Doppler spectrum analysis and vascular imaging in the diagnosis of extracranial carotid artery disease.

Ultrasound methods are well suited for the exploration of the carotid system. High resolution echography can visualize atheromatous defects on the vessels walls with a resolution better than one mm, whereas Doppler examination detects haemodynamic disturbances due to these plaques. Conventional Doppler examination can reveal moderate or severe stenosis (greater than 60%); the recent development of frequency analysis of the Doppler audio signal makes now possible the detection of very light haemodynamic disturbances due to low grade stenosis even as small as 15%. Spectral distribution abnormalities have been classified in four grades according to their amplitude. The combination of the morphological and functional data provided by echography and Doppler spectrum analysis has drastically increased the diagnostic possibilities of the ultrasound methods in the field of the extracranial vascular pathology. With a new duplex system which combines echography and C.W. Doppler examination (duplex probe) it is possible to detect, and quantify carotid stenosis (in percentage of the lumen reduction), and to evaluate blood flow volume in ml/mn.