Method of imaging with a chelating agent

A method of imaging a cancer, the method comprising administering to a patient an unlabeled compound according to Formula I

• or a pharmaceutically acceptable salt thereof, wherein R′ is hydrogen, or R′ is selected from the group consisting of alkyl, aminoalkyl, carboxyalkyl, hydroxyalkyl, heteroalkyl, aryl, arylalkyl and heteroarylalkyl, each of which is optionally substituted, wherein D is a divalent linker, and wherein n is 0 or 1, and administering to the patient a labeled compound according to Formula II
• or a pharmaceutically acceptable salt thereof, wherein R′ is hydrogen, or R′ is selected from the group consisting of alkyl, aminoalkyl, carboxyalkyl, hydroxyalkyl, heteroalkyl, aryl, arylalkyl and heteroarylalkyl, each of which is optionally substituted, wherein D is a divalent linker, wherein n is 0 or 1, and wherein M is a cation of a radionuclide.