Effect of Doppler Angle in Diagnosis of Internal Carotid Artery Stenosis

Objective. The purpose of this study was to compare velocity measurements obtained with 2 fixed insonation angles and to investigate whether there is a difference in their ability in determining internal carotid artery (ICA) stenosis. Methods. Eighty‐seven patients with ICA stenosis were examined with color duplex ultrasonography. Velocity measurements were made at 60° and 45° insonation angles, and they were compared with Bland‐Altman and receiver operating characteristic curve analysis. Results. Peak systolic velocity (PSV) and end‐diastolic velocity measurements obtained at the 60° insonation angle were higher compared with those obtained at the 45° insonation angle (24.2% and 24.7%, respectively). The ICA‐to‐common carotid artery PSV ratio, conversely, was slightly higher (3.9%). Although the threshold values for the same velocity parameters obtained at 2 different insonation angles were different, the accuracy ratios (sensitivity and specificity) were not. With application of the Society of Radiologists in Ultrasound consensus criteria to the data obtained at either of the 2 insonation angles, the accuracy ratios of PSV and end‐diastolic velocity were found to be statistically different. In the ICA‐to‐common carotid artery PSV ratio, however, there were no statistically significant differences in the accuracy ratios. Conclusions. Doppler velocity measurements made at different fixed insonation angles show considerable differences. In determining ICA stenosis, although optimal thresholds are different, the diagnostic performance is not different. In determining ICA stenosis with color duplex ultrasonography, angle‐specific thresholds must be determined, and examinations must be made at a fixed angle.