Gd III -loaded porous systems as MRI contrast agents

The authors conclude that contamination of the zeolites with paramagnetic ions might also play a role in the relaxation rate enhancement. 

After the partial exchange of the Na counter cations for Gd , the specific relaxivity (here defined as the measured water relaxation rate per gram of material) was measured at Larmor frequencies ranging from 0.01 to 30 MHz. The NMRD profiles obtained were compared with that obtained after complexing the encapsulated Gd(III) with DTPA. After correction for the differences in the Gd(III) content of the samples, the NMRD curves appeared to be superimposable. Based on this result, a 

Balkus et al. investigated the commercially available Y zeolites with an unspecified particle size, after Gd(III) exchange (82,83). A detailed study was made not only on the magnetic properties, but also on the preparation and the characterization of these materials. Several factors infiu-encing the exchange, including the pH, time, and concentration, were optimized. Procedures to control the Gd(III) loading of the zeolites were developed. 

The FT-IR spectra of the resulting Gd(III)-exchanged NaY zeolites did not show any loss of crystallinity or dealumination during the gadolinium exchange. A detailed XRD study also confirmed the retained crystallinity nevertheless, there are significant changes in the relative intensities of certain refiections. 

Two issues concerning the in vivo stability were evaluated the effect of pH and the possibility of exchange of Gd(III) with cations that may be found in the GI tract. However, it should be noted that the acute toxicity of orally administered GdCla is relatively low (LD50 mice 2000 mg/kg). 

---