title: On the safety margin of using simplified human head models for local SAR simulations of B1-shimming at 7 Tesla.
abstract: OBJECTIVE
  Using simplified human models significantly alleviates the difficulty of rendering human models for subject-specific local specific absorption rate (SAR) simulations. Although its accuracy has been demonstrated with the birdcage mode combination of RF transmitters, its accuracy in general B1-shimming, where numerous phase and magnitude combinations can take place, is yet unknown.
  
  
  METHODS
  The electromagnetic fields of a 7-Tesla eight-channel brain imaging array were simulated by using four detailed human models from the Virtual Family and their two-, three-, and four-tissue simplifications. The 10-g averaged local SAR was computed for each case with 1,000 sets of uniformly distributed random B1-shimming parameters. Linear regression was applied to relate the local SAR obtained by using detailed and simplified human models. The 99% confidence prediction interval was determined as the safety margin in order to cover the largest local SAR variability introduced by using simplified human models.
  
  
  RESULTS
  The local SAR computed by using three- and four-tissue simplifications are strongly correlated with those computed by using detailed models. Safety margins of 0.38 and 0.45W/kg/W were found appropriate for each case being considered.
  
  
  CONCLUSIONS
  The proposed procedure can be applied to evaluate the safety margin of the local SAR simulated by using simplified human models. However, discretion needs to be exercised since the safety margins in some cases may represent more than 50% overestimation.
authors: Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, USA.
authors: Yu
authors: Y
authors: Shao
authors: Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, USA.
authors: Shuo
authors: S
authors: Shang
authors: Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, USA. Electronic address: james.wang@ieee.org.
authors: Shumin
authors: S
authors: Wang
mesh_terms: D001921:Brain / Q000033:anatomy & histology*; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006257:Head; D006801:Humans; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D015203:Reproducibility of Results; D012449:Safety
keywords: High-field MRI; Local SAR; RF safety; Statistical simulation