Csajbók Eva, Bányai István, Vander Elst Luce, Muller Robert N, Zhou Wuzong, Peters Joop A
Laboratory of Applied Organic Chemistry and Catalysis, Delft University of Technology, The Netherlands.
Chemistry. 2005 Aug 5;11(16):4799-807. doi: 10.1002/chem.200500039.
The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+-loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H 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 Gd3+-loaded cavities did not change significantly, which suggests that the windows of the Gd3+-loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ 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 Gd3+-loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+-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 T1 MRI contrast agents at low field, and as T2 agents at higher fields.
研究了脱铝、孔径和煅烧对负载钆（Gd3+）的沸石作为磁共振成像（MRI）造影剂潜在应用时的效率（以弛豫率表示）的影响。通过用（NH4）2SiF6或稀盐酸处理对沸石NaY或NaA进行部分脱铝，得到的材料在负载Gd3+后，其弛豫率比相应的未脱铝材料高得多。对各种沸石的1H NMR色散曲线分析表明，这主要归因于由于孔间壁的破坏导致沸石腔内水量增加。然而，负载Gd3+的腔内水的平均停留时间没有显著变化，这表明负载Gd3+的腔的窗口不受脱铝影响。煅烧后，Gd3+离子迁移到小方钠石腔内，水难以进入，导致弛豫率降低。通过比较负载Gd3+的沸石NaY和NaA样品的弛豫率，证明了扩散对弛豫率的重要作用。由于孔径较小，NaA的弛豫率要低得多。在低磁场（<60 MHz）下，掺杂Gd3+的沸石的横向弛豫率在大小上与纵向弛豫率相当。然而，在较高磁场下，横向弛豫率急剧增加，而纵向弛豫率随着场强增加而降低。因此，这些材料在低场下有作为T1 MRI造影剂的潜力，在高场下有作为T2造影剂的潜力。
