High proton relaxivity for gadolinium oxide nanoparticles

Objective: Nanosized materials of gadolinium oxide can provide high-contrast enhancement in magnetic resonance imaging (MRI). The objective of the present study was to investigate proton relaxation enhancement by ultrasmall (5 to 10 nm) Gd₂O₃ nanocrystals. Materials and methods: Gd₂O₃ nanocrystals were synthesized by a colloidal method and capped with diethylene glycol (DEG). The oxidation state of Gd₂O₃ was confirmed by X-ray photoelectron spectroscopy. Proton relaxation times were measured with a 1.5-T MRI scanner. The measurements were performed in aqueous solutions and cell culture medium (RPMI). Results: Results showed a considerable relaxivity increase for the Gd₂O₃–DEG particles compared to Gd-DTPA. Both T ₁ and T ₂ relaxivities in the presence of Gd₂O₃–DEG particles were approximately twice the corresponding values for Gd–DTPA in aqueous solution and even larger in RPMI. Higher signal intensity at low concentrations was predicted for the nanoparticle solutions, using experimental data to simulate a T₁-weighted spin echo sequence. Conclusion: The study indicates the possibility of obtaining at least doubled relaxivity compared to Gd–DTPA using Gd₂O₃–DEG nanocrystals as contrast agent. The high T ₁ relaxation rate at low concentrations of Gd₂O₃ nanoparticles is very promising for future studies of contrast agents based on gadolinium-containing nanocrystals.