• Colour flow Duplex scan was introduced by Strand-ness et al. .
• It was a major turning point in vascular diagnosis, by providing safe, noninvasive and reliable technology to evaluate both the morphological changes within the arterial wall and their repercussions on blood flow.
• It combines real-time B-mode ultrasound imaging technology with a pulsed Doppler flow detector and spectral analyser.
• The effect of arterial stenosis on flow is recognized by acceleration with a significant increase in peak systolic and diastolic velocities in association with increased disorganization of the velocity spectra (Fig. 2.2.5c).
a NASCET: 1-(A/C)x 100 b Arterial a rea/Luminal area c
Fig. 2.2.5a-c Quantification of the degree of stenosis by colour flow Duplex scan. a Diameter measurement of longitudinal section. b Area measurement on cross-section. c Haemodynamic assessment with peak systolic and end diastolic velocities calculation a NASCET: 1-(A/C)x 100 b Arterial a rea/Luminal area c
Fig. 2.2.5a-c Quantification of the degree of stenosis by colour flow Duplex scan. a Diameter measurement of longitudinal section. b Area measurement on cross-section. c Haemodynamic assessment with peak systolic and end diastolic velocities calculation
Several limitations of colour flow Duplex scan are recognized:
• Difficult insonation at the base of the neck with failure to identify proximal stenotic lesions (innominate artery, left common carotid) that may require treatment, suspected by abnormal velocity tracings in the proximal common carotid artery.
• Impossibility to visualize the distal segments of the internal carotid artery, which may be diseased (distal and/or siphon stenosis).
Distinction between high-grade stenosis and complete occlusion, which could be overcome by new technological advances for recording low velocities and the use of acoustic contrast .
Absence of information on the intracranial circulation and detection of stenosis and arterial aneurysms. The clinical relevance of concomitant intracranial occlusive disease for the management of extracranial carotid disease has been controversial; siphon stenosis is rare - <6% - and its significance as a risk factor af fecting the outcome of carotid endarterectomy or as a cause of recurrence of symptoms has not been confirmed .
Cerebral aneurysms are also a rare event (<2%)  and can be suspected on the basis of clinical symptomatology, or by modern brain imaging techniques.
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