The purpose of this study was to prospectively compare CT angiography with conventional angiography for detecting stenosis at the carotid bifurcation.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 ste...