Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure gamma -Fe sub(2)O sub(3) Phase

Pure and highly crystalline gamma -Fe sub(2)O sub(3) nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe super(II) organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150nm that exhibit a high transversal relaxivity (r sub(2)=466mM super(-1)s super(-1)) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements. Faster contrast: Pure and highly crystalline gamma -Fe sub(2)O sub(3) nanocrystals (NCs) are obtained when hydrolysis and oxidation of an iron(II) organometallic precursor are performed in successive steps (see figure). In the presence of poly(vinyl)pyrrolidone, such pristine NCs form aggregates that exhibit a transversal relaxivity higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent.