In vitro and in vivo spin echo diffusion imaging characteristics of synovial fluid: potential non-invasive differentiation of inflammatory and degenerative arthritis.
OBJECTIVE: This study was undertaken to analyse the diffusion characteristics of synovial fluid in degenerative and inflammatory arthropathies. DESIGN AND PATIENTS: Ten in vitro specimens of synovial fluid from patients with both degenerative and inflammatory arthropathy were studied at body temperature with a navigator-corrected spin echo diffusion sequence (B values 0-512 s/mm2), on a Philips 1.5-T Gyroscan. Subsequently synovial fluid from knee joint effusions of 25 patients (10 patients with osteoarthritis, 10 patients with effusions following trauma and 5 patients with effusions secondary to inflammatory arthritis) was evaluated with the same navigator-corrected spin echo diffusion sequence. RESULTS: Both in vitro and in vivo study demonstrated decreased diffusion in patients with effusions secondary to degenerative joint disease (less than 2.40 x 10(-5) cm2/s) relative to patients with effusions accompanying knee trauma (greater than 2.75 x 10(-5) cm2/s) and inflammatory arthritis (in vitro and in vivo greater than 3.00 x 10(-5) cm2/s). CONCLUSION: Synovial fluid in degenerative arthritis shows less diffusion or free water movement than synovial fluid in inflammatory arthritis. Diffusion characteristics of synovial fluid may be used to predict the nature of the underlying form of arthritis in patients presenting with knee joint effusions.