COMPARISON OF CAROTID STENOSIS GRADING BY CT ANGIOGRAPHY AND DOPPLER ULTRASONOGRAPHY: HOW THE STATISTICAL METHODS APPLIED INFLUENCE THE RESULTS*

In this study, we compared the measurement of carotid stenosis by computed tomography angiography (CTA) based on the narrowest diameter versus cross sectional area (CSA) with the measurement by color Doppler ultrasonography (CDUS) as a reference standard, and analyzed how the application of different statistical methods affected the result. On 113 carotid arteries with ≥50% stenosis, we quantified the level of correlation among the three measurements, sensitivity, specificity, and differences in the estimated stenosis level. Correlation between both CTA measurements was good with Pearson’s ρ between 0.87 and 0.91 (p<0.001). Correlation between CDUS and CTA measurements was only modest with Pearson’s ρ between 0.2 (p=0.075) and 0.4 (p=0,007) for CDUS CTA (CSA), and between 0.23 (p=0.062) and 0.39 (p=0.008) for CDUS CTA (diameter). Differences in stenosis between CTA (CSA) and CDUS were centered around 0%, and between CTA (diameter) and CDUS around 20%. Sensitivity and specificity for CTA (CSA) method were 81% and 77%, and for CTA (diameter) 23% and 100%, respectively. A good correlation between CSA and diameter measurement just means that these are two related features of stenosis, it does not mean good agreement. CTA (CSA) method better detected surgical stenoses, whereas CTA (diameter) systematically underestimated stenosis level. The study of differences between the measurements indicated agreement better than the calculation of correlation coefficients.