title: Diffusion-weighted imaging during MR-guided radiofrequency ablation of hepatic malignancies: analysis of immediate pre- and post-ablative diffusion characteristics.
abstract: BACKGROUND
  Previous studies have shown a benefit of magnetic resonance (MR)-diffusion-weighted imaging (DWI) for follow-up after liver radiofrequency (RF) ablation. However, no data are available concerning acute changes of DWI characteristics immediately after RF ablation.
  
  
  OBJECTIVE
  To analyze and compare the MR-diffusion characteristics of pre-interventional hepatic malignancies and the ablation zone during successful MR-guided RF ablation.
  
  
  METHODS
  This retrospective study was conducted in accordance with the guidelines of the local institutional review board. Forty-seven patients with 29 HCC (24 patients) and 30 hepatic metastases (23 patients) underwent MR-guided radiofrequency ablation including DWI before and immediately after ablation (b =  0, 400, 800 s/mm(2)). Two reviewers (A and B) analyzed DWI with focus on detectability of the tumor before ablation and characteristics of the coagulative area after treatment. Mean apparent diffusion coefficient (ADC) was compared between liver, untreated tumor, and hyperintense areas in post-ablative DWI (b = 800 s/mm(2)) with the paired Student's t-test.
  
  
  RESULTS
  Pre-ablative: the reviewers classified 19/29 (A) and 23/29 (B) HCC and 25/30 (A and B) metastases as detectable in DWI. Post-ablative: a hyperintense rim surrounding the ablation zone was observed in 28/29 treated HCC and 30/30 treated metastases (A and B). A homogenous hypointense central ablation zone was found in 18/29 (A) and 20/29 (B) treated HCC and 17/30 (A & B) treated metastases in DWI. ADC of the rim was significantly lower than ADC of the liver (P < 0.001).
  
  
  CONCLUSIONS
  DWI enables visualization of the target tumor in MR-guided liver radiofrequency ablation in most cases. A common post-ablative DWI finding is a hyperintense rim with decreased ADC surrounding the ablation zone.
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany Ruediger.Hoffmann@med.uni-tuebingen.de.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hoffmann
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Rempp
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Schraml
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Schwenzer
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Grözinger
authors.affiliation: Department of Clinical Epidemiology and Applied Biometry, Eberhard Karls University, Tübingen, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Blumenstock
authors.affiliation: Center for Applied Medical Imaging, Siemens Corporate Research, Germany and Baltimore, MD, USA.
authors.forename: Eva
authors.initials: E
authors.lastname: Rothgang
authors.affiliation: Department of Radiology, Minimally Invasive Therapies and Nuclear Medicine, SLK-Kliniken Heilbronn GmbH, Heilbronn, Germany.
authors.forename: Philippe L
authors.initials: PL
authors.lastname: Pereira
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Claus D
authors.initials: CD
authors.lastname: Claussen
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University, Tübingen, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Clasen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006528:Carcinoma, Hepatocellular / Q000473:pathology* / Q000601:surgery*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011182:Postoperative Care / Q000379:methods; D011300:Preoperative Care / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods*; D016896:Treatment Outcome
keywords: Radiofrequency ablation; ablation zone; diffusion-weighted imaging; interventional MRI; magnetic resonance imaging