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  Decoupling of Folded-End Dipole Antenna Elements of a 9.4 T Human Head Array Using an RF Shield

Avdievich, N., Solomakha, G., Ruhm, L., Scheffler, K., & Henning, A. (2020). Decoupling of Folded-End Dipole Antenna Elements of a 9.4 T Human Head Array Using an RF Shield. NMR in Biomedicine, Epub ahead. doi:10.1002/nbm.4351.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-A855-D Version Permalink: http://hdl.handle.net/21.11116/0000-0006-A856-C
Genre: Journal Article

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Avdievich, NI1, 2, Author              
Solomakha, G, Author
Ruhm, L2, 3, Author              
Scheffler, K1, 2, Author              
Henning, A2, 3, Author              
Affiliations:
1Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497796              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              
3Research Group MR Spectroscopy and Ultra-High Field Methodology, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528692              

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 Abstract: Dipole antennas have recently been introduced to the field of MRI and successfully used, mostly as elements of ultra-high field (UHF, ≥ 7 T) human body arrays. Usage of dipole antennas for UHF human head transmit (Tx) arrays is still under development. Due to the substantially smaller size of the sample, dipoles must be made significantly shorter than in the body array. Additionally, head Tx arrays are commonly placed on the surface of rigid helmets made sufficiently large to accommodate tight-fit receive arrays. As a result, dipoles are not well loaded and are often poorly decoupled, which compromises Tx efficiency. Commonly, adjacent array elements are decoupled by circuits electrically connected to them. Placement of such circuits between distantly located dipoles is difficult. Alternatively, decoupling is provided by placing passive antennas between adjacent dipole elements. This method only works when these additional components are sufficiently small (compared with the size of active dipoles). Otherwise, RF fields produced by passive elements interfere destructively with the RF field of the array itself, and previously reported designs have used passive dipoles of about the size of array dipoles. In this work, we developed a novel method of decoupling for adjacent dipole antennas, and used this technique while constructing a 9.4 T human head eight-element transceiver array. Decoupling is provided without any additional circuits by simply folding the dipoles and using an RF shield located close to the folded portion of the dipoles. The array reported in this work demonstrates good decoupling and whole-brain coverage.

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 Dates: 2020-07
 Publication Status: Published online
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 Identifiers: DOI: 10.1002/nbm.4351
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Title: NMR in Biomedicine
Source Genre: Journal
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Publ. Info: London : Heyden & Son
Pages: - Volume / Issue: Epub ahead Sequence Number: - Start / End Page: - Identifier: ISSN: 0952-3480
CoNE: https://pure.mpg.de/cone/journals/resource/954925574973