Radiocontrast agent

Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically iodine, or more rarely barium sulfate. The contrast agents absorb external X-rays, resulting in decreased exposure on the X-ray detector. This is different from radiopharmaceuticals used in nuclear medicine which emit radiation.

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