Carotid Stenosis Index Revisited With Direct CT Angiography Measurement of Carotid Arteries to Quantify Carotid Stenosis

BACKGROUND AND PURPOSE: All carotid stenosis ratio methods are based on the inability of digital subtraction angiography to measure in millimeters. Each method has potential flaws. The Carotid Stenosis Index (CSI) was designed to reduce ambiguities of NASCET and ECST ratios. We test this method's ability to correctly estimate carotid stenosis using direct computed tomography angiography millimeter measures of the carotid arteries. METHODS: Two neuroradiologists reviewed computed tomography angiographies of 268 carotids with atherosclerotic disease. Millimeter measurements were obtained at the narrowest diameter of the residual stenotic lumen, actual carotid bulb diameter (at level of greatest stenosis), and common carotid artery. Pearson correlation compared the CSI estimate of the carotid bulb to the actual carotid bulb measurement. Ratio calculations of the stenosis were performed using (1) CSI carotid bulb estimate and (2) actual carotid bulb measurement as denominator data. A paired-sample Wilcoxon signed rank test compared the results of these 2 ratio measurements per carotid. RESULTS: Interobserver variability was good to excellent (0.64 to 0.87). The CSI estimate of the carotid bulb size overestimated the measured carotid bulb by an average of 1.5 mm in a random distribution (correlation=0.39, N=151). Paired-sample Wilcoxon signed rank test demonstrated a significant difference between the 2 sets of ratios (z-value of -9.87, P<0.001). CONCLUSIONS: Direct measurement of carotid stenosis, vessel wall soft tissues, and computed tomography plaque imaging is now possible with the high-resolution anatomic data present in high-speed computed tomography angiography, alleviating the need for ratios and inaccurate mathematic estimations of carotid anatomy for carotid stenosis quantification.