title: A dual-slot microwave antenna for more spherical ablation zones: ex vivo and in vivo validation.
abstract: OBJECTIVE
  To compare the performance of a microwave antenna design with two annular slots to that of a monopole antenna design in creating a more spherical ablation zone.
  
  
  METHODS
  Animal care and use committee approval was obtained before in vivo experiments were performed. Microwave ablation zones were created by using dual-slot and monopole control antennas for 2, 5, and 10 minutes at 50 and 100 W in ex vivo bovine livers. Dual-slot and monopole antennas were then used to create ablation zones at 100 W for 5 minutes in in vivo porcine livers, which also underwent intraprocedural imaging. Ablation diameter, length, and aspect ratio (diameter ÷ length) were measured at gross pathologic examination and compared at each combination of power and time by using the paired Student t test. A P value less than .05 was considered to indicate a significant difference. Aspect ratios closer to 1 reflected a more spherical ablation zone.
  
  
  RESULTS
  The dual-slot antenna created ablation zones with a higher aspect ratio at 50 W for 2 minutes (0.75 vs 0.53, P = .003) and 5 minutes (0.82 vs 0.63, P = .053) than did the monopole antenna in ex vivo liver tissue, although the difference was only significant at 2 minutes. At 100 W, the dual-slot antenna had a significantly higher aspect ratio at 2 minutes (0.52 vs 0.42, P = .002). In vivo studies showed significantly higher aspect ratios at 100 W for 5 minutes (0.63 vs 0.53, respectively, P = .029). Intraprocedural imaging confirmed this characterization, showing higher rates of ablation zone growth and heating primarily at the early stages of the ablation procedure when the dual-slot antenna was used.
  
  
  CONCLUSIONS
  The dual-slot microwave antenna created a more spherical ablation zone than did the monopole antenna both in vivo and ex vivo liver tissue. Greater control over power delivery can potentially extend the advantages of the dual-slot antenna design to higher power and longer treatment times.
authors.affiliation: Departments of Radiology, Biomedical Engineering, and Chemistry, University of Wisconsin, 1111 Highland Ave, WIMR 1303-O, Madison, WI 53705, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Chiang
authors.forename: Kieran A
authors.initials: KA
authors.lastname: Hynes
authors.forename: Mariajose
authors.initials: M
authors.lastname: Bedoya
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Brace
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D004867:Equipment Design; D008099:Liver / Q000000981:diagnostic imaging / Q000601:surgery*; D008872:Microwaves; D011857:Radiographic Image Interpretation, Computer-Assisted; D013552:Swine; D014057:Tomography, X-Ray Computed