Comparison of intra-arterial digital subtraction angiography, magnetic resonance angiography and duplex ultrasonography for measuring carotid artery stenosis

Background: Duplex ultrasonography and magnetic resonance angiography (MRA) are becoming competitive alternatives to angiography for determining the degree of internal carotid artery (ICA) stenosis. Varying reports have been published regarding the suitability of each technique for grading ICA disease. This retrospective study compared the merits of these three modalities for measuring ICA stenosis. Methods: One hundred and eleven patients being considered for carotid endarterectomy underwent intra-arterial digital subtraction angiography (DSA) via arch injection. Duplex imaging was performed in all patients and MRA. in 50. The degree of carotid stenosis estimated by the three modalities was compared. Results: There was good correlation between subjectively graded MRA and DSA images (r = 0.87, P < 0.001, n = 82 carotids) but poor correlation for objective estimates. MRA tended to underestimate the degree of stenosis (bias -4.5 per cent) compared with DSA, but showed good correlation with duplex ultrasonography estimates r = 0.86, P < 0.001, n = 87 carotids). Both non-invasive modalities produced high values of sensitivity and specificity in estimating stenoses of greater than 70 per cent. MRA was less sensitive for distinguishing between severe stenosis and complete occlusion. Conclusion: This study did not resolve the debate regarding the method of choice as both MRA and duplex ultrasonography were accurate for imaging carotid stenoses.