Common Carotid Intima-Media Thickness and Risk of Stroke and Myocardial Infarction : The Rotterdam Study

To assess whether carotid atherosclerosis measured by B-mode ultrasound is related to cardiovascular risk factors, 386 cases with carotid artery wall thickening and an equal number of controls free of arterial intima-media thickening were drawn from the cohort of the Atherosclerosis Risk in Communities (ARIC) Study examined in four communities in the United States between 1988 and 1990. Cases and controls were individually matched on sex, race, age group, study center, and date of examination. The mean values of total cholesterol, low density lipoprotein (LDL) cholesterol, total triglyceride, blood pressure, and pack-years of cigarette smoking were higher in cases than controls. Mean high density lipoprotein (HDL) cholesterol was lower in cases than controls. Case-control differences were all statistically significant. Multivariable-adjusted odds ratios point to differences of considerable magnitude in the risk of carotid atherosclerosis between groups defined by clinical and public health-oriented risk factor cut-points.

A B-mode [two-dimensional (2D)] image from the carotid artery may be described as containing seven echo zones. The aim of the present work is to discuss how lumen diameter and wall thickness can be measured from these zones, and to review some of the basic principles of ultrasound physics and imaging. Simple experiments were performed to identify the echoes defining intima-lumen interfaces. The results showed that: (1) The intima-media thickness of the near wall cannot be measured in a valid way. (2) The lumen diameter of a blood vessel is defined by the distance from the leading edge of the intima-lumen interface of the near wall (echo zone 3) to the leading edge of the lumen-intima interface of the fall wall (echo zone 5). (3) Previously published studies have validated the intima-media complex of the far wall as the distance from the leading edge of the lumen-intima interface of the far wall to the leading edge of the media-adventitia interface of the far wall (echo zone 7). We suggest that if measurements on the near wall are performed, measurements from the far wall should also be presented separately, and if lumen diameter is measured, that this measurement is carried out according to the leading edge principle. We describe a computerized analysing system for the measurement of wall thickness and plaque area on the carotid and femoral arteries. The system is based on a low-cost PC and a frame grabber board and calculates minimum, maximum and mean values of lumen diameter and wall thickness from a section of the artery.