Synthesis of Well‐Dispersed Aqueous‐Phase Magnetite Nanoparticles and Their Metabolism as an MRI Contrast Agent for the Reticuloendothelial System

Aqueous‐phase Fe3O4 nanoparticles (NPs), with a size of 9.8 ± 3.0 nm, are directly synthesized by a modified iron salt coprecipitation process, stabilized by the synergistic effect of a combination of poly(vinylpyrrolidone) (PVP), trisodium citrate (TSC), and maleic anhydride (MAH). These NPs show good aqueous‐phase dispersion stability and excellent superparamagnetic properties with a saturation magnetization of 48.0 emu/g at a low magnetic field of 0.5 T. Their biocompatibility and metabolism for application in magnetic resonance reticuloendothelial system examinations are investigated by using rabbits as animal models for the determination of optimized dosage and diagnosis time for the enhanced imaging contrast for the early diagnosis of diseases. Results indicate that a significant darkening effect on the liver epithelial net lymph tissue can be observed in less than 30 min, with about 20 % reduction of the spin–spin relaxation time of T2 after injection. A metabolism study on the NPs indicates that they show little toxicity to the living organs examined, and finally enter into the spleen without obvious retention in any related organs after recycling for more than 2 d.