Radiographic contrast agents and contrast reactions

[Ernesto]

Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based.
Iodinated contrast agents may be

Ionic
Nonionic

Ionic contrast agents, which are salts, are hyperosmolar to blood. These agents should not be used for myelography or in injections that may enter the spinal canal (because neurotoxicity is a risk) or the bronchial tree (because pulmonary edema is a risk).
Nonionic contrast agents are low-osmolar (but still hyperosmolar relative to blood) or iso-osmolar (with the same osmolarity as blood). Newer nonionic contrast agents are now routinely used at nearly all institutions because they have fewer adverse effects.
The most serious contrast reactions are

Allergic-type reactions
Contrast nephropathy (renal damage after intravascular injection of a contrast agent)