The Evaluation of Dielectric Resonators Containing H2O or D2O as RF Coils for High-Field MR Imaging and Spectroscopy
✍ Scribed by Han Wen; Farouc A. Jaffer; Timothy J. Denison; Stefan Duewell; A.Scott Chesnick; Robert S. Balaban
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 199 KB
- Volume
- 110
- Category
- Article
- ISSN
- 1064-1866
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✦ Synopsis
Electromagnetic resonators consisting of low-loss dielectric mathe same phenomenon was also described in head imaging in terial and/or metallic boundaries are widely used in microwave vivo (3). Dielectric material has been used to change the technologies. These dielectric resonators usually have high Q facboundary condition of high-pass bird-cage coils, resulting in tors and well-defined field distributions. Magnetic resonance imimproved B 1 uniformity in the transaxial plane (4). The idea aging was shown as a way of visualizing the magnetic field distriof using dielectric resonators as RF coils has been proposed bution of the resonant modes of these resonators, if the dielectric previously (5).
body contains NMR sensitive nuclei. Dielectric resonators have
The resonant frequency of a particular resonant mode is also been proposed as RF coils for magnetic resonance experidetermined by the shape and the size of the dielectric volments. The feasibility of this idea in high-field MR is discussed ume, and the electromagnetic wavelength in the material.
here. Specifically, the dielectric resonances of cylindrical water columns were characterized at 170.7 MHz (4 T 1 H Larmor fre-For the first few modes, the resonant wavelength is on the quency), and evaluated as NMR transmit and receive coils. The same order as the size of the volume. Water has one of the dielectric resonance of a cylindrical volume of D 2 O was used to highest dielectric constants of fluids (approximately 78 up image a hand at 170.7 MHz. This study demonstrated that MRI to gigahertz range). The wavelength in water is approxiis an effective way of visualizing the magnetic field in dielectric mately 20 cm at the 4 T 1 H frequency of 170 MHz. When structures such as a water cylinder, and can potentially be generala water column on this scale is adjusted to resonate at preized to solid-state dielectric devices. The possible applications of cisely this frequency, the magnetic field distribution of the dielectric resonators other than simple cylindrical volumes in MRI dielectric resonance can be visualized with MRI on a 4 T and MR solution spectroscopy at high field strengths are also imager.
discussed.