Urography into the 21st century: new contrast media, renal handling, imaging characteristics, and nephrotoxicity.

All currently used x-ray contrast media are based on the triiodinated benzene ring (Fig 1), acetrizoate being the parent triiodinated contrast medium first in clinical use (3-6). Contrast media are characterized as ionic or nonionic and as monomers or dimers (6-14). Ionic media dissociate in water; the iodinated benzene ring contains the ionizing carboxyl group (valence, -1) with a cation (valence, +1), usually sodium or meglumine. Nonionic contrast agents have the desirable property of being soluble in water (hydrophilic) and yet do not dissociate in solution. The ratio of iodine atoms to dissolved particles is an important characteristic of contrast media and is a commonly used term in the literature. This describes the important relationship between the imaging effect (attenuation of x rays) and the osmotoxic effect of the media. Since the ratio represents the number of iodine atoms divided by the numbers of particles of the contrast medium in solution, a higher ratio is more desirable, since more iodine means better opacification and fewer particles of contrast medium means a lower osmotoxic effect (6). Agents with a ratio of 1.5 (ratio 1.5 agents) have been termed high-osmolar contrast media (HOCM), agents with a ratio of 3 have been termed low-osmolar contrast media (LOCM), and agents with a ratio of 6 have been termed isotonic contrast media (10CM).