Application Of Gadolinium Cluster Nanoparticles In MRI

Magnetic resonance imaging（MRI）,as a noninvasive and non-radiation imaging technology,offers significant advantages in many disease diagnosis,especially soft tissues disease,such as tumor.MRI contrast agents,which have been widely used in clinic,are able to produce robust contrast in MRI,which is a great help for diagnosis in clinic.Herein,a new kind of MRI contrast agent was developed.Firstly,two gadolinium cluster（Gd6 and Gd20）were synthesized.Then,by capping with poly（ethylene glycol）-derivatized poly（styrene-co-maleic anhydride）（PSMA-PEG）,the Gd6-PSMA-PEG and Gd20-PSMA-PEG hydrophilic nanoparticles（NPs）can be prepared.The Gd6-PSMA-PEG NPs and Gd20-PSMA-PEG NPs with uniform distribution present a spherical shape.Hydrodynamic diameters of Gd6-PSMA-PEG NPs and Gd20-PSMA-PEG NPs were 110 and 284.3 nm respectively.The Gd6-PSMA-PEG NPs and Gd20-PSMA-PEG NPs exhibited high longitudinal relaxivity of 59.02 and 39.98 mM^-1 s^-1（0.5 T）and 18.68 and 19.83 mM^-1 s^-1（3 T）,respectively.While the commercial MRI agent,Magnevist,only exhibited a longitudinal relaxivity of 4.49（0.5 T）and 4.11 mM^-1 s^-1（3 T）.According to the Solomon-Bloembergen-Morgan（SBM）theory,the Gd6-PSMA-PEG NPs and Gd20-PSMA-PEG NPs high longitudinal relaxivity were contributed to their high rotational correlation time（τ_R）,low mean square zero field splitting（ZFS）energy（Δ²）and low characteristic diffusion time（τ_D）.Robust contrast MRI were obtained when low dose Gd6-PSMA-PEG NPs（1/10 of the recommended dose for Magnevist）were intravenous injection of to the 4T1 tumor transplantation mice.