Cyclotron-produced Zn-62: its possible use in prostate and pancreas scanning as a Zn-62 amino acid chelate

Zinc-62 is a positron emitter that localizes in pancreas, prostate, and liver. Cyclotron-produced Zn-62 was separated by column chromatography and evaluated in vivo as the chelate of five amino acids and also as 62ZnCl2. Tissue-distribution studies were done in normal animals from 0.7-23 hr after intravenous administration. Pancreas-to-liver ratios (per gram) of about 1.0 were found at 1.5 hr in studies on rats, dogs, and monkeys. Pancreas was as difficult to separate from liver in Zn-62 (amino acid) images as in [75Se] selenomethionine images. Some studies were done with Zn-65 to determine the effects of carrier zinc and molar ratios of ligand. The highest ratio of pancreas to liver in these studies was 1.44. This uptake ratio decreases with increasing amounts of histidine, but the ratio is increased by adding carrier zinc because there results a decrease in liver uptake and no change in the pancreas uptake. There is sufficient specificity of pancreas and prostate uptake to make feasible emission computed tomography with Zn-62.