Paramagnetic Ultrasmall Gadolinium Oxide Nanoparticles as Advanced <i>T</i>₁ MRI Contrast Agent: Account for Large Longitudinal Relaxivity, Optimal Particle Diameter, and <i>In Vivo</i> <i>T</i>₁ MR Images

TLDR

Ultrasmall Gd₂O₃ nanoparticles (~1 nm) were synthesized by refluxing three Gd(III) precursors in tripropylene glycol under an oxygen flow. The particles displayed a high longitudinal relaxivity of 9.9 s⁻¹ mM⁻¹, yielding strong T1 contrast in rat brain tumor images, with optimal size for maximal relaxivity determined to be 1–2.5 nm due to their large surface‑to‑volume ratio and surface Gd(III) ion contribution.

Abstract

Paramagnetic ultrasmall gadolinium oxide (Gd2O3) nanoparticles with particle diameters (d) of ∼1 nm were synthesized by using three kinds of Gd(III) ion precursors and by refluxing each of them in tripropylene glycol under an O2 flow. A large longitudinal relaxivity (r1) of water proton of 9.9 s−1 mM−1 was estimated. As a result, high contrast in vivo T1 MR images of the brain tumor of a rat were observed. This large r1 is discussed in terms of the huge surface to volume ratio (S/V) of the ultrasmall gadolinium oxide nanoparticles coupled with the cooperative induction of surface Gd(III) ions for the longitudinal relaxation of a water proton. It is found from the d dependence of r1 that the optimal range of d for the maximal r1, which may be used as an advanced T1 MRI contrast agent, is 1−2.5 nm.