Paramagnetic ultrasmall gadolinium oxide nanoparticles as advanced T _1 MRI contrast agent: Account for large longitudinal relaxivity, optimal particle diameter, and in Vivo T_1 MR images

摘要

Abstract Paramagnetic ultrasmall gadolinium oxide (Gd_2O _3) 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 O_2 flow. A large longitudinal relaxivity (r_1) of water proton of 9.9 s~(-1) mM~(-1) was estimated. As a result, high contrast in vivo T_1 MR images of the brain tumor of a rat were observed. This large r_1 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 r_1 that the optimal range of d for the maximal r_1, which may be used as an advanced T_1 MRI contrast agent, is 1-2.5 nm.