Radiology in Rheumatoid Arthritis
Radiology plays a central role in the diagnosis, monitoring, and prognostication of rheumatoid arthritis (RA), a chronic systemic autoimmune disease characterized by inflammatory synovitis and progressive joint destruction. Conventional radiography, ultrasound (US), and magnetic resonance imaging (MRI) each contribute distinct information across the disease course, from initial detection of synovial inflammation to the assessment of irreversible structural damage.[^c1] Nuclear medicine techniques including FDG-PET/CT and emerging fibroblast activation protein inhibitor (FAPI) PET/CT provide molecular insights into the inflammatory and stromal processes underlying RA.[^c2]
Radiography remains the most widely available and cost-effective first-line imaging modality for RA, offering a permanent record of joint pathology used for baseline assessment and longitudinal monitoring in clinical trials and routine practice.[^c3] However, radiographs are insensitive to early inflammatory changes, with erosions often not visible until one to two years after disease onset.[^c4] Ultrasound and MRI detect synovitis and tenosynovitis with far greater sensitivity and have been incorporated into the 2010 ACR/EULAR classification criteria for RA, enabling earlier diagnosis and more timely treatment.[^c5]
MRI is the most sensitive modality for detecting bone marrow edema, which is the strongest independent predictor of future erosive progression.[^c6] Ultrasound provides real-time, dynamic assessment of superficial joints and tendons, can distinguish active from inactive synovitis through power Doppler signal, and is well suited for guiding interventions and monitoring treatment response.[^c7] Advanced techniques such as FAPI-PET/CT visualize fibroblast activation in the synovium and may predict treatment response before structural damage occurs.[^c8] The RA MRI scoring system (RAMRIS) and various ultrasound scoring systems provide standardized, validated measures of inflammation and damage that are widely used as endpoints in clinical trials.[^c9]