High‐permittivity solid ceramic resonators for high‐field human MRI |
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Authors: | S A Aussenhofer A G Webb |
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Institution: | C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, , Leiden, The Netherlands |
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Abstract: | The properties of a ceramic‐based annular dielectric resonator designed for 7 T MRI have been examined. Electromagnetic simulations and experimentally determined modal frequencies agree to within ~1%. The dependence of the resonance frequency of the degenerate quadrature HEM11 modes on hole diameter and shield diameter was also investigated. The constructed coil, with a 2.5 cm diameter hole, had an unloaded Q value of 400, which was reduced to 150 when loaded with a human finger. Simulated and experimental B1+ maps show a high degree of homogeneity with a sensitivity of ~11.5 μT/√W at the centre. A comparison with a loop gap resonator showed an approximately 25% higher sensitivity for the dielectric resonator. High‐resolution images of the digital interphalangeal (DIP) and proximal interphalangeal (PIP) joints of volunteers were acquired in imaging times of less than 2 min. Finally, novel methods of double tuning such ceramic resonators to two relatively close frequencies, e.g. proton and fluorine, have been shown. Copyright © 2013 John Wiley & Sons, Ltd. |
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Keywords: | high‐permittivity ceramics hybrid electromagnetic modes high‐field MRI RF coils dielectric resonators |
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