A radioconjugate composed of a ligand for the 18 kDa translocator protein (TSPO) conjugated to the radioisotope carbon C 11, that can be used as a diagnostic imaging agent to detect TSPO-expressing cells using positron emission tomography (PET). Upon administration of carbon C 11 PBR-28, the PBR-28 moiety targets and binds to TSPO-expressing cells. Upon PET, carbon C 11 can be detected and TSPO-expressing cells can be visualized. This can facilitate detection of inflammatory sites and cancer cells. TSPO, also called the peripheral benzodiazepine receptor (PBR), is found on the outer mitochondrial membrane and is overexpressed on a variety of cancer cells and during inflammation. Check for active clinical trials using this agent. (NCI Thesaurus)