Technetium radionuclides

Stress myocardial perfusion imaging with the radionuclides technetium-99m sestamibi or thallium-201 allows for the identification of multivessel disease and assessment of myocardial viability. 

Huie Z., Zishu Z., and Lanying Z. (1988) Sorption of radionuclides technetium and iodine on minerals. Radiochim. Acta 44/45, 143-145. 

Radiopharmaceuticals labeled with " Tc are commercially available and are employed in more than 80% of all nuclear medicine investigations. Among the radionuclides, technetium-99m is most attractive to the nuclear medicine physician because of its optimal gamma energy for SPECT, its availability, its relatively low cost, and its easy-to-la-bel kit preparations for in-house use. Another advantage is the low radiation burden to patients, due primarily to its short half-life. The decay within hours also facilitates the handling of waste. 

Figures 3, 4 and 5 provide the long term trends of radionuclide concentrations (where available at each site) in seafood, seaweed and sediments, respectively. Overall, low concentrations of radionuclides were detected in the marine enviromnent aroimd all the Northern Ireland sites. Generally, in each of the sample categories, site locations and types of radionuclides, activity concentrations have declined in the environment around the coast of Northern Ireland reflecting reduced discharges at Sellafield over the years. Where this is not apparent from the individual trends this is mostly due to values being reported at or just above the limit of detection. Furthermore, there is variability in activity concentrations from year to year, particularly for the more mobile radionuclides (technetium-99 and caesium-13 7). Variations of these observations are also likely to have resulted from a combination of mechanisms including natural environmental variability, complex seawater transport patterns and redistribution of sediments due to natural processes.

Durand JP, Milcent MC, Goudard F, et al. 1994. Chemical behavior of three radionuclides (cesium, americium and technetium) and their uptake at the cystosolic level in aquatic organisms. Biochem Mol Biol Int 33(3) 521-534. 

Nuclear reactions involving technetium have been actively studied until today. Our interest in the nuclear chemistry of technetium is based on various reasons. Technetium was the first artificially produced element in the periodic table, a weighable amount of technetium ("Tc) is now available, and 99mTc is one of the most important radionuclides in nuclear medicine. In addition, technetium is an element of importance from a nuclear safety point of view. 

ICP-MS (inductively coupled plasma mass spectrometry) is frequently used for determining ultratrace amounts of technetium [9]. In spite of the high cost of the equipment, this detection method is far superior to other radiometric methods as regards sensitivity. When a double focussing high-resolution system is used (HR-ICP-MS) and an ultrasonic nebulizer is introduced [10], the detection limit is in the order 0.002 mBq. The ICP-MS method has been successfully applied to the determination of environmental "Tc as well as to other long-lived radionuclides of neptunium and plutonium in the environment. 

However, problems are encountered in production of rhenium radionuclides and work is being done to increase the yields of the radionuclides to meet urgent demands for their use in therapy. Moreover, rhenium is not as reactive as technetium. This situation makes rhenium chemistry somewhat specific - optimum conditions in the preparation of rhenium complexes or in antibody labeling using bifunctional ligands must be identified. 

Sebesta et al. describe a method for the separation of Tc and s + issj g adsorption chromatography using a solution of iV-benzoyl-A-phenylhydroxylamine in chloroform sorbed on Chromosorb W DMCS. The mixture of the radionuclides of technetium and rhenium in 5 M HCIO4 is passed through the coliunn. 

A technique for the determination of Tc amounts as little as 4 x 10 g by neutron activation analysis has been described by Foti et al. . Tc in triply distilled water is irradiated in a thermal neutron flux of 5 x 10 neutrons per cm and per second to produce °°Tc. Other radionuclides are removed by co-precipi-tation with Fe(OH)j. Then, °°Tc is co-precipitated twice with tetraphenylarsonium perrhenate which can be removed by sublimation. The chemical purification of °°Tc requires 40-45 s and the technetium yield is about 53%. 

The major driving force for the development of technetium coordination chemistry has undoubtedly been the potential applications in diagnostic nuclear medicine. The primary requirements for a radionuclide to be used in imaging are that the radiation emitted must be of appropriate energy, the decay half-life must lie in a suitable time window, it must be relatively cheap and readily available in the radiopharmacy, and finally it must have highly flexible co-ordination chemistry. 

The radionuclides commercially available and most commonly used for a number of the foregoing applications include anhmony-125 banum-133, 207 bismuth-207 bromine-82 cadmium-109, 115 m calcium-45 carbon-14 cerium-141 cesium-134, 137 chlorine-36 chromium-51 cobalt-57, 58, 60 copper-64 gadolimum-153 germanium-68 gold-195. 198 hydrogen-3 (tritium) indium-111, 114 m iodine-125, 129, 131 iron-55, 59 krypton-85 manganese-54 mercury-203 molvbdenum-99 nickel-63 phosphorus-32. 33 potassium-42 promethium-147 rubidium-86 ruthenium-103 samarium-151 scandium-46 selenium-75 silver-110 m sodium-22, strontium-85 sulfur-35 technetium-99 thallium-204 thulium-171 tin-113, 119 m, 121 m. titamum-44 ytterbium-169, and zinc-65. 

Scientists at PNNL have developed an automated radiochemical sample preparation-separation-detection system for the determination of total "Tc in nuclear-waste process streams.46 85 86 144145 This analyzer was designed to support a technetium removal process planned as part of the development of a nuclear-waste processing plant. The process stream composition is both complex and variable, with a high pH, high salt matrix. Depending on the source of the feed, the total base content, the concentration of organics, and complexant concentrations will vary, as will the aluminum, nitrate, nitrite, dichromate, and radionuclide composition. 

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