Rapid assessment of perfusion-diffusion mismatch.
OBJECTIVE
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 >or=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.
Department of Neurology, Royal Melbourne Hospital, University of Melbourne, Melbourne, Australia. ken.butcher@ualberta.ca
Ken
K
Butcher
Mark
M
Parsons
Louise
L
Allport
Sang Bong
SB
Lee
P Alan
PA
Barber
Brian
B
Tress
Geoffrey A
GA
Donnan
Stephen M
SM
Davis
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000098:blood supply / Q000473:pathology / Q000503:physiopathology; D002544:Cerebral Infarction / Q000175:diagnosis* / Q000473:pathology* / Q000503:physiopathology; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity; D015912:Thrombolytic Therapy