Zeolite GdNaY Nanoparticles with Very High Relaxivity for Application as Contrast Agents in Magnetic Resonance Imaging

• Published in: Chemistry : a European journal Vol. 8; no. 22; pp. 5121 - 5131
• Main Authors: Platas-Iglesias, Carlos, Vander Elst, Luce, Zhou, Wuzong, Muller, Robert N., Geraldes, Carlos F. G. C., Maschmeyer, Thomas, Peters, Joop A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 15.11.2002; WILEY‐VCH Verlag
• Subjects: contrast agents; Contrast Media - chemical synthesis; Contrast Media - chemistry; Electron Spin Resonance Spectroscopy; gadolinium; Gadolinium - chemistry; lanthanides; Lanthanoid Series Elements - chemistry; magnetic resonance imaging; Magnetic Resonance Spectroscopy - methods; Microchemistry; Protons; Solutions - chemistry; zeolites; Zeolites - chemical synthesis; Zeolites - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20021115)8:22<5121::AID-CHEM5121>3.0.CO;2-W

In this paper we explore Gd3+‐doped zeolite NaY nanoparticles for their potential application as a contrast agent in magnetic resonance imaging (MRI). The nanoparticles have an average size of 80–100 nm, as determined by TEM and XRD. A powdered sample loaded with La3+ was characterised by means of multinuclear solid‐state NMR spectroscopy. The NMR dispersion (NMRD) profiles obtained from aqueous suspensions of samples with Gd3+ doping ratios of 1.3–5.4 wt % were obtained at different temperatures. The relaxivity increases drastically as the Gd3+ loading decreases, with values ranging between 11.4 and 37.7 s−1 mM−1 at 60 MHz and 37 °C. EPR spectra of aqueous suspensions of the samples suggest that an interaction between neighbouring Gd3+ ions within the same particle produces a significant increase in the transversal electronic relaxation rates in samples with a high Gd3+ content. The experimental NMRD and EPR data are explained with the use of a model that considers the system as a concentrated aqueous solution of Gd3+ in the interior of the zeolite that is in exchange with the bulk water outside the zeolite. The results obtained indicate that the Gd3+ ion is immobilised in the interior of the zeolite and that the relaxivity is mainly limited by the relatively slow diffusion of water protons from the pores of the zeolite channels into the bulk water. Gd3+‐containing zeolite NaY nanoparticles (80–100 nm) display a very high relaxivity in aqueous suspensions. Experimental NMRD curves and EPR spectra are explained by a two‐step model that considers the interior of the zeolite to contain a concentrated solution of Gd3+ exchanging with the bulk water (see diagram).