Radiopharmaceuticals consisting essentially of a lipophilic, charge neutral radionuclide complex of a diaminedithiol ligand having 1-4 ester groups of the formula --A--COOR where A is a straight or branched chain alkylene of 0-10 carbon atoms and R is an alkyl group of 1-10 carbon atoms are useful in radioimaging brain perfusion in primates. Ester-substituted diaminedithiols in sterile, pharmaceutically acceptable form, and kits of the diaminedithiols and sterile, non-pyrogenic reducing agents for reducing preselected radionuclides are also provided. Technetium-99m is a preferred radionuclide.