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Central brightening due to constructive interference with, without, and despite dielectric resonance
Author(s) -
Collins Christopher M.,
Liu Wanzhan,
Schreiber Weston,
Yang Qing X.,
Smith Michael B.
Publication year - 2005
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.20245
Subject(s) - dielectric , resonance (particle physics) , electrical conductor , imaging phantom , electromagnetic coil , optics , interference (communication) , physics , wavelength , magnetic resonance imaging , constructive , materials science , nuclear magnetic resonance , intensity (physics) , computational physics , atomic physics , optoelectronics , computer science , telecommunications , quantum mechanics , medicine , channel (broadcasting) , process (computing) , radiology , operating system
Purpose To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. Materials and Methods We present both numerical calculations and experimental images at 3 T of a 35‐cm‐diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. Results With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. Conclusion Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. J. Magn. Reson. Imaging 2005;21:192–196. © 2005 Wiley‐Liss, Inc.