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@ARTICLE{Liu:203230,
      author       = {Liu, Chao and Chang, Baolin and Qiu, Longqing and Dong, Hui
                      and Qiu, Yang and Zhang, Yi and Krause, Hans-Joachim and
                      Offenhäusser, Andreas and Xie, Xiaoming},
      title        = {{E}ffect of magnetic field fluctuation on ultra-low field
                      {MRI} measurements in the unshielded laboratory environment},
      journal      = {Journal of magnetic resonance},
      volume       = {257},
      issn         = {1090-7807},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2015-05216},
      pages        = {8 - 14},
      year         = {2015},
      abstract     = {Magnetic field fluctuations in our unshielded urban
                      laboratory can reach hundreds of nT in the noisy daytime and
                      is only a few nT in the quiet midnight. The field
                      fluctuation causes the Larmor frequency fL to drift randomly
                      for several Hz during the unshielded ultra-low field (ULF)
                      nuclear magnetic resonance (NMR) and magnetic resonance
                      imaging (MRI) measurements, thus seriously spoiling the
                      averaging effect and causing imaging artifacts. By using an
                      active compensation (AC) technique based on the spatial
                      correlation of the low-frequency magnetic field fluctuation,
                      the field fluctuation can be suppressed to tens of nT, which
                      is a moderate situation between the noisy daytime and the
                      quiet midnight. In this paper, the effect of the field
                      fluctuation on ULF MRI measurements was investigated. The 1D
                      and 2D MRI signals of a water phantom were measured using a
                      second-order low-Tc superconducting quantum interference
                      device (SQUID) in three fluctuation cases: severe
                      fluctuation (noisy daytime), moderate fluctuation (daytime
                      with AC) and minute fluctuation (quiet midnight) when
                      different gradient fields were applied. When the active
                      compensation is applied or when the frequency encoding
                      gradient field Gx reaches a sufficiently strong value in our
                      measurements, the image artifacts become invisible in all
                      three fluctuation cases. Therefore it is feasible to perform
                      ULF-MRI measurements in unshielded urban environment without
                      imaging artifacts originating from magnetic fluctuations by
                      using the active compensation technique and/or strong
                      gradient fields.},
      cin          = {PGI-8 / ICS-8 / JARA-FIT},
      ddc          = {550},
      cid          = {I:(DE-Juel1)PGI-8-20110106 / I:(DE-Juel1)ICS-8-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {552 - Engineering Cell Function (POF3-552) / 553 - Physical
                      Basis of Diseases (POF3-553)},
      pid          = {G:(DE-HGF)POF3-552 / G:(DE-HGF)POF3-553},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000358339700002},
      doi          = {10.1016/j.jmr.2015.04.014},
      url          = {https://juser.fz-juelich.de/record/203230},
}