Numerical and experimental evaluation of RF shimming in the human brain at 9.4 T using a dual-row transmit array

  • Jens Hoffmann
  • Gunamony Shajan
  • Klaus Scheffler
  • Rolf Pohmann
Research Article

Abstract

Objective

To provide a numerical and experimental investigation of the static RF shimming capabilities in the human brain at 9.4 T using a dual-row transmit array.

Materials and methods

A detailed numerical model of an existing 16-channel, inductively decoupled dual-row array was constructed using time-domain software together with circuit co-simulation. Experiments were conducted on a 9.4 T scanner. Investigation of RF shimming focused on B1+ homogeneity, efficiency and local specific absorption rate (SAR) when applied to large brain volumes and on a slice-by-slice basis.

Results

Numerical results were consistent with experiments regarding component values, S-parameters and B1+ pattern, though the B1+ field was about 25 % weaker in measurements than simulations. Global shim settings were able to prevent B1+ field voids across the entire brain but the capability to simultaneously reduce inhomogeneities was limited. On a slice-by-slice basis, B1+ standard deviations of below 10 % without field dropouts could be achieved in axial, sagittal and coronal orientations across the brain, even with phase-only shimming, but decreased B1+ efficiency and SAR limitations must be considered.

Conclusion

Dual-row transmit arrays facilitate flexible 3D RF management across the entire brain at 9.4 T in order to trade off B1+ homogeneity against power-efficiency and local SAR.

Keywords

RF shimming 9.4 T Transmit array Local SAR RF simulations 

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Copyright information

© ESMRMB 2013

Authors and Affiliations

  • Jens Hoffmann
    • 1
    • 2
  • Gunamony Shajan
    • 1
  • Klaus Scheffler
    • 1
    • 3
  • Rolf Pohmann
    • 1
  1. 1.High-Field Magnetic Resonance CenterMax Planck Institute for Biological CyberneticsTübingenGermany
  2. 2.Graduate School of Neural and Behavioural SciencesTübingenGermany
  3. 3.Department for Biomedical Magnetic ResonanceUniversity of TübingenTübingenGermany

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