title: Magnetic resonance temperature imaging of laser-induced thermotherapy: assessment of fast sequences in ex vivo porcine liver.
abstract: OBJECTIVE
  To evaluate magnetic resonance sequences for T(1) and proton resonance frequency (PRF) thermometry during laser-induced thermotherapy (LITT) in liver tissue.
  
  
  METHODS
  During LITT (1064 nm; 30 W; 3-cm diffuser; 2-3 min) in ex vivo porcine liver, temperature was measured (25-70°C) utilizing a fiberoptic thermometer and MRI was performed with a 1.5-T scanner through the following sequences: segmented echo planar imaging (seg-EPI) for the PRF method; fast low-angle shot (FLASH), inversion-recovery turbo FLASH (IRTF), saturation-recovery turbo FLASH (SRTF) and true-fast imaging (TRUFI) for the T(1) method. Phase angle and signal amplitude (regarding PRF/T(1)) was recorded in regions of interest, on images under fiberoptic probe tips. Sequences' thermal coefficients were determined by calibrating phase angle and signal amplitude against temperature and subsequently validated.
  
  
  RESULTS
  Coefficients of -0.0089 ± 0.0003 ppm °C(-1) (seg-EPI) and -0.917 ± 0.046, -1.166 ± 0.058, -1.038 ± 0.054 and -1.443 ± 0.118°C(-1) (FLASH, IRTF, SRTF and TRUFI, respectively) were obtained. Precisions of 0.71, 1.34, 2.07, 2.44 and 3.21°C and, through Bland-Altman analysis, accuracies of -0.67, 0.79, 1.65, 1.57 and 2.13°C (seg-EPI, FLASH, IRTF, SRTF and TRUFI, respectively) were determined.
  
  
  CONCLUSIONS
  The PRF method with seg-EPI sequence is preferred for thermometry during LITT owing to higher precision and accuracy. Among T(1)-method sequences, FLASH showed higher accuracy and robustness.
authors.affiliation: Institute for Diagnostic & Interventional Radiology, Johann Wolfgang Goethe-University Hospital, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany. babak.bazrafshan@kgu.de
authors.forename: Babak
authors.initials: B
authors.lastname: Bazrafshan
authors.forename: Frank
authors.initials: F
authors.lastname: Hübner
authors.forename: Parviz
authors.initials: P
authors.lastname: Farshid
authors.forename: Jijo
authors.initials: J
authors.lastname: Paul
authors.forename: Renate
authors.initials: R
authors.lastname: Hammerstingl
authors.forename: Vitali
authors.initials: V
authors.lastname: Vogel
authors.forename: Werner
authors.initials: W
authors.lastname: Mäntele
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Vogl
mesh_terms: D000818:Animals; D006979:Hyperthermia, Induced / Q000295:instrumentation / Q000379:methods*; D066298:In Vitro Techniques; D053685:Laser Therapy; D007834:Lasers; D008099:Liver / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D013552:Swine; D062125:Thermometry / Q000379:methods*