The carotid artery/ arteries consist of 3 layers- the intima (the inner most thin layer of endothelium), the middle layer or media (formed by smooth muscles) and the outermost layer- the adventitia (formed by loose connective tissue. On grey scale sonography, the long section ultrasound image produces 2 parallel lines - the inner most line is bright (echogenic), thin and corresponds to the intima; the media is the dark line just outer to the intima. The measurement of the total thickness (intima media thickness) or IMT helps assess the arterial wall for presence of plaques or thickening. Normal common carotid artery thickness should be less than 0.9 mm. In the ultrasound images above, the IMT measures 0.6 to 0.7 mm. (normal). 
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