Radiocontrast agent

Radiocontrast agents are per definition of drugs, but lack therapeutic effects.Contrast medium is used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (CT), radiography,and fluoroscopy. Radiocontrast agents are typically iodine or barium compounds.

Magnetic resonance imaging (MRI) functions through different principles and thus utilizes different contrast agents. These compounds work by altering the magnetic properties of nearby hydrogen nuclei.

Radiocontrast agents used in X-ray examinations can be grouped based on its use.

Iodine-based contrast media are usually classified as ionic or non-ionic. Both types are used most commonly in radiology due to their relatively harmless interaction with the body and its solubility. Contrast media are primarily used to visualize vessels and changes in tissues on radiography and CT. Contrast media can also be used for tests of the urinary tract, uterus and fallopian tubes. It may cause the patient to feel as if he or she has urinated on him- or herself. It also puts a metallic taste in the mouth of the patient.

Modern intravenous contrast agents are typically based on iodine. This may be bound either in an organic (non-ionic) compound or an ionic compound. Ionic agents were developed first and are still in widespread use depending on the requirements, but may result in additional complications. Organic agents which covalently bind the iodine have fewer side effects as they do not dissociate into component molecules. Many of the side effects are due to the hyperosmolar solution being injected. i.e. they deliver more iodine atoms per molecule. The more iodine, the more "dense" the X-ray effect.

Organic iodine molecules used for contrast include iohexol, iodixanol and ioversol. Iodine-based contrast media are water-soluble. These contrast agents are sold as clear, colorless water solutions, with the concentration usually expressed as mg I/ml. Modern iodinated contrast agents can be used almost anywhere in the body. Most often they are used intravenously, but for various purposes they can also be used intraarterially, intrathecally (as in diskography of the spine) and intraabdominally – just about any body cavity or potential space.

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