Abstract
Objective: Four positron emitters, 18F, 13N, 11C and 15O, were studied immediately after production for possible radionuclidic contaminants.
Methods: A series of activity measurements was performed with a dose calibrator over decay periods of 20 half-lives for each radionuclide. Individual semilogarithmic time-activity curves were generated over a wide range of activities (from a few hundred MBq to the 370 kBq (10 μCi) level). The presence of radionuclidic contaminants in activity measurements over reasonably long periods will manifest as deviations from linearity in these plot presentations.
Results: Nitrogen-13 samples showed significant deviation from linear response even at the MBq level due to the presence of a 18F contaminant. However, 18F, 11C and 18O samples showed a virtually linear response over the entire activity range.
Conclusions: Although most of these positron emitters maintain the linear decay characteristics in the practical use range, investigators should be aware of the increasing contribution of long-lived contaminants in the low end of the activity range. Although the 2-min half-life of 15O might be sufficient to allow performance of linearity measurements within minutes, we feel that 11C might be an ideal positron emitter to accomplish this task due to its more practical half-life period.
