Background: With an increasing number of randomized studies investigating the anti-atherosclerotic effects of different preventive measures utilizing ultrasound evaluation of intima-media thickness of the carotid artery as the primary endpoint, it is of interest to critically evaluate the validity of these measurements.
Methods and results: Small structures, the dimensions of which are far beyond the resolution limits of the equipment, may produce an ultrasound echo. Thus the very thin interface between two fluids such as oil and water will produce an echo that is much thicker than the interface itself, which is infinitely thin. Thus, the thickness of any echo defining an interface is of no anatomical interest. The thickness of an anatomical entity, such as the intima-media complex, is always defined as the distance between the leading edges of two different echoes. In spite of the similarity of the near and far wall images the thickness of the intima-media complex can only be measured in a valid way in the far wall position.
Conclusions: We conclude that main outcome variables in ultrasound studies of atherosclerosis should be from the far wall. It would seem advisable to focus on far wall common carotid artery and carotid artery bulb recordings. It is likely that including near wall measurements and measurements from the internal carotid artery will decrease measurement precision and lead to increases in sample size in scientific studies; or even dilute positive results in an otherwise well designed study.