title: High-powered gas-cooled microwave ablation: shaft cooling creates an effective stick function without altering the ablation zone.
abstract: OBJECTIVE
  The purpose of our study was to validate the ability of a new gas-cooled microwave device to secure antennas into tissue before ablation via shaft cooling and to verify that such cooling does not compromise the intended ablation.
  
  
  METHODS
  The force required to extract several types of applicators from ex vivo bovine liver before and after ablation was measured. Six groups were compared: cooled needle and multitined radiofrequency electrodes, secured and unsecured cryoprobes, and gas-cooled microwave antennas (n = 6 each). Ablations were next created in in vivo porcine livers for 2 and 10 minutes (n = 6 each) using the gas-cooled microwave system at 140 W. Extraction force was again measured before and after ablation and compared between groups using analysis of variance with post hoc Student t tests. Histologic analysis of the ablation zone was performed to evaluate cellular necrosis along the antenna shaft.
  
  
  RESULTS
  Ex vivo, the secured cryoprobe and microwave antenna required significantly more force to remove than unsecured radiofrequency, cryoprobe, and microwave applicators (p < 0.05, all comparisons). The multitined radiofrequency electrode and cooled radiofrequency electrode required significantly more force to remove after ablation than before ablation (p = 0.006 and 0.02, respectively). In vivo, the secured antenna required significantly more force to remove before ablation than after ablation at both 2 (p < 0.0001) and 10 minutes (p < 0.0001). There was no histologic evidence of cell preservation along the antenna shaft.
  
  
  CONCLUSIONS
  The gas cooling used in this microwave device can effectively secure antennas into tissue without altering ablation shape or reducing the intended thermal damage.
authors.affiliation: Department of Radiology, University of Wisconsin, E3/311 CSC, 600 Highland Ave, Madison, WI 53792, USA.
authors.forename: Erica M
authors.initials: EM
authors.lastname: Knavel
authors.forename: J Louis
authors.initials: JL
authors.lastname: Hinshaw
authors.forename: Meghan G
authors.initials: MG
authors.lastname: Lubner
authors.forename: Anita
authors.initials: A
authors.lastname: Andreano
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Warner
authors.forename: Fred T
authors.initials: FT
authors.lastname: Lee
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Brace
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D004566:Electrodes; D005740:Gases; D066298:In Vitro Techniques; D008099:Liver / Q000601:surgery*; D008872:Microwaves / Q000627:therapeutic use*; D013552:Swine
chemical_list: D005740:Gases