Transverse Relaxivity of Nanoparticle Contrast Agents for MRI: Different Magnetic Cores and Coatings

摘要

Four types of magnetic nanoparticles were synthesized, namely, the La_0.65Sr_0.35MnO₃and La_0.80Na_0.20MnO₃perovskite manganites and the Mn_0.61Zn_0.42Fe_1.97O₃and Co_0.44Zn_0.70Fe_1.86O₄spinel ferrites. Subsequent coating with silica provided typical core-shell particles with the mean shell thickness of 14-19 nm and the mean size of cores of 49-52 nm in the case of manganites and 26-33 nm in the case of ferrites. Moreover, two other surface modifications were employed for Mn-Zn ferrite nanoparticles, specifically coating with titania, leading to larger clusters with more complex morphology, and the stabilization by citrate anions. The products were characterized by powder X-ray diffraction and transmission electron microscopy, and their magnetic properties were probed by SQUID magnetometry. The main attention was devoted to the relaxometry on aqueous suspensions of particles in a magnetic field of 0.5 T. For distinct types of the prepared core-shell nanoparticles, the temperature dependence of transverse relaxivity was measured and the role of different relaxation regimes was analyzed.