Non 99mTc generators
By far the most widely used radionuclide generator is the 99Mo → 99mTc system presented here in the first row of the table. There are a number of generators for other radionuclides that are commercially available for medical and research purposes. There are technical and practical issues associated with the preparation of the parent radionuclide, the preparation of the generator itself and the shipping of these devices to distant users. The demand is generally small for generators other than the 99Mo → 99mTc system and the price is consequently high and availability will often depend on special arrangements with reactor or cyclotron radionuclide producers. There are also cases where a particular product will be available by direct cyclotron or reactor production as well as from a generator.
Any generator with a parent radionuclide half-life shorter than one or two days will present shipping problems and many of the shorter-lived parent systems are only used "in house" at the site of the parent radionuclide production. The half-life and decay characteristics of the daughter will dictate whether it will be useful for human studies. Many of the systems below are of theoretical interest but will not have a practical medical imaging, medical therapy or research application. As far as possible the table is referenced and a short description of the application (if any) is provided.
Special consideration must be given to those generators with daughter radionuclides having half-lives of less than 10 minutes because quality-control tests cannot be carried out on the eluates. Samples are tested occasionally to detect possible breakthrough of the parent radionuclides but by necessity those tests are done after the daughter radionuclides have been administered to patients. This procedure is called retrospective testing and can be used to confirm product quality.
For medical imaging, ideal physical decay characteristics include the emission of a high abundance gamma ray between 0.1 and 0.2 MeV, decay mode such as isomeric transition (IT) or electron capture (EC), absence of particulate radiation and half-life of a few hours. For medical therapy we require particulate emission such as beta and alpha particles and a longer half-life. Daughter radionuclides that decay by positron (β ) decay are also of interest for positron emission tomography (PET) imaging.
The following table is organized in ascending molecular weight of the parent radionuclide.