Examples of SPECT tracers that specifically target macrophages include imaging of a radiolabeled translocator protein (TSPO) small molecule in the inflamed ankles of a murine model of rheumatoid arthritis (203), of a second generation variant of the TSPO-targeting small molecule (iodo-DPA-713) in the pancreas, liver, and intestines of mice treated with cerulein (198), and of combined 14C-methionine and 99mTc-methoxyisobutylisonitrile in a murine model of acute myocardial infarction (204). The gene discussed is TSPO; the disease is rheumatoid arthritis.