Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T
Objective The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern. Materials and methods We engineered a s...
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| Veröffentlicht in: | Magma (New York, N.Y.) N.Y.), 2016-06, Vol.29 (3), p.371-378 |
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| creator | Weidemann, Gerd Seifert, Frank Hoffmann, Werner Pfeiffer, Harald Seemann, Reiner Ittermann, Bernd |
| description | Objective
The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern.
Materials and methods
We engineered a system for in situ measurement of complex-valued scattering parameter (S-parameter) matrices of multichannel transmit coils that allows for the calculation of the reflected and accepted power for arbitrary steering conditions. The radiated power from an RF coil inside a large single-mode waveguide couples to that mode. Finite-difference time-domain simulations were used for the calculations, and
E
-field probes were used to measure the electric field distribution, and hence the radiated power, in the waveguide. To test this concept, an eight-channel shielded-loop array for 7T imaging was studied inside a 280-cm-long cylindrical waveguide with a 60-cm diameter.
Results
For a 7T parallel-transmit coil, the S-parameters were measured and the reflected power calculated as a function of steering conditions. Maximum radiated power was observed for the circularly polarized mode.
Conclusion
A system was developed for in situ S-parameter measurements combined with a method for determining radiated power, allowing a complete assessment of the power balance of multichannel transmit coils at 7T. |
| doi_str_mv | 10.1007/s10334-016-0551-6 |
| format | Article |
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The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern.
Materials and methods
We engineered a system for in situ measurement of complex-valued scattering parameter (S-parameter) matrices of multichannel transmit coils that allows for the calculation of the reflected and accepted power for arbitrary steering conditions. The radiated power from an RF coil inside a large single-mode waveguide couples to that mode. Finite-difference time-domain simulations were used for the calculations, and
E
-field probes were used to measure the electric field distribution, and hence the radiated power, in the waveguide. To test this concept, an eight-channel shielded-loop array for 7T imaging was studied inside a 280-cm-long cylindrical waveguide with a 60-cm diameter.
Results
For a 7T parallel-transmit coil, the S-parameters were measured and the reflected power calculated as a function of steering conditions. Maximum radiated power was observed for the circularly polarized mode.
Conclusion
A system was developed for in situ S-parameter measurements combined with a method for determining radiated power, allowing a complete assessment of the power balance of multichannel transmit coils at 7T.</description><identifier>ISSN: 0968-5243</identifier><identifier>EISSN: 1352-8661</identifier><identifier>DOI: 10.1007/s10334-016-0551-6</identifier><identifier>PMID: 27038936</identifier><language>eng</language><publisher>Berlin/Heidelberg: Springer Berlin Heidelberg</publisher><subject>Algorithms ; Arrays ; Biomedical Engineering and Bioengineering ; Coils ; Computer Appl. in Life Sciences ; Electric fields ; Electric power generation ; Electromagnetic Radiation ; Equipment and Supplies ; Equipment Design ; Health Informatics ; Imaging ; Magnetic Resonance Imaging - methods ; Magnetic Resonance Spectroscopy ; Mathematical analysis ; Medicine ; Medicine & Public Health ; Multichannel ; Patient Safety ; Phantoms, Imaging ; Polyethylene - chemistry ; Radio Waves ; Radiology ; Research Article ; Scattering, Radiation ; Solid State Physics ; Steering ; Waveguides</subject><ispartof>Magma (New York, N.Y.), 2016-06, Vol.29 (3), p.371-378</ispartof><rights>ESMRMB 2016</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c410t-e92486504f7eb7dee7aae00f136ec7ae034e049541c52b664b2adc99192b4a443</citedby><cites>FETCH-LOGICAL-c410t-e92486504f7eb7dee7aae00f136ec7ae034e049541c52b664b2adc99192b4a443</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://link.springer.com/content/pdf/10.1007/s10334-016-0551-6$$EPDF$$P50$$Gspringer$$H</linktopdf><linktohtml>$$Uhttps://link.springer.com/10.1007/s10334-016-0551-6$$EHTML$$P50$$Gspringer$$H</linktohtml><link.rule.ids>314,776,780,27901,27902,41464,42533,51294</link.rule.ids><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/27038936$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink></links><search><creatorcontrib>Weidemann, Gerd</creatorcontrib><creatorcontrib>Seifert, Frank</creatorcontrib><creatorcontrib>Hoffmann, Werner</creatorcontrib><creatorcontrib>Pfeiffer, Harald</creatorcontrib><creatorcontrib>Seemann, Reiner</creatorcontrib><creatorcontrib>Ittermann, Bernd</creatorcontrib><title>Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T</title><title>Magma (New York, N.Y.)</title><addtitle>Magn Reson Mater Phy</addtitle><addtitle>MAGMA</addtitle><description>Objective
The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern.
