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Magnetic Resonance Materials in Physics, Biology and Medicine

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01-10-2014 | Research Article

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

Authors: Jens Hoffmann, Gunamony Shajan, Klaus Scheffler, Rolf Pohmann

Published in: Magnetic Resonance Materials in Physics, Biology and Medicine | Issue 5/2014

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.

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Title: Numerical and experimental evaluation of RF shimming in the human brain at 9.4 T using a dual-row transmit array
Authors: Jens Hoffmann
Gunamony Shajan
Klaus Scheffler
Rolf Pohmann
Publication date: 01-10-2014
Publisher: Springer Berlin Heidelberg
Published in: Magnetic Resonance Materials in Physics, Biology and Medicine / Issue 5/2014
Print ISSN: 0968-5243
Electronic ISSN: 1352-8661
DOI: https://doi.org/10.1007/s10334-013-0419-y

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Springer Medicine

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

Abstract

Objective

Materials and methods

Results

Conclusion

Keynote webinar | Spotlight on medication adherence

Springer Medicine

Abstract

Objective

Materials and methods

Results

Conclusion

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