Magnetic resonance imaging quantification and biodistribution of magnetic nanoparticles using T₁-enhanced contrast

Magnetic iron oxide nanoparticles have been used for various applications such as in the treatment of iron deficiency, as theranostic agents, and as drug carriers. The effective delivery of magnetic iron oxide nanoparticles into the lesion and iron quantification are vital for in vivo theranostic application. To determine the feasibility of using T₁ contrast to non-invasively quantify and monitor the IONPs in vivo, monodispersed Gd-doped iron oxide nanoparticles (GdIONPs) with 4 nm core size were fabricated and were used as T₁-weighted contrast agents to quantify iron contents based on MRI longitudinal relaxation times (T₁). Signal enhancement in positive T₁ contrast caused by GdIONPs was observed in this work. The in vivo T₁ relaxivity of GdIONPs in a tumor matched well with both in vitro T₁ relaxivity and ICP-MS results, demonstrating that the concentration of iron at the tumor site can be directly read from real-time in vivo MRI T₁ relaxivity. Hence, by using this strategy, the Fe content in the lesion can be accurately monitored based on MRI longitudinal relaxation times, and this may shed light on effective magnetic hyperthermia cancer therapy in future.