Quantitative Assessment of Arthritis Activity in Rheumatoid Arthritis Patients Using [(11)C]DPA-713 Positron Emission Tomography

Treatment for rheumatoid arthritis (RA) should be started as early as possible to prevent destruction of bone and cartilage in affected joints. A new diagnostic tool for both early diagnosis and therapy monitoring would be valuable to reduce permanent joint damage. Positron emission tomography (PET) imaging of macrophages is a previously demonstrated non-invasive means to visualize (sub)clinical arthritis in RA patients. We developed a kinetic model to quantify uptake of the macrophage tracer [(11)C]DPA-713 (N,N-diethyl-2-[2-(4-methoxyphenyl)-5,7-dimethylpyrazolo [1,5-a]pyrimidin-3-yl]acetamide) in arthritic joints of RA patients and to assess the performance of several simplified methods. Dynamic [(11)C]DPA-713 scans of 60 min with both arterial and venous blood sampling were performed in five patients with clinically active disease. [(11)C]DPA-713 showed enhanced uptake in affected joints of RA patients, with tracer uptake levels corresponding to clinical presence and severity of arthritis. The optimal quantitative model for assessment of [(11)C]DPA-713 uptake was the irreversible two tissue compartment model (2T3k). Both K(i) and standardized uptake value (SUV) correlated with the presence of arthritis in RA patients. Using SUV as an outcome measure allows for a simplified static imaging protocol that can be used in larger cohorts.