Technetium in biology and medicine

Abstract

Ever since the availability on a large scale [1] of technetium-99m and its application in science and technology [2], followed by an increasing use of technetium-99m in non-invasive diagnostic nuclear medicine [3], there has been great interest in the biological behaviour of this element in animals and humans [4]. Formerly the use of technetium-99m in functional imaging of different organs and tissues was based on its very favorable physical properties: pure gamma emission of 140 Kev, and short half-life of 6 h, ideal for external imaging, with low radiation risk both to the patient and to the nuclear medicine department personnel. During the past 20 years since its first use in nuclear medicine, it has been increasingly realized that for the synthesis of new technetium-99m radiopharmaceuticals and for evaluations of their biological behaviour a rigorous knowledge of the aqueous solution chemistry of technetium-99m in its various oxidation states, from −1 to +7, is needed. for pertechnetate-99m ion, now widely used for the imaging of the thyroid glands, brain, stomach and salivary glands, and also forming the starting material for the synthesis of other technetium-99m radiopharmaceuticals, little solution chemistry and consequently biological behaviour is known [5]. We have shown that the presence of a small amount (∼4 ppm) of free aluminum in the generator-produced pertechnetate-99m eluate not only gives false images of the thyroid gland, but also produces impure technetium-99m radiopharmaceuticals [4-6]. These inconveniences are easily avoided by chromatographic quality control of generator produced pertechnetate-99m eluate before its administration for radionuclidic imaging, or before its use for the preparation of other radiopharmaceuticals. The results we have explained by complexation of the pertechnetate-99m ion with free Al 3+ present in the generator column. These conclusions are supported by the chromatographic and electrophoretic examinations of all eluates during the useful life of the generator. Chromatography and electrophoresis are the only techniques which lend themselves to the study of solution chemistry of technetium-99m at the radiopharmaceuticals concentrations level (which is of the order of nanomolar).