DIAGNOSTIC NEURORADIOLOGY Correlation of volumetric mismatch and mismatch of Alberta Stroke Program Early CT Scores on CT perfusion maps Ke Lin & Otto Rapalino & Benjamin Lee & Kinh G. Do & Amado R. Sussmann & Meng Law & Bidyut K. Pramanik Received: 11 May 2008 / Accepted: 26 August 2008 / Published online: 12 September 2008 # Springer-Verlag 2008 Abstract Introduction We aimed to determine if volumetric mis- match between tissue at risk and tissue destined to infarct on computed tomography perfusion (CTP) can be described by the mismatch of Alberta Stroke Program Early CT Score (ASPECTS). Materials and methods Forty patients with nonlacunar middle cerebral artery infarct <6 h old who had CTP on admission were retrospectively reviewed. Two raters seg- mented the lesion volume on mean transit time (MTT) and cerebral blood volume (CBV) maps using thresholds of >6 s and <2.0 mL per 100 g, respectively. Two other raters assigned ASPECTS to the same MTT and CBV maps while blinded to the volumetric data. Volumetric mismatch was deemed present if ≥20%. ASPECTS mismatch (=CBV ASPECTS - MTT ASPECTS) was deemed present if ≥1. Correlation between the two types of mismatches was assessed by Spearman’ s coefficient (ρ). ROC curve analyses were performed to determine the optimal ASPECTS mismatch cut point for volumetric mismatch ≥20%, ≥50%, ≥100%, and ≥150%. Results Median volumetric mismatch was 130% (range 10.9–2,031%) with 31 (77.5%) being ≥20%. Median ASPECTS mismatch was 2 (range 0–6) with 26 (65%) being ≥1. ASPECTS mismatch correlated strongly with volumetric mismatch with ρ =0.763 [95% CI 0.585–0.870], p <0.0001. Sensitivity and specificity for volumetric mis- match ≥20% was 83.9% [95% CI 65.5–93.5] and 100% [95% CI 65.9–100], respectively, using ASPECTS mis- match ≥1. Volumetric mismatch ≥50%, ≥100%, and ≥150% were optimally identified using ASPECTS mismatch ≥1, ≥2, and ≥2, respectively. Conclusion On CTP, ASPECTS mismatch showed strong correlation to volumetric mismatch. ASPECTS mismatch ≥1 was the optimal cut point for volumetric mismatch ≥20%. Keywords Perfusion computed tomography . Perfusion diffusion mismatch . Alberta Stroke Program Early CT Score . Ischemic stroke . Recanalization therapy Introduction A common presenting profile of acute ischemic stroke is a mismatch between the amount of tissue at risk of infarction and the amount of tissue that is already destined to infarct. The “mismatch hypothesis” asserts that this difference represents potentially salvageable tissue (ischemic penumbra) and is (1) detectable by dynamic perfusion imaging and (2) critical to patient selection for thrombolysis beyond the conventional 3-h window. Prospective randomized stroke trials, such as Desmoteplase in Acute Stroke (DIAS) [1], Diffusion-weighted imaging Evaluation for Understanding Stroke Evolution (DEFUSE) [2], and Echoplanar Imaging Thrombolysis Evaluation Trial (EPITHET) [3], tested the mismatch hypothesis using magnetic resonance (MR) perfu- sion-weighted (PWI) and diffusion-weighted imaging (DWI). In these trials, a volumetric mismatch of at least 20% between the region of perfusion abnormality and the zone of restricted Neuroradiology (2009) 51:17–23 DOI 10.1007/s00234-008-0454-y K. Lin (*) : O. Rapalino : B. Lee : K. G. Do : A. R. Sussmann : B. K. Pramanik Department of Radiology, NYU Medical Center/Bellevue Hospital, 462 First Avenue, NBV 3W39, New York, NY 10016, USA e-mail: kelinmd@gmail.com M. Law Department of Radiology, Mount Sinai Medical Center, New York, NY, USA