Magnetic resonance imaging (MRI) (see “The Modern Chemical Lab”) contrast agents are used to make tissues and other structures inside the body easier to view in an MRI scan. Many of these contrast agents are based on gadolinium with various ligands attached. The contrast agents are injected or ingested into the body, and they function by changing the relaxation time of the atoms observed in an MRI scan. The overall result is that these complexes improve the ability of MRI to see what is going on in your body.