title: Switching monopolar radiofrequency ablation technique using multiple, internally cooled electrodes and a multichannel generator: ex vivo and in vivo pilot study.
abstract: OBJECTIVE
  We sought to determine the optimal switching time and interprobe distance for creating a large coagulation zone in the liver by switching monopolar radiofrequency ablation (RFA) technique using a prototype multichannel radiofrequency generator and multiple electrodes.
  
  
  METHODS
  Using 3, 17-gauge, internally cooled electrodes and a prototype multichannel radiofrequency (RF) generator to allow automatic switching of RF energy among 3 electrodes according to their impedance changes, RF energy was applied in a switching monopolar mode to explanted bovine livers or to the livers of 7 dogs. In the ex vivo study, we evaluated the effect of the switching time (5, 15, 30, and 60 seconds) and the interprobe distance (3 cm and 4 cm) on the mean volume of the ablation zone using the switching RFA; we then compared the ablation volume of the switching RFA group (12 minutes) with that of the overlapping RFA group (12 minutes x 3 = 36 minutes). In our preliminary in vivo experiments using 2 dogs, the electrodes were placed in a triangular array (spacing 2 cm, 3 cm, 3.5 cm, or 4 cm) and were activated for 12 minutes or 20 minutes in a monopolar mode (power output 200 W). In our primary experiments using 5 dogs, RFA in a switching mode created 10 coagulation zones at a 2- to 3-cm interprobe distance. The duration of the RFA was 12 minutes. The size and geometry of the coagulation zone also were assessed.
  
  
  RESULTS
  In this ex vivo study, switching monopolar RFA at a 3-cm interprobe distance and at a 30-second switching time allowed the creation of a large, confluent ablation zone. There was no significant difference in the mean ablation volume between the overlapping (72.9 +/- 12.6(3) cm) and the switching RFA groups (65.7 +/- 12.6 cm(3); P>0.05). In the preliminary in vivo experiments, RFA created spherical coagulations at interprobe distances of 2 cm and 3 cm but at larger distances than 3 cm, RFA created partially confluent coagulation zones. In our principal experiments, switching RFA created areas of well-defined coagulation, ie, at a 2-cm interprobe distance, the volume and short-axis coagulation diameter were 35.5+/- 5.7(3) cm and 4.6 +/- 0.5 cm, respectively, whereas at 3 cm, they were 40.7 +/- 12.8(3) cm and 4.8 +/- 0.8 cm, respectively. The mean values of the circularity (isometric ratio) of the coagulation at the 2- and 3-cm interprobe distances were 0.95 +/- 0.02, and 0.85+/- 0.06, respectively.
  
  
  CONCLUSIONS
  Our study demonstrated that switching monopolar RFA using the multichannel RF system at a 2- or 3-cm interprobe distance and at a 30-second switching time can create a large, confluent coagulation zone in the liver within a clinically acceptable time frame. We believe that this technology will provide a useful tool for the treatment of large liver tumors.
authors.affiliation: Department of Radiology, and Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea.
authors.forename: Jeong Min
authors.initials: JM
authors.lastname: Lee
authors.forename: Joon Koo
authors.initials: JK
authors.lastname: Han
authors.forename: Hyo Cheol
authors.initials: HC
authors.lastname: Kim
authors.forename: Young Hun
authors.initials: YH
authors.lastname: Choi
authors.forename: Se Hyung
authors.initials: SH
authors.lastname: Kim
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Byung Ihn
authors.initials: BI
authors.lastname: Choi
mesh_terms: D000818:Animals; D001777:Blood Coagulation; D017115:Catheter Ablation / Q000295:instrumentation / Q000379:methods*; D004285:Dogs; D004566:Electrodes; D008099:Liver / Q000502:physiology; D008113:Liver Neoplasms / Q000097:blood*; D008297:Male; D009336:Necrosis; D010865:Pilot Projects; D013997:Time Factors; D014914:Whole Blood Coagulation Time