NOTA-FAPI-4 is an analogue of FAPI-4 and a fibroblast activation protein (FAP) inhibitor. NOTA-FAPI-4 is useful in the diagnosis or treatment of a disease characterized by overexpression of fibroblast activation protein (FAP). NOTA-FAPI-4 can be used as a PET tracer for detection of diseases or disorders related to fibroblast activation protein.