Osmolality
A measure of total number of particles dissolved in a fluid, usually in water. Particles can be small or large, have an electrical charge (ions from salts, acids or bases) or be electrically neutral (sugars, proteins). High osmolality is an important contributing factor to toxicity. Ioniccontrast media are salts and split into an anion and a cation when dissolved, while non-ionic contrast media result in a solution of solution of intact molecules. This means that ionic contrast media will have 2 particles per 3 iodine atoms ("ratio 1.5 ") while non-ionic monomeric contrast media will have only particle per 3 iodine atoms ("ratio 3"), i.e. more iodine per unit. Ionic dimeric contrast media behave like "ratio 3" contrast media or low-osmolar contrast media. Dimeric non-ionic contrast media have 6 iodine atoms per particle ("ratio 6 "), and are isosmolar with blood and body fluids at all available concentrations.
GE Healthcare Glossary