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      Sheared two-dimensional radiofrequency excitation for off-resonance robustness and fat suppression in reduced field-of-view imaging

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      Author(s)
      Barlas, Bahadır Alp
      Bahadır, Çağla Deniz
      Kafalı, Sevgi Gökçe
      Yılmaz, Uğur
      Sarıtaş, Emine Ülkü
      Date
      2022-09-30
      Source Title
      Magnetic Resonance in Medicine
      Print ISSN
      0740-3194
      Electronic ISSN
      1522-2594
      Publisher
      Wiley
      Volume
      88
      Issue
      6
      Pages
      2504 - 2519
      Language
      English
      Type
      Article
      Item Usage Stats
      30
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      6
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      Abstract
      Purpose: Two-dimensional (2D) echo-planar radiofrequency (RF) pulses are widely used for reduced field-of-view (FOV) imaging in applications such as diffusion-weighted imaging. However, long pulse durations render the 2D RF pulses sensitive to off-resonance effects, causing local signal losses in reduced-FOV images. This work aims to achieve off-resonance robustness for 2D RF pulses via a sheared trajectory design. Theory and Methods: A sheared 2D RF pulse design is proposed to reduce pulse durations while covering identical excitation k-space extent as a standard 2D RF pulse. For a given shear angle, the number of sheared trajectory lines is minimized to obtain the shortest pulse duration, such that the excitation replicas are repositioned outside the slice stack to guarantee unlimited slice coverage. A target fat/water signal ratio of 5% is chosen to achieve robust fat suppression. Results: Simulations, imaging experiments on a custom head and neck phantom, and in vivo imaging experiments in the spinal cord at 3 T demonstrate that the sheared 2D RF design provides significant improvement in image quality while preserving profile sharpnesses. In regions with high off-resonance effects, the sheared 2D RF pulse improves the signal by more than 50% when compared to the standard 2D RF pulse. Conclusion: The proposed sheared 2D RF design successfully reduces pulse durations, exhibiting significantly improved through-plane off-resonance robustness, while providing unlimited slice coverage and high fidelity fat suppression. This method will be especially beneficial in regions suffering from a variety of off-resonance effects, such as spinal cord and breast. © 2022 International Society for Magnetic Resonance in Medicine.
      Keywords
      2D RF pulse
      Fat suppression
      Multislice imaging
      Off-resonance robustness
      Reduced field-of-view imaging
      Sheared trajectory
      Permalink
      http://hdl.handle.net/11693/111213
      Published Version (Please cite this version)
      https://doi.org/10.1002/mrm.29416
      Collections
      • Aysel Sabuncu Brain Research Center (BAM) 249
      • Department of Electrical and Electronics Engineering 4011
      • Graduate School of Engineering and Science 5
      • National Magnetic Resonance Research Center (UMRAM) 301
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