Colour-coded carotid Doppler imaging: an angiographic comparison of 324 bifurcations

The accuracy of a colour-coded Doppler ultrasound imaging system in the assessment of the extracranial carotid tree is presented. A series of 162 consecutive patients (324 bifurcations) were assessed with angiographic control. Doppler frequency shifts of between 3600 and 5000 Hz, corresponding to yellow on the colour code, detected carotid arteries that were stenosed greater than or equal to 50% with a sensitivity of 95%, a specificity of 72% and an overall accuracy of 81%. At frequency shifts of over 5000 Hz corresponding to the blue code, the sensitivity was 83%, specificity 90% and accuracy 87%. With highly stenosed lesions (90-99%), 24% were incorrectly diagnosed as occlusion by the imager. In those cases with a haemodynamically significant lesion on one side there is no evidence of a compensatory increase in velocity on the other side. The technique is readily learnt but an awareness of its pitfalls is essential for accurate scanning and these are discussed. Carotid Doppler imaging has superseded phono-angiography and peri-orbital Doppler examination in our laboratory and is used with the oculoplethysmograph in the routine assessment of patients with suspected carotid bifurcation disease.