Materials and methods
We engineered a system for in situ measurement of complex-valued scattering parameter (S-parameter) matrices of multichannel transmit coils that allows for the calculation of the reflected and accepted power for arbitrary steering conditions. The radiated power from an RF coil inside a large single-mode waveguide couples to that mode. Finite-difference time-domain simulations were used for the calculations, and
E
-field probes were used to measure the electric field distribution, and hence the radiated power, in the waveguide. To test this concept, an eight-channel shielded-loop array for 7T imaging was studied inside a 280-cm-long cylindrical waveguide with a 60-cm diameter.
Results
For a 7T parallel-transmit coil, the S-parameters were measured and the reflected power calculated as a function of steering conditions. Maximum radiated power was observed for the circularly polarized mode.
Conclusion
A system was developed for in situ S-parameter measurements combined with a method for determining radiated power, allowing a complete assessment of the power balance of multichannel transmit coils at 7T.</description><subject>Algorithms</subject><subject>Arrays</subject><subject>Biomedical Engineering and Bioengineering</subject><subject>Coils</subject><subject>Computer Appl. in Life Sciences</subject><subject>Electric fields</subject><subject>Electric power generation</subject><subject>Electromagnetic Radiation</subject><subject>Equipment and Supplies</subject><subject>Equipment Design</subject><subject>Health Informatics</subject><subject>Imaging</subject><subject>Magnetic Resonance Imaging - methods</subject><subject>Magnetic Resonance Spectroscopy</subject><subject>Mathematical analysis</subject><subject>Medicine</subject><subject>Medicine & Public Health</subject><subject>Multichannel</subject><subject>Patient Safety</subject><subject>Phantoms, Imaging</subject><subject>Polyethylene - chemistry</subject><subject>Radio Waves</subject><subject>Radiology</subject><subject>Research Article</subject><subject>Scattering, Radiation</subject><subject>Solid State Physics</subject><subject>Steering</subject><subject>Waveguides</subject><issn>0968-5243</issn><issn>1352-8661</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2016</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNqNkctKxTAURYMoen18gBPJ0En15N0MRXyBIojiMKTpqVb6uCYtcv_elqsO1VESss7msBchhwxOGIA5TQyEkBkwnYFSLNMbZMGE4lmuNdskC7A6zxSXYofspvQGwJkCsU12uAGRW6EX5PkOfRojttgNifYVfbiky_4DI41YNRgGLKnvShp9Wfv5UaxoOzZDHV5912FDh-i71NYDvXugoa-bRP1AzeM-2ap8k_Dg69wjT5cXj-fX2e391c352W0WJIMhQ8tlrhXIymBhSkTjPQJUTGgMZroKiSCtkiwoXmgtC-7LYC2zvJBeSrFHjte5y9i_j5gG19YpYNP4DvsxOZZzJbWdmvgHCtMqNlfsb9RYYUFzM6eyNRpin9JUmlvGuvVx5Ri42ZJbW3KTJTdbcvPM0Vf8WLRY_kx8a5kAvgbS9NW9YHRv_Ri7qchfUj8Bm3WbGg</recordid><startdate>20160601</startdate><enddate>20160601</enddate><creator>Weidemann, Gerd</creator><creator>Seifert, Frank</creator><creator>Hoffmann, Werner</creator><creator>Pfeiffer, Harald</creator><creator>Seemann, Reiner</creator><creator>Ittermann, Bernd</creator><general>Springer Berlin Heidelberg</general><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7X8</scope><scope>7QO</scope><scope>8FD</scope><scope>FR3</scope><scope>P64</scope><scope>7U5</scope><scope>L7M</scope></search><sort><creationdate>20160601</creationdate><title>Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T</title><author>Weidemann, Gerd ; Seifert, Frank ; Hoffmann, Werner ; Pfeiffer, Harald ; Seemann, Reiner ; Ittermann, Bernd</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c410t-e92486504f7eb7dee7aae00f136ec7ae034e049541c52b664b2adc99192b4a443</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2016</creationdate><topic>Algorithms</topic><topic>Arrays</topic><topic>Biomedical Engineering and Bioengineering</topic><topic>Coils</topic><topic>Computer Appl. in Life Sciences</topic><topic>Electric fields</topic><topic>Electric power generation</topic><topic>Electromagnetic Radiation</topic><topic>Equipment and Supplies</topic><topic>Equipment