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Proposed radiofrequency phased‐array excitation scheme for homogenous and localized 7‐Tesla whole‐body imaging based on full‐wave numerical simulations
Author(s) -
Abraham Roney,
Ibrahim Tamer S.
Publication year - 2007
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.21139
Subject(s) - finite difference time domain method , excitation , electromagnetic coil , rf power amplifier , radiofrequency coil , physics , phased array , radio frequency , acoustics , resonator , electromagnetic field , nuclear magnetic resonance , optics , computer science , optoelectronics , antenna (radio) , telecommunications , amplifier , cmos , quantum mechanics
In this article, a radiofrequency (RF) excitation scheme for 7‐Tesla (T) whole‐body applications is derived and analyzed using the finite difference time domain (FDTD) method. Important features of the proposed excitation scheme and coil (a potential 7T whole‐body transverse electromagnetic [TEM] resonator design), from both operational and electromagnetic perspectives, are discussed. The choice of the coil's operational mode is unconventional; instead of the typical “homogenous mode,” we use a mode that provides a null field in the center of the coil at low‐field applications. Using a 3D FDTD implementation of Maxwell's equations, we demonstrate that the whole‐body 7T TEM coil (tuned to the aforementioned unconventional mode and excited in an optimized near‐field, phased‐array fashion) can potentially provide 1) homogenous whole‐slice (demonstrated in three axial, sagittal, and coronal slices) and 2) 3D localized (demonstrated in the heart) excitations. As RF power was not considered as a part of the optimization in several cases, the significant improvements achieved by whole‐slice RF excitation came at the cost of considerable increases in RF power requirements. Magn Reson Med 57:235–242, 2007. © 2007 Wiley‐Liss, Inc.