• (contrast agent) Substances administered during imaging procedures that allows delineation of internal structures. Contrast agents appear opaque due to the difference in absorption of X-rays or other electromagnetic waves and surrounding tissue.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• Substances used in radiography that allow visualization of certain tissues.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Substances used to allow enhanced visualization of tissues.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• (contrast medium) A fluid injected into the bloodstream or swallowed so that organs will show up on x-rays.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• (contrast material) A dye or other substance that helps show abnormal areas inside the body. It is given by injection into a vein, by enema, or by mouth. Contrast material may be used with x-rays, CT scans, MRI, or other imaging tests.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• Contrast medium, substance comparatively opaque to X ray, which, when present in an organ or tissue, causes a lighter appearance--i.e., a more definite image--on the X-ray film. Some body structures, such as the lungs, show in X-ray films and in fluoroscopic images by virtue of the sharp difference...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2020