Dynamic contrast-enhanced MRI of patients with rheumatoid arthritis has shown a decrease in the early enhancement rate (EER) of synovitis after treatment. The purpose of this work was to investigate the underlying changes.
3D dynamic contrast-enhanced images were acquired from 13 patients before and 1-2 weeks after anti-TNF alpha treatment. The EER of the inflamed synovium was measured. The T1 relaxation time of the synovitis was calculated from images at different flip angles. The time course of the arrival of gadolinium at the radial artery was determined. The gadolinium enhancement of the inflamed synovium was modeled to calculate the fractional plasma volume (vp), the fractional extravascular, extracellular fluid volume (ve), and the volume transfer constant (Ktrans). Pre- and post-treatment values were compared and the dependence of the EER on each parameter was assessed.
There was a decrease in the EER measured over 26 s after treatment (29%, p = 0.002). Reductions in T1 (12%, p = 0.001), Ktrans (31%, p = 0.002), and vp (43%, p = 0.01) contributed to this; however, the EER was relatively insensitive to changes in ve.
The decrease in EER after anti-TNF alpha treatment is largely caused by reductions in the volume transfer constant Ktrans, the fractional plasma volume vp, and the T1 relaxation time. Only the contributions from Ktrans and vp directly reflect synovial vascularity.