% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@ARTICLE{Fiedler:119325,
      author       = {T. Fiedler$^*$ and M. Ladd$^*$ and A. Bitz$^*$},
      title        = {{RF} safety assessment of a bilateral four-channel
                      transmit/receive 7 {T}esla breast coil: {SAR} versus tissue
                      temperature limits.15},
      journal      = {Medical physics},
      volume       = {44},
      number       = {1},
      issn         = {0094-2405},
      address      = {New York, NY},
      reportid     = {DKFZ-2017-00080},
      pages        = {143 - 157},
      year         = {2017},
      abstract     = {The purpose of this work was to perform an RF safety
                      evaluation for a bilateral four-channel transmit/receive
                      breast coil and to determine the maximum permissible input
                      power for which RF exposure of the subject stays within
                      recommended limits. The safety evaluation was done based on
                      SAR as well as on temperature simulations. In comparison to
                      SAR, temperature is more directly correlated with tissue
                      damage, which allows a more precise safety assessment. The
                      temperature simulations were performed by applying three
                      different blood perfusion models as well as two different
                      ambient temperatures. The goal was to evaluate whether the
                      SAR and temperature distributions correlate inside the human
                      body and whether SAR or temperature is more conservative
                      with respect to the limits specified by the IEC.A simulation
                      model was constructed including coil housing and MR
                      environment. Lumped elements and feed networks were modeled
                      by a network co-simulation. The model was validated by
                      comparison of S-parameters and B1(+) maps obtained in an
                      anatomical phantom. Three numerical body models were
                      generated based on 3 Tesla MRI images to conform to the coil
                      housing. SAR calculations were performed and the maximal
                      permissible input power was calculated based on IEC
                      guidelines. Temperature simulations were performed based on
                      the Pennes bioheat equation with the power absorption from
                      the RF simulations as heat source. The blood perfusion was
                      modeled as constant to reflect impaired patients as well as
                      with a linear and exponential temperature-dependent increase
                      to reflect two possible models for healthy subjects. Two
                      ambient temperatures were considered to account for cooling
                      effects from the environment.The simulation model was
                      validated with a mean deviation of $3\%$ between measurement
                      and simulation results. The highest 10 g-averaged SAR was
                      found in lung and muscle tissue on the right side of the
                      upper torso. The maximum permissible input power was
                      calculated to be 17 W. The temperature simulations showed
                      that temperature maximums do not correlate well with the
                      position of the SAR maximums in all considered cases. The
                      body models with an exponential blood perfusion increase did
                      not exceed the temperature limit when an RF power according
                      to the SAR limit was applied; in this case, a higher input
                      power level by up to $73\%$ would be allowed. The models
                      with a constant or linear perfusion exceeded the limit for
                      the local temperature when the local SAR limit was adhered
                      to and would require a decrease in the input power level by
                      up to $62\%.The$ maximum permissible input power was
                      determined based on SAR simulations with three newly
                      generated body models and compared with results from
                      temperature simulations. While SAR calculations are
                      state-of-the-art and well defined as they are based on more
                      or less well-known material parameters, temperature
                      simulations depend strongly on additional material,
                      environmental and physiological parameters. The simulations
                      demonstrated that more consideration needs be made by the MR
                      community in defining the parameters for temperature
                      simulations in order to apply temperature limits instead of
                      SAR limits in the context of MR RF safety evaluations.},
      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:28102957},
      doi          = {10.1002/mp.12034},
      url          = {https://inrepo02.dkfz.de/record/119325},
}