Bismuth labeling for the CT assessment of local administration of magnetic nanoparticles

Many therapeutic applications of magnetic nanoparticles involve the local administration of nanometric iron oxide based materials as seeds for magnetothermia or drug carriers. A simple and widespread way of controlling the process using x-ray computed tomography (CT) scanners is desirable. The combination of iron and bismuth in one entity will increase the atenuation of xrays, offering such a possibility. In order to check this possibility core-shell nanocrystals of iron oxide@bismuth oxide have been synthesized by an aqueous route and stabilized in water by polyethylene glycol (PEG), and we have evaluated their ability to generate contrast by CT and magnetic resonance imaging (MRI) to measure the radiopacity and proton relaxivities using phantoms. High-resolution scanning transmission electron microscopy (STEM) revealed that the material consists of a highly crystalline 8 nm core of maghemite and a 1 nm shell of bismuth atoms either isolated or clustered on the nanocrystal's surface. The comparison of μCT and MRI images of mice acquired in the presence of the contrast shows that when local accumulations of the magnetic nanoparticles take place, CT images are more superior in the localization of the magnetic nanoparticles than MRI images, which results in magnetic field inhomogeneity artifacts.
This work was supported by the Spanish Ministry of Economy and Competitiveness through Project MAT2011-23641. The authors acknowledge the help of Dr Ruiz Cabello and Dr Herranz in the relaxometric measurements at the Centro Nacional de Investigaciones Cardiovasculares CNIC and acknowledge Guerbet Group for the economic support and the supply of Xenetix®. The research at ORNL US, the Department of Energy (DOE), Basic Energy Sciences (BES), the Materials Sciences and Energy Division (MV) and the Complutense University of Madrid (UCM) was supported by the ERC Starting Investigator Award STEMOX 739239.