Technetium and Rhenium in Nuclear Medicine

The appreciation of short-lived radionuclides in nuclear medicine has led to the development of radionuclide generators that serve as a convenient source of these radionuclides to prepare a wide range of radiopharmaceuticals. Of all the potentially useful generator systems, the ^99mTc generator has found the most widespread use. Although originally chosen because of its excellent disintegration characteristics and its ready availability, ^99mTc would not be so widely used today were it not for its ability to exhibit a versatile coordination chemistry.
During the first phase of research into the development of ^99mTc based imaging agents in the 1970s the agents were relatively simple in nature (pertechnetate, colloids, particles, albumin, and complexes with DTPA, phosphonates). Then new complexes have been developed which provide images of flow and metabolism, e.g. kidney and liver functions as well as regional heart and brain perfusion. Antibodies, antibody fragments and numerous peptides have been successfully labelled with ^99mTc. Progress in technetium chemistry has led to an assortment of building blocks in the form of various cores and valuable combinations of donor groups in a number of chelating ligands. Research is still going on to extend and improve these tools. Using new concepts and methods, current research is being directed at an area of technetium chemistry well beyond perfusion tracers to open a window on biochemistry. The recent advances in the design of new technetium ^99mTc imaging agents illustrate the continued expansion of the use.

Rhenium and technetium belong to the same group of the periodic table and have similar chemical properties. Radioisotopes of rhenium (¹⁸⁶Re and ¹⁸⁸Re) have been suggested as radiopharmaceuticals for therapy. Similar to the in-house use of the ^99mTc generator for the preparation of a great variety of ^99mTc labeled diagnostic agents, the ¹⁸⁸Re generator can provide the therapeutically useful radionuclide for the preparation of ¹⁸⁸Re agents for bone pain palliation, cancer therapy, radiotherapy of chronic degenerative joint diseases and brachytherapy to reduce restenosis risks after coronary dilatation.