Background and purpose: New advances in B-mode imaging technologies have led to improved quality in the detection of minute changes in the surface of intima-media thickness (IMT) and plaques. The new digital systems, with increased numbers of imaging channels, multiple frequency probes, and increased microprocessing speeds, now generate images comparable to those of the analog predecessors. Can these digital systems have reproducibility comparable to that of a pure analog system? We compared the Biosound 2000II (analog) system with the Esaote AU4 (digital) system.
Methods: Twenty-two subjects were chosen who had varying degrees of IMT on the far wall of the common carotid artery. Common carotid IMT was determined twice: the first time with the analog system and the second time with the digital system. With each system, replicate scans were made within 2 weeks.
Results: The intramethod agreement was high with the analog system, with a bias between readings of -0.010+/-0.033 mm, mean absolute difference of 0.027+/-0.020 mm, repeatability coefficient of 0.067, and correlation coefficient of 0.97. The digital system provided the highest reproducibility with a bias between readings of 0.002+/-0.016 mm, mean absolute difference of 0.012+/-0.011 mm, repeatability coefficient of 0.033, and correlation coefficient of 0. 99. When the analog and digital systems were compared, the bias between readings was -0.011+/-0.024 mm with good agreement between the 2 systems; the repeatability coefficient was 0.047, with all points within +/-2 SDs of the mean difference. The mean absolute difference between the 2 measurements was 0.018+/-0.015 mm with a correlation coefficient of 0.98.
Conclusions: The digital system for IMT evaluation compares well with the more widely used analog system and provides a reliable technology for common carotid IMT measurement that can be applied to clinical trials.