Paramagnetic ultrasmall Ho2O3 and Tm2O3 nanoparticles: characterization of r(2) values and in vivo T-2 MR images at a 3.0 T MR field

Paramagnetic ultrasmall Ho2O3 and Tm2O3 nanoparticles (d(avg) = similar to 2.1 nm) grafted with various hydrophilic and biocompatible ligands such as poly(ethylene glycol) diacid (M-n = 250 and 600 amu) and polyacrylic acid (M-w = 1800 amu) were synthesized via a one-pot polyol method. Appreciable transverse (r(2)) and negligible longitudinal (r(1)) water proton spin relaxivity values were observed for all nanoparticle samples. The r(2) values increased with increasing nanoparticle magnetic moment and decreased with increasing ligand size. Owing to the aforementioned r(1) and r(2) values, the nanoparticle samples exhibited appreciable negative contrast enhancements in in vivo T-2 magnetic resonance (MR) images at a 3.0 T MR field after intravenous injection, demonstrating their potential as efficient T-2 MRI contrast agents.