Aqueous Dispersion of Manganese-Zinc Ferrite Nanoparticles Protected by PEG as a T2 MRI Temperature Contrast Agent

Mixed manganese-zinc ferrite nanoparticles coated with PEG were studied for their potential usefulness in MRI thermometry as temperature-sensitive contrast agents. Particles in the form of an 8.5 nm core coated with a 3.5 nm layer of PEG were fabricated using a newly developed, one-step method. The composition of Mn0.48Zn0.46Fe2.06O4 was found to have a strong thermal dependence of magnetization in the temperature range between 5 and 50 C-degrees. Nanoparticles suspended in an agar gel mimicking animal tissue and showing non-significant impact on cell viability in the biological test were studied with NMR and MRI over the same temperature range. For the concentration of 0.017 mg/mL of Fe, the spin-spin relaxation time T-2 increased from 3.1 to 8.3 ms, while longitudinal relaxation time T-1 shows a moderate decrease from 149.0 to 125.1 ms. A temperature map of the phantom exposed to the radial temperature gradient obtained by heating it with an 808 nm laser was calculated from T-2 weighted spin-echo differential MR images. Analysis of temperature maps yields thermal/spatial resolution of 3.2 C-degrees at the distance of 2.9 mm. The experimental relaxation rate R-2 data of water protons were compared with those obtained from calculations using a theoretical model incorporating the motion averaging regime.

Automated summary

Mixed manganese-zinc ferrite nanoparticles coated with PEG were investigated for their potential as temperature-sensitive contrast agents in MRI thermometry. These nanoparticles showed strong thermal dependence of magnetization and were found to have good temperature and spatial resolution when studied using NMR and MRI. The experimental data were compared with calculations using a theoretical model, validating the accuracy of the results.