B-Mode ultrasound imaging: prospective investigation of carotid atherosclerosis

High resolution B-mode ultrasonography is a non-invasive technique that allows the visualization of both lumen and walls of the superificial arteries. This technique allows to visualize on the vessel wall two echogenic lines separated by a relatively anechoic space. The two lines are generated by the blood-intima and media-adventitia interfaces, and the distance between them identifies a complex previously defined as “intima-media thickness” (IMT). It is now generally accepted that an increased IMT of extra cranial carotid arteries may represent an expression of carotid and possibly also of coronary atherosclerosis. In the last years a number of epidemiological and clinical trials designed to identify novel atherosclerotic risk factors as well as to define the progression/regression of atherosclerosis, induced by pharmacological or dietary approaches, have been carried out using the IMT of extracranial carotid arteries as a “surrogate” of coronary atherosclerosis. The follow-up period of the longitudinal studies, usually, did not exceed two or three years, and the IMT changes that may take place in these relatively short-term periods were always small (0.02-0.04 mm/year). Therefore, to appreciate these little IMT changes, methods for high quality IMT measurements have been developed. Specifically, studies have been performed in order to evaluate the feasibility and reproducibility of IMT measurements. The results of these studies indicate that several variables affect the quality of IMT ultrasonographic measurements. The following have to be considered: 1) the resolution of ultrasonographic instrumentation, 2) the sonographers/readers performance, 3) the post-processing instrumentation, 4) the IMT changes related to the cardiac cycle, 5) the choice of the end-points (mean-IMT, mean-MAXIMT or single-MAXIMT) and of the carotid segment to be investigated (common carotid, bifurcation.... or 12 sites), 6) the choice of the wall to analyse (near wall, far wall or both). Some of these sources of variability will be described and discussed.