The amount of colour Doppler activity in the inflamed synovium is used to quantify inflammatory activity. The measurements may vary due to image selection, quantification method, and point in cardiac cycle. This study investigated the test-retest reliability of ultrasound colour Doppler measurements in the wrist of patients with rheumatoid arthritis (RA) using different selection and quantification methods.
14 patients with RA had their wrist scanned twice by the same investigator with an interval of 30 minutes. The images for analysis were selected either by the anatomical position only or by the anatomical position with maximum colour Doppler activity. Subsequently, the amount of colour Doppler was measured in an area defined by either the synovial tissue or by specific anatomical structures surrounding the synovial tissue.
The best test-retest reliability was obtained when the images were selected guided by colour Doppler and the subsequent quantification was done in an area defined by anatomical structures. With this method, the intra-class coefficient ICC (2.1) was 0.95 and the within-subject SD (SW) was 0.017, indicating good reliability. In contrast, poor test-retest reliability was found if the images were selected by anatomical position only and the quantification was done in an area defined by the synovial tissue (ICC [2.1] = 0.48 and SW = 0.049).
The study showed that colour Doppler measurements are reliable if the images for analysis are selected by anatomical position in combination with colour Doppler activity and the subsequent analysis is performed in an area defined by anatomical structures.