(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.

(MAA) Macroaggregated albumin is used in pulmonary perfusion scintigraphy to record the pulmonary circulation. Macroaggregated albumin is usually prepared by heating human serum albumin. The produced particle sizes range from 10 to 100 µm in diameter. The albumin may be labeled with 131I, 99mTc, or 113mI.

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.

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.

(Osm) A unit of osmotic pressure used in physical chemistry, cell biology, and medicine.
Definition: 1 osmole is the osmotic pressure of a one molar solution (that is, a solution with a concentration of one mole per liter of solvent) of a substance that does not dissociate.
If chemical solutions are separated by a semipermeable membrane (a membrane that resists the passage of dissolved substances but permits the passage of the solvent, usually water), then the solvent will diffuse across the membrane to equalize the concentrations. This process is called osmosis.
Solutions with higher concentrations of dissolved substances are said to have higher osmotic pressure than solutions having lower concentrations; thus the solvent moves from an area of low osmotic pressure to an area of higher osmotic pressure.
Osmotic pressure depends on the total number of dissolved particles, so for a substance that dissociates into two ions, such as ordinary salt (sodium chloride), a one molar solution has an osmotic pressure of 2 osmoles. In practice, most measurements are in milliosmoles (mOsm). Typical values range from 20 mOsm for fresh water through 290 mOsm for typical human blood plasma to 1010 mOsm for salt water from the open ocean.
See also Part Per Million.