**4. Radiometals: special needs?**

Radiolabeling with radiometals is in some ways challenging. Due to the very low amount of substance, other metals present in the reaction mixture can be serious problem and noticeably effect the radiolabeling. These metallic impurities can compete with gallium-68 for the chelating function of the precursor and are compared with gallium-68 (1 GBq equals to 9.73×10<sup>−</sup>12 mol) even when present at low levels (<ppm) clearly in excess number. They are result of external influences (e.g. production of starting materials) or are an intrinsic generator property (e.g. matrix; decay product). To avoid additional or larger impurities than necessary, the following is recommended by the IAEA [21]:

