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Dielectric Resonance Phenomena in Ultra High Field MRI
- 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.
- Subjects :
- Radio Waves
Relative permittivity
Dielectric
Sodium Chloride
Imaging phantom
Resonator
Optics
Nuclear magnetic resonance
Quality (physics)
Image Processing, Computer-Assisted
Humans
Mineral Oil
Medicine
Radiology, Nuclear Medicine and imaging
Human head
Phantoms, Imaging
business.industry
Electric Conductivity
Electron Spin Resonance Spectroscopy
Brain
Water
Resonance
Dielectric resonator
Models, Theoretical
Image Enhancement
equipment and supplies
Magnetic Resonance Imaging
Protons
Artifacts
business
Electromagnetic Phenomena
Algorithms
Subjects
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