title: Thermal simulations in the human head for high field MRI using parallel transmission.
abstract: OBJECTIVE
  To investigate, via numerical simulations, the compliance of the specific absorption rate (SAR) versus temperature guidelines for the human head in magnetic resonance imaging procedures utilizing parallel transmission at high field.
  
  
  METHODS
  A combination of finite element and finite-difference time-domain methods was used to calculate the evolution of the temperature distribution in the human head for a large number of parallel transmission scenarios. The computations were performed on a new model containing 20 anatomical structures.
  
  
  RESULTS
  Among all the radiofrequency field exposure schemes simulated, the recommended 39°C maximum local temperature was never exceeded when the local 10-g average SAR threshold was reached. On the other hand, the maximum temperature barely complied with its guideline when the global SAR reached 3.2 W/kg. The maximal temperature in the eye could very well rise by more than 1°C in both cases.
  
  
  CONCLUSIONS
  Considering parallel transmission, the recommended values of local 10-g SAR may remain a relevant metric to ensure that the local temperature inside the human head never exceeds 39°C, although it can lead to rises larger than 1°C in the eye. Monitoring temperature instead of SAR can provide increased flexibility in pulse design for parallel transmission.
authors.affiliation: CEA, DSV, I2BM, NeuroSpin, LRMN, Gif-sur-Yvette, France.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Massire
authors.forename: Martjin A
authors.initials: MA
authors.lastname: Cloos
authors.forename: Michel
authors.initials: M
authors.lastname: Luong
authors.forename: Alexis
authors.initials: A
authors.lastname: Amadon
authors.forename: Alexandre
authors.initials: A
authors.lastname: Vignaud
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wiggins
authors.forename: Nicolas
authors.initials: N
authors.lastname: Boulant
mesh_terms: D001831:Body Temperature / Q000502:physiology* / Q000528:radiation effects*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006257:Head / Q000502:physiology* / Q000528:radiation effects*; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D011829:Radiation Dosage