Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics
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Comparison of simulated.pdf
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Author(s)
Guérin, Bastien
Gebhardt, Matthias
Serano, Peter
Adalsteinsson, Elfar
Hamm, Michael
Pfeuffer, Josef
Nistler, Juergen
Wald, Lawrence L.
Date Issued
February 2015
Journal
Magnetic Resonance in Medicine
Publisher
Wiley Blackwell
Citation
Guérin, Bastien; Gebhardt, Matthias; Serano, Peter et al. “Comparison of Simulated Parallel Transmit Body Arrays at 3 T Using Excitation Uniformity, Global SAR, Local SAR, and Power Efficiency Metrics.” Magnetic Resonance in Medicine 73, 3 (April 2014): 1137–1150 © 2014 Wiley Periodicals, Inc.
Version
Author's final manuscript
Abstract
Purpose
We compare the performance of eight parallel transmit (pTx) body arrays with up to 32 channels and a standard birdcage design. Excitation uniformity, local specific absorption rate (SAR), global SAR, and power metrics are analyzed in the torso at 3 T for radiofrequency (RF)-shimming and 2-spoke excitations.
Methods
We used a fast cosimulation strategy for field calculation in the presence of coupling between transmit channels. We designed spoke pulses using magnitude least squares optimization with explicit constraint of SAR and power and compared the performance of the different pTx coils using the L-curve method.
Results
PTx arrays outperformed the conventional birdcage coil in all metrics except peak and average power efficiency. The presence of coupling exacerbated this power efficiency problem. At constant excitation fidelity, the pTx array with 24 channels arranged in three z-rows could decrease local SAR more than 4-fold (2-fold) for RF-shimming (2-spoke) compared to the birdcage coil for pulses of equal duration. Multi-row pTx coils had a marked performance advantage compared to single row designs, especially for coronal imaging.
Conclusion
PTx coils can simultaneously improve the excitation uniformity and reduce SAR compared to a birdcage coil when SAR metrics are explicitly constrained in the pulse design.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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DOI of Published Version
https://doi.org/10.1002/mrm.25243
