Diagnostic accuracy of grayscale, power Doppler and contrast-enhanced ultrasound compared with contrast-enhanced MRI in the visualization of synovitis in knee osteoarthritis

Purpose: To assess the diagnostic accuracy of grayscale (GSUS), power Doppler (PDUS) and contrast-enhanced ultrasound (CEUS) for detecting synovitis in knee osteoarthritis (OA). Method: Patients with different degrees of radiographic knee OA were included prospectively. All underwent GSUS, PDUS, CEUS, and contrast-enhanced magnetic resonance imaging (CE-MRI), on which synovitis was assessed semi-quantitatively. Correlations of synovitis severity on ultrasound based techniques with CE-MRI were determined. Receiver operating characteristic (ROC) analysis was performed to assess diagnostic performance of GSUS, PDUS, and CEUS, for detecting synovitis, using CE-MRI as reference-standard. Results: In the 31 patients included, synovitis scoring on GSUS and CEUS was significantly correlated (rho = 0.608, p < 0.001 and rho = 0.391, p = 0.033) with CE-MRI. For detecting mild synovitis, the area under the curve (AUC) was 0.781 (95 %CI 0.609-0.953) for GSUS, 0.788 (0.622-0.954) for PDUS, and 0.653 (0.452-0.853) for CEUS. Sensitivity and specificity were 0.667 (0.431-0.845) and 0.700 (0.354-0.919) for GSUS, 0.905 (0.682-0.983) and 0.500 (0.201-0.799) for PDUS, and 0.550 (0.320-0.762) and 0.700 (0.354-0.919) for CEUS, respectively. The AUC of GSUS increased to 0.862 (0.735-0.989), 0.823 (0.666-0.979), and 0.885 (0.767-1.000), when combined with PDUS, CEUS, or both, respectively. For detecting moderate synovitis, the AUC of GSUS was higher (0.882 (0.750-1.000)) and no added value of PDUS and CEUS was observed. Conclusions: GSUS has limited overall accuracy for detecting synovitis in knee OA. When GSUS is combined with PDUS or CEUS, overall diagnostic performance improves for detecting mild synovitis, but not for moderate synovitis.