Doppler flow maps of the carotid artery compared with the findings on angiography.

One noninvasive method of evaluating the condition of the carotid arteries is by the Echoflow Doppler device, which produces colour-coded images of the flow pattern in the arteries. Normal velocities are represented in red, accelerated flow in yellow and turbulences in blue. The authors present the results of Echoflow studies in 317 patients who also underwent cerebral angiography. Of 660 normal carotid vessels, 21 showed appreciable abnormalities on Echoflow study (false positive 3.2%). Of 87 vessels with stenosis of 50% or more, the Echoflow study showed normal flow in 26 (false negative 29.9%). The Echoflow study indicated no abnormalities in 3 of 22 patients with severe stenosis (more than 80%) (false negative 13.6%). Of nine patients with carotid occlusion, the Echoflow study gave normal findings in one (false negative 11.1%). Sensitivity was 70.1%, specificity was 96.9%, with a positive predictive accuracy of 93.9%. Sources of error include misidentification of arteries, signal attenuation (acoustic shadow), hemodynamic changes and timing of the Echoflow study relative to angiography. Combined studies with B-mode ultrasonography and spectral analysis of the Doppler signal should reduce error. These studies should not be used to replace angiography, but to help select for angiography patients for whom the study might be contraindicated because of advanced age or cardiac disease.