![]() Other nuclides obtainable from generator systems include 62Cu (from 62Zn, half-life 9.15 hr) and 82Rb (from 82Sr, half-life 25 days). For example, a generator containing 68Ge (half-life 287 days) may be used for production of the positron emitter 68Ga (half-life 68 min), which is formed following electron-capture decay of the parent nuclide. Chemical differences between the parent and daughter nuclides permit their separation, usually by column chromatography. ![]() Some positron-emitting radionuclides are obtained from generators, which contain a long-lived, reactor-produced parent nuclide that decays, yielding the positron emitter as a daughter radionuclide. Because the isotopes used have short half-lives ( Table 54-1), a cyclotron dedicated for nuclide production and facilities and methods for rapid radiochemical synthesis are usually required. Of particular importance, isotopes of carbon and nitrogen may be directly incorporated, and 18F can be substituted for hydrogen or a hydroxyl substituent in many compounds without loss of bioactivity. Isotopes used frequently in PET research allow a variety of radiochemical approaches to ligand synthesis. Positron-emitting nuclides share unique physical properties that permit great flexibility and sensitivity in the design of tracer distribution experiments. Positron-emitting tracers are used to produce maps of radioactivity distribution in brain
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