Ejbjerg B J et al. (2005) Optimized, low cost, low field dedicated extremity MRI is highly specific and sensitive for synovitis and bone erosions in rheumatoid arthritis wrist and finger joints: comparison with conventional high field MRI and radiography. Ann Rheum Dis 64: 1280–1287

Treatment for rheumatoid arthritis (RA) aims to suppress joint inflammation in order to prevent structural damage and functional disability as early as possible in the course of the disease. To do this effectively there is a need for sensitive and specific detection techniques for early diagnosis and for monitoring disease progression.

Low-field dedicated-extremity MRI units have potential advantages over conventional MRI units but are largely unvalidated. In this study, 37 patients with RA and 28 healthy controls underwent clinical assessment and conventional radiography before MRI scanning of the wrist and 2nd–5th metacarpophalangeal joints using conventional and low-field dedicated-extremity MRI units on two consecutive days. The sensitivity, specificity and accuracy of low-field 3D gradient echo MRI for erosions were high relative to high-field, spin echo MRI (94%, 93% and 95%, respectively); the corresponding values for radiography were 33%, 98% and 83%, respectively. Results of low-field MRI were equally high for synovitis (90%, 96% and 94%, respectively). Although specificity and accuracy were also high for bone marrow edema (99% and 95%, respectively), sensitivity was only moderate (39%).

Low-field dedicated-extremity MRI is therefore as effective as high-field MRI for detecting and grading erosions and synovitis, and offers potential advantages with regard to patient comfort and compliance, and unit cost.