title: In vivo T2 -based MR thermometry in adipose tissue layers for high-intensity focused ultrasound near-field monitoring.
abstract: OBJECTIVE
  During MR-guided high-intensity focused ultrasound (HIFU) therapy, ultrasound absorption in the near field represents a safety risk and limits efficient energy deposition at the target. In this study, we investigated the feasibility of using T2 mapping to monitor the temperature change in subcutaneous adipose tissue layers.
  
  
  METHODS
  The T2 temperature dependence and reversibility was determined for fresh adipose porcine samples. The accuracy was evaluated by comparing T2 -based temperature measurements with probe readings in an ex vivo HIFU experiment. The in vivo feasibility of T2 -based thermometry was studied during HIFU ablations in the liver in pigs and of uterine fibroids in human patients.
  
  
  RESULTS
  T2 changed linearly and reversibly with temperature with an average coefficient of 5.2 ± 0.1 ms/°C. For the ex vivo HIFU experiment, the difference between the T2 -based temperature change and the probe temperature was <0.9°C. All in vivo experiments showed temperature-related T2 changes in the near field directly after sonications. As expected, considerable intersubject variations in the cooling times were measured in the in vivo porcine experiments.
  
  
  CONCLUSIONS
  The reversibility and linearity of the T2 -temperature dependence of adipose tissue allows for the monitoring of the temperature in the subcutaneous adipose tissue layers.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Paul
authors.initials: P
authors.lastname: Baron
authors.forename: Mario
authors.initials: M
authors.lastname: Ries
authors.forename: Roel
authors.initials: R
authors.lastname: Deckers
authors.forename: Martijn
authors.initials: M
authors.lastname: de Greef
authors.forename: Jukka
authors.initials: J
authors.lastname: Tanttu
authors.forename: Max
authors.initials: M
authors.lastname: Köhler
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
authors.forename: Chrit T W
authors.initials: CT
authors.lastname: Moonen
authors.forename: Lambertus W
authors.initials: LW
authors.lastname: Bartels
mesh_terms: D000273:Adipose Tissue / Q000502:physiology* / Q000528:radiation effects / Q000601:surgery*; D000818:Animals; D001831:Body Temperature / Q000502:physiology* / Q000528:radiation effects; D005260:Female; D019220:High-Energy Shock Waves; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods; D013552:Swine; D013817:Thermography / Q000379:methods*
keywords: MR thermometry; T2 mapping; high-intensity focused ultrasound; thermal therapy