Gadolinium(III)-Loaded Nanoparticulate Zeolites as Potential High-Field MRI Contrast Agents: Relationship Between Structure and Relaxivity
✍ Scribed by Éva Csajbók; István Bányai; Luce Vander Elst; Robert N. Muller; Wuzong Zhou; Joop A. Peters
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 372 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd^3+^‐loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH~4~)~2~SiF~6~ or diluted HCl resulted in materials that, upon loading with Gd^3+^, had a much higher relaxivity than the corresponding non‐dealuminated materials. Analysis of the ^1^H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd^3+^‐loaded cavities did not change significantly, which suggests that the windows of the Gd^3+^‐loaded cavities are not affected by the dealumination. Upon calcination, the Gd^3+^ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd^3+^‐loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd^3+^‐doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T~1~ MRI contrast agents at low field, and as T~2~ agents at higher fields.