[99mTc]TRODAT: Dopamine Transporter Imaging Agent for SPECT

In 1996, the rst formulation, which could provide the most reliable labeling procedure, was tested. e ligand, TRODAT-1, a thiol compound, had a tendency toward oxidation by air to form a disulde bond. To preserve this thiol compound for ecient labeling of TcO core, it was dissolved in methanol, dispensed in glass ampoules, dried by a stream of nitrogen, and sealed under nitrogen. It was found that the ligand, TRODAT-1, in the glass ampoules, was not very soluble in water, which contributed to the inconsistency in labeling. e solubility was dramatically improved by adding ethanol and 2N hydrochloric acid. Without the ligand being fully dissolved, a consistent labeling (radiochemical yield >90%) could not be obtained. To avoid this problem, 100-200 μL of 2N hydrochloric acid in ethanol was rst added to the vial containing the dried TRODAT-1. e dissolution was readily accomplished. e TRODAT-1 ligand was not very stable in 2N hydrochloric acid;

therefore, the ligand could not be stored in the acidic solution. e ethanol/acid solution was added just prior to initiation of the labeling procedure. A buered saline solution was added to adjust the pH to neutral, before [99mTc]TRODAT-1 was injected into human subjects.