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Magnetic resonance relaxation properties of superparamagnetic particles
Author(s) -
Gossuin Yves,
Gillis Pierre,
Hocq Aline,
Vuong Quoc L,
Roch Alain
Publication year - 2009
Publication title -
wiley interdisciplinary reviews: nanomedicine and nanobiotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 72
eISSN - 1939-0041
pISSN - 1939-5116
DOI - 10.1002/wnan.36
Subject(s) - maghemite , superparamagnetism , ferrihydrite , nuclear magnetic resonance , relaxation (psychology) , magnetite , magnetic moment , ferritin , materials science , magnetization , chemistry , condensed matter physics , magnetic field , physics , medicine , adsorption , biochemistry , quantum mechanics , metallurgy
Nanometric crystals of maghemite are known to exhibit superparamagnetism. Because of the significance of their magnetic moment, maghemite nanoparticles are exceptional contrast agents and are used for magnetic resonance imaging (of the liver, spleen, lymph nodes), for magnetic resonance angiography and for molecular and cellular imaging. The relaxivity of these agents depends on their size, saturation magnetization and magnetic field and also on their degree of clustering. There are different types of maghemite particles whose relaxation characteristics are suited to a specific MRI application. The relaxation induced by maghemite particles is caused by the diffusion of water protons in the inhomogeneous field surrounding the particles. This is well described by a theoretical model that takes magnetite crystal anisotropy and Néel relaxation into account. Another type of superparamagnetic compound is ferritin, the iron‐storing protein: it contains a superparamagnetic ferrihydrite core. Even if the resulting magnetic moment of ferritin is far smaller than for magnetite nanoparticles, its massive presence in different organs darkens T 2 ‐weighted MR images, allowing the noninvasive estimation of iron content, thanks to MRI. The relaxation induced by ferritin in aqueous solutions has been demonstrated to be caused by the exchange of protons between bulk water protons and the surface of the ferrihydrite crystal. However, in vivo, the relaxation properties of ferritin are still unexplained, probably because of protein clustering. Copyright © 2009 John Wiley & Sons, Inc. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging