Magnetic Resonance Imaging Contrast Agents Based on Iron Oxide Superparamagnetic Ferrofluids

Novel systems based on suspensions or colloidal magnetic nanoparticles have been investigated as perspective super paramagnetic contrast agents (CA) for magnetic resonance imaging (MRI) The nanostructures that we have studied contain surfactant-capped magnetic (Fe3O4) inorganic cores wall different controlled sizes, ranging from 5 5 to 12 nm The as-synthesized nanostructures are passivated by hydrophobic surfactants and thus are fully dispersible in nonpolar media The magnetic nanocrystals have been transferred into aqueous meta by a procedure based on the surface intercalation and coating with an amphiphilic polymer shell The MRI efficiency in contrasting images. i.e. the NMR relaxivities r(1) and r(2), have been compared with Endorem and Sinerem, commercial super paramagnetic MRI contrast agents We found that out nanostructures exhibit r(1) and r(2) relaxivities comparable to those of commercial CA over the whole frequency range The MRI efficiency of our samples was related to their microstructural and magnetic properties. The transverse relaxivity r(2), leading the contrast in "negative" super-paramagnetic agents, was round to improve as the diameter of the inorganic core is increased. The NMR relaxometry profile confirmed the nature or the physical mechanisms inducing the increase of the nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) fields.