Importance of timing of post-contrast MRI in rheumatoid arthritis: what happens during the first 60 minutes after IV gadolinium-DTPA?

Background-Volumes of inflamed synovial membrane determined by magnetic res onance imaging (MRI) are closely related to histopathological synovitis and may predict erosive progression in rheumatoid arthritis (RA). However, aft er IV injection, leakage of MRI contrast from the synovium gradually compro mises the differentiation of synovium from joint fluid. Objective-To determine the time period after IV MRI contrast (gadolinium-DT PA (Gd)) injection in which synovial membrane volume determination is relia ble. Methods-MRI of five RA knees with clinical synovitis was carried out, with axial, T-1 weighted, spin echo images before IV Gd injection and every 1.75 minutes for 60 minutes post-Gd. By a semiautomated "signal enhancement thr eshold" method, including voxels with > 35% or > 45% relative post-Gd enhan cement, synovial membrane volumes were estimated at each time point. At 4.2 5 minutes post-Gd, volumes were also determined by a more accurate but time consuming "manual method". Results-The initially observed synovium-effusion borderline remained clearl y visible, and on the same location, within at least the initial 11 minutes post-Gd (that is, within the normal time frame of post-Gd imaging in RA) b ut started blurring and moving centripetally thereafter. Compared with volu mes at all other time points, synovial membrane volumes at 0.75 and 2.50 mi nutes post-Gd were significantly lower (Wilcoxon-Pratt), suggesting that so me synovial membrane areas had not yet exceeded the enhancement threshold. Thereafter, the measured volumes remained practically unchanged. Conclusion-This study suggests that MR image acquisition in arthritic knee joints should be performed within the initial approximately 10 minutes afte r gadolinium contrast injection to achieve the most accurate distinction be tween synovium and joint fluid but that small time variations are not of ma jor importance to the measured synovial membrane volumes.