Background: Carotid intima-media thickness (IMT) is as an indicator of atherosclerosis, and manual measurement of IMT (manual IMT) is the most applied method to assess atherosclerosis. Recently, a newly developed software allows semi-automatic measurement of mean IMT (auto IMT). This study aimed to compare the feasibility and reproducibility of manual IMT and auto IMT measurement in healthy subjects. Furthermore, we investigated the relationship between surrogate markers of atherosclerosis and the IMT obtained by using the 2 methods.
Methods: This study included 50 healthy subjects (19 men and 31 women) with a mean age of 29±11 years who had no cardiovascular disease, hypertension, diabetes mellitus, or smoking habit. Ultrasound examination of the right and left common carotid arteries (CCAs) was performed and images along with longitudinal axis were recorded by GE Vivid7. Manual measurements of IMT were taken at the far wall approximately 1–2 cm proximal to the beginning carotid bulbs. Region of interest extended from the beginning of the carotid bulbs up to 2 cm proximal to the beginning of the carotid bulbs. Auto IMT of the CCAs were measured using a semi-automated edge-detection software. Stiffness parameter β of both CCAs was measured using M-mode ultrasonography, and bilateral cardio-ankle vascular index (CAVI) was estimated using a VaSeraVS-1000. Mean values of manual IMT, auto IMT, stiffness parameter β, and CAVI were calculated by averaging the results obtained for each site. Intra- and interobserver variabilities in measuring manual and auto IMT were calculated in 20 subjects.
Results: Both manual and auto IMT were measured in all subjects. The mean values of auto and manual IMT were 0.43±0.08 mm and 0.46±0.09 mm, respectively. Auto IMT significantly correlated with manual IMT (p<0.0001, r=0.70). Coefficient of variance (CV) of intra- and interobserver variabilities for auto IMT (3.8% and 8.0%, respectively) were lower than that for manual IMT (14.1% and 16.7%, respectively). Both stiffness parameter β and CAVI significantly correlated with auto IMT (r=0.33, r=0.51, respectively) and manual IMT (r=0.29, r=0.44, respectively).
Conclusions: Auto IMT measurement allows excellent reproducibility as compared with manual IMT measurement. The surrogate markers of atherosclerosis were more highly correlated with the measures of auto IMT than with those of manual IMT. Thus, auto IMT measures may be more useful than manual IMT for the detection of early atherosclerotic change in the carotid artery and further studies are required to confirm this finding.

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