title: Irreversible electroporation: treatment effect is susceptible to local environment and tissue properties.
abstract: OBJECTIVE
  To study the effects of the surrounding electrical microenvironment and local tissue parameters on the electrical parameters and outcome of irreversible electroporation (IRE) ablation in porcine muscle, kidney, and liver tissue.
  
  
  METHODS
  Animal Care and Use Committee approval was obtained, and National Institutes of Health guidelines were followed. IRE ablation (n = 90) was applied in muscle (n = 44), kidney (n = 28), and liver (n = 18) tissue in 18 pigs. Two electrodes with tip exposure of 1.5-2 cm were used at varying voltages (1500-3000 V), pulse repetitions (n = 70-100), pulse length (70-100 µsec), and electrode spacing (1.5-2 cm). In muscle tissue, electrodes were placed exactly parallel, in plane, or perpendicular to paraspinal muscle fibers; in kidney tissue, in the cortex or adjacent to the renal medulla; and in liver tissue, with and without metallic or plastic plates placed 1-2 cm from electrodes. Ablation zones were determined at gross pathologic (90-120 minutes after IRE) and immunohistopathologic examination (6 hours after) for apoptosis and heat-shock protein markers. Multivariate analysis of variance with multiple comparisons and/or paired t tests and regression analysis were used for analysis.
  
  
  RESULTS
  Mean (± standard deviation) ablation zones in muscle were 6.2 cm ± 0.3 × 4.2 cm ± 0.3 for parallel electrodes and 4.2 cm ± 0.8 × 3.0 cm ± 0.5 for in-plane application. Perpendicular orientation resulted in a cross-shaped zone. Orientation significantly affected IRE current applied (28.5-31.7A for parallel, 29.5-39.7A for perpendicular; P = .003). For kidney cortex, ovoid zones of 1.5 cm ± 0.1 × 0.5 cm ± 0.0 to 2.5 cm ± 0.1 × 1.3 cm ± 0.1 were seen. Placement of electrodes less than 5 mm from the medullary pyramids resulted in treatment effect arcing into the collecting system. For liver tissue, symmetric 2.7 cm ± 0.2 × 1.4 cm ± 0.3 coagulation areas were seen without the metallic plate but asymmetric coagulation was seen with the metallic plate.
  
  
  CONCLUSIONS
  IRE treatment zones are sensitive to varying electrical conductivity in tissues. Electrode location, orientation, and heterogeneities in local environment must be considered in planning ablation treatment. Online supplemental material is available for this article.
authors.affiliation: From the Department of Radiology, Hadassah Medical Organization, Hadassah Campus, POB 12000, Jerusalem 91120, Israel.
authors.forename: Eliel
authors.initials: E
authors.lastname: Ben-David
authors.forename: Muneeb
authors.initials: M
authors.lastname: Ahmed
authors.forename: Mohammad
authors.initials: M
authors.lastname: Faroja
authors.forename: Marwan
authors.initials: M
authors.lastname: Moussa
authors.forename: Ayelet
authors.initials: A
authors.lastname: Wandel
authors.forename: Jacob
authors.initials: J
authors.lastname: Sosna
authors.forename: Liat
authors.initials: L
authors.lastname: Appelbaum
authors.forename: Isaac
authors.initials: I
authors.lastname: Nissenbaum
authors.forename: S Nahum
authors.initials: SN
authors.lastname: Goldberg
mesh_terms: D000465:Algorithms; D000818:Animals; D017209:Apoptosis; D004553:Electric Conductivity; D018274:Electroporation / Q000379:methods*; D006360:Heat-Shock Proteins / Q000032:analysis; D007150:Immunohistochemistry; D007668:Kidney / Q000000981:diagnostic imaging / Q000601:surgery*; D008099:Liver / Q000000981:diagnostic imaging / Q000601:surgery*; D064170:Paraspinal Muscles / Q000000981:diagnostic imaging / Q000601:surgery*; D013552:Swine; D018084:Ultrasonography, Interventional
chemical_list: D006360:Heat-Shock Proteins