title: Radiofrequency heating induced by 7T head MRI: thermal assessment using discrete vasculature or Pennes' bioheat equation.
abstract: OBJECTIVE
  To evaluate and compare the maximum temperature (T(max) ) in the head after exposure to a 300 MHz radiofrequency (RF) field induced by a magnetic resonance imaging (MRI) coil using two thermal simulation methods: Pennes' bioheat equation (PBHE) and discrete vasculature (DIVA).
  
  
  METHODS
  The electromagnetic field induced in the head by a 7T birdcage coil was simulated using finite-difference time-domain (FDTD) and validated by MRI. The specific absorption rate (SAR) distributions normalized to the 10-gram maximum or the whole-head average were used for PBHE and DIVA simulations.
  
  
  RESULTS
  For all cases, the T(max) in PBHE was slightly higher than in DIVA. The T(max) was 37.9-38.4°C, depending on the simulation method or perfusion rate.
  
  
  CONCLUSIONS
  In some situations, RF exposure limited to SAR(max,10g) led to a T(max) higher than allowed by International Electrotechnical Commission (IEC) regulations. Therefore, it is advisable to use thermal simulations to evaluate RF safety of MRI. The simulation method used only slightly influenced the observed maximum temperature; the observed temperature with PBHE was higher in all situations. So PBHE is an appropriate method for RF safety assessment of MRI in the head. Using DIVA simulations, it was found unlikely that the body temperature increases significantly due to energy deposited by a head coil under normal circumstances.
authors: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands. a.l.h.m.w.vanlier@umcutrecht.nl
authors: Astrid L H M W
authors: AL
authors: van Lier
authors: Alexis N T J
authors: AN
authors: Kotte
authors: Bas W
authors: BW
authors: Raaymakers
authors: Jan J W
authors: JJ
authors: Lagendijk
authors: Cornelis A T
authors: CA
authors: van den Berg
mesh_terms: D001831:Body Temperature / Q000502:physiology* / Q000528:radiation effects; D001921:Brain / Q000502:physiology* / Q000528:radiation effects; D002536:Cerebral Arteries / Q000502:physiology*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006257:Head / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008954:Models, Biological; D011829:Radiation Dosage; D011846:Radio Waves; D013814:Thermal Conductivity