Long-lived contaminants are introduced into cyclotron produced radiopharmaceuticals from the activation and spallation of elements in the HAVAR target window into the target water. They are removed during the synthesis of the final imaging agent. Below, are a series of papers on the measurement of these contaminants, their retention in the body, and the dose delivered to the patient from them. The quantity of the contaminants is strictly controlled by the FDA which requires all drugs be 99.5% pure. The vast majority of prepared radiopharmaceuticals have only a tiny fraction of the allowed levels in them. The radiation dose these contaminants deliver to the patient, if present, is trivial.
They do, however, outlive the imaging isotope (typically F-18) and may alarm Homeland Security detectors found in many locations. The length of time these isotopes can alarm the detectors will be determined and published in the near future.
New method to detect and quantify contaminants
Keith Eckerman and Richard Leggett have provided uptake retention functions for soluble injected forms of each possible contaminating isotope and these tables are also presented in the link above.