Other than from ulceration, TIA's and strokes originating from the extracranial carotid circulation result either from plaque embolization or from flow reduction, i.e. the disease process is already at an advance stage. Detection at an earlier stage than this can identify those persons at risk of developing stroke and could enable lifestyle and/or medication changes to slow or reverse the disease process. Such early changes in the artery wall can be detected by measuring the distance between the intima and the far wall of the media - the Intima-Media wall thickness (IMT).

The most reproducible measurement of IMT is from the far wall of the mid-distal common carotid artery. A 7-12MHz is used to locate the mid/distal common carotid. The grayscale image is optimized with the wall horizontal in zoom mode (using harmonics if available). The first distance cursor is positioned no closer than 1cm to the bifurcation (or the beginning of the carotid bulb), and the second cursor at the media-adventitia interface. At least four positions should be measured and averaged, unless the imager offers an automated system, allowing selection of the segment to be measured.

Age, sex and race influence IMT values, so these should be considered when reporting results and assigning degrees of risk.