Ultra-Low-Dose Computed Tomography Subtraction for the Detection of Synovitis in Patients with Inflammatory Joint Disease

Introduction: Enhancement after contrast injection is a key imaging finding in patients with active inflammatory joint disease. The aim of this study was to prove the feasibility of ultra-low-dose computed tomography (ULD-CT) with contrast injection for the detection of active inflammation in patients with suspected rheumatoid arthritis.

Material and Methods: Institutional review board and Federal Office for Radiation Protection (BfS) approval was obtained. Thirty-six prospectively and consecutively recruited patients underwent ULD-CT and magnetic resonance imaging (MRI) of the hand and wrist with weight-adapted contrast administration. Subtraction images were calculated for ULD-CT and scored according to a modified Rheumatoid Arthritis Magnetic Resonance Imaging Score (RAMRIS) using MRI as the standard of reference. Sensitivity and specificity were calculated. An imaging diagnosis in MRI and ULD-CT was compared with a final clinical diagnosis. Patients were asked which modality they would prefer for future examinations.

Results: All patients showed active inflammation on MRI. Sensitivity of ULD-CT was 69% on patients and 65% at the joint level; specificity was 87%. The sensitivity increased with increasing inflammation (80% for MRI-RAMRIS score > 1). ULD-CT detected more differential diagnoses than MRI (8 versus 2/12) but showed less sensitivity for rheumatoid arthritis (20 versus 23/24). The estimated effective dose was < 0.01 mSv. Overall, 85% of the patients preferred ULD-CT over MRI due to a shorter examination time.

Conclusion: ULD-CT after contrast injection with calculation of subtraction images allows for detection of synovitis of the hand. It shows better accuracy for differential diagnosis; however, it is less sensitive for mild disease compared with MRI.