassification of thrombectomy eligibility in some patients.MethodsWe conducted a retrospective multisite study of consecutive patients with anterior large vessel occlusion (LVO) undergoing CTP (6/2017-12/2017). The primary outcome was the RAPID automated Tmax  > 6 seconds volume that was discordant with clinical symptoms and vessel imaging, manually assessed by two independent readers. The discordant penumbral volume was compared to the automated output and corrected mismatch ratios were generated.ResultsOf 410 consecutive patients who underwent CTP for suspected stroke, 60 (15%) had acute anterior circulation LVO. Of these, 26 (43%) had Tmax > 6 seconds abnormalities discordant with clinical symptoms and vessel imaging. There was strong interrater agreement on artifact volume (r2 = 0.927). Among patients with discordant Tmax imaging, the median artifactual volume was 12cc (IQR 3-21cc), accounting for a median of 8% of the automated Tmax > 6 seconds volume (IQR 3-16%, range 1-64%). Recalculation of the Tmax > 6 seconds volume resulted in 1 patient being reclassified as having an "unfavorable" mismatch ratio (2.04-1.40).ConclusionNearly half of patients had evidence of artifactual penumbral imaging on automated CTP, which rarely lead to misclassification of thrombectomy eligibility. Although artifactual findings are reliably identified by trained raters, our results emphasize the need to evaluate CTP results with knowledge of the patient's clinical symptoms and vascular imaging.© 2019 by the American Society of Neuroimaging.

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