Objectives-The accuracy of magnetic resonance angiography (MRA) was determi
ned in patients with recently symptomatic tight (80%-99%) carotid stenosis
(on Doppler ultrasound), and the effect of stenosis severity on the accurac
y and interobserver variability of MRA was studied.
Methods-Forty four consecutive patients undergoing intra-arterial angiograp
hy (IAA) before carotid endarterectomy were prospectively studied, in two c
entres with identical MR scanners and sequences. All patients had undergone
Doppler ultrasound, showing a 70% or worse carotid stenosis on the symptom
atic side. MRA and IAA were done during the same admission. The MRA films w
ere each independently and blindly read for percentage stenosis (signal gap
if present) by four observers. The IA angiograms were read separately by o
ne observer, blind to symptoms, and Doppler and MRA results.
Results-Signal gaps on MRA were seen in stenoses ranging from 67% to 99% on
intraarterial angiography. Magnetic resonance angiograms consistently over
estimated the percentage stenosis according to intraarterial angiography. C
linically significant misclassification of stenosis occurred according to M
RA in 7% of patients, and was more frequent as carotid stenosis increased.
Conclusion-Significant diagnostic errors occur with MRA in patients with ti
ght carotid stenosis. Any morbidity occurring as a result of misclassificat
ion by MRA is likely to be offset by the avoidance of complications; howeve
r, this could only be determined with certainty in a randomised controlled