New Radiopaque Contrast Agents based on RE Tantalates and Their Solid Solutions

At present, the largest group of radiopaque contrast agents (RCA) is represented by iodinecontaining RCA. However, the development of abdominal interventional X-ray surgery places stringent requirements upon RCA. High contrast must be combined with pharmacological and physiological inertness, low toxicity, with the ability to be uniformly adsorbed as a thin layer on the surface of mucous organs and cavity walls without accumulating in minor-diameter lumens to avoid their obstruction, as well as with the ability to be quickly excreted from the organism. With oil or water-soluble iodineand barium-containing RCA it is not possible for several reasons to completely estimate for example the hepatic tree lumens or the ducts of other organs since these preparations not always provide uniform and fine contrasting. Water-soluble iodine-containing RCA intended for parenteral introduction enjoyed wide application (urographin, trazograph, omnipaque, etc.). The preparations of this group are also used for direct contrast studies of hollow organs. However, they are found to be absorbed into blood in the small intestine during contrast studies of gastrointestinal tract organs and hepatobiliary system. They have a toxic effect on blood, kidneys, liver, and especially on the thyroid gland. The aim of this study was to develop new gel RCA, in which the substances are tantalates of rare-earth elements or solid solutions based thereon. Lanthanum orthotantalate LaTaO4 and solid solutions La1 X GdX TaO4 were considered as such substances. The RCA were examined in vitro and in vivo. When gel lanthanum orthotantalate was used as a RCA for contrast studies of the bile passages, this method exhibited a high resolving power in the examination of the hepatic tree and the gallbladder and in the diagnostics of intracavitory masses in ducts and the gallbladder. In contrast to iodine-containing urografin, this RCA has no negative effect on the mucous tunic of the bile passages of laboratory animals. Using the substitutional solid solutions, one can continuously change the specific effectiveness of RCA by gradual varying of the composition and the average size of the substance particles.