Normal value of carotid intima-media thickness--a surrogate marker of atherosclerosis: quantitative assessment by B-mode carotid ultrasound

BACKGROUND: Carotid intima-media thickness (IMT) is a surrogate marker of atherosclerosis and imparts prognostic information independent of traditional cardiovascular risk factors. Quantitative assessment of IMT using semiautomated border detection software is a new and easy technique that has been previously shown to be accurate, effective, and reproducible. The study is aimed to define the upper limit of carotid IMT at the common carotid artery (CCA) and its bifurcation among a healthy population in the United Kingdom. METHODS: Asymptomatic men and women aged 35 to 75 years, without evidence of clinical atherosclerosis, underwent B-mode carotid duplex ultrasound (Sonos 7500, Philips, Best, The Netherlands). Mean carotid IMT at the far wall of both left and right CCA were quantitatively determined using a semiautomated edge-detection algorithm (Q-lab 4, Philips). Healthy population was defined as participants with no cardiovascular disease and no evidence of diabetes mellitus or hypertension with a body mass index less than 30 kg/m2, serum cholesterol less than 6 mmol/L, and absence of carotid plaque on ultrasound. RESULTS: Of the 453 participants, 137 were found to be healthy. IMT measured at the bifurcation was found to be significantly higher compared with that at the CCA. Carotid IMT in both CCA and its bifurcation increased significantly with age. The upper limits (97.5 percentile) of IMT at CCA for participants age 35 to 39, 40 to 49, 50 to 59, and 60 years or older were 0.60, 0.64, 0.71, and 0.81 mm, respectively, whereas for that at bifurcation were 0.83, 0.77, 0.85, and 1.05 mm, respectively. CONCLUSION: This study demonstrated the value of IMT at CCA and its bifurcation in a healthy population in the United Kingdom using a semiautomated edge-detection software, which is easy to use and reproducible.