NMR Transversal relaxivity of aqueous suspensions of particles of Ln(3+)-based zeolite type materials
authors Pereira, GA; Norek, M; Peters, JA; Ananias, D; Rocha, J; Geraldes, CFGC
nationality International
journal DALTON TRANSACTIONS
keywords MRI CONTRAST AGENTS; MAGNETIC-SUSCEPTIBILITY SHIFTS; OXIDE NANOPARTICLES; RELAXATION; RESONANCE; EXCHANGE; TISSUES; SPHERES; MODEL
abstract A series of zeolite-type silicates containing stoichiometric amounts of Ln(3+) ions in the framework (Ln-AV-9 materials), with composition (Na4K2)(Ln(2)Si(16)O(38)) center dot 10H(2)O (Ln = Nd, Sm, Eu, Tb, Gd, Dy) has recently been synthesized and characterized. They form paramagnetic microparticles, which as aqueous suspensions have negligible water H-1 longitudinal relaxivities (r(1)) for all Ln(3+) ions studied and quite large transverse relaxivities (r(2)). In this work we further analysed the size distribution of the Ln-AV-9 particles and their r(2)* and r(2) relaxivities. The r(2)* relaxivity effects are explained by the static dephasing regime (SDR) theory. The r(2) relaxivities appear to be strongly dependent on the interval between two consecutive refocusing pulses (tau(CP)) in the train of 180 degrees pulses applied. For long tau(CP) values, the r(2) of the systems saturates at a value, which is always an order of magnitude smaller than r(2)*. These features are explained by a crude model, which takes into account the residual diffusion effect in the static dephasing regime. The large microparticles, although not efficient in T-1 relaxation, are quite effective in enhancing T-2 relaxation, particularly at high magnetic fields. The r(2)* values and the saturation values for r(2) were found to increase linearly with B-0 and mu(2)(0). The largest transversal relaxation rate enhancements were observed for Dy-AV-9 with a saturation value of r2 of 60 s(-1) mM(-1) and a r(2)* value of 566 s(-1) mM(-1) at 9.4 T and 298 K.
publisher ROYAL SOC CHEMISTRY
issn 1477-9226
year published 2008
issue 17
beginning page 2241
ending page 2247
digital object identifier (doi) 10.1039/b718438g
web of science category Chemistry, Inorganic & Nuclear
subject category Chemistry
unique article identifier WOS:000254999200006
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