Abstract

An early sign of atherosclerosis is hypertrophy of the arterial wall. Increased intima-media thickness (IMT) is a non-invasive marker of arterial wall alteration, which can easily be assessed in the carotid arteries by high-resolution B-mode ultrasound. There are important differences in B-mode measurements of carotid IMT between laboratories. These might concern on IMT image acquisition (in relation to the segment and/or the wall of measure) as well as determination of the echo boundary defining the IMT interfaces and the difference in relationship between anatomic and sonographic structures of the near and far arterial wall. Measurements derived from the near wall reflect thickness of a part of media and intima influenced by sonographic artefacts, rather than that of the total intima-media complex. Two main approaches are used for measuring IMT: 1) manual measurement at multiple extracranial carotid sites in near and far walls, and 2) automated computerized measurement, restricted to the far wall of the distal common carotid artery. Intra- and inter-observer variabilities have been found to vary in manual measurements between 0.09 to 0.13 mm and 0.12 to 0.18 mm (absolute differences). The best reproducibility of manual IMT-measurements is found at the far wall of the common carotid artery 1 cm from the bulb in the site of two parallel wall contours without local thickening. For automated measurements lower intra- and inter-observer variabilities have been reported. IMT of the common carotid artery is strongly influenced by age. For younger age groups (20 to 30 years) mean IMT values of 0.5 mm have been reported, while IMT values of 0.9 mm have been found for older subjects (60 to 70 years). Carotid IMT correlates with other risk factors such as systolic blood pressure, serum lipids and smoking, as well as being positively linked to the presence and extend of coronary artery disease in both women and men. The demonstration of a correlation between IMT and cardiovascular events such as stroke and myocardial infarction in clinical studies of atherosclerosis progression and cardiovascular outcomes have led to FDA accepting 2D ultrasound as a valid technique in clinical studies of atherosclerosis. Regression or slowing of progression of increased carotid IMT by various antihypertensive and lipid-lowering drugs agents have been reported. In addition to carotid IMT measurement as a predictive value of future vascular events the presence of plaques or stenosis in the carotid artery tree increases drastically the risk for cardiovascular events. Therefore the authors of this article propose the use of high resolution Duplex-Sonography for the assessment IMT of the common carotid artery as well as the detection of plaques and stenosis in clinical practice. In conclusion, high-resolution Duplex-sonography seems promising for the detection, quantification and serial investigations of structural alterations of the arterial wall. The method is sensitive enough to be applied in clinical studies of the progression and regression of early preintrusive atherosclerotic lesions in extracranial carotid arteries. Moreover IMT of the common carotid artery can be used as a therapeutic endpoint.