Oxo-acid salts, halogenated oxo-acid salts, double oxides or complex oxides contain 0. A tropane compound is linked through the N atom at the 8-position to a chelating ligand capable of complexing technetium or rhenium to produce a neutral labeled complex that selectively binds to the dopamine transporter over the serotonin transporter with a ratio of 10 or more. The method comprises compiling a sample of image data from the received, substantially low amount of X-radiation.