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Interobserver agreement in perfusion computed tomography evaluation in acute ischaemic stroke.

BACKGROUND AND PURPOSE
A growing body of evidence suggests that semiquantitative assessment of perfusion computed tomography (PCT) may improve evaluation of acute ischaemic stroke patients and provide some prognostic values. The Alberta Stroke Program Early CT Score (ASPECTS) is one of the tools quantifying ischaemic changes on CT scans. While introducing PCT for routine evaluation of patients with clinical suspicion of acute stroke in our Neurology Department, we aimed to investigate the agreement in analysis of non-contrast CT (NCCT) and PCT using ASPECTS between neuroradiologists and stroke neurologists.


MATERIAL AND METHODS
We analyzed the data of 34 patients with hemispheric ischaemic stroke, in whom NCCT and PCT were performed within 12 hours after stroke onset. Two pairs of reviewers independently assessed NCCT and PCT [colour-coded maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and time-to-peak (TTP)] using ASPECTS. Based on the literature data, we dichotomized the score. The chosen cut-off points were: 6 vs. <6, 7 vs. <7, and 8 vs. <8. The agreement was determined using kappa statistics.


RESULTS
A better agreement was achieved for PCT maps compared with NCCT scans and when the cut-off point was 7 vs. <7. The results were as follows: for NCCT fair agreement (k=0.27), for CBF and for CBV moderate agreement (k=0.46 and k=0.57, respectively), for TTP substantial agreement (k=0.77).


CONCLUSIONS
A good agreement in semiquantitative assessment of PCT using ASPECTS indicates that it is a reliable tool to analyze acute ischaemic stroke patients and superior to NCCT.