
The main purpose of studying the carotid arteries (the common carotid artery (CCA), the internal carotid (ICA) and the external carotid (ECA) and lastly the Vertebral artery - is to assess the possibility of stroke due to stenosis and embolism. Any of these conditions in the carotid system, can be fatal at worst or at best result in serious disability including hemiplegia, or partial paralysis.
The following are the main steps to evaluating the carotid arterial system:-
1) differentiate the CCA from the IJV (internal jugular vein)- this is easy as the Jugular veins shows a typical venous flow on Color Doppler imaging and has thin walls which are not visualized clearly on B-mode ultrasound imaging.
2) differentiate the ICA from the ECA. Here the going becomes a little difficult, as the bifurcation of the CCA into the ICA and ECA is not always clearly visualized (see image above).
For more details of step -2 (see: http://www.ultrasound-images.com/vascular.htm )
The temporal tap sign : see Spectral Doppler waveforms of ECA below) is vital to clearly distinguish the ECA from the ICA.


3) Thirdly the next step in carotid sonography is visualization of the carotid arterial walls and the measurement of the combined thickness of the inner layer-the intima and the middle layer- the media. This is called IMT or intima media thickness.





