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@ARTICLE{Hetherington:878677,
      author       = {Hetherington, Hoby P. and Moon, Chan Hong and Schwerter,
                      Michael and Shah, N. J. and Pan, Jullie W.},
      title        = {{D}ynamic {B} 0 shimming for multiband imaging using high
                      order spherical harmonic shims},
      journal      = {Magnetic resonance in medicine},
      volume       = {85},
      number       = {1},
      issn         = {1522-2594},
      address      = {New York, NY [u.a.]},
      publisher    = {Wiley-Liss},
      reportid     = {FZJ-2020-02995},
      pages        = {531-543},
      year         = {2021},
      abstract     = {PurposeTo describe and implement a strategy for dynamic
                      slice‐by‐slice and multiband B0 shimming using spherical
                      harmonic shims in the human brain at 7T.TheoryFor thin axial
                      slices, spherical harmonic shims can be divided into pairs
                      of shims (z‐degenerate and non‐z‐degenerate) that are
                      spatially degenerate, such that only ½ of the shims
                      (non‐z‐degenerate) are required for single slice
                      optimizations. However, when combined, the pairs of shims
                      can be used to simultaneously generate the same in‐plane
                      symmetries but with different amplitudes as a function of
                      their z location. This enables multiband shimming equivalent
                      to that achievable by single slice‐by‐slice
                      optimization.MethodsAll data were acquired at 7T using a
                      spherical harmonic shim insert enabling shimming up through
                      4th order with two additional 5th order shims (1st‐4th+).
                      Dynamic shim updating was achieved using a 10A shim power
                      supply with 2 ms ramps and constrained optimizations to
                      minimize eddy currents.ResultsIn groups of eight subjects,
                      we demonstrated that: 1) dynamic updating using 1st‐4th+
                      order shims reduced the SD of the B0 field over the whole
                      brain from 32.4 ± 2.6 and 24.9 ± 2 Hz with 1st‐2nd and
                      1st‐4th+ static global shimming to 15.1 ± 1.7 Hz; 2) near
                      equivalent performance was achieved when dynamically
                      updating only the non‐z‐degenerate shims (14.3 ± 1.5
                      Hz), or when a using multiband shim factor of 2, MBs = 2,
                      and all shims (14.4 ± 2.0 Hz).ConclusionHigh order
                      spherical harmonics provide substantial improvements over
                      static global shimming and enable dynamic multiband shimming
                      with near equivalent performance to that of dynamic
                      slice‐by‐slice shimming. This reduces distortion in echo
                      planar imaging.},
      cin          = {INM-4 / INM-11 / JARA-BRAIN},
      ddc          = {610},
      cid          = {I:(DE-Juel1)INM-4-20090406 / I:(DE-Juel1)INM-11-20170113 /
                      I:(DE-Juel1)VDB1046},
      pnm          = {573 - Neuroimaging (POF3-573)},
      pid          = {G:(DE-HGF)POF3-573},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:32857424},
      UT           = {WOS:000563308400001},
      doi          = {10.1002/mrm.28438},
      url          = {https://juser.fz-juelich.de/record/878677},
}