gadolinium (Gd) /gad′əlin″ē·əm/ [Johan Gadolin, Finnish chemist, 1760–1852] , 1. a rare earth metallic element. Its atomic number is 64, and its atomic mass is 157.25. It is now widely used as an MRI contrast agent. 2. (in radiology) a phosphor used for its fluorescent properties in the manufacture of extraoral radiography intensifying screens. 3. an element used for shielding in neutron radiography.
