Nonionic contrast agents are a group of contrast media that do not dissociate into charged particles. Many of the side effects of contrast agents are due to the injection of a solution with high osmolality compared to blood. Nonionic contrast agents have a low osmolality and tend to have less toxicity. However, as with all iodinated contrast agents, serious or fatal reactions have been associated with their use.
Due to their lower neurotoxicity, nonionic contrast agents can also be used for myelography. The only FDA approved agent, iodixanol, is iso-osmolar to blood, which makes it preferable for examinations of the central nervous system and cardiovascular studies. Because of its higher costs relative to other nonionic agents, the use is sometimes reserved for patients with high risk of nephrotoxicity.

See also Nonionic Dimer, Nonionic Monomer and CM Ratio.

Radiographic contrast media (RCM) contributes important information to the diagnostic process. Actual contrast agents are safe drugs. Adverse reactions are rare, the incidence and severity of side effects decrease with the use of nonionic and low-osmolar contrast media. Adverse reactions are diverse, ranging from mild physiological disturbances to very rare life-threatening anaphylactic or anaphylactoid reactions. Users of contrast agents must be aware of the risk factors and be prepared to promptly manage adverse effects.
Side effects that may occur with intravascular administration of contrast agents are also possible after administration by other paths. Increased risk to an adverse reaction includes patients with a history of a previous reaction to a contrast medium, a known sensitivity to iodine, or a known clinical hypersensitivity (bronchial asthma, hay fever, and food allergies).

See also Contrast-Induced Nephropathy, Iodide-Induced Hyperthyroidism and Idiosyncratic Reactions.

(LCD) The low contrast detectability represents the ability of a CT scanner to distinguish between objects that have similar x-ray attenuation coefficients. In cases of other diagnostic imaging modalities it means the ability of imaging equipment to differentiate between objects that have similar properties.

(LOCM) Low-osmolar contrast media have a wide range of indications due to their lower side effects. The type of contrast media is an important risk factor for an adverse reaction.
LOCM have not completely replaced contrast media with higher osmolality due to their higher cost. Guidelines of professional organizations give recommendations for the selective use of low-osmolar contrast media for certain high-risk patients.
There are ionic and nonionic iodinated contrast materials with low osmolality available:
An adverse reaction occurs in low-risk patients who receive conventional ionic contrast agents more often than in high-risk patients who receive nonionic LOCM.

See also Contrast Enhancement, Biliary Contrast Agents, Safety of Contrast Agents and Contrast-Induced Nephropathy.

Contrast-induced nephropathy is a serious complication of intravascular x-ray contrast agents. The osmolality of the contrast medium is an important fact in contrast-induced nephropathy and should ideally be iso-osmolar to blood. Today, nonionic contrast agents are state of the art for vascular use, the ionic contrast agents caused more adverse reactions.
Signs of contrast-induced nephropathy after the application of vascular contrast agents are a serum creatinine increase of 0.5 mg/dL (In the United States, creatinine is typically reported in mg/dL, while in Canada and Europe µmol/L may be used. 1 mg/dL of creatinine is 88.4 µmol/L) or an increase of serum creatinine greater than 25%.

A higher risk of contrast-induced nephropathy is associated with:
The use of a nonionic contrast agent, iso-osmolar to blood and a low dose reduces the risk for contrast-induced nephropathy.