Electromagnetic perspective on the operation of RF coils at 1.5-11.7 Tesla.
In this work experimental and numerical studies of the MR signal were performed at frequencies ranging from 64 MHz to 485 MHz, utilizing three different MRI coils: a single-strut transverse electromagnetic (TEM)-based coil, a TEM resonator, and a high-pass birdcage coil. The experimental analyses were conducted using 1.5 and 8 Tesla whole-body systems and volume RF head coils. The simulation data were obtained utilizing an in-house-developed finite difference time domain (FDTD) model. Pertinent data from the numerical and experimental setups were compared, and a remarkable agreement between the two methods was found that clearly demonstrates the effectiveness of the FDTD method when it is applied rigorously. The numerical and experimental studies demonstrate the complexity of the electromagnetic (EM) fields and their role in the MR signal. These studies also reveal unique similarities and differences between the transmit and receive field distributions at various field strengths. Finally, for ultra high-field operations, it was demonstrated mathematically, numerically, and experimentally that highly asymmetric inhomogeneous images can be acquired even for linear excitation, symmetrical load geometries, and symmetrical load positioning within the coil.
Ibrahim
Tamer S
TS
School of Electrical and Computer Engineering and Center of BioEngineering, University of Oklahoma, Norman, Oklahoma 73019-1023, USA. ibrahim@ou.edu
Mitchell
Chad
C
Schmalbrock
Petra
P
Lee
Robert
R
Chakeres
Donald W
DW
D004574:Electromagnetic Fields; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011846:Radio Waves; D012815:Signal Processing, Computer-Assisted