Objective. To evaluate the metric qualities of power Doppler ultrasound (PDUS) for different quantification methods and devices in the assessment of arthritis during anti-inflammatory treatment

Methods. Twenty-four patients with active arthritis and first-time treatment with the TNF-alpha inhibitor adalimumab underwent sequential clinical, laboratory and US examination at baseline, weeks 2, 6 and 12. 2D and 3D PDUS was performed by two independent investigators. The images and movies were scored from 0 to 3 and the amount of colour pixels and voxels was calculated. In addition, the resistance index of a synovial artery was measured. Thirteen patients were examined with a second US machine.

Results. Treatment response was already observed at week 2 with a significant reduction of 2D (P < 0.01) and 3D scores (P < 0.001). A moderate correlation to 28-joint disease activity score was found for 3D voxel count (r(s) = 0.35, P < 0.001). Interobserver agreement was k or ICC >= 0.8 for all methods except the resistance index (ICC = 0.60). Intermachine agreement was 0.57 for 2D PDUS score.

Conclusions. The study demonstrates good to excellent interobserver and moderate intermachine reliability of different PDUS assessment methods in a longitudinal open-label study.