Compressed perovskite aqueous mixtures near their phase transitions show very high permittivities: New prospects for high-field MRI dielectric shimming
Résumé
Purpose: Perovskites are greatly used nowadays in many technological applications because of their high permittivity, more specifically in the form of aqueous solutions, for MRI dielectric shimming. In this study, full dielectric characterizations of highly concentrated CaTiO 3 /BaTiO 3 water mixtures were carried out and new permittivity maxima was reached. Methods: Permittivity measurements were done on aqueous solutions from 0%v/v to dry powder. The permittivity dependence with pressure was investigated. Scanning electron micros-copy images were performed on a few representative solutions. BaTiO 3 pressed pads of different thicknesses, permittivities, and distances to the head were compared in a 7T MRI scanner. Results: Perovskite aqueous mixtures undergo a pressure-dependent phase transition in terms of permittivity, with increasing water content. A new relative permittivity maximum of 475 was achieved. Microscopic images revealed structural differences between phases. A B þ 1 improvement in the temporal lobe was obtained with thin, high permittivity BaTiO 3 head. Conclusions: This new preparation method allows improved pad geometry and placement, as a result of the high relative permittivity values achieved. This method has great significance for medical applications of MRI dielectric shimming, being easy to replicate and implement on a large scale.
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