The octopod-shaped iron oxide nanoparticles of this technology significantly enhance contrast in MRI imaging compared to spherical superparamagnetic iron oxide nanoparticle T₂ contrast agents. These octopod iron oxide nanoparticles show a transverse relaxivity that is over five times greater than comparable spherical agents. Because the unique octopod shape creates a greater effective radius than spherical agents, but maintains similar magnetization properties, the relaxation rate is improved. The improved relaxation rate greatly enhances the contrast of images. These octopod agents appear to be bio-compatible and may be suitable for intravenous delivery. The synthesis of these agents is also easily reproducible and scaled. The superior contrast greatly improves diagnostic sensitivities, compared to current FDA approved spherical contrast agents. These octopod-shaped iron oxide nanoparticle T₂ contrast agents may have a number of medical imaging uses, such as tumor detection, atherosclerosis imaging and delivery of therapeutic treatments.