A design strategy of ultrasmall Gd2O3 nanoparticles for T1 MRI with high performance

Abstract

It is still a big challenge to design Gd³⁺ based nanoparticles (NPs) for T₁ MRI (Magnetic Resonance Imaging) with high performance and clarify the effects of relative time parameters on longitudinal relaxivity r₁. In this paper, we simulated the influences of different time parameters on the longitudinal relaxivity of Gd³⁺ based NPs with inner-sphere and outer-sphere theories, respectively. In particular, we investigated the effects of τ_R (the rotational time), τ_M (the residence time), T_ie (the electronic relation time) and τ_d (the diffusion time) on longitudinal relaxivity. In the relaxation process of Gd³⁺ based NPs, the inner-sphere plays a dominant role, in which τ_R and τ_M have a greater impact on r₁. Based on the simulation results, we proposed a design strategy of Gd³⁺ based NPs for T₁ MRI, which focuses on the rational decrease of hydrated radius, and the optimal range of the hydrated radius is about 0.8–2.5 nm. In addition, we synthesized ultrasmall Gd₂O₃ NPs with a hydrated radius of about 2.5 nm, which have a high longitudinal relaxivity r₁ of 10.8 mM⁻¹ s⁻¹ at 3.0 T. Moreover, the in vivo imaging results confirm that the ultrasmall Gd₂O₃ NPs have a good imaging effect on the tumor, and it can be a good candidate as a T₁ MRI contrast agent with high performance.