TSPO and rheumatoid arthritis: Most imaging probes used for RA diagnosis and monitoring are unspecific, although several classic or novel targeted imaging agents have been assessed, such as 18F-fluorodeoxyglucose (18F-FDG), [11C]Choline, (R)-[11C]PK11195 and other translocator protein (TSPO)-targeted radiotracers, [67Ga]Citrate, [99mTc]- and [111In] human immunoglobulin G (HIG), [99mTc]- and [111In]anti-E-selectin, [99mTc]- and [111In]Octreotide, [99mTc]Anti-TNF-α and [99mTc]Annexin V, etc. [21–23].