TSPO and rheumatoid arthritis: PK11195 (1-[2-chlorophenyl]-N-methyl-N-[1-methyl-propyl]-3-isoquinoline carboxamide) ((R)-[11C]PK11195) binds to the upregulated translocator protein (TSPO) in activated macrophages (validated by histological examination of synovial RA tissue in relation to PET) and is able to visualize synovitis in both established and pre-RA patients [7, 8], the latter allowing early diagnostics of RA.