Surface and Gradiometer Coils near a Conducting Body: The Lift-off Effect
The use of surface coils in magnetic resonance is widespread. Examples include MRI, detection of subsurface aquifers by NMR, and, more recently, landmine detection by nuclear quadrupole resonance. In many of these cases a finite-sized sample to be examined is contained within a larger medium that is...
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Veröffentlicht in: | Journal of magnetic resonance (1997) 1998-12, Vol.135 (2), p.373-379 |
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description | The use of surface coils in magnetic resonance is widespread. Examples include MRI, detection of subsurface aquifers by NMR, and, more recently, landmine detection by nuclear quadrupole resonance. In many of these cases a finite-sized sample to be examined is contained within a larger medium that is a poor electrical conductor, and eddy currents induced by the RF fields provide a loss mechanism that reduces the effective quality factorQof the transmitter and receiver coils. Here the losses induced in a circular surface coil (a horizontal loop antenna) separated a distance from a dissipative medium are calculated and compared to measurements. It is shown that often the overall efficiency of the coil for magnetic resonance can be improved by displacing the coil away from the conducting medium a prescribed “lift-off” distance. The use of a gradiometer as a surface coil is also examined, and it is shown by theory and experiment that in certain circumstances such a gradiometer can be more efficient than a conventional surface coil for inspection of conducting media. |
doi_str_mv | 10.1006/jmre.1998.1608 |
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The use of a gradiometer as a surface coil is also examined, and it is shown by theory and experiment that in certain circumstances such a gradiometer can be more efficient than a conventional surface coil for inspection of conducting media.</description><subject>dissipative media</subject><subject>gradiometer</subject><subject>lift-off</subject><subject>magnetic resonance</subject><subject>Magnetic Resonance Spectroscopy - instrumentation</subject><subject>MRI</subject><subject>NMR</subject><subject>NQR</subject><subject>sensitivity</subject><subject>signal-to-noise ratio</subject><subject>small loop antenna</subject><subject>surface coils</subject><issn>1090-7807</issn><issn>1096-0856</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>1998</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNp1kL1PwzAQxS0EKlBY2ZA8sSX4msZ22KAqpVIlhna3XPsMrvJR7ASp_z0JrdiY7k7v3ZPej5A7YCkwxh93VcAUikKmwJk8I1fACp4wmfPz350lQjJxSa5j3DEGkAs2IqNCCjnl_Ios111w2iDVtaWLoK1vKmwx0Fnjy0hr1IHq_qhtZ1pff9CXxh6e6OYT6cq7Nmmco3Pn0LQ35MLpMuLtaY7J-nW-mb0lq_fFcva8SkyWFW1S5JpLIYSdYpZn4Ca60NwBM7nb5mChv5kAQLACMycyybdGC8mtkw5lNiYPx9R9aL46jK2qfDRYlrrGpouKF5DBZDIY06PRhCbGgE7tg690OChgaiCnBnJqIKcGcv3D_Sm521Zo_-wnVL0ujzr25b49BhWNx9qg9aGvr2zj_4v-AWvBe_0</recordid><startdate>19981201</startdate><enddate>19981201</enddate><creator>Suits, B.H.</creator><creator>Garroway, A.N.</creator><creator>Miller, J.B.</creator><general>Elsevier Inc</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></search><sort><creationdate>19981201</creationdate><title>Surface and Gradiometer Coils near a Conducting Body: The Lift-off Effect</title><author>Suits, B.H. ; Garroway, A.N. ; Miller, J.B.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c339t-95a68777d4e3531f2a9a6f10c5fb51d12a90711e1d7e3f7386bca786df8fe83</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>1998</creationdate><topic>dissipative media</topic><topic>gradiometer</topic><topic>lift-off</topic><topic>magnetic resonance</topic><topic>Magnetic Resonance Spectroscopy - instrumentation</topic><topic>MRI</topic><topic>NMR</topic><topic>NQR</topic><topic>sensitivity</topic><topic>signal-to-noise ratio</topic><topic>small loop antenna</topic><topic>surface coils</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Suits, B.H.</creatorcontrib><creatorcontrib>Garroway, A.N.</creatorcontrib><creatorcontrib>Miller, J.B.</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><jtitle>Journal of magnetic resonance (1997)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Suits, B.H.</au><au>Garroway, A.N.</au><au>Miller, J.B.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Surface and Gradiometer Coils near a Conducting Body: The Lift-off Effect</atitle><jtitle>Journal of magnetic resonance (1997)</jtitle><addtitle>J Magn Reson</addtitle><date>1998-12-01</date><risdate>1998</risdate><volume>135</volume><issue>2</issue><spage>373</spage><epage>379</epage><pages>373-379</pages><issn>1090-7807</issn><eissn>1096-0856</eissn><abstract>The use of surface coils in magnetic resonance is widespread. Examples include MRI, detection of subsurface aquifers by NMR, and, more recently, landmine detection by nuclear quadrupole resonance. In many of these cases a finite-sized sample to be examined is contained within a larger medium that is a poor electrical conductor, and eddy currents induced by the RF fields provide a loss mechanism that reduces the effective quality factorQof the transmitter and receiver coils. Here the losses induced in a circular surface coil (a horizontal loop antenna) separated a distance from a dissipative medium are calculated and compared to measurements. It is shown that often the overall efficiency of the coil for magnetic resonance can be improved by displacing the coil away from the conducting medium a prescribed “lift-off” distance. 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subjects | dissipative media gradiometer lift-off magnetic resonance Magnetic Resonance Spectroscopy - instrumentation MRI NMR NQR sensitivity signal-to-noise ratio small loop antenna surface coils |
title | Surface and Gradiometer Coils near a Conducting Body: The Lift-off Effect |
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