A method of evaluating a subject suspected of harboring a prostrate tumor includes administering to the subject an effective amount of a gamma-emitting transition metal complex conjugated to a targeting moiety that selectively binds to prostate-specific membrane antigen (PSMA), including PSMA expressed on the surface of a prostate tumor； subjecting the subject to a nuclear medicine tomographic imaging technique to obtain one or more images of at least a portion of prostate tissue that comprises tumor lesions； assessing a level of uptake of said gamma-emitting transition metal complex conjugated to a targeting moiety by said at least a portion of prostate tissue compared to a level of uptake by control tissue； and determining if a ratio of the level of uptake by said at least a portion of prostate tissue compared the level of uptake by control tissue is at or above a predetermined threshold.
