The cancer is one of the biggest causes of death in the world, having as great difficulty the diagnosis in its initial phase. Among the techniques used in the cancer diagnosis, we can highlight the Magnetic Resonance Imaging (MRI). The MRI is an effective diagnostic method, which by means of the use of contrast agents (CAs) is able to locate tumors of various natures. The most used CAs are the Gd3+ complexes, although they are very effective and very toxic to the organism. Thus, new CAs are being studied to replace the Gd3+ complexes, among them superparamagnetic iron oxide nanoparticles (SPIONs) and the Ni2+ complexes (paraCEST) stand out. The SPIONs and the paraCEST are able to change the relaxation time T1 and T2 of the water molecules of the organism. In this work, we studied the face 100 of various iron oxides (Gamma-Fe2O3, d-FeOOH, -FeOOH, Fe2O3 and Fe3O4) and the Ni2+ complexes ([Ni(ACAC)2(H2O)2], [Ni(TEA)]2+) coordinating with explicit water molecules, in order to obtainthe hyperfine coupling constants (Aiso) of 1H and 17O atoms of the water molecules.