The use of different metals in Magnetic Resonance Imaging will be briefly described.This overview will be more a qualitative description than a full paper on this topic, in other words, this paper contributes to explaining how and why some metal ions have been chosen for MRI.Paramagnetic compounds are currently used in clinical practice. The main differencesin the four gadolinium complexes come from their different chemical structures. The macrocyclic compounds display a high symmetry and rigidity and therefore a high level of stability.All these four complexes display the same efficacyon the signal in MRI. In addition, they are very well tolerated.The second main class of compounds consists of the iron oxide superparamagnetic particles. They are used in the detection of focal liver lesions. Through their action in dephasing the spin, they are used as negative enhancers.