Proposed radiofrequency phased-array excitation scheme for homogenous and localized 7-Tesla whole-body imaging based on full-wave numerical simulations.
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.
Abraham
Roney
R
School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma, USA.
Ibrahim
Tamer S
TS
D004574:Electromagnetic Fields; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D011846:Radio Waves; D012815:Signal Processing, Computer-Assisted; D051598:Whole Body Imaging / Q000295:instrumentation / Q000379:methods*