Technetium-99 levels in pertechnetate solutions from (n,y) and (n,f) molybdenum-99 generators

Abstract

There is increasing evidence that in some radiopharmaceutical kits Tc-99 has an adverse effect on the imaging and labelling performance of Tc-99m. For example labelling efficiency with red blood cells can be affected when 99/99m ratios exceed about 4:1. The 99/99m ratio in a target is about 13.5:1 after a seven-day irradiation in a nuclear reactor. The ratio increases slightly during the time needed for processing. With the chromatographic generators used in hospitals up to 90 hours may elapse between the final wash stage of manufacture and the first elution during which time 99/99m ratios can increase to about 90:1. If elution efficiencies are high and the time between elutions is between 12 and 24 hours ratios in the generator hence in the eluates may actually increase with each elution. In the case of ready-to-inject pertechnetate solutions the critical time at which 99/99m ratios increase rapidly is the time between elution and use. If production conditions are poor ratios may increase to more than 600:1 by the time of use. With better conditions and production schedules Tc-99 levels at the time of use are comparable to those from chromatographic generators.