Radiocontrast agent

Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy.

The substance exists as a water-insoluble white powder that is made into a slurry with water and administered directly into the gastrointestinal tract.

[citation needed] Barium sulfate, an insoluble white powder, is typically used for enhancing contrast in the GI tract.

As the barium sulfate doesn't dissolve, this type of contrast agent is an opaque white mixture.

Before the advent of modern neuroimaging techniques, air or other gases were used as contrast agents employed to displace the cerebrospinal fluid in the brain while performing a pneumoencephalography.

Sometimes called an "air study", this once common yet highly-unpleasant procedure was used to enhance the outline of structures in the brain, looking for shape distortions caused by the presence of lesions.

Given that the substance remained in the bodies of those to whom it was administered, it gave a continuous radiation exposure and was associated with a risk of cancers of the liver, bile ducts and bones, as well as higher rates of hematological malignancy (leukemia and lymphoma).

[7] Iodinated contrast may be toxic to the kidneys, especially when given via the arteries prior to studies such as catheter coronary angiography.

The risk of either condition developing after a single examination is 2–3 times that of those who have not undergone a scan with iodinated contrast.

Children exposed to iodinated contrast during pregnancy may develop hypothyroidism after birth and monitoring of the thyroid function is recommended.