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Hypoechoic wall, inner bright line produced by reflection from the interface between the intimal surface and the blood.

Internal Carotid Artery (ICA)

Low resistance arterial flow (broad systolic peaks and diastolic flow), larger than ECA, posterior and lateral position, no branches

External Carotid Artery (ECA)

High resistance flow (decreased or absent diastolic flow), smaller than ICA, anterior and medial position, temporal tap will appear on the waveform of ECA.
Stenosis > 70% requires endarterectomy. Evaluated by Doppler Peak Systolic Velocity PSV, End-Diastolic Velocity EDV and ratio of PSV(ICA) / PSV(CCA).

No flow means complete occlusion or severe stenosis not detectable by Doppler. Complete occlusion is not amenable for surgery but severe stenosis is → order MRA or CTA.

Secondary sign of ICA occlusion is externalization of the CCA waveform (all CCA flow goes into ECA). If there is an occlusion of the CCA, collaterals through the neck develops from contralateral ECA and retrograde flow can be seen in ipsilateral ECA which feed ipsilateral ICA.

Vertebral arteries

Reversal of flow indicates stenosis or occlusion at the subclavian or innominate artery - subclavian steel; develops as stenosis increases from partial steel to full

Jugular Vein thrombosis

Loss of characteristic venous pulsatile waveform, usually after central venous catheters