The present invention relates to compounds particularly asymmetric urea compounds which are labeled with one or more radioisotopes and which are suitable for imaging or therapeutic treatment of tissues, organs, or tumors which express NAALADase and/or PSMA. In another embodiment, the invention relates to methods of imaging tissues, organs, or tumors using radiolabeled compounds of the invention, particularly tissues, organs, or tumors which express NAALADase and/or PSMA to which the compounds of the invention have an affinity.