Quantification of (R)-[C-11]PK11195 binding in rheumatoid arthritis

Rheumatoid arthritis (RA) involves migration of macrophages into inflamed areas. (R)-[C-11]PK11195 binds to peripheral benzodiazepine receptors, expressed on macrophages, and may be used to quantify inflammation using positron emission tomography (PET). This study evaluated methods for the quantification of (R)-[C-11]PK11195 binding in the knee joints of RA patients. Data from six patients with RA were analysed. Dynamic PET scans were acquired in 3-D mode following (R)-[C-11]PK11195 injection. During scanning arterial radioactivity concentrations were measured to determine the plasma (R)-[C-11]PK11195 concentrations. Data were analysed using irreversible and reversible one-tissue and two-tissue compartment models and input functions with various types of metabolite correction. Model preferences according to the Akaike information criterion (AIC) and correlations between measures were evaluated. Correlations between distribution volume (V-d) and standardized uptake values (SUV) were evaluated. AIC indicated optimal performance for a one-tissue reversible compartment model including blood volume. High correlations were observed between V-d obtained using different input functions (R (2)=0.80-1.00) and between V-d obtained with one- and two-tissue reversible compartment models (R (2)=0.75-0.94). A high correlation was observed between optimal V-d and SUV after injection (R (2)=0.73). (R)-[C-11]PK11195 kinetics in the knee were best described by a reversible single-tissue compartment model including blood volume. Applying metabolite corrections did not increase sensitivity. Due to the high correlation with V-d, SUV is a practical alternative for clinical use