SUMMARY:

This chapter reviews the radiopharmaceutical chemistry of technetium. In an introductory section, limitations resulting from application in nuclear medicine are analyzed and requirements from chemistry, routine application and market are discussed. Subsequently, commercial ^99mTc based radiopharmaceuticals for the important target organs heart, brain or kidney are treated. These radiopharmaceuticals fulfil the requirements outlined earlier and are discussed in this context. Then, the different generations of radiopharmaceuticals, perfusion agents and receptor specific molecules, are described. Tc chemistry for the synthesis of perfusion agents and labeling approaches for target specific biomolecules are summarized, comprising a general introduction to the N _xS _{4 - x}, [3+1] and HYNIC approaches as well as to the more recent carbonyl and TcN strategies. Direct labeling is briefly reviewed. Recent developments in the labeling of targeting molecules are discussed. Examples for antibodies/peptides, neuroreceptor targeting molecules and complexes relevant to MRD are given. The section concentrates on coordination and labeling chemistry but biological results are briefly summarized. The last section gives a (subjective) outlook for ^99mTc based radiopharmaceuticals. Critical comments are spread over the article but concentrated in this section. Despite the strong competition by MRI or ultra sound, the authors conclude that ^99mTc radiopharmaceuticals will play a key role if novel approaches are introduced and the requirements considered in research to a stronger extent.