Magnetic resonance imaging (MRI) is a powerful diagnostic tool that allows a precise investigation of the human body, anatomic structures, physiological functions, molecular composition of tissues, providing clear and three-dimensional images. The addition of a contrast agent (CA) has become a crucial step for enhancing image contrast. CAs have received a lot of attention in terms of research and development pursuing the preparation of an imaging probe with adequate biocompatibility, good colloidal stability, and improved relaxometric properties. After the advent of nanotechnologies, the use of magnetic nanostructured agents has been the main focus of MRI CAs development up to this point.