Simulation-based evaluation of SAR and flip angle homogeneity for five transmit head arrays at 14 T

Seb D Harrevelt, Thomas H M Roos, Dennis W J Klomp, Bart R Steensma, Alexander J E Raaijmakers

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Abstract

INTRODUCTION: Various research sites are pursuing 14 T MRI systems. However, both local SAR and RF transmit field inhomogeneity will increase. The aim of this simulation study is to investigate the trade-offs between peak local SAR and flip angle uniformity for five transmit coil array designs at 14 T in comparison to 7 T.

METHODS: Investigated coil array designs are: 8 dipole antennas (8D), 16 dipole antennas (16D), 8 loop coils (8D), 16 loop coils (16L), 8 dipoles/8 loop coils (8D8L) and for reference 8 dipoles at 7 T. Both RF shimming and k T-points were investigated by plotting L-curves of peak SAR levels vs flip angle homogeneity.

RESULTS: For RF shimming, the 16L array performs best. For k T-points, superior flip angle homogeneity is achieved at the expense of more power deposition, and the dipole arrays outperform the loop coil arrays.

DISCUSSION AND CONCLUSION: For most arrays and regular imaging, the constraint on head SAR is reached before constraints on peak local SAR are violated. Furthermore, the different drive vectors in k T-points alleviate strong peaks in local SAR. Flip angle inhomogeneity can be alleviated by k T-points at the expense of larger power deposition. For k T-points, the dipole arrays seem to outperform loop coil arrays.

Original languageEnglish
Pages (from-to)245-255
Number of pages11
JournalMagma - Magnetic Resonance Materials In Physics Biology And Medicine
Volume36
Issue number2
DOIs
Publication statusPublished - Apr 2023

Keywords

  • Computer Simulation
  • Magnetic Resonance Imaging/methods
  • Phantoms, Imaging
  • Radio Waves
  • 14T
  • Simulation study
  • Flip angle homogeneity
  • SAR assesment
  • Coil designs

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