title: Therapy monitoring of magnetic resonance-guided radiofrequency ablation using T1- and T2-weighted sequences at 1.5 T: reliability of estimated ablation zones.
abstract: OBJECTIVE
  The aim of this study was to compare the size and shape of the indicated ablation zone using magnetic resonance (MR) imaging with different contrast weightings after MR-guided radiofrequency ablation (RFA) at 1.5 T.
  
  
  METHODS
  Magnetic resonance images of 50 patients treated for hepatic malignancies using MR-guided RFA were retrospectively evaluated. Areas indicating ablation zones in contrast-enhanced images were compared with nonenhanced T1- and T2-weighted images acquired after the intervention and 1 and 7 months after therapy. Corresponding slices were selected and registered to each other. Regions indicating ablation zones were segmented and compared. Areas in cm, positive predictive value, and sensitivity of native T1- and T2-weighted images were calculated with regard to their accordance with the contrast-enhanced images.
  
  
  RESULTS
  Directly after the intervention, the ratios between the areas of the ablation zone in the contrast-enhanced and the tested sequences were 1.02 ± 0.12 in the T1-weighted images and 2.03 ± 0.78 in the T2-weighted images. Sensitivity (portion of the coagulation zone that was correctly detected based on the tested sequences) was 0.88 ± 0.08 using the T1-weighted and 0.54 ± 0.20 using the T2-weighted images. The positive predictive values were 0.89 ± 0.06 (T1 weighted) and 0.93 ± 0.06 (T2 weighted). One month after therapy, the ratios between the areas in the contrast-enhanced and the tested sequences were 1.02 ± 0.12 in the T1-weighted images and 1.04 ± 0.25 in the T2-weighted images. Seven months after therapy, the ratios were 1.04 ± 0.16 in the T1-weighted and 1.18 ± 0.22 in the T2-weighted images.
  
  
  CONCLUSIONS
  In examinations performed directly after the intervention, the T2-weighted images tend to underestimate the ablation zone, whereas T1-weighted images clearly better reflect the ablation zone. T1-weighted images therefore seem more adequate for repetitive monitoring of MR-guided RFA at 1.5 T.
authors.affiliation: Eberhard Karls University of Tübingen, Department of Diagnostic and Interventional Radiology, Tübingen, Germany. Hansjoerg.rempp@med.uni-tuebingen.de
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Rempp
authors.forename: Johannes
authors.initials: J
authors.lastname: Unterberg
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hoffmann
authors.forename: Philippe L
authors.initials: PL
authors.lastname: Pereira
authors.forename: Fritz
authors.initials: F
authors.lastname: Schick
authors.forename: Claus D
authors.initials: CD
authors.lastname: Claussen
authors.forename: Stephan
authors.initials: S
authors.lastname: Clasen
mesh_terms: D017115:Catheter Ablation / Q000379:methods*; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D016343:Monitoring, Intraoperative / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods*; D016896:Treatment Outcome