Pulsed Doppler techniques for measuring instantaneous maximum and mean flow velocities in carotid arteries

A 5 MHz pulsed Doppler instrument measuring instantaneous maximum and mean flow velocities is presented. The maximum velocity estimator is based on the principle of frequency variable filtering controlled by a feedback loop to follow the velocity spectrum envelope. Findings by Doppler and bilateral selective carotid arteriography in 216 patients were compared. Extracranial carotid stenoses were identified by the finding of a vessel segment with locally increased flow velocity. Peak Velocity Ratio (PVR) was calculated from maximum velocities measured in the stenosis and in more distal Internal Carotid Artery (ICA) segments. Using PVR, ICA stenoses greater than 20% were detected with sensitivity 96%, specificity 94%, positive accuracy 94% and negative accuracy 96%. Total ICA occlusions were identified with sensitivity 97% and specificity 99%.