Radiopacity is a measurement of the ability of electromagnetism to pass through a particular material. Materials that prevent the passage of electromagnetic radiation are called 'radiopaque'. In modern medicine, radiopaque usually refers to substances that will not allow X-rays or similar radiation to pass. Radiologic imaging has been revolutionized by radiopaque dyes, or contrast media, which can be passed through the bloodstream, the intestinal tract, or into the cerebral spinal fluid and utilized to highlight computed tomography (CT), magnetic resonance imaging (MRI), or X-ray images.

Medical imaging