Longitudinal water proton relaxivities of ultrasmall 3d and 4f transition metal oxide nanoparticles

We report the longitudinal water proton relaxivities (r1) of several 3d and 3f transition metal oxide nanoparticles. These include ultrasmall iron oxide, manganese oxide, europium oxide, gadolinium oxide, and dysprosium oxide nanoparticles. The nanoparticles ranged from 1.0 to 3.0 nm in diameter. Ultrasmall metal oxide nanoparticles with metal ions of high and pure S-state electron magnetic moments showed high r1 relaxivities. The measured relaxivities indicate that ultrasmall gadolinium oxide nanoparticles with a high r1 relaxivity of 12.6 mM-1s-1 may be suitable for use as a sensitive T1 MRI contrast agent.