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Polarized multichannel transmit MRI to reduce shading near metal implants
Author(s) -
Bachschmidt Theresa J.,
Köhler Michael,
Nistler Jürgen,
Geppert Christian,
Jakob Peter M.,
Nittka Mathias
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25621
Subject(s) - shading , computer science , magnetic resonance imaging , materials science , nuclear magnetic resonance , biomedical engineering , nuclear medicine , medicine , radiology , physics , computer graphics (images)
Purpose To investigate the benefit of a two‐channel transmit system on shading close to total hip replacements and other elongated metal structures in parallel to the magnet bore. Methods An analytical model comprising a water cylinder and a metal rod is introduced to describe the B 1 effects close to elongated metal structures and it is verified. The dependence of the optimal polarization, which induces minimum shading, on the position of the metal is analyzed. Furthermore, the optimal polarization for two patients is determined both on the basis of the model and experimentally and its benefit compared with circular polarization is investigated. Results The cylindrical model approximates the modification of the B 1 field due to the metal well, and the optimal polarization strongly depends on the position of the rod. In vivo, shading can be ameliorated by the use of the optimal polarization; for total hip replacements with shafts of titanium, this polarization can be determined on the basis of both the analytical model and the experimental data. Conclusion Parallel transmission offers the possibility of a substantial reduction of shading close to long metal structures in parallel to the magnet bore. Magn Reson Med 75:217–226, 2016. © 2015 Wiley Periodicals, Inc.