Gadolinium
Gadolinium. Vial containing samples of the rare earth metal Gadolinium (Gd). The rare earth metals, or rare earth elements, are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium. Gadolinium is a soft silvery-white metallic element. It is only found in salt form in nature. It is used to shield nuclear reactors and as a contrast medium for MRI (magnetic resonance imaging) scans.