A radiopharmaceutical capable of localizing at a site of thrombus containing activated platelets within a mammalian body is provided wherein the radiopharmaceutical comprises a linear peptidomimetic containing ligand capable of specifically binding to the GPIIb/IIIa integrin receptor of platelets in the thrombus and a radionuclide covalently bound to the peptidomimetic containing ligand. The ligand compositions of the invention are provided complexed with a selected metal radionuclide to form a diagnostic or therapeutic radiopharmaceutical to image a site of thrombus or provide radiotherapy to the site of thrombus, respectively. Methods of imaging a site of thrombus in a mammalian body by administering a diagnostically effective amount of the radiopharmaceutical composition of this invention complexed with a selected diagnostic metal radionuclide and methods of providing therapy to a site of thrombus in a mammalian body by administering a therapeutically effective amount of the radiopharmaceutical composition of this invention complexed with a selected therapeutic metal radionuclide are also provided as well as kits for preparing such radiopharmaceutical compositions.