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Radiographic Contrast Agents


Mustafa A. Mafraji

, MD, Rush University Medical Center

Reviewed/Revised Nov 2023

Radiographic contrast agents are substances used to distinguish between internal structures in medical imaging, such as various types of x-rays and magnetic resonance imaging (MRI).

Contrast agents include

Radiopaque Contrast Agents

A radiopaque contrast agent absorbs x-rays and thus appears white on x-rays. It is typically used to show the following:

  • Blood vessels

  • The interior of the gastrointestinal, biliary, or urinary tract

  • Blood flow in organs

Usually, the contrast agent is injected into a vein (intravenous contrast), artery (angiography Angiography Angiography is a type of medical imaging that uses x-rays and a contrast agent to produce images of blood vessels. In angiography, x-rays are used to produce detailed images of blood vessels... read more ), taken by mouth (oral contrast), inserted through the anus (rectal contrast), or injected into a joint using a needle.

The contrast agent used depends on what type of test is done and which body part is being evaluated:

  • For blood vessels: Usually contrast agents that contain iodine (iodinated contrast agents)

  • For the gastrointestinal tract: Contrast agents that contain barium or iodine (gastrografin)

Before a test that uses a contrast agent, people may be asked to refrain from eating for several hours and from drinking for 1 hour. After the test, drinking extra fluids for the rest of the day is recommended.

When some contrast agents are injected, people may feel a warm sensation throughout the body. Other contrast agents may cause a cold sensation at the injection site. Contrast agents taken by mouth may have an unpleasant taste.

Side effects of radiopaque contrast agents

Generally, radiopaque contrast agents are very safe, particularly when given by mouth or into the rectum.

Side effects of injected iodinated contrast agents occur in a few people. They include

Allergic-type contrast reactions

Allergic-type contrast reactions vary in severity:

At the first sign of a reaction, the contrast agent is stopped. Mild or moderate reactions are treated with the antihistamine diphenhydramine, given intravenously. Severe reactions may be treated with oxygen, fluids given intravenously, epinephrine, or other medications, depending on the type of reaction.

Allergic-type contrast reactions are most likely to occur in people who have one of the following:

If people have had several severe reactions to iodinated contrast agents, an imaging test that does not require this contrast agent should be done instead. If an iodinated contrast agent must be used, medications (diphenhydramine and a corticosteroid) may be given before the test to prevent a reaction. People who previously have had a reaction to a contrast agent should tell their doctor before an imaging test is done.

Kidney damage

In almost all people, the kidney damage causes no symptoms and goes away within 1 week or so. Very rarely, a person has lasting damage, and only a very few of them require kidney dialysis Dialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more Dialysis .

If tests that require radiopaque contrast agents must be used in people at risk of kidney damage, people are given fluids intravenously before and after the agent is given. They do this to avoid any accumulation of these drugs in the event that contrast agents impair kidney function. A low dose of the contrast agent is used if possible. Doctors may also withhold the medication metformin for 48 hours after IV radiopaque contrast agents are given to people with severe kidney disease who take metformin.

Did You Know...

  • If you have severe kidney disease and are taking metformin, doctors may have you discontinue metformin for 48 hours after exposure to radiopaque contrast agents.

Paramagnetic Contrast Agents

Paramagnetic contrast agents change the magnetic properties of particles in a way that increases the contrast between different tissues, making MRI images clearer. These agents usually contain gadolinium.

Side effects of paramagnetic contrast agents

Usually, no side effects occur. However, in a few people who have severe kidney disease or who are undergoing dialysis, these agents may cause a life-threatening disorder called

  • Nephrogenic systemic fibrosis

In nephrogenic systemic fibrosis, the skin, connective tissue, and organs thicken. Red or dark patches may develop on the skin. The skin may feel tight, movement is difficult and limited, and organs may malfunction. This disorder is now very rare because doctors use gadolinium paramagnetic contrast agents in people with kidney problems only when necessary, and they use the lowest dose and safest agent possible. Doctors also consider using other imaging tests in people with severe kidney problems.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Aid to Sleep, Alka-Seltzer Plus Allergy, Aller-G-Time , Altaryl, Banophen , Benadryl, Benadryl Allergy, Benadryl Allergy Children's , Benadryl Allergy Dye Free, Benadryl Allergy Kapgel, Benadryl Allergy Quick Dissolve, Benadryl Allergy Ultratab, Benadryl Children's Allergy, Benadryl Children's Allergy Fastmelt, Benadryl Children's Perfect Measure, Benadryl Itch Stopping, Ben-Tann , Compoz Nighttime Sleep Aid, Diphedryl , DIPHEN, Diphen AF , Diphenhist, DiphenMax , Dytan, ElixSure Allergy, Genahist , Geri-Dryl, Hydramine, Itch Relief , M-Dryl, Nighttime Sleep Aid, Nytol, PediaCare Children's Allergy, PediaCare Nighttime Cough, PediaClear Children's Cough, PHARBEDRYL, Q-Dryl, Quenalin , Siladryl Allergy, Silphen , Simply Sleep , Sleep Tabs, Sleepinal, Sominex, Sominex Maximum Strength, Theraflu Multi-Symptom Strip, Triaminic Allergy Thin Strip, Triaminic Cough and Runny Nose Strip, Tusstat, Unisom, Uni-Tann, Valu-Dryl , Vanamine PD, Vicks Qlearquil Nighttime Allergy Relief, Vicks ZzzQuil Nightime Sleep-Aid
Adrenaclick, Adrenalin, Auvi-Q, Epifrin, EpiPen, Epipen Jr , Primatene Mist, SYMJEPI, Twinject
Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet, RIOMET ER
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