Quantification of dynamic contrast-enhanced MR imaging of the knee in children with juvenile rheumatoid arthritis based on pharmacokinetic modeling

Improved management of arthritis requires a reliable, quantifiable, noninvasive method to monitor the degree of inflammation and therapeutic response during the early phase of the disease. For this purpose, the uptake of Gd-DTPA in the distal femoral physis and synovium in children with juvenile rheumatoid arthritis (JRA) was evaluated with a two-compartment pharmacokinetic model and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Employing a two-compartment pharmacokinetic model, the theoretical signal enhancement from Gd-DTPA enhanced dynamic 3D gradient-recalled echo (GRE) images was shown to have a simple linear relationship with tissue concentration independent of flip angle. The signal-enhancement patterns for each individual knee were found to be characterized by three pharmacokinetic parameters: kep (min−1), the rate constant; kel (min−1), the elimination rate constant; and ER (min−1), the initial enhancement rate, which is proportional to the transfer constant Ktrans (min−1). Characteristic patterns were observed in the image signal intensity–time course. The initial enhancement rate, ER, in regions of interest (ROIs) was found to have a wide range of variation: 5 to 38 min−1 over the distal femoral physis and 1 to 10 min−1 in the synovium. The ER of the synovium was correlated with the ER of the distal femoral physis (P<.05). In addition, the ER of the synovium was correlated to the clinical outcome measures of knee swelling. Further investigation is needed to determine whether wide variations in the pharmacokinetic parameters reflect the degree of disease activity, and whether there are changes in response to therapy. This method can also be applied in adults with rheumatoid arthritis (RA) and other disorders where T1-weighted contrast is used (breast cancer, brain tumors).