A Semi-Analytical Model of High-Permittivity Dielectric Ring Resonators for Magnetic Resonance Imaging

Abstract

Magnetic resonance imaging (MRI) is an imaging technique exploiting the magnetic resonance (MR) of specific nuclear spins, like protons. In this article, MR probes based on dielectric ring resonators are investigated from a theoretical approach. We take advantage of the high-permittivity and lowloss properties of the ceramic material used for manufacturing these probes for microscopy applications. Magnetic resonance microscopy (MRM) aims at imaging tiny samples with a sufficient resolution to distinguish small details. In this framework, compact resonators, called volume probes, contain the investigated sample and are used for both signal transmission and reception. The newly developed semi-analytical model enables the estimation of the frequency of the first transverse electric mode of a cylindrical resonator. It also provides a method to compute the corresponding magnetic field distribution, the dielectric losses contributions from the probe and the sample, and the signal-Manuscript

Imaging of two samples with a single transmit/receive channel using coupled ceramic resonators for MR microscopy at 17.2 T

“…As the first TE mode generates a low electric field in the center of the resonator, considering the disk instead of the ring and its sample is a reasonable approximation. Quantitatively speaking, for the relative permittivity ( ɛ r ~500) and the inner to outer radii ratio of the ring ( r h / r d ~0.3) considered here, the frequency shift between the disk and the ring is less than 2% 15 …”

“…To be precise, besides the sample, only the ceramic ring contributes to losses, and this contribution is low, due to the low dissipation factor tan δ of the material itself. Another advantage of using ceramic rings to provide the excitation field B 1 is that the ratio E / H in the sample is reduced compared with a solenoid 13,15 . It follows that, for a given sample diameter, the electric field being minimum in the FOV region, a change in sample permittivity has a limited impact on the mode frequency and on the field distribution.…”

“…In practice, an experimental demonstration of this work showed an enhancement factor of 2.2. This was made possible by using a unique ceramic material specially designed to have low dielectric losses and high permittivity, which enables the confinement of the electric field in the ceramics and minimizes its conservative component within the hole in which the sample is located, and therefore ensures a low E / H ratio in the sample 15 …”

A comprehensive review on magnetic imaging techniques for biomedical applications

“…Energy is exchanged between the capacitor and the inductor when the coil is driven at this frequency, decreasing the load on the power amplifier. [59] The system will produce a significant number of signals and differentiation between them is a considerable issue. To differentiate them, the following methods are proposed: With the methods mentioned above, signal localization can be performed without any confusion.…”

A Novel Ultrawideband Gear-Shaped Dielectric Ring Resonator Antenna

“…Other shapes of feeding include L-shaped microstrip [9], annular-shaped microstrip [10], a tilted modified square-shaped aperture [11], and circularshaped offset feed [12] for 3-band applications. In [13], the high permittivity and low losses properties of the ceramic material were used for manufacturing the magnetic resonance probes.…”