Contrast medium

A medical contrast medium (or contrast agent) is a substance used to enhance the contrast of structures or fluids within the body in medical imaging. It is commonly used to enhance the visibility of blood vessels and the gastrointestinal tract.

Types

Several types of contrast media are in use in medical imaging and they can roughly be classified based on the imaging modalities where they are used. Although other types exist, most common contrast agents work based on X-ray attenuation and magnetic resonance signal enhancement.

X-ray attenuation

Iodine and barium are the most common types of contrast medium for enhancing x-ray-based imaging methods. Various sorts of iodinated contrast media exist, with variations occurring between the osmolarity, viscosity and absolute iodine content of different media. Non-ionic dimers are favored for their low osmolarity and toxicity, but have a correspondingly higher price attached to their use.

MR signal enhancing

Gadolinium is used in magnetic resonance imaging as a MRI contrast agent. In the 3+ oxidation state the metal has 7 unpaired of electrons. This causes water around the contrast agent to relax quickly, enhancing the quality of the MRI scan.