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The field of radiography including the development of contrast media for this diagnostic tool is based on the discovery of X-rays by the physicist Wilhelm Conrad Röntgen. Later on, the rays he discovered came to be called “Roentgen rays” in his honor.

Contrast in an X-ray image is brought about by differences in absorption of X-rays by the tissues being irradiated. Absorption is dependent on the atomic number of the atoms present in the molecules, the concentration of these molecules and the thickness of the irradiated slice. When a chest radiograph is obtained, the bones, the aeriferous lungs, the heart and other tissues provide adequate natural contrast.

Optimal use of CM in radiology requires a knowledge of the nature and relevant properties of the available substances. This chapter describes the properties of currently used and newly developed contrast-giving agents that influence their behavior in the human body, their side effects, and their practical utility.

Each year, over 3000 tons of X-ray contrast media are used by medical facilities across the globe. About 90 % of those contrast agents reach our environment largely unaltered through clarification plants. To the present day, degradation products of these substances, which would imply decomposition of the iodinated benzene by microorganisms, have not been identified in sewage sludge.

The most important physicochemical properties of water-soluble, iodinated CM are their solubility, the viscosity and osmolality of the solutions, the lipophilic or hydrophilic properties of the iodine-containing molecule, and the electrical charge (table 4).

Because of the high doses employed - which can exceed 100 g of substance per patient and examination – very high demands are made on CM in terms of chemical purity. The molecular structure of the CM substance is confirmed by NMR (nuclear magnetic resonance),, IR (infra red), MS (mass spectrometry) and UV (ultraviolet) spectra (fig. 13a-e).

Contrast agents influence the human organism not only because of their physical properties such as osmolality, viscosity and hydrophilicity but also because of their special chemical structure. Contrary to former beliefs, effects are not induced by free iodine, but by the contrast medium molecule. Hemodynamic, neurological and pseudoallergic effects are partially attributable to the chemical structure of contrast media molecules.

The mechanisms of action of X-ray CM range from purely mechanical filling of certain cavities to opacification in a functional manner.

The influence of different ionic and nonionic CM on clinicochemical parameters determined in serum and urine was examined systematically in the laboratory.

For this purpose, reference sera (normal and pathological values) were mixed with up to 20 vol % CM solution and urine with up to 50 % CM solution. Higher concentrations are unlikely to occur in humans even a very short time after a CM injection.

The aim of using CM is to visualize certain structures in the organism or improve their visualization and to obtain information on organ functions. A CM must have low toxicity and be safe to use since it is often injected at a high dose and for certain purposes very quickly.