dF 4 nanoparticles as T 2 contrast agents for high-fi eld magnetic resonance imaging †

It is important to get high-quality magnetic resonance images at high magnetic field (>3 T) for medical diagnoses. However, the efficiency of the commonly used magnetic resonance imaging (MRI) contrast agents (CAs) always decrease with the increasing of magnetic field intensity. Thus, it is necessary to design MRI CAs with high relaxivity at high magnetic field. In this study, the hydrophilic and biocompatible NaGdF4@SiO2 nanoparticles (NPs) were feasibly synthesized and exhibited highly effective T2 contrast imaging at 7 T magnetic field. Furthermore, the obtained NPs had a higher r2/r1 value than the other typical T2 CAs (such as Dy-based NPs and Fe-based NPs) at high magnetic field. The observed large r2 of the current NaGdF4@SiO2 was mainly ascribed to the increased particle sizes. For in vivo application, 250 nm NaGdF4@SiO2 (with the highest relaxivity) as T2-weighted MRI CAs was further assessed. Toxicity studies demonstrated that NaGdF4@SiO2 NPs exhibited little toxicity both in vitro and in vivo. Therefore, NaGdF4@SiO2 NPs with appropriate size could be used as high-performance T2 CAs in the high magnetic field.