Potential for Significantly Overestimating Doppler Velocity Measurements in Angulated Internal Carotid Arteries

Abstract

Purpose

Carotid artery tortuosity presents significant technical challenges in angle correction and cursor alignment. Although these spectral Doppler issues have been known to hinder carotid ultrasound accuracy, the potential for these errors is generally unknown. We evaluated angle correction and velocity measurements in patients with insignificant internal carotid artery (ICA) disease and angulated vessels.

Methods

Data from assenting patients with ICA tortuosity and insignificant (<50% diameter reduction) disease were prospectively entered into a database during a 15-month period. Only initial duplex examinations were included in this study. Tortuosity was defined as an ICA “S”-shaped curvature with at least one area of <90-degree angulation. Eight peak systolic velocity (PSV) measurements were performed, the first immediately before the first bend in the S-curvature (V1), the second at the 60-degree angle at the apex of the first curvature (V2), the third at the 0° angle at the apex of the first curvature (V3), the fourth at the first curvature apex and angle corrected to the inside wall after the curvature (V4), the fifth at the 60-degree angle at the apex of the second bend in the S-curvature (V5), the sixth at the zero-degree angle at the apex of the second curvature (V6), the seventh at the second curvature apex and angle corrected to the inside wall after the second curvature (V7), and the eighth after the second bend in the S-curvature (V8). Insignificant ICA disease was defined by PSV of <125 cm/sec.

Results

A total of 47 patients and 56 vessels were analyzed. Mean PSV (cm/sec) and standard deviation (SD) for the eight PSV measurements were as follows: 76.4/20.0 (V1), 137.8/37.8 (V2), 67.5/18.6 (V3), 86.7/24.8 (V4), 138.8/37.6 (V5), 66.2/17.6 (V6), 91.1/25.6 (V7), and 77.0/19.9 (V8). All PSV measurements were less than 125 cm/sec at the apex of the curvature when we used a zero-degree Doppler angle of incidence (V3 and V6). A minority of velocities were overestimated when angle corrected to the inside walls of the first and second bend, 7% (V4) and 11% (V7), respectively. The majority of V2 (71%) and V5 (70%) PSV measurements were significantly overestimated.

Conclusions

The use of a 60-degree Doppler angle of incidence at the apex of tortuous ICA vessels resulted in significant overestimations of PSV in ≥70% of all vessels analyzed. Spectral analysis within this area should be standardized at zero degrees to minimize false positive impressions of hemodynamically significant carotid occlusive disease.