Design</topic><topic>Health Informatics</topic><topic>Imaging</topic><topic>Magnetic Resonance Imaging - methods</topic><topic>Magnetic Resonance Spectroscopy</topic><topic>Mathematical analysis</topic><topic>Medicine</topic><topic>Medicine & Public Health</topic><topic>Multichannel</topic><topic>Patient Safety</topic><topic>Phantoms, Imaging</topic><topic>Polyethylene - chemistry</topic><topic>Radio Waves</topic><topic>Radiology</topic><topic>Research Article</topic><topic>Scattering, Radiation</topic><topic>Solid State Physics</topic><topic>Steering</topic><topic>Waveguides</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Weidemann, Gerd</creatorcontrib><creatorcontrib>Seifert, Frank</creatorcontrib><creatorcontrib>Hoffmann, Werner</creatorcontrib><creatorcontrib>Pfeiffer, Harald</creatorcontrib><creatorcontrib>Seemann, Reiner</creatorcontrib><creatorcontrib>Ittermann, Bernd</creatorcontrib><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>MEDLINE - Academic</collection><collection>Biotechnology Research Abstracts</collection><collection>Technology Research Database</collection><collection>Engineering Research Database</collection><collection>Biotechnology and BioEngineering Abstracts</collection><collection>Solid State and Superconductivity Abstracts</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Magma (New York, N.Y.)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Weidemann, Gerd</au><au>Seifert, Frank</au><au>Hoffmann, Werner</au><au>Pfeiffer, Harald</au><au>Seemann, Reiner</au><au>Ittermann, Bernd</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T</atitle><jtitle>Magma (New York, N.Y.)</jtitle><stitle>Magn Reson Mater Phy</stitle><addtitle>MAGMA</addtitle><date>2016-06-01</date><risdate>2016</risdate><volume>29</volume><issue>3</issue><spage>371</spage><epage>378</epage><pages>371-378</pages><issn>0968-5243</issn><eissn>1352-8661</eissn><abstract>Objective
The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern.
Materials and methods
We engineered a system for in situ measurement of complex-valued scattering parameter (S-parameter) matrices of multichannel transmit coils that allows for the calculation of the reflected and accepted power for arbitrary steering conditions. The radiated power from an RF coil inside a large single-mode waveguide couples to that mode. Finite-difference time-domain simulations were used for the calculations, and
E
-field probes were used to measure the electric field distribution, and hence the radiated power, in the waveguide. To test this concept, an eight-channel shielded-loop array for 7T imaging was studied inside a 280-cm-long cylindrical waveguide with a 60-cm diameter.
Results
For a 7T parallel-transmit coil, the S-parameters were measured and the reflected power calculated as a function of steering conditions. Maximum radiated power was observed for the circularly polarized mode.
Conclusion
A system was developed for in situ S-parameter measurements combined with a method for determining radiated power, allowing a complete assessment of the power balance of multichannel transmit coils at 7T.</abstract><cop>Berlin/Heidelberg</cop><pub>Springer Berlin Heidelberg</pub><pmid>27038936</pmid><doi>10.1007/s10334-016-0551-6</doi><tpages>8</tpages></addata></record> |
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| source | MEDLINE; Springer Nature - Complete Springer Journals |
| subjects | Algorithms Arrays Biomedical Engineering and Bioengineering Coils Computer Appl. in Life Sciences Electric fields Electric power generation Electromagnetic Radiation Equipment and Supplies Equipment Design Health Informatics Imaging Magnetic Resonance Imaging - methods Magnetic Resonance Spectroscopy Mathematical analysis Medicine Medicine & Public Health Multichannel Patient Safety Phantoms, Imaging Polyethylene - chemistry Radio Waves Radiology Research Article Scattering, Radiation Solid State Physics Steering Waveguides |
| title | Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T |
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