title: Feasibility of measuring thermoregulation during RF heating of the human calf muscle using MR based methods.
abstract: OBJECTIVE
  One of the main safety concerns in MR is heating of the subject due to radiofrequency (RF) exposure. Recently was shown that local peak temperatures can reach dangerous values and the most prominent parameter for accurate temperature estimations is thermoregulation. Therefore, the goal of this research is testing the feasibility of measuring thermoregulation in vivo using MR methods.
  
  
  METHODS
  The calves of 13 volunteers were scanned at 3 tesla. A Proton Resonance Frequency Shift method was used for temperature measurement. Arterial Spin Labeling and phase contrast scans were used for perfusion and flow measurements respectively. The calves were monitored during extreme RF exposure (20 W/kg, 16 min) and after physical exercise.
  
  
  RESULTS
  Temperature increases due to RF absorption (range of the 90th percentile of all volunteers: 1.1-2.5°C) matched with the reference skin temperature changes. Increases in perfusion and flow were defined on the whole leg and normalized to baseline. Perfusion showed a significant increase due to RF heating (ratio compared with baseline: 1.28 ± 0.37; P < 0.05), the influence of exercise was much greater, however (2.97 ± 2.45, P < 0.01).
  
  
  CONCLUSIONS
  This study represents a first exploration of measuring thermoregulation, which will become essential when new safety guidelines are based on thermal dose.
authors.affiliation: Department of Radiotherapy, Imaging Division, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: Frank F J
authors.initials: FF
authors.lastname: Simonis
authors.affiliation: Department of Radiotherapy, Imaging Division, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: Esben T
authors.initials: ET
authors.lastname: Petersen
authors.affiliation: Department of Radiotherapy, Imaging Division, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: Jan J W
authors.initials: JJ
authors.lastname: Lagendijk
authors.affiliation: Department of Radiotherapy, Imaging Division, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: Cornelis A T
authors.initials: CA
authors.lastname: van den Berg
mesh_terms: D001833:Body Temperature Regulation / Q000502:physiology*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007866:Leg / Q000000981:diagnostic imaging* / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology; D019047:Phantoms, Imaging; D012881:Skin Temperature; D013817:Thermography / Q000379:methods*
keywords: ASL; MR thermometry; RF safety; calf muscle; thermoregulation