Multi-examiner reliability of automated radio frequency-based ultrasound measurements of common carotid intima–media thickness in rheumatoid arthritis

OBJECTIVES: To assess the reliability of the automated radio frequency (RF)-based US measurement of carotid intima-media thickness (IMT) performed by rheumatologists and to evaluate the variability between this method and the conventional B-mode US measurement of carotid IMT in RA patients. METHODS: Twelve rheumatologists measured in two blinded rounds the IMT of both common carotid arteries (CCAs) of seven RA patients with an automated RF-based method. At each round, a cardiologist measured both CCA-IMTs of the patients using an automated B-mode method. Inter-observer reliability for RF-based IMT measurements was evaluated by the intra-class correlation coefficient (ICC). Intra-observer reliability for RF-based IMT measurements was assessed using the root mean square coefficient of variation (RMS-CV), Bland-Altman method and ICC. Agreement between the two US methods was evaluated by the Bland-Altman method, ICC and RMS-CV. RESULTS: Inter-observer ICCs for the RF-based CCA-IMT measurements were 0.85 (95% CI 0.69, 0.94) for the first round, and 0.77 (95% CI 0.55, 0.91) for the second round. RMS-CVs for the RF-based CCA-IMT measurements varied from 5.6 to 11.7%. The mean intra-observer ICC for the RF-based CCA-IMT measurements was 0.61 (95% CI 0.46, 0.71). In the Bland-Altman analysis for agreement between RF-based and B-mode CCA-IMT measurements, the mean difference varied from -0.6 to -19.7 μm. Inter-method ICCs varied from 0.57 to 0.83 for 11 rheumatologists. Inter-method RMS-CVs varied from 11.3 to 13.7%. CONCLUSIONS: Our results suggest that automated RF-based CCA-IMT measurement performed by rheumatologists can be a reliable method for assessing cardiovascular risk in RA patients.