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      2D RF pulse design for optimized reduced field-of-view imaging at 1.5T and 3T

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      Embargo Lift Date: 2023-10-22
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      Author(s)
      Eren, Orhun Caner
      Barlas, Bahadır Alp
      Sarıtaş, Emine Ülkü
      Date
      2021-10-22
      Source Title
      Magnetic Resonance Imaging
      Print ISSN
      0730725X
      Electronic ISSN
      1873-5894
      Publisher
      Elsevier Inc.
      Volume
      85
      Pages
      210 - 216
      Language
      English
      Type
      Article
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      Abstract
      Two-dimensional spatially selective radiofrequency (2DRF) excitation pulses are widely used for reduced field-of-view (FOV) targeted high-resolution diffusion weighted imaging (DWI), especially for anatomically small regions such as the spinal cord and prostate. The reduction in FOV achieved by 2DRF pulses significantly improve the in-plane off-resonance artifacts in single-shot echo planar imaging (ss-EPI). However, long durations of 2DRF pulses create a sensitivity to through-plane off-resonance effects, especially at 3 T where the off-resonance field doubles with respect to 1.5 T. This work proposes a parameter-based optimization approach to design 2DRF pulses with blips along the slice-select axis, with the goal of maximizing slab sharpness while minimizing off-resonance effects on 1.5 T and 3 T MRI scanners, separately. Extensive Bloch simulations are performed to evaluate the off-resonance robustness of 2DRF pulses. Three different metrics are proposed to quantify the similarity between the actual and ideal 2D excitation profiles, based on the signals within and outside the targeted reduced-FOV region. In addition, simulations on a digital brain phantom are performed for visual comparison purposes. The results show that maintaining a sharp profile is the primary design requirement at 1.5 T, necessitating the usage of relatively high slab sharpness with a time-bandwidth product (TBW) around 8–10. In contrast, off-resonance robustness is the primary design requirement at 3 T, requiring the usage of a moderate slap sharpness with TBW around 5–7.
      Keywords
      Reduced field-of-view imaging
      Two-dimensional RF pulse
      Excitation profile
      Off-resonance robustness
      Diffusion weighted imaging
      Permalink
      http://hdl.handle.net/11693/111298
      Published Version (Please cite this version)
      https://doi.org/10.1016/j.mri.2021.10.021
      Collections
      • Aysel Sabuncu Brain Research Center (BAM) 249
      • Department of Electrical and Electronics Engineering 4011
      • National Magnetic Resonance Research Center (UMRAM) 301
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