Contrast agents are used in medical imaging to enhance visibility of internal structures. They can be ingested, injected, inserted or inhaled, and are generally safe but can cause allergic reactions. Radiologists decide which type of contrast to use and monitor for adverse reactions.
A contrast agent is a substance that is used in a medical imaging study to make it easier to see internal structures in the body. A number of different types of contrasts are used; they are sometimes called “dyes” because they appear to dye the fabric being studied. If you are scheduled for medical imaging, a radiologist will discuss the use of contrasts with you, if needed. Most of the agents are very safe and will be expressed by the body very quickly after studies; in rare cases, someone has an allergic reaction.
One of the most common types of contrast agent is an ingested agent such as barium sulfate, which is taken orally for studies of the gastrointestinal tract. This substance is radiopaque, which means that x-rays cannot pass through it. As a result, the X-ray film is not exposed and the doctor has a bright white image of the patient’s intestine. For MRI, a substance is used that affects the magnetism of the tissue of interest.
A contrast medium can also be injected. A wide variety of agents are used for injection with various types of imaging machines. Injected agents can sometimes be uncomfortable for patients; they may cause a burning sensation or a strange sensation, but are usually safe. Such agents can illuminate the inner workings of the brain and central nervous system in incredible detail.
Contrast agents can also be inserted through the rectum or inhaled for very rare imaging studies. Typically, a radiologist decides which type of contrast to use, although the patient’s medical records will be consulted to check for any potential allergic risks. The contrast may be administered to the patient immediately prior to the study, or additional time may be allowed to ensure that the agent reaches its intended destination; once the contrast medium has flooded the area of interest, the radiologist acquires images of the site for later analysis.
Using a contrast agent is generally very safe for the patient, as most radiologists want to avoid harmful reactions. However, allergic reactions do occur. If a contrast imaging study is ordered, ask the radiologist about common side effects and notify him if you start to feel unwell. If the radiologist thinks you may be having an adverse reaction, he will take the appropriate steps to treat you.
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