Contrast media, also known as medical contrast mediums and contrast agents, are chemical compounds and gases used to supplement medical imaging techniques by enhancing the image results during the medical testing processes. Contrast agents work in combination with either magnetic resonance signal augmentation or x-ray attenuation. Adverse effects related to contrast media are fairly uncommon, but can occur and vary in how they manifest and their severity.
Magnetic resonance imaging (MRI) employs gadolinium, a rare metal, as a contrasting agent to produce high contrast images of soft tissue in the body. Used for cardiovascular, oncological, and neurological imaging, the MRI does not utilize radioactive materials such as high frequency gamma or x-rays. Administered intravenously, the oxidized metal works with existing hydrogenated atoms of water in the body, resulting in enhanced imaging results.
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X-ray attenuation, often referred to as radiocontrast, is a form of radiography that utilizes a contrast agent to improve image resonance. Historically, a concentration of thorium dioxide was used as a contrast agent until it was proven to be hazardous. Based on application, barium and iodine are the most commonly employed contrast agents in x-ray imaging.
Barium, a white insoluble powder, is generally used as a contrast agent for medical imaging tests of the gastrointestinal tract. When combined with water, the barium powder creates an opaque mixture that functions to define the digestive tract during the imaging process. Iodine contrast media, which can be classified as either ionic or non-ionic in composition, is used to accentuate blood vessels and soft tissue. As a soluble contrast agent, iodine is generally harmless and, as a result, most intravenous contrast dyes are iodine-based.
Contrast-enhanced ultrasound uses micro-bubbles filled with trace amounts of nitrogen or fluorocarbons as contrast agents which are administered intravenously. The bubbles reflect the sound waves back to the transducer as a higher signal which is used to formulate a high resolution image. Ultrasonography is employed to image organ-specific blood flow rate and perfusion.
Side effects associated with the use of contrast media are dose dependent on the type of media used and vary in severity. Mild side effects, including vomiting, nausea, and a metallic taste in the mouth, may manifest shortly after the contrast agent is administered and usually subside relatively quickly. More moderate to severe side effects, such as anaphylactic reactions and renal failure, can occur in individuals who have never had contrast agents administered before and can result in death if left untreated. Delayed reactions to contrast media, including abdominal pain, fatigue, and fever, are more common when ionic agents are administered.