Evaluation of cross-sectional luminal morphology in carotid atherosclerotic disease by use of spiral CT angiography.

BACKGROUND AND PURPOSE This study sought to determine the frequency of noncircular lumens in patients with significant carotid atherosclerotic disease and to evaluate the effect of noncircular lumens on stenosis measurement derived from angiographic projections. METHODS One hundred consecutive patients presenting with an internal carotid artery stenosis of at least 50% were imaged with spiral CT angiography. The transverse morphology of the diseased lumen was assessed on axial images, and the frequency of noncircular lumens was determined. In these cases, maximum intensity projection angiograms were reconstructed in standardized angiographic planes and in a plane selected according to the luminal obliquity, which was chosen to optimize the angiographic representation of the maximal stenosis. North American Symptomatic Carotid Endarterectomy Trial (NASCET) measurements were calculated from the maximum intensity projection images, and differences between values obtained from standard and optimized projections were recorded. RESULTS Noncircular lumens were observed in 18 of 100 patients and consisted of elliptical and linear transverse profiles. The transverse orientation of the lumen in these cases ranged from +90 degrees to -87 degrees relative to the anteroposterior plane. An increase in the calculated NASCET stenosis was demonstrated when measurements were obtained from angiographic reconstructions obtained in the exact plane of the luminal obliquity compared with standard angiographic projections. As a result, the stenosis severity was upgraded from moderate to severe in 2 patients. CONCLUSIONS Noncircular transverse luminal profiles are not uncommon and may introduce error into NASCET calculations obtained from standard angiographic projections.