title: Percutaneous radiofrequency tissue ablation: optimization of pulsed-radiofrequency technique to increase coagulation necrosis.
abstract: OBJECTIVE
  To develop a computerized algorithm for pulsed, high-current percutaneous radiofrequency (RF) ablation, which maximally increases the extent of induced coagulation necrosis.
  
  
  METHODS
  An automated, programmable algorithm for pulsed-RF deposition was designed to permit high-current deposition by periodically reducing current for 5-30 seconds during RF application. Two strategies for pulsed-RF deposition were evaluated: (i) constant peak current (900-1,800 mA) of variable duration and (ii) variable peak current (1,200-2,000 mA) for a specified minimum duration. The extent of induced coagulation was compared to results obtained with continuous (lower current) RF application. Trials were performed in ex vivo calf liver (n = 115) and in vivo porcine liver (n = 30) and muscle (n = 18) with use of 2-4-cm tip, internally cooled electrodes.
  
  
  RESULTS
  For 3-cm electrodes in ex vivo liver, applying pulsed-RF with constant peak current for 12 minutes produced 3.5 cm +/- 0.2 of necrosis. Greater necrosis was produced with use of the variable current strategy, in which 4.5 cm +/- 0.2 of coagulation was achieved with use of an initial current > or =1,500 mA (minimum peak-RF duration of 10 sec, with 15 sec of reduced current to 100 mA between peaks; P < .01). This variable peak current algorithm also produced 3.7 cm +/- 0.6 of necrosis in in vivo liver, and 6.5 cm +/- 0.9 in in vivo muscle. Without pulsing, a maximum of 750 mA, 1,100 mA, and 1,500 mA could be applied in ex vivo liver, in vivo liver, and in vivo muscle, respectively, which resulted in 2.9 cm +/- 0.2, 2.4 cm +/- 0.2, and 5.1 cm +/- 0.4 of coagulation (P < .05, all comparisons).
  
  
  CONCLUSIONS
  A variable peak current algorithm for pulsed-RF deposition can increase coagulation necrosis diameter over other ablation strategies. This innovation may ultimately enable the percutaneous treatment of larger tumors.
authors.affiliation: Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
authors.forename: S N
authors.initials: SN
authors.lastname: Goldberg
authors.forename: M C
authors.initials: MC
authors.lastname: Stein
authors.forename: G S
authors.initials: GS
authors.lastname: Gazelle
authors.forename: R G
authors.initials: RG
authors.lastname: Sheiman
authors.forename: J B
authors.initials: JB
authors.lastname: Kruskal
authors.forename: M E
authors.initials: ME
authors.lastname: Clouse
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000379:methods*; D002417:Cattle; D066298:In Vitro Techniques; D008099:Liver / Q000473:pathology* / Q000601:surgery; D018482:Muscle, Skeletal / Q000473:pathology / Q000601:surgery; D009336:Necrosis; D013552:Swine; D013813:Therapy, Computer-Assisted