Changes underlying the dynamic contrast-enhanced MRI response to treatment in rheumatoid arthritis

Objective 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. Methods 3D dynamic contrast-enhanced images were acquired from 13 patients before and 1–2 weeks after anti-TNFα 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 (v_p), the fractional extravascular, extracellular fluid volume (v_e), and the volume transfer constant (K^trans). Pre- and post-treatment values were compared and the dependence of the EER on each parameter was assessed. Results There was a decrease in the EER measured over 26 s after treatment (29%, p = 0.002). Reductions in T₁ (12%, p = 0.001), K^trans (31%, p = 0.002), and v_p (43%, p = 0.01) contributed to this; however, the EER was relatively insensitive to changes in v_e. Conclusions The decrease in EER after anti-TNFα treatment is largely caused by reductions in the volume transfer constant K^trans, the fractional plasma volume v_p, and the T₁ relaxation time. Only the contributions from K^trans and v_p directly reflect synovial vascularity.