Carotid IMT measurements: a comparison between s-VHS or CD-rom recorded Ultrasonic scans

Objective: To assess whether the use of new B-mode imaging technologies, which allow the direct storage of series of single digitalized images in electronic supports (CD-rom) in place of movies continuously recorded on analogical supports (s-VHS videotapes), may compromise the accuracy, precision and repeatability of carotid artery intima media thickness (IMT) measurements. Methods: The agreement between 121 replicated-scans stored as movies on s-VHS videotapes was compared with the agreement obtained with 121 replicated-scans stored as series of single frozen images on CD-rom. Results: The intra-method agreement was highest with movies recorded on s-VHS videotapes, with a bias between log-transformed readings of 0.0017±0.0305, mean absolute difference of 0.0210±0.0222 and repeatability coefficient of 0.061. The digital system provided a slightly lower repeatability with a bias between readings of −0.0040±0.0343, mean absolute difference of 0.0266±0.0219 and repeatability coefficient of 0.069. When the two methods were compared, the log-transformed bias between readings was 0.0169±0.06 with higher values obtained with s-VHS, the repeatability coefficient being 0.124, with almost all points within ±2SD of the mean difference. The mean absolute difference between the two measurements was 0.042±0.046. Conclusions: Compared with movies recorded on videotapes, the direct storage of series of single digitalized images in CD-rom for IMT evaluation associates with a lower agreement (-28%) between replicate scans. This implies the need of sample size larger of about 28% when this technology is used in IMT-progression clinical trials. Funding: European Project, IMPROVE QLG1-CT-2002-00896.