SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy
Purpose: Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high-field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a “dark mode”) to attempt a partial cancellation of...
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| Format: | Article |
| Language: | en_US |
| Published: |
Wiley Blackwell
2017
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| Online Access: | http://hdl.handle.net/1721.1/110711 https://orcid.org/0000-0002-7637-2914 https://orcid.org/0000-0001-7208-8863 |
| _version_ | 1826194295975051264 |
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| author | Guerin, Bastien Keil, Boris Mareyam, Azma Kosior, Robert K. Martin, Adrian Torrado-Carvajal, Angel Malpica, Norberto Hernandez-Tamames, Juan A. Schiavi, Emanuele Eryaman, Yigitcan Adalsteinsson, Elfar Lopez Herraiz, Joaquin Wald, Lawrence |
| author2 | Institute for Medical Engineering and Science |
| author_facet | Institute for Medical Engineering and Science Guerin, Bastien Keil, Boris Mareyam, Azma Kosior, Robert K. Martin, Adrian Torrado-Carvajal, Angel Malpica, Norberto Hernandez-Tamames, Juan A. Schiavi, Emanuele Eryaman, Yigitcan Adalsteinsson, Elfar Lopez Herraiz, Joaquin Wald, Lawrence |
| author_sort | Guerin, Bastien |
| collection | MIT |
| description | Purpose: Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high-field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a “dark mode”) to attempt a partial cancellation of the electric field from those elements that do generate excitation. We show that adding dipole elements oriented orthogonal to their conventional orientation to a linear array of conventional loop elements can lower the local SAR hotspot in a C-spine array at 7 T.
Methods: We model electromagnetic fields in a head/torso model to calculate SAR and excitation B1+ patterns generated by conventional loop arrays and loop arrays with added electric dipole elements. We utilize the dark modes that are generated by the intentional and inefficient orientation of dipole elements in order to reduce peak 10g local SAR while maintaining excitation fidelity.
Results: For B[subscript 1][superscript +] shimming in the spine, the addition of dipole elements did not significantly alter the B[subscript 1][superscript +] spatial pattern but reduced local SAR by 36%.
Conclusion: The dipole elements provide a sufficiently complimentary B1+ and electric field pattern to the loop array that can be exploited by the radiofrequency shimming algorithm to reduce local SAR. |
| first_indexed | 2024-09-23T09:53:51Z |
| format | Article |
| id | mit-1721.1/110711 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T09:53:51Z |
| publishDate | 2017 |
| publisher | Wiley Blackwell |
| record_format | dspace |
| spelling | mit-1721.1/1107112022-09-26T14:24:23Z SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy Guerin, Bastien Keil, Boris Mareyam, Azma Kosior, Robert K. Martin, Adrian Torrado-Carvajal, Angel Malpica, Norberto Hernandez-Tamames, Juan A. Schiavi, Emanuele Eryaman, Yigitcan Adalsteinsson, Elfar Lopez Herraiz, Joaquin Wald, Lawrence Institute for Medical Engineering and Science Harvard-MIT Program in Health Sciences and Technology Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology. Research Laboratory of Electronics Eryaman, Yigitcan Adalsteinsson, Elfar Lopez Herraiz, Joaquin Wald, Lawrence Purpose: Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high-field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a “dark mode”) to attempt a partial cancellation of the electric field from those elements that do generate excitation. We show that adding dipole elements oriented orthogonal to their conventional orientation to a linear array of conventional loop elements can lower the local SAR hotspot in a C-spine array at 7 T. Methods: We model electromagnetic fields in a head/torso model to calculate SAR and excitation B1+ patterns generated by conventional loop arrays and loop arrays with added electric dipole elements. We utilize the dark modes that are generated by the intentional and inefficient orientation of dipole elements in order to reduce peak 10g local SAR while maintaining excitation fidelity. Results: For B[subscript 1][superscript +] shimming in the spine, the addition of dipole elements did not significantly alter the B[subscript 1][superscript +] spatial pattern but reduced local SAR by 36%. Conclusion: The dipole elements provide a sufficiently complimentary B1+ and electric field pattern to the loop array that can be exploited by the radiofrequency shimming algorithm to reduce local SAR. National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant R01EB006847) National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant R01EB007942) Madrid-MIT M+Vision Consortium 2017-07-14T19:27:34Z 2017-07-14T19:27:34Z 2014-04 2013-10 Article http://purl.org/eprint/type/JournalArticle 0740-3194 1522-2594 http://hdl.handle.net/1721.1/110711 Eryaman, Yigitcan et al. “SAR Reduction in 7T C-Spine Imaging Using a ‘dark Modes’ Transmit Array Strategy: SAR Reduction Using a ‘Dark Modes’ Strategy.” Magnetic Resonance in Medicine 73.4 (2015): 1533–1539. https://orcid.org/0000-0002-7637-2914 https://orcid.org/0000-0001-7208-8863 en_US http://dx.doi.org/10.1002/mrm.25246 Magnetic Resonance in Medicine Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf Wiley Blackwell PMC |
| spellingShingle | Guerin, Bastien Keil, Boris Mareyam, Azma Kosior, Robert K. Martin, Adrian Torrado-Carvajal, Angel Malpica, Norberto Hernandez-Tamames, Juan A. Schiavi, Emanuele Eryaman, Yigitcan Adalsteinsson, Elfar Lopez Herraiz, Joaquin Wald, Lawrence SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title | SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title_full | SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title_fullStr | SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title_full_unstemmed | SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title_short | SAR reduction in 7T C-spine imaging using a “dark modes” transmit array strategy |
| title_sort | sar reduction in 7t c spine imaging using a dark modes transmit array strategy |
| url | http://hdl.handle.net/1721.1/110711 https://orcid.org/0000-0002-7637-2914 https://orcid.org/0000-0001-7208-8863 |
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