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@ARTICLE{Orzada:125307,
      author       = {S. Orzada and M. Ladd$^*$ and A. Bitz$^*$},
      title        = {{A} method to approximate maximum local {SAR} in
                      multichannel transmit {MR} systems without transmit phase
                      information.},
      journal      = {Magnetic resonance in medicine},
      volume       = {78},
      number       = {2},
      issn         = {0740-3194},
      address      = {New York, NY [u.a.]},
      publisher    = {Wiley-Liss},
      reportid     = {DKFZ-2017-01440},
      pages        = {805 - 811},
      year         = {2017},
      abstract     = {To calculate local specific absorption rate (SAR)
                      correctly, both the amplitude and phase of the signal in
                      each transmit channel have to be known. In this work, we
                      propose a method to derive a conservative upper bound for
                      the local SAR, with a reasonable safety margin without
                      knowledge of the transmit phases of the channels.The
                      proposed method uses virtual observation points (VOPs).
                      Correction factors are calculated for each set of VOPs that
                      prevent underestimation of local SAR when the VOPs are
                      applied with the correct amplitudes but fixed phases.The
                      proposed method proved to be superior to the worst-case
                      calculation based on the maximum eigenvalue of the VOPs. The
                      mean overestimation for six coil setups could be reduced,
                      whereas no underestimation of the maximum local SAR
                      occurred. In the best investigated case, the overestimation
                      could be reduced from a factor of 3.3 to a factor of 1.7.The
                      upper bound for the local SAR calculated with the proposed
                      method allows a fast estimation of the local SAR based on
                      power measurements in the transmit channels and facilitates
                      SAR monitoring in systems that do not have the capability to
                      monitor transmit phases. Magn Reson Med 78:805-811, 2017. ©
                      2016 International Society for Magnetic Resonance in
                      Medicine.},
      cin          = {E020},
      ddc          = {610},
      cid          = {I:(DE-He78)E020-20160331},
      pnm          = {315 - Imaging and radiooncology (POF3-315)},
      pid          = {G:(DE-HGF)POF3-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:27604749},
      doi          = {10.1002/mrm.26398},
      url          = {https://inrepo02.dkfz.de/record/125307},
}