Quantitative assessment of synovial inflammation by dynamic gadolinium-enhanced magnetic resonance imaging. A study of the effect of intra-articular methylprednisolone on the rate of early synovial enhancement.

The effect of temporary inflammatory suppression on synovial membrane enhancement, as determined by dynamic and static gadolinium-DTPA enhanced magnetic resonance imaging (MRI), was studied. MRI of 18 arthritic knees was performed before and 1, 7, 30 and 180 days after intra-articular methylprednisolone injection until clinical relapse. MRI of another six knees was performed twice within 2-4 days in order to assess interobserver and inter-MRI variation. The rate of early enhancement of the entire synovial membrane of a pre-selected central sagittal slice (REEsyn,tot), determined by dynamic T1-weighted FLASH MRI, decreased in all knees within the first post-treatment week and remained low during remission, although gradually increasing. In cases of clinical relapse, REEsyn,tot increased to pre-treatment levels. The interobserver plus inter-MRI variation was maximally 27%. The predictive values of a REEsyn,tot below/above 1.0%/s were 0.94 and 0.91, respectively, with respect to the absence/presence of clinical synovitis. Evaluation of small synovial areas revealed marked regional heterogeneity. Static spin echo MRI was not informative. The study indicates that the rate of early synovial enhancement reflects synovial inflammatory activity. Subclinical changes may be revealed. Evaluation of large synovial areas increases reproducibility and reduces the effect of regional heterogeneity. Dynamic MRI may prove a clinically useful measure of synovial inflammation.