2026-09-18T21:23:52Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/476872021-07-05T14:03:20Zcom_1721.1_7582com_1721.1_7581col_1721.1_131023
J. Thomas Vaughan, Jr.
Skubis, Mark D. (Mark David), 1974-
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
2009-10-01T15:32:22Z
2009-10-01T15:32:22Z
1998
1998
http://hdl.handle.net/1721.1/47687
42254923
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998.
Includes bibliographical references (leaves 58-65).
Radiofrequency energy loss has been investigated for a resonant NMR surface coil between 20 MHz and 400 MHz. High-field NMR (> 64 MHz) is used increasingly for human imaging and spectroscopy to achieve improved SNR and spectral resolution. RF losses in coils designed using conventional lumped-element principles, however, often limit the practicality of high-field imaging. New design principles are required for the construction of efficient high-field RF coils. The RF energy losses investigated include RF coil losses and losses to a phantom load. These were studied using single-loop, resonant surface coils. Coil Q values, both unloaded and loaded, were measured and used to determine the coil radiation resistance, load resistance, B, field magnitude, and SNR. Radiation resistance is shown to increase like RR ~ f04. It is widely believed that load losses dominate all other losses in biomedical NMR. This study indicates that limiting radiation losses may improve loaded coil SNR at high frequencies. To this end, one may decrease the coil electrical length and/or apply transmission line principles in the construction of RF coils. Decreasing the coil electrical wavelength may be accomplished by decreasing the coil dimensions. Transmission line principles, which have been demonstrated for volume coils, improve performance by minimizing the coil radiation resistance.
by Mark D. Skubis.
S.M.
65 leaves
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by
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http://dspace.mit.edu/handle/1721.1/7582
Nuclear Engineering
Radiofrequency losses in an NMR surface coil
Radiofrequency losses in a nuclear magnetic resonance surface coil
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<Abstract>Radiofrequency energy loss has been investigated for a resonant NMR surface coil between 20 MHz and 400 MHz. High-field NMR (> 64 MHz) is used increasingly for human imaging and spectroscopy to achieve improved SNR and spectral resolution. RF losses in coils designed using conventional lumped-element principles, however, often limit the practicality of high-field imaging. New design principles are required for the construction of efficient high-field RF coils. The RF energy losses investigated include RF coil losses and losses to a phantom load. These were studied using single-loop, resonant surface coils. Coil Q values, both unloaded and loaded, were measured and used to determine the coil radiation resistance, load resistance, B, field magnitude, and SNR. Radiation resistance is shown to increase like RR ~ f04. It is widely believed that load losses dominate all other losses in biomedical NMR. This study indicates that limiting radiation losses may improve loaded coil SNR at high frequencies. To this end, one may decrease the coil electrical length and/or apply transmission line principles in the construction of RF coils. Decreasing the coil electrical wavelength may be accomplished by decreasing the coil dimensions. Transmission line principles, which have been demonstrated for volume coils, improve performance by minimizing the coil radiation resistance.</Abstract>
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