title: Comparison of two fiber-optical temperature measurement systems in magnetic fields up to 9.4 Tesla.
abstract: OBJECTIVE
  Precise temperature measurements in the magnetic field are indispensable for MR safety studies and for temperature calibration during MR-guided thermotherapy. In this work, the interference of two commonly used fiber-optical temperature measurement systems with the static magnetic field B0 was determined.
  
  
  METHODS
  Two fiber-optical temperature measurement systems, a GaAs-semiconductor and a phosphorescent phosphor ceramic, were compared for temperature measurements in B0 . The probes and a glass thermometer for reference were placed in an MR-compatible tube phantom within a water bath. Temperature measurements were carried out at three different MR systems covering static magnetic fields up to B0  = 9.4T, and water temperatures were changed between 25°C and 65°C.
  
  
  RESULTS
  The GaAs-probe significantly underestimated absolute temperatures by an amount related to the square of B0 . A maximum difference of ΔT = -4.6°C was seen at 9.4T. No systematic temperature difference was found with the phosphor ceramic probe. For both systems, the measurements were not dependent on the orientation of the sensor to B0 .
  
  
  CONCLUSIONS
  Temperature measurements with the phosphor ceramic probe are immune to magnetic fields up to 9.4T, whereas the GaAs-probes either require a recalibration inside the MR system or a correction based on the square of B0.
authors.affiliation: University Medical Center Freiburg, Radiology - Medical Physics, Freiburg, Germany.
authors.forename: Waltraud B
authors.initials: WB
authors.lastname: Buchenberg
authors.forename: Tetiana
authors.initials: T
authors.lastname: Dadakova
authors.forename: Jens
authors.initials: J
authors.lastname: Groebner
authors.forename: Michael
authors.initials: M
authors.lastname: Bock
authors.forename: Bernd
authors.initials: B
authors.lastname: Jung
mesh_terms: D001152:Arsenicals; D002138:Calibration; D004574:Electromagnetic Fields; D004869:Equipment Safety; D005336:Fiber Optic Technology / Q000295:instrumentation*; D005708:Gallium; D006979:Hyperthermia, Induced / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation*; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity; D062125:Thermometry / Q000295:instrumentation*
chemical_list: D001152:Arsenicals; C043055:gallium arsenide; D005708:Gallium
keywords: MR safety; MR thermometry; fiber-optical temperature measurement; temperature measurements in high magnetic fields