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Title: Cryogenically-cooled high temperature superconducting (HTS) coils for low field MRI
Author: Cheong, Hoon Sin
ISNI:       0000 0004 2742 8269
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2011
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In low field MRl (<0.5T), the signal-to-noise ratio (SNR) is predominantly degraded by thermal noise of the imaging coil when the sample loading is minimized. This means surface coils made of high temperature superconductors (HTS) should have an SNR significantly higher than their room-temperature copper equivalents due to the reduction in resistivities. While this hypothesis has been reportedly validated, the actual efficacy of HTS coils is still debatable as the benchmark setups in the prior art had an unfavorably large coil-to-sample separation which diminished the SNR yield. This thesis is intended to perform a quantitative validation on the said hypothesis against a novel benchmark setup where the equivalent room-temperature copper coil was placed directly next to the sample to achieve the best SNR sensitivity. The HTS coil used was an YBCO surface coil having a l0-tum, 70mm-circular spiral layout. For sufficient thermal insulation, there was a 10mm gap between the YBCO coil and the sample while the sample separation for the copper coil was merely I mm. By studying the simulated B1 sensitivity profile of the designated layout, the sample loss and intrinsic resistance of both coils were calculated to allow a theoretical evaluation on the research hypothesis. Each coil was then fabricated and configured with an inductively-coupled matching circuit. The quality factors (Q) of the coils in different loading conditions were measured to allow an empirical estimation on the SNR advantage of the YBCO coil. Both coils were then tested on a saline phantom in a 0.17T MRI system where in-vivo hand images were also acquired. The results showed that the YBCO coil had an SNR gain of 2.0 over the proposed benchmark setup. Such a finding is a valuable addition to the prior art as the efficacy of HTS coils for low field MRl was conclusively proven.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available