Generator radionuclides, labeling

We envision several potential generator-produced radionuclide labels for cryptates (Table I). Fortunately, early evaluations can be performed more conveniently with longer-lived tracers that are commercially available. The cryptate complexes are conveniently formed from the metal in deionized water and the cryptand dissolved in water or methanol. The complexes form instantly upon... 

Table I. Generator Radionuclides for Labeling Cryptates Isotope Decay Properties Parent...

The development of PET radiopharmaceuticals labeled with generator-produced radionuclides has facilitated greater use of PET in clinical nuclear medicine. The 68Ge/68Ga parent/daughter pair is ideal as a source of PET radiopharmaceuticals as a result of the favorable half-lives of both the parent and daughter radionuclides (43-45). The 271 days half-life of the 68Ge parent... 

The composition of radiopharmaceuticals is not constant as it varies with time as the radionuclide disintegrates. Very often, the half-life of the labeled molecule is so short that it must be readily prepared just before its administration to the patient. This implies in many cases the use of semimanufactured , such as radionuclide generators, precursors, and cold kits that are also considered a medicinal product according to directive 2001/83/EC. 

Radiopharmaceuticals are labeled with artificial radionuclides that are obtained by bombardment of stable nuclei with subatomic particles or photons. Nuclear reactions produced in such a way convert stable in unstable (radioactive nuclei). Several kind of devices are used for such purposes, including nuclear reactors, particle accelerators, and generators. 

Mo/"mTc Generators The essential part of the most commonly available generator system is a simple chromatography column to which the mother radionuclide is absorbed on a suitable support material. The daughter radionuclide is a decay product of the mother nuclide. Since it is the daughter nuclide that is used to label the carrier molecules, it must be possible to separate this from the parent nuclide by a chemical separation. 

PET Radiopharmaceuticals PET radiopharmaceuticals are labeled with shortlived positron-emitting radionuclides. Such radionuclides can either be produced in a cyclotron or obtained from an appropriate radionuclide generator. 

Nowadays, nuclear medicine has become an indispensible section of medical science, and the production of radionuclides and labelled compounds for application in nuclear medicine is an important branch of nuclear and radiochemistry. The development of radionuclide generators made short-lived radionuclides available at any time for medical application. New imaging devices, such as single photon emission tomography (SPET) and positron emission tomography (PET) made it possible to study local biochemical reactions and their kinetics in the living human body. 

In 1965, Richards and his collaborators at Brookhaven National Laboratories (N.Y.) have introduced the Mo/ Tc generator for clinical application (Richards 1966). This radionuclide system made technetium-99m available for clinical research and has stimulated the development of the first labeled compounds, which had a considerable impact on radiochemistry and nuclear medicine (Andros et al. 1965 Harper et al. 1966 McAfee et al. 1964a, b Stern et al. 1965, 1966). In the years to follow, diagnostic nuclear medicine procedures based on " Tc pharmaceuticals increased to approximately 85%. The reasons for this rapid growth were the ideal nuclear properties of techne-tium-99m, its availability worldwide as a radionuclide generator system, and the development of new labeling techniques. 

At the same time that new instruments, such as the Anger camera, were being invented, chemists were developing technetium-99m labeled tracers, based on the reduction of sodium pertechnetate to technetium-tin complexes, the latter being a more useful diemical form for labeling molecules. Radionuclide generators in which molybdenum-99 decayed to technetium-99m made radiotracers readily available in nuclear medicine clinics in hospitals. One after the other new tests were invented and soon put into clinical practice. 

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