title: Morphologic and functional changes in nontumorous liver tissue after radiofrequency ablation in an in vivo model: comparison of 18F-FDG PET/CT, MRI, ultrasound, and CT.
abstract: Rimlike contrast enhancement on morphologic imaging and increased tracer uptake on (18)F-FDG PET in the periphery of the necrosis can hamper differentiation of residual tumor from regenerative tissue after radiofrequency ablation of liver lesions. This study used MRI, CT, ultrasound, and (18)F-FDG PET/CT to assess the typical appearance of lesions in nontumorous animal liver tissue after radiofrequency ablation.
  
  
  METHODS
  Lesions were created by radiofrequency ablation of normal liver parenchyma in 21 minipigs. Follow-up was performed by 3 contrast-enhanced morphologic modalities-MRI, CT, and ultrasound-and by (18)F-FDG PET/CT immediately, 3 and 10 d, and 1, 2, 3, and 6 mo after radiofrequency ablation. Images were evaluated qualitatively for areas of increased enhancement and regions of elevated tracer uptake. Furthermore, all images were assessed quantitatively by determination of ratios comparing enhancement/tracer uptake in the periphery of the necrosis with enhancement/tracer uptake in normal liver parenchyma. Imaging findings were compared with histopathology findings.
  
  
  RESULTS
  Immediately after radiofrequency ablation, no increase in (18)F-FDG uptake was visible, whereas elevated enhancement was noticed in the periphery of the necrosis on all morphologic imaging procedures. At further follow-up, an area of rimlike increase in (18)F-FDG uptake surrounding the necrosis was detected on PET/CT. The rimlike pattern of increased enhancement in the arterial phase was present for all liver lesions on CT, MRI, and ultrasound, especially between day 3 and month 1 after the radiofrequency ablation. Both elevated glucose metabolism and enhancement persisted for 6 mo postinterventionally. Histologic examination showed a hemorrhagic border converting into a regeneration capsule.
  
  
  CONCLUSIONS
  If performed immediately after radiofrequency ablation, (18)F-FDG PET/CT probably has benefits over those of morphologic imaging procedures when assessing liver tissue for residual tumor. Later follow-up may be hampered by visualization of peripheral hyperperfusion and tissue regeneration. Further studies on a patient population are essential.
authors.affiliation: Department of Diagnostic and Interventional Radiology and Neuroradiology, University Duisburg-Essen, Essen, Germany. florian.vogt@uni-essen.de
authors.forename: Florian M
authors.initials: FM
authors.lastname: Vogt
authors.forename: Gerald
authors.initials: G
authors.lastname: Antoch
authors.forename: Patrick
authors.initials: P
authors.lastname: Veit
authors.forename: Lutz S
authors.initials: LS
authors.lastname: Freudenberg
authors.forename: Nina
authors.initials: N
authors.lastname: Blechschmid
authors.forename: Olaf
authors.initials: O
authors.lastname: Diersch
authors.forename: Andreas
authors.initials: A
authors.lastname: Bockisch
authors.forename: Jörg
authors.initials: J
authors.lastname: Barkhausen
authors.forename: Hilmar
authors.initials: H
authors.lastname: Kuehl
mesh_terms: D000818:Animals; D017115:Catheter Ablation; D019788:Fluorodeoxyglucose F18; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009336:Necrosis; D018365:Neoplasm, Residual; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D013552:Swine; D013556:Swine, Miniature; D014057:Tomography, X-Ray Computed / Q000379:methods; D014463:Ultrasonography
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18