Contrast-enhanced MR angiography for carotid disease

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Abstract
Objective: To compare contrast-enhanced MR angiography (CEMRA) with intra-arterial digital subtraction angiography (DSA) for evaluating carotid stenosis. Methods: A total of 167 consecutive symptomatic patients, scheduled for DSA following screening duplex ultrasound (DUS), were prospectively recruited to have CEMRA. Three independent readers reported on each examination in a blinded and random manner. Agreement was assessed using the Bland-Altman method. Diagnostic and potential clinical impact of CEMRA was evaluated, singly and in combination with DUS. Results: CEMRA tended to overestimate stenosis by a mean bias ranging from 2.4 to 3.8%. A significant part of the disagreement between CEMRA and DSA was directly caused by interobserver variability. For detection of severe stenosis, CEMRA alone had a sensitivity of 93.0% and specificity of 80.6%, with a diagnostic misclassification rate of 15.0% (n = 30). More importantly, clinical decision-making would, however, have been potentially altered only in 6.0% of cases (n = 12). The combination of concordant DUS and CEMRA reduced diagnostic misclassification rate to 10.1% (n = 19) at the expense of 47 (24.9%) discordant cases needing to proceed to DSA. An intermediate approach of selective DUS review resulted in a marginally worse diagnostic misclassification rate of 11.6% (n = 22) but with only 6.8% of discordant cases (n = 13). Conclusions: DSA remains the gold standard for carotid imaging. The clinical misclassification rate with CEMRA, however, is acceptably low to support its safe use instead of DSA. The appropriateness of combination strategies depends on institutional choice and cost-effectiveness issues.