Limitations in the accuracy of peak frequency measurements in the diagnosis of carotid disease.

Peak Doppler frequency is an index of the severity of carotid stenosis. Variability in this measurement is examined through in vitro and clinical studies. In vitro studies, using a carotid flow model, show that observers locate a stenosis and interpret the peak frequency differently, and each observer uses a different probe-vessel angle. Clinical studies support these findings. Comparison of 304 carotid Doppler studies with arteriograms demonstrates 90% overall clinical accuracy. Each observer has a consistent range of peak frequency measurements, yet the description of a discrete percent stenosis is limited by observer variability.