Magnetic La1−x Sr x MnO3 nanoparticles as contrast agents for MRI: the parameters affecting 1H transverse relaxation
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Magnetic nanoparticles of the La1−x Sr x MnO3 perovskite phase (x = 0.20–0.45) were synthesized by a sol–gel method followed by thermal and mechanical treatments. The particles were coated with a uniform silica shell, and differential centrifugation yielded a product with high colloidal stability in water. X-ray powder diffraction (XRD) data showed that the mechanical processing did not affect the lattice parameters of the magnetic cores but only reduced their mean size d XRD. The magnetic properties of the bare particles were mainly controlled by the chemical composition and were also affected by the size of the particles. Subsequent silica coating led to an effective decrease in magnetization. Relaxometry measurements were focused primarily on colloids using magnetic cores of the same size (d XRD ≈ 20 nm) and different compositions, and coated with a shell measuring approximately 20 nm in thickness. The exceedingly high transverse relaxivities [r 2(20 °C) = 290–430 s−1 mmol−1 L at B 0 = 0.5 T] of the samples exhibited pronounced temperature dependence and correlated very well with the magnetic data. Additional samples differing in the size of the cores and silica shell thickness were prepared as well to analyze the effect of the particles on 1H transverse relaxation. The results suggest that the dominant regime of transverse relaxation is the static dephasing regime.
KeywordsManganese perovskites Manganite Magnetic nanoparticles Magnetic resonance imaging Relaxivity Core–shell particles
This study was supported by the Grant Agency of the Czech Republic through the project P108/11/0807 and by the Ministry of Industry and Trade of the Czech Republic through the project FR-TI3/521. Measurements performed by E.S. at Magnetism and Low Temperatures Laboratories (MLTL) were supported by the project LM2011025, part of the Czech Research Infrastructures Program.
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