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Analysis of wave behavior in lossy dielectric samples at high field
Author(s) -
Yang Qing X.,
Wang Jinghua,
Zhang Xiaoliang,
Collins Christopher M.,
Smith Michael B.,
Liu Haiying,
Zhu XiaoHong,
Vaughan J. Thomas,
Ugurbil Kamil,
Chen Wei
Publication year - 2002
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10137
Subject(s) - imaging phantom , radio frequency , optics , dielectric , amplitude , electromagnetic coil , materials science , human head , intensity (physics) , field (mathematics) , nuclear magnetic resonance , electromagnetic field , phase (matter) , physics , optoelectronics , electrical engineering , mathematics , quantum mechanics , pure mathematics , absorption (acoustics) , engineering
Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10‐cm‐diameter surface coil at 300 MHz is evaluated in a 16‐cm‐diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample‐coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42–350 MHz is also analyzed. Magn Reson Med 47:982–989, 2002. © 2002 Wiley‐Liss, Inc.