TSPO and arthritic joint disease: Previously, feasibility of imaging (sub)clinical arthritis was demonstrated using the macrophage targeting PET tracer (R)-[11C]PK11195 (1-[2-chlorophenyl]-N-methyl-N-[1-methyl-propyl]-3-isoquinoline carboxamide), that binds to the translocator protein that is up-regulated in activated macrophages [6].