BLINDED-READER COMPARISON OF MAGNETIC-RESONANCE ANGIOGRAPHY AND DUPLEX ULTRASONOGRAPHY FOR CAROTID-ARTERY BIFURCATION STENOSIS

Background and Purpose We compared two-dimensional time-of-flight magn etic resonance angiography (MRA) and duplex ultrasonography with arter iography for the detection of 70% to 99% stenoses at the carotid arter y bifurcation (ie, surgical disease according to findings of the North American Carotid Endarterectomy Trial). Methods Three blinded readers independently measured stenoses on MRA in 73 vessels from 38 patients . Duplex ultrasonography was available in 66 vessels from 35 of these patients, and blinded reading was performed by one reader. Comparison was made to arteriography. Results Magnetic resonance angiography demo nstrated a sensitivity of 92.4%, specificity of 74.5%, and negative pr edictive value of 95.8% for 70% to 99% stenoses. Interobserver agreeme nt was high (kappa=0.91). Absence of signal at stenoses with evidence of distal flow usually, but not always, corresponded to surgical disea se. Duplex ultrasonography demonstrated a sensitivity of 81.0%, specif icity of 82.2%, and negative predictive value of 90.2% for surgical di sease. There was no significant difference between MRA and duplex ultr asonography for the sensitivity or specificity in detecting 70% to 99% stenoses (P>.1, exact form of the McNemar test). MRA had no false pos itives or false negatives for complete occlusions of the carotid arter y, whereas duplex ultrasonography missed one occlusion and falsely cal led two patent vessels occluded. In seven cases, both MRA and duplex u ltrasonography overestimated stenoses to miscategorize them as surgica l disease. Conclusions Although the sensitivity and specificity of MRA and duplex ultrasonography are not significantly different for distin guishing surgical and nonsurgical degrees of stenosis at the carotid b ifurcation, MRA has some advantages that may make it the screening tes t of choice. Concordant MRA and duplex ultrasonography for surgical di sease does not necessarily obviate the need for catheter arteriography .