Quadrature operation of segmented dielectric resonators facilitated with metallic connectors

Abstract

Purpose: To design and characterize dual-segment dielectric resonators (DR) and assess their performance for in vivo imaging and localized proton spectroscopy at 7 Tesla. Methods: Annular DRs operating in the HEM11 mode at ultrahigh field have advantage of a simple design with an intrinsically circularly polarized homogeneous mode. However, practical realization for extremity imaging requires a splittable design for patient comfort and positioning. Splitting the annulus segments breaks the resonator symmetry and the circularly polarized distribution is lost. Here, we show that one can restore the electromagnetic modes by incorporating copper connectors between the segments. By designing the connectors such that two modes become frequency degenerate, one can also generate circularly polarized modes in a half-annular resonator. Electromagnetic simulations were performed and phantom and in vivo experiments conducted using custom-built DRs. Results: Electromagnetic simulations showed that using copper interconnectors, the resonant modes could be restored. This was confirmed in phantom experiments, as well as in vivo images of the human knee using a dual-segment splittable annular DR and images and localized spectra of the human calf muscle acquired using a dual-segment half-annular resonator. Conclusion: A new approach incorporating copper connectors into the DR structure allows efficient operation of splittable DRs. Magn Reson Med 77:2431–2437, 2017. © 2016 International Society for Magnetic Resonance in Medicine.