Insight into RF power requirements and B1 field homogeneity for human MRI via rigorous FDTD approach
Article first published online: 22 MAY 2007
Copyright © 2007 Wiley-Liss, Inc.
Journal of Magnetic Resonance Imaging
Volume 25, Issue 6, pages 1235–1247, June 2007
How to Cite
Ibrahim, T. S. and Tang, L. (2007), Insight into RF power requirements and B1 field homogeneity for human MRI via rigorous FDTD approach. J. Magn. Reson. Imaging, 25: 1235–1247. doi: 10.1002/jmri.20919
- Issue published online: 22 MAY 2007
- Article first published online: 22 MAY 2007
- Manuscript Accepted: 21 DEC 2006
- Manuscript Received: 17 MAY 2006
- RF power requirements;
- RF coil;
- transmit array;
- FDTD modeling;
- B1 field homogeneity;
- high field MRI
To study the dependence of radiofrequency (RF) power deposition on B0 field strength for different loads and excitation mechanisms.
Material and Methods
Studies were performed utilizing a finite difference time domain (FDTD) model that treats the transmit array and the load as a single system. Since it was possible to achieve homogenous excitations across the human head model by varying the amplitudes/phases of the voltages driving the transmit array, studies of the RF power/B0 field strength (frequency) dependence were achievable under well-defined/fixed/homogenous RF excitation.
Analysis illustrating the regime in which the RF power is dependent on the square of the operating frequency is presented. Detailed studies focusing on the RF power requirements as a function of number of excitation ports, driving mechanism, and orientations/positioning within the load are presented.
With variable phase/amplitude excitation, as a function of frequency, the peak-then-decrease relation observed in the upper axial slices of brain with quadrature excitation becomes more evident in the lower slices as well. Additionally, homogeneity optimization targeted at minimizing the ratio of maximum/minimum B1+ field intensity within the region of interest, typically results in increased RF power requirements (standard deviation was not considered in this study). Increasing the number of excitation ports, however, can result in significant RF power reduction. J. Magn. Reson. Imaging 2007;25:1235–1247. © 2007 Wiley-Liss, Inc.