Monodisperse magnetite nanoparticles with high sensitivity as MRI contrast agents

Abstract

The preparation of monodisperse and biocompatible water-soluble super-paramagnetic iron oxide nanoparticles (SPIONs) with high sensitivity in Magnetic Resonance Imaging (MRI) represents a challenge for the development of contrast agents. Here we report the synthesis of highly monodisperse citric acid (CA) coated SPIONs with an average diameter of 9 nm and spherical shape, prepared through a suitably optimized coprecipitation method. CA-SPIONs show a high solubility and stability in aqueous medium. Imaging of CA-SPIONs aqueous suspensions was performed in a clinical 1.5-T MRI scanner and different clinical acquisition sequences were exploited. Results show that image contrast can be effectively improved when concentrations of SPIONs lower than 1 ppm are present, and that the echo time is the main parameter influencing the image contrast of SPION-loaded solutions. Moreover, we found that CA-SPIONs show a high value of transverse relaxivity of 128 L mmol^-1 s^-1 (higher than the commercial contrast agents). Our results are encouraging for the further development of clinical application of SPIONs in MRI, and can represent a starting point for the optimization of clinical imaging exploiting the contrast enhancement of such agents. Namely, it seems possible to achieve an optimal image contrast with low concentration of SPIONs; this could lead to a lower probability of side effects.