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      Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra-high field MRI

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      Embargo Lift Date: 2021-12-01
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      Author(s)
      Sadeghi-Tarakameh, Alireza
      Adriany, G.
      Metzger, G. J.
      Lagore, R. L.
      Jungst, S.
      DelaBarre, L.
      Van de Moortele, P. F.
      Uğurbil, K.
      Atalar, Ergin
      Eryaman, Y.
      Date
      2020
      Source Title
      Magnetic Resonance in Medicine
      Print ISSN
      0740-3194
      Publisher
      Wiley
      Volume
      84
      Issue
      6
      Pages
      3485 - 3493
      Language
      English
      Type
      Article
      Item Usage Stats
      11
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      Abstract
      Purpose: In this study, we investigate a strategy to reduce the local specific absorption rate (SAR) while keeping constant inside the region of interest (ROI) at the ultra‐high field (B0 ≥ 7T) MRI. Methods: Locally raising the resonance structure under the discontinuity (i.e., creating a bump) increases the distance between the accumulated charges and the tissue. As a result, it reduces the electric field and local SAR generated by these charges inside the tissue. The at a point that is sufficiently far from the coil, however, is not affected by this modification. In this study, three different resonant elements (i.e., loop coil, snake antenna, and fractionated dipole [FD]) are investigated. For experimental validation, a bumped FD is further investigated at 10.5T. After the validation, the transmit performances of eight‐channel arrays of each element are compared through electromagnetic (EM) simulations. Results: Introducing a bump reduced the peak 10g‐averaged SAR by 21, 26, 23% for the loop and snake antenna at 7T, and FD at 10.5T, respectively. In addition, eight‐channel bumped FD array at 10.5T had a 27% lower peak 10g‐averaged SAR in a realistic human body simulation (i.e., prostate imaging) compared to an eight‐channel FD array. Conclusion: In this study, we investigated a simple design strategy based on adding bumps to a resonant element to reduce the local SAR while maintaining inside an ROI. As an example, we modified an FD and performed EM simulations and phantom experiments with a 10.5T scanner. Results show that the peak 10g‐averaged SAR can be reduced more than 25%.
      Keywords
      10.5 Tesla
      Bumped transmitter
      MRI
      Radiofrequency safety
      Ultra-high field
      Permalink
      http://hdl.handle.net/11693/75834
      Published Version (Please cite this version)
      https://dx.doi.org/10.1002/mrm.28382
      Collections
      • Department of Electrical and Electronics Engineering 3702
      • National Magnetic Resonance Research Center (UMRAM) 218
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