VARIABILITY IN MEASUREMENT OF EXTRACRANIAL INTERNAL CAROTID-ARTERY STENOSIS AS DISPLAYED BY BOTH DIGITAL SUBTRACTION AND MAGNETIC-RESONANCEANGIOGRAPHY - AN ASSESSMENT OF 3 CALIPER TECHNIQUES AND VISUAL IMPRESSION OF STENOSIS

Background and Purpose The degree of stenosis in the extracranial inte rnal carotid artery helps predict the risk of an individual suffering subsequent cerebrovascular ischemic events. Different techniques have evolved to measure stenosis from angiograms, leading to some confusion and a call for the adoption of a single technique. To help choose the most reliable technique, this study assessed observer variability in reporting carotid stenosis for four different techniques, from both di gital subtraction (DSA) and MR angiograms (MRA). Three of the techniqu es used caliper measurements; the fourth was the visual impression of stenosis. Methods From a total of 137 angiograms, caliper measurements were possible on 105 DSAs and 74 MRAs. Measurements from these angiog rams were made by two independent observers on two separate occasions to assess interobserver and intraobserver variation in reporting. Resu lts For DSA, the variability in reporting and the number of clinically significant differences arising as a result were similar for each of the four techniques. While the typical measurement errors for each of the techniques studied were on the order of +/-5%, each technique prod uced some sizable individual differences for the same angiogram, with resultant wide 95% limits of agreement. Observer variability for repor ting MRA was generally a little greater than for DSA. Compared with th e caliper techniques, the visual impression of stenosis technique perf ormed well, particularly for MRA. Conclusions Although observer variab ility in reporting can be considerable, no important differences were found among the different techniques widely used for measuring carotid stenosis.