Technetium and gallium derived radiopharmaceuticals: Comparing and contrasting the chemistry of two important radiometals for the molecular imaging era

A comparison of two radiometals, technetium and gallium derived radiopharmaceuticals is presented. ^99mTc is available from a commercial generator technology where a parent isotope (⁹⁹Mo) is loaded onto an alumina column and the desired daughter is isolated by passing a saline solution through the system. Technetium is a transition metal that presents a major challenge with respect to designing radiopharmaceuticals that have suitable in vivo properties. While the technetium- and rhenium- organohydrazino cores display the advantages of facile preparation and chemical robustness, the intimate details of the chemistry are complex, dependent upon reaction conditions and the presence of coligands. Gallium-67 is cyclotron produced by the ⁶⁸Zn (p, 2n)-⁶⁷Ga reaction in which a thin layer of enriched 68Zn is electrochemically plated on an appropriate metal target. With advanced molecular imaging there is an increasing demand for new agents and a need for innovative radiopharmaceutical discovery and design paradigms.