B-mode imaging and intima media thickness: analog vs digital technologies

New advances in B-mode imaging technologies have led to increased image quality for detecting minute changes of IMT and plaques. The new digital systems with multiple frequency probes and increased micro-processing speeds, now generate images comparable to those of their analog predecessors. To assess whether digital systems have reproducibility values comparable to pure analog systems, a study comparing a Biosound 2000II (analog) and a Esaote AU4 (digital) was performed. Twenty-two subjects with varying degrees of IMT on the far wall of the Common Carotid Artery were chosen. Common Carotid Intima-Media Thickness (CC-IMT) was determined in each patients first with Biosound 2000II and then with Esaote AU4. With each system, replicate scans were made within two weeks. The images were recorded for off-line CC-IMT measurements. The intra-method agreement was high with the Biosound system (mean absolute differences = 0.027±0.020 mm; repeatability coefficient = 0.067). AU4 system provided the highest reproducibility (mean absolute differences = 0.012±0.01 mm; repeatability coefficient = 0.033). When analog and digital processing were compared the mean difference was 0.018±0.015 mm with good agreement between the 2 systems, since the mean relative difference was -0.011 and the repeatability coefficient was 0.047. These results suggest that digital system is a reliable technology for long-term clinical trials.