Value of contrast-enhanced ultrasound for detection of synovial vascularity in experimental rheumatoid arthritis: an exploratory study

Objective This study aimed to examine the associations between contrast-enhanced ultrasound (CEUS) imaging and synovial hypervascularity and synovitis score in a rabbit model of antigen-induced arthritis (AIA), compared with power Doppler ultrasound (PDUS). Methods We investigated 50 knee joints in 25 AIA rabbits (AIA group), and 10 knee joints in five sham-injected rabbits (control group). PDUS and CEUS images were evaluated at the 8 th week. Ultrasound-guided synovial biopsies were targeted in the area with hypervascularity, and synovial microvessel density (MVD) was evaluated by immunohistochemical staining of CD31. Results The PDUS score was significantly higher in the AIA group (2.61 ± 0.78) compared with the control group (0.50 ± 0.53). CEUS in the AIA group revealed a fast-in/slow-out pattern of contrast enhancement. MVD revealed by CD31+ vessel count and the synovitis score were significantly higher in the AIA group compared with the control group. In the AIA group, CEUS findings showed a better correlation with MVD revealed by CD31+ and synovitis score than PDUS findings. Conclusion CEUS is superior to PDUS for estimating synovial hypervascularity and hyperplasia in experimental rheumatoid arthritis.