Back to Search Start Over

Dielectric Resonance Phenomena in Ultra High Field MRI

Authors :
Pierre-Marie Robitaille
Brian A. Baertlein
Allahyar Kangarlu
Amir M. Abduljalil
R. Lee
Lining Yang
Tamer S. Ibrahim
Source :
Journal of Computer Assisted Tomography. 23:821-831
Publication Year :
1999
Publisher :
Ovid Technologies (Wolters Kluwer Health), 1999.

Abstract

Purpose: Dielectric resonances have previously been advanced as a significant cause of image degradation at higher fields. In this work, a study of dielectric resonances in ultra high field MRI is presented to explore the real importance of dielectric resonances in the human brain in this setting. Method: Gradient-recalled echo images were acquired using a transverse electromagnetic resonator at 1.5, 4.7, and 8 T. Images were obtained from the human head and from phantoms filled with pure water, saline, and mineral oil. In addition, an exact theoretical analysis of dielectric resonances is presented for a spherical phantom and for a model of the human head. Results: Theoretical results demonstrate that distilled water can sustain dielectric resonances in head-sized spheres near 200 and 360 MHz, but the presence of significant conductivity suppresses these resonances. These findings are confirmed experimentally with proton images of water and saline (0.05 and 0.125 M NaCl). For lossy phantoms, coupling between the source and phantom overwhelms the dielectric resonance. Because of their low relative permittivity, mineral oil phantoms with 20 cm diameter do not exhibit dielectric resonances below -900 MHz. Significant dielectric resonances were not observed in human head images obtained at 1.5, 4.7, and 8 T. Conclusion: It appears that dielectric resonances do not have any real importance in determining image quality for MR studies of the human head. It is advanced that RF coils are much more likely to be the source of any inhomogeneity. Index Terms: Magnetic resonance imaging, artifacts-Magnetic resonance imaging, ultra high frequency-Dielectric resonance-Image quality.

Details

ISSN :
03638715
Volume :
23
Database :
OpenAIRE
Journal :
Journal of Computer Assisted Tomography
Accession number :
edsair.doi.dedup.....aae6840bf11295906710f300f2924991
Full Text :
https://doi.org/10.1097/00004728-199911000-00003