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(Stroke. 2008;39:75.)
© 2008 American Heart Association, Inc.

Original Contributions

Rapid Assessment of Perfusion–Diffusion Mismatch

Ken Butcher, MD, PhD; Mark Parsons, PhD, FRACP; Louise Allport, FRACP; Sang Bong Lee, PhD; P. Alan Barber, PhD, ZRACP; Brian Tress, FRACR; Geoffrey A. Donnan, MD, FRACP; Stephen M. Davis, MD, FRACP for the EPITHET Investigators

From the Department of Neurology (K.B., L.A., S.D.) and Radiology (B.T.), Royal Melbourne Hospital, University of Melbourne, Melbourne Australia; the Department of Neurology (K.B.), University of Alberta, Edmonton, Alberta, Canada; the Department of Neurology (S.B.L.), Catholic University of Korea, Seoul, South Korea; the Department of Neurology (P.A.B.), Auckland City Hospital, Auckland, New Zealand; the Department of Neurology (M.P.), John Hunter Hospital, Newcastle, Australia; and the Department of Neurology (G.D.), Austin Hospital, Melbourne, Australia.

Correspondence to Ken Butcher, MD, PhD, 2E3.13 WMC Health Sciences Centre, University of Alberta, Edmonton, Alberta, Canada. E-mail ken.butcher{at}ualberta.ca

Background and Purpose— For MR perfusion–diffusion (PWI-DWI) mismatch to become routine in thrombolysis patient selection, rapid and reliable assessment tools are required. We examined interrater variability in PWI/DWI volume measurements and developed a rapid assessment tool based on the Alberta Stroke Program Early CT Scores (ASPECTS) system.

Methods— DWI and PWI were performed in 35 patients with stroke <6 hours after symptom onset. DWI lesion and PWI (time to peak) volumes were measured with planimetric techniques by 4 raters and the 95% limits of agreement calculated. ASPECT scores were assessed separately by 4 investigators (2 experienced and 2 inexperienced) for DWI (MR DWI scores) and PWI (MR time to peak scores). MR mismatch scores were calculated as MR DWI-MR time to peak scores.

Results— Interobserver variability was much greater for PWI (95% limit of agreement=±72.3 mL) than for DWI (95% limit of agreement=±12.6 mL). A semiautomated PWI volume (time to peak+2 s) was therefore used to calculate mismatch volume. MR mismatch scores 2 predicted 20% PWI-DWI mismatch by volume with mean 78% sensitivity (range, 72% to 84%) and 88% specificity (range, 83% to 90%). There was excellent agreement on mismatch classification using MR mismatch scores between experienced raters (weighted kappa scores of 0.94) with agreement in 34 of 35 cases. Agreement was less consistent between inexperienced raters (weighted kappa=0.49, 28 of 35 cases).

Conclusions— Variability in planimetric mismatch measurements arises primarily from differences in PWI volume assessment. High specificity and interrater reliability may make MR mismatch scores an ideal rapid screening tool for potential thrombolysis patients.

Key Words: brain imaging • cerebral blood flow • cerebral infarct • diffusion-weighted imaging • perfusion-weighed imaging