SPECIFICITY OF MR-ANGIOGRAPHY AS A CONFIRMATORY TEST OF CAROTID-ARTERY STENOSIS

PURPOSE: To estimate from available literature the specificity (true-n egative rate) of MR angiography for detecting severe carotid artery st enoses when applied as a confirmatory test after screening with duplex Doppler sonography. METHODS: We reviewed the pertinent MR angiographi c literature published between 1990 and 1994 and recalculated the spec ificity of MR angiography after deleting from the database results for normal vessels and for vessels with mild and moderate stenoses, since the study of these vessels is not germane to an exploration of the ut ility of MR angiography as a confirmatory test. RESULTS: Seventeen art icles provided data for our analysis. We divided vessels into four cat egories on the basis of data supplied within each article. Seven of th e articles provided data that could be configured to match the categor ies used in the North American Symptomatic Carotid Endarterectomy Tria l (NASCET). In one study, the criterion of severe stenosis was more th an 70% constriction, but the moderate category was limited to stenoses of 50% to 69%. The remaining series defined severe stenoses as more t han 80% (four series), more than 75% (two series), or more than 60% (t hree series) constriction. The stated specificity of MR angiography ra nged from 64% to 100%. Before revision, 15 of 17 articles had stated s pecificity values above 75%. Our recalculated values ranged from 18% t o 100%. Only seven of 17 studies would have had MR angiographic specif icity of greater than 75%. Nine of 17 articles would have had specific ities of less than 60%. For all articles specifically identifying vess els with false-positive findings at sonography, the specificity of MR angiography was 16%. CONCLUSION: To base specificity values for MR ang iography as a confirmatory test of carotid artery stenosis on studies that include nondiseased vessels incurs spectrum bias. The actual spec ificity for MR angiography as a confirmatory test remains unknown, but it is lower than that reported in the literature.