Objective: Ultrasound protocols to measure carotid intima-media thickness (CIMT) differ in the number of carotid walls, segments and angles measured. No published evidence is available to help decide which approach is best, i.e. the most reproducible and providing the largest CIMT progression rate measured with highest precision. We compared different ultrasound protocols in a post-hoc analysis in the 'Osteoporosis Prevention and Arterial effects of tiboLone' (OPAL) study, a 3-year randomized controlled trial among healthy postmenopausal women.
Research design and methods: Based on combinations of 60 CIMT measurements per participant (two sides, two walls, three segments, five angles), 66 theoretical protocols were constructed. Each protocol was assessed and ranked on: (1) reproducibility (intra-class correlation (ICC), mean difference of duplicate scans) and (2) CIMT progression rate and its precision (standard error) in the placebo group.
Results: Duplicate scans at baseline and end of study were available for 675 women (89% of 759 subjects). ICC ranged from 0.69 to 0.88. Mean difference in CIMT of duplicate scans and its standard deviation, ranged from 0.0010 to 0.0137 mm and from 0.0561 to 0.1770, respectively. CIMT rate of progression ranged from -0.0001 to 0.0113 mm/year. The protocols with highest reproducibility and highest CIMT progression-precision were mean common CIMT protocols measuring both near and far wall at > or = 2 angles. The mean maximum protocol measuring three segments at > or = 2 angles performed best, yet with lower estimates as for common CIMT protocols.
Conclusions: In healthy middle-aged subjects mean common CIMT protocols that include measurements at both near and far walls at multiple (> or = 2) angles provide highest reproducibility combined with largest estimates of CIMT progression measured with high precision and are to be recommended in this population.