title: SAR and temperature: simulations and comparison to regulatory limits for MRI.
abstract: OBJECTIVE
  To present and discuss numerical calculations of the specific absorption rate (SAR) and temperature in comparison to regulatory limits. While it is possible to monitor whole-body or whole-head average SAR and/or core body temperature during MRI in practice, this is not generally true for local SAR values or local temperatures throughout the body. While methods of calculation for SAR and temperature are constantly being refined, methods for interpreting results of these calculations in light of regulatory limits also warrant discussion.
  
  
  METHODS
  Numerical calculations of SAR and temperature for the human head in a volume coil for MRI at several different frequencies are presented.
  
  
  RESULTS
  Just as the field pattern changes with the frequency, so do the temperature distribution and the ratio of maximum local SAR (in 1-g or 10-g regions) to whole-head average SAR. In all of the cases studied here this ratio is far greater than that in the regulatory limits, indicating that existing limits on local SAR will be exceeded before limits on whole-body or whole-head average SAR are reached.
  
  
  CONCLUSIONS
  Calculations indicate that both SAR and temperature distributions vary greatly with B(1) field frequency, that temperature distributions do not always correlate well with SAR distributions, and that regulatory limits on local temperature may not be exceeded as readily as those on local SAR.
authors.affiliation: Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Zhangwei
authors.initials: Z
authors.lastname: Wang
authors.forename: James C
authors.initials: JC
authors.lastname: Lin
authors.forename: Weihua
authors.initials: W
authors.lastname: Mao
authors.forename: Wanzhan
authors.initials: W
authors.lastname: Liu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Smith
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Collins
mesh_terms: D001921:Brain / Q000473:pathology*; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D013696:Temperature; D013814:Thermal Conductivity; D013817:Thermography