title: Time-related changes of radiofrequency ablation lesion in the normal rabbit liver: findings of magnetic resonance imaging and histopathology.
abstract: OBJECTIVE
  To study time-related magnetic resonance imaging (MRI) and histopathological findings after radiofrequency ablation (RFA) in the normal liver.
  
  
  METHODS
  Under ultrasound guidance, RFA was performed in 22 rabbits with a 15-gauge expandable probe inserted into the liver. The RF power was applied at 10 W initially with a 5-W increment every minute until RF power "roll-off" occurred. The rabbits subjected to postmortem MRI at 3 days (n = 6), 2 weeks (n = 6), 4 weeks (n = 6), and 12 weeks (n = 4) after RFA. Spin-echo (SE) T(1)-weighted image (WI) (TR/TE=500/12) and fast SE T2-WI (TR/TE= 3500/99) were obtained. The liver specimens were excised and processed for conventional histologic study. The MRI and pathologic findings were compared qualitatively and quantitatively.
  
  
  RESULTS
  The lesion diameters measured with MRI and liver specimen were well correlated (P < 0.05). The coagulated regions presented 2 of 4 laminar patterns on T1/T2-WI 3 days after RFA, and 2 of 3 laminar patterns on T1/T2-WI 2 to 4 weeks after RFA. 12 weeks after RFA, the signal intensity in coagulated regions increased on T1-WI with a 2-laminar pattern still visible on T2-WI, the same as that of 2 to 4 weeks. The observed pathologic changes (enlarged sinusoids, marginal fibrous tissue and hepatocyte degeneration) could be responsible for the MRI laminar patterns and signal intensity changes.
  
  
  CONCLUSIONS
  The time-related pathologic changes of RFA lesions in rabbit livers can be reflected as laminar patterns on MR images. Understanding of the zone structure of the lesions is useful for the evaluation of follow-up MRI.
authors.affiliation: Department of Diagnostic Radiology, Tohoku University Graduated School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, 980-8574, Japan. mtsuda@rad.med.tohoku.ac.jp
authors.forename: Masashi
authors.initials: M
authors.lastname: Tsuda
authors.forename: Hiroya
authors.initials: H
authors.lastname: Rikimaru
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Majima
authors.forename: Takayuki
authors.initials: T
authors.lastname: Yamada
authors.forename: Haruo
authors.initials: H
authors.lastname: Saito
authors.forename: Tadashi
authors.initials: T
authors.lastname: Ishibashi
authors.forename: Shoki
authors.initials: S
authors.lastname: Takahashi
authors.forename: Hideo
authors.initials: H
authors.lastname: Miyachi
authors.forename: Mareyuki
authors.initials: M
authors.lastname: Endoh
authors.forename: Shogo
authors.initials: S
authors.lastname: Yamada
mesh_terms: D000818:Animals; D017115:Catheter Ablation; D008099:Liver / Q000473:pathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D011817:Rabbits; D011846:Radio Waves; D013997:Time Factors