Duplex carotid sonography: criteria for stenosis, accuracy, and pitfalls.

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Abstract
Both carotid bifurcations were examined in 353 patients, over a 20-mo. interval, using a combination of real-time and pulsed Doppler ultrasound (duplex scanning). Angiographic correlation was available in 72 cases. Stenosis of the internal carotid was evaluated using a Doppler input frequency of 5 MHz and a scan angle of 60.degree.. A peak frequency shift of < 3.5 kHz was found to be a sign of .ltoreq. 30% stenosis; 3.5-4 kHz with moderate turbulence suggested 31-50% stenosis, 4-8 kHz 51-90% stenosis and > 8 kHz > 90% stenosis. Subtotal stenosis (> 95%) was manifested by a frequency shift of < 8 kHz, but the waveform was totally distorted. Overall accuracy improved from 77% for the first 6 mo. to 87% for the last 14 mo. For stenosis > 50%, sensitivity improved from 82-97% during this period. Analysis of errors and suggestions for avoiding them are presented.

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