Potential Errors Caused by Variable Radionuclidic Purity of Iodine-123

Abstract

The commercial accelerator production of iodine-123 in the United States has changedfrom the Te-122 (d,n) I-123 reaction to the Te-124 (p,2n) I-123 reaction—and a greater amount of I-124 contamination results. This impurity causes only slight elevation in thyroid uptake value when counted 24 hr after calibration time of the capsule, but a significant elevation in uptake value 48 hr after calibration time (when I-123 is administered 24 hr after calibration time). There is no image degradation on 24- and 48-hr scintigraphs obtained with a pinhole collimator. A significant time-dependent change in potentiometer settings on dose calibrators is required to assay the capsules.