Contrast agents
Also known as: contrast media, contrast dyes, imaging contrast
Substances given to make blood vessels, organs, the gut or joints stand out on imaging: iodinated agents for X-ray and CT, gadolinium agents for MRI, microbubbles for ultrasound and barium for the gut.
- Biological target
- The imaging signal of the tissue the agent occupies (X-ray attenuation, MRI relaxation, ultrasound reflection)
- Also called
- contrast media, contrast dyes, imaging contrast
Mechanism of action
Each agent changes how the tissue it fills interacts with the imaging energy. Iodine and barium absorb X-rays, so filled vessels and cavities appear bright on X-ray and CT; gadolinium shortens the relaxation time of nearby water protons, brightening perfused tissue on MRI; microbubbles reflect ultrasound strongly and outline blood flow. Timing the scan to when the agent is in arteries, veins or tissue shows different structures.
Members of the class
Members with a page on this site are linked.
Conditions treated
Class effects
- A warm flush, metallic taste and nausea during injection
- Allergic-type reactions, rarely severe
- Kidney injury with iodinated agents in people at risk; gadolinium retention concerns in repeated MRI
Cautions
- Kidney function checked before iodinated and gadolinium agents in people at risk
- Previous contrast reactions and severe allergy declared beforehand
- Pregnancy: used only when the imaging is essential
Class interactions
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