Omnipaque is a low-osmolar, nonionic, contrast medium with a broad range of indications, for example intravascular diagnostic procedures such as coronary angiography, spinal cord imaging, and body cavity procedures including shoulder and knee joints. Omnipaque is approved for use in adults and children, and is available in a wide variety of packagings.

See also Nonionic Contrast Agents.

(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.

A nonionic dimer consists of 2 joined nonionic monomers. Nonionic dimers are used as x-ray and CT contrast media.
Nonionic dimers have the lowest osmolarity. These contrast materials contain 6 iodine atoms for every 1 particle in solution (CM ratio=6). Modern CT techniques require fast bolus injections and thus low-viscosity, high-concentration, well-tolerated contrast agents. Nonionic dimers have the highest viscosity, which limits the clinical usefulness. Examples of nonionic dimers are iotrolan (Isovist®) and iodixanol (Visipaque).

See also Contrast Agents.

Ionic dimers are used as x-ray contrast agents. They are formed by joining 2 ionic monomers and eliminating 1 carboxyl group and contain 6 iodine atoms for every 2 particles in solution (CM ratio=3).
Ionic dimers have an intermediate osmolarity, intermediate viscosity and an intermediate hydrophilicity between that of ionic and nonionic monomers. The only commercially available ionic dimer is ioxaglate (Hexabrix). Ioxaglate is used primarily for peripheral arteriography.

Nonionic monomers are used as x-ray contrast agents. To create a nonionic monomer, the tri-iodinated benzene ring is made water soluble by the addition of hydrophilic hydroxyl groups to organic side chains (CM ratio=3). Nonionic monomers have an intermediate osmolarity, intermediate viscosity and elevated hydrophilicity with three atoms of iodine per molecule. Lacking a carboxyl group, nonionic monomers do not ionize in solution. A nonionic monomer is potentially less chemotoxic than an ionic monomer.
Common nonionic monomers are iohexol (Omnipaque), iopamidol (Isovue®), ioversol (Optiray®), and iopromide (Ultravist®). Nonionic monomers are contrast agents with a wide range of indications due to their nonionic nature and lower osmolalities.