title: DCE-MRI and IVIM-MRI of rabbit Vx2 tumors treated with MR-HIFU-induced mild hyperthermia.
abstract: BACKGROUND
  The purpose of this study is to investigate whether changes could be detected in dynamic contrast-enhanced (DCE) and intra-voxel incoherent motion (IVIM) MR parameters upon MR-guided high-intensity focused ultrasound (MR-HIFU)-induced hyperthermia in a rabbit Vx2 tumor model.
  
  
  METHODS
  Five Vx2 tumor-bearing New Zealand white rabbits were treated with hyperthermia using a clinical MR-HIFU system. Data were acquired before and after hyperthermia. For the DCE analysis, the extended Tofts model was used. For the IVIM analysis, a Bayesian approach was used. Maps were reconstructed of the DCE parameters (K (trans), k ep, and v p ) and IVIM parameters (D t , f p , and D p ). Individual parameter histograms and two-dimensional cross-correlation histograms were constructed to analyze changes in the parameters after hyperthermia. Changes in median values were tested for statistical significance with the Mann-Whitney U test.
  
  
  RESULTS
  The MR temperature measurements confirmed that mild hyperthermia (40 to 42 °C) was successfully achieved in all rabbits. One rabbit died during treatment and was excluded from the analysis. In the remaining four rabbits, an increase in D t was observed. In three rabbits, an increase in K (trans) was observed, while in the other rabbits, all three DCE parameter values decreased. Mixed changes were seen for v p and f p .
  
  
  CONCLUSIONS
  Changes in DCE and IVIM parameters were detected after hyperthermia and were variable between the rabbits. DCE- and IVIM-MRI may be promising tools to assess tumor responses to hyperthermia. Further research in a larger number of subjects is necessary in order to assess their value for treatment response monitoring.
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Mie K
authors.initials: MK
authors.lastname: Lam
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Chris
authors.initials: C
authors.lastname: Oerlemans
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: Froeling
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Roel
authors.initials: R
authors.lastname: Deckers
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Angelique D
authors.initials: AD
authors.lastname: Barten-Van Rijbroek
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Chrit T W
authors.initials: CT
authors.lastname: Moonen
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Clemens
authors.initials: C
authors.lastname: Bos
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Lambertus W
authors.initials: LW
authors.lastname: Bartels
keywords: Dynamic contrast-enhanced MRI; Hyperthermia; Intra-voxel incoherent motion MRI; MR-HIFU