Carotid artery stenosis: a prospective comparison of CT angiography and conventional angiography.

OBJECTIVE: The purpose of this study was to prospectively compare CT angiography with conventional angiography for detecting stenosis at the carotid bifurcation. SUBJECTS AND METHODS: Thirty-five patients referred for evaluation of carotid artery disease were studied with conventional angiography followed by CT angiography 4-24 hr later. Seventy carotid arteries were studied. CT angiograms were acquired by using 40-sec spiral scans with a 2-mm/sec table speed, 2-mm beam collimation, and IV iodinated contrast material injected at 2.5 ml/sec. Studies were interpreted on the CT workstation by using three-dimensional shaded surface objects and multiplanar reformations requiring 10-15 min per artery. The conventional and CT angiograms were interpreted by separate observers who did not know the results of the other imaging study. The degree of stenosis was determined by using the guidelines of the North American Symptomatic Carotid Endarterectomy Trial collaborators. Each artery was categorized as normal, mildly stenosed (1-29%), moderately stenosed (30-69%), severely stenosed (70-99%), or occluded. RESULTS: The degree of carotid artery stenosis on the CT angiograms correlated well with that seen on the conventional angiograms (r = .928, p < .001). With CT angiography, all occluded internal carotid arteries were correctly identified, and no arteries were wrongly classified as occluded. The degree of stenosis was overestimated on CT angiograms by greater than 10% in 16 arteries, especially when calcified atherosclerotic plaque was present. In some of these cases, the severity of the stenosis was underestimated on the conventional angiograms. All arteries, except one, with severe disease seen on conventional angiograms were correctly classified on the basis of the results of CT angiography. CONCLUSION: Results of CT angiography had a high degree of correlation with results of conventional angiography in the evaluation of carotid artery stenosis. CT angiography is multiplanar and allows differentiation of calcified plaque from contrast material, which provides information about plaque calcification, ulceration, and size that cannot be obtained with conventional angiography.