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@ARTICLE{Fiedler:168724,
      author       = {T. Fiedler$^*$ and S. Orzada$^*$ and M. Flöser$^*$ and S.
                      H. G. Rietsch and H. H. Quick and M. E. Ladd$^*$ and A. K.
                      Bitz},
      title        = {{P}erformance analysis of integrated {RF} microstrip
                      transmit antenna arrays with high channel count for body
                      imaging at 7 {T}.},
      journal      = {NMR in biomedicine},
      volume       = {34},
      number       = {7},
      issn         = {1099-1492},
      address      = {New York, NY},
      publisher    = {Wiley},
      reportid     = {DKFZ-2021-01028},
      pages        = {e4515},
      year         = {2021},
      note         = {#EA:E020#/2021 Jul;34(7):e4515},
      abstract     = {The aim of the current study was to investigate the
                      performance of integrated RF transmit arrays with high
                      channel count consisting of meander microstrip antennas for
                      body imaging at 7 T and to optimize the position and number
                      of transmit elements. RF simulations using multiring antenna
                      arrays placed behind the bore liner were performed for
                      realistic exposure conditions for body imaging. Simulations
                      were performed for arrays with as few as eight elements and
                      for arrays with high channel counts of up to 48 elements.
                      The B1+ field was evaluated regarding the degrees of freedom
                      for RF shimming in the abdomen. Worst-case specific
                      absorption rate (SARwc ), SAR overestimation in the matrix
                      compression, the number of virtual observation points (VOPs)
                      and SAR efficiency were evaluated. Constrained RF shimming
                      was performed in differently oriented regions of interest in
                      the body, and the deviation from a target B1+ field was
                      evaluated. Results show that integrated multiring arrays are
                      able to generate homogeneous B1+ field distributions for
                      large FOVs, especially for coronal/sagittal slices, and thus
                      enable body imaging at 7 T with a clinical workflow;
                      however, a low duty cycle or a high SAR is required to
                      achieve homogeneous B1+ distributions and to exploit the
                      full potential. In conclusion, integrated arrays allow for
                      high element counts that have high degrees of freedom for
                      the pulse optimization but also produce high SARwc , which
                      reduces the SAR accuracy in the VOP compression for low-SAR
                      protocols, leading to a potential reduction in array
                      performance. Smaller SAR overestimations can increase SAR
                      accuracy, but lead to a high number of VOPs, which increases
                      the computational cost for VOP evaluation and makes online
                      SAR monitoring or pulse optimization challenging. Arrays
                      with interleaved rings showed the best results in the
                      study.},
      keywords     = {VOP compression (Other) / body imaging at UHF MRI (Other) /
                      integrated transmit coil arrays (Other)},
      cin          = {E020},
      ddc          = {610},
      cid          = {I:(DE-He78)E020-20160331},
      pnm          = {315 - Bildgebung und Radioonkologie (POF4-315)},
      pid          = {G:(DE-HGF)POF4-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:33942938},
      doi          = {10.1002/nbm.4515},
      url          = {https://inrepo02.dkfz.de/record/168724},
}