title: High-permittivity solid ceramic resonators for high-field human MRI.
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.
authors.affiliation: C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: S A
authors.initials: SA
authors.lastname: Aussenhofer
authors.forename: A G
authors.initials: AG
authors.lastname: Webb
mesh_terms: D002516:Ceramics; D003198:Computer Simulation; D004560:Electricity; D004574:Electromagnetic Fields; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D019047:Phantoms, Imaging
keywords: RF coils; dielectric resonators; high-field MRI; high-permittivity ceramics; hybrid electromagnetic modes