Radionuclide generator systems

Ultra short lived radionuclides, with a half-life of a few seconds to a few minutes are readily available from long-lived parent radionuclides adsorbed to an organic or inorganic ion exchange support matrix (1-3). These radionuclide generator systems are an inexpensive alternative to an on-site cyclotron, especially for positron emitters used for positron emission tomography (PET). 

The requirements for a successful nuclear medicine radionuclide generator system include high selectivity between the daugh-... 

Also for conventional radiopharmaceuticals used in diagnostic, it is favorable to use products with short half-lives. Radionuclide generator systems are widely used for supply of short-lived radionuclides/radiopharmaceuticals. Several generator systems are available and routinely in use within nuclear medicine. Some of these are listed in Table 1. 

TABLE 1 Several Radionuclide Generator Systems Useful in Nuclear Medicine... 

FIGURE 4 Typical radionuclide generator system (ISOTEC, GE Healthcare, AS). 

Radionuclidic Purity Radionuclidic purity is defined as the fraction of the total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical. Radionuclide impurities may arise from impurities in the target material or from fission of heavy elements in the reactor [2], In radionuclide generator systems, the appearance of the parent nuclide in the daughter nuclide product is a radionuclidic impurity. In a "Mo/"mTc generator, "Mo may be found in the "mTc eluate due to breakthrough of "Mo on the aluminum column. The presence of these extraneous radionuclides increases the radiation dose to the patient and may also obscure the scintigraphic image. 

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. 

Generally, the decay of a radioactive nuclide results in a longer-lived or even stable daughter nuclide. In this respect, radionuclide generator systems where the daughter nuclide presents a shorter half-life are a welcome exception from the general properties of P decay. In particular, for a clinical application, a state of a radioactive equilibrium is mandatory. Thus, mainly the transient and secular equilibria of radionuclide generations are relevant for... 

Radionuclide generator systems relevant for life-sciences application... 

A third source for radionuclide generator systems is the recovery of radioactive parents from extinct radioactive decay processes, such as Th, which is recovered from decay products. The Th represents a convenient, long-lived iT i = 7,340 years) source from which Ac is recovered, which is the parent of the Ac/ Bi generator system. 

Knapp FF Jr, Butler TA (eds) (1984) Radionuclide generators new systems for nuclear medicine applications, vol 241, ACS symposium series. American Chemical Society, Washingon, DC Knapp FF Jr, Mirzadeh S, Callahan AP (eds) (1992) Symposium on radionuclide generator systems for nuclear medicine applications, August 1992, American Chemical Society, Washington, DC, Radioact Radiochem (Special Issue) 3... 

Bismuth-213 has a 45.6-min half-life and ot-particle emission is associated with each of its decays, either directly to 2.2-min ° T1 (2%) or after P decay to 4.2- xs Po (98%), followed by a emission to 3.25-h ° Pb. A radionuclide generator system has been developed using 10-day Ac as the parent that can provide cKnically useful levels of Bi (McDevitt et al. 1996, 1999b Ma et al. 2001). The generator consists of an AGMP-50 column and is eluted with 0.1 M HCl/Nal. 

Three new positron emitting generator systems have been described. The practical availability of these radionuclides could significantly broaden the potential applications of positron emission tomography. The next few years should see human clinical trials undertaken to fully evaluate their utility for nuclear medicine. 

Automated radionuclide generators capable of providing precise dose delivery of multi-millicurie amounts of short-lived positron emitters on demand from a safe and easily operated system are an attractive alternative to on-site cyclotrons for positron emission tomography. The availability of curie quantities of parent radionuclides from national laboratories and the development of microprocessor automation makes it feasible to utilize these generators in the clinical setting. 

A Radionuclide Generator and Infusion System for Pharmaceutical Quality Rb-82... 

When dealing with a short-lived radionuclide generator, an infusion system will be needed for elution of the generator, recording of patient dose, and administration of the activity. The effective utilization of 76 sec Rb-82 will depend on its rapid extraction from the generator. Thus, the foremost feature of an infusion system will be the attainment of a high and uniform flow... 

Production and Recovery of Large Quantities of Radionuclides for Nuclear Medicine Generator Systems... 

A radionuclide generator can be described as a parent-daughter pair from which the daughter nuclide is separated from the parent in as pure a nuclear form as possible throughout the operating life of the system. A variety of publications (1-3) have emphasized the general principles of the medical use and qualitative aspects of radionuclide generators. The most frequent example discussed is the Mo-99/Tc-99m system. 

The fundamental conclusion of this study is that the optimal clinical elution flow rate in the case of continuous elution of a short-lived radionuclide from a perfusion generator does not necessarily correspond to the conditions for maximum elution yield. This conclusion was confirmed by experimental studies with various short-lived radionuclide generators such as the Hg-195m/Au-195m and Sr-82/Rb-82 systems. 

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. 

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