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  Bent Folded-End Dipole Head Array for Ultrahigh-Field MRI Turns "Dielectric Resonance" From an Enemy to a Friend

Avdievich, N., Solomakha, G., Ruhm, L., Bause, J., Scheffler, K., & Henning, A. (2020). Bent Folded-End Dipole Head Array for Ultrahigh-Field MRI Turns "Dielectric Resonance" From an Enemy to a Friend. Magnetic Resonance in Medicine, Epub ahead. doi:10.1002/mrm.28336.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-A992-6 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-A993-5
Genre: Journal Article

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Avdievich, NI1, 2, Author              
Solomakha, G, Author
Ruhm, L1, 2, Author              
Bause, J2, 3, Author              
Scheffler, K2, 3, Author              
Henning, A1, 2, Author              
Affiliations:
1Research Group MR Spectroscopy and Ultra-High Field Methodology, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528692              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              
3Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497796              

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 Abstract: Purpose: To provide transmit whole-brain coverage at 9.4 T using an array with only eight elements and improve the specific absorption rate (SAR) performance, a novel dipole array was developed, constructed, and tested. Methods: The array consists of eight optimized bent folded-end dipole antennas circumscribing a head. Due to the asymmetrical shape of the dipoles (bending and folding) and the presence of an RF shield near the folded portion, the array simultaneously excites two modes: a circular polarized mode of the array itself, and the TE mode ("dielectric resonance") of the human head. Mode mixing can be controlled by changing the length of the folded portion. Due to this mixing, the new dipole array improves longitudinal coverage as compared with unfolded dipoles. By optimizing the length of the folded portion, we can also minimize the peak local SAR (pSAR) value and decouple adjacent dipole elements. Results: The new array improves the SEE (< B+1 >/√pSAR) value by about 50%, as compared with the unfolded bent dipole array. It also provides better whole-brain coverage compared with common single-row eight-element dipole arrays, or even to a more complex double-row 16-element surface loop array. Conclusion: In general, we demonstrate that rather than compensating for the constructive interference effect using additional hardware, we can use the "dielectric resonance" to improve coverage, transmit field homogeneity, and SAR efficiency. Overall, this design approach not only improves the transmit performance in terms of the coverage and SAR, but substantially simplifies the common surface loop array design, making it more robust, and therefore safer.

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 Dates: 2020-07
 Publication Status: Published online
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 Identifiers: DOI: 10.1002/mrm.28336
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Title: Magnetic Resonance in Medicine
Source Genre: Journal
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Publ. Info: New York : Wiley-Liss
Pages: - Volume / Issue: Epub ahead Sequence Number: - Start / End Page: - Identifier: ISSN: 0740-3194
CoNE: https://pure.mpg.de/cone/journals/resource/954925538149