Objective: The purpose of this study was to prospectively characterize and optimize irreversible electroporation ablation to determine the best parameters to achieve the largest target zones of coagulation for two electrodes.
Materials and methods: Ultrasound-guided irreversible electroporation ablation (n=110) was performed in vivo in 25 pig livers using two 18-gauge electroporation electrodes and an irreversible electroporation generator. Five variables for energy deposition and electrode configuration were sequentially studied: number of electrical pulses (n=20-90), length of pulses (20-100 microseconds), generator voltage (2250-3000 V), interelectrode spacing (1.5-2.5 cm), and length of active electrode exposure (1.0-3.0 cm). Zones of ablation were determined at gross pathology and histopathology 2-3 hours after irreversible electroporation. Dimensions were compared and subjected to statistical analysis.
Results: For 1.5-cm spacing and 2-cm electrode exposure at 2250 V, there was no statistical difference in the size of coagulation when varying the number or length of pulses from 50 to 90 repetitions or 50-100 microseconds, respectively, with each parameter combination yielding 3.0±0.4×1.7±0.4×3.0±0.6 cm (width, depth, and height, respectively). Yet, increasing the pulse width or number over 70 caused increased hyperechogenic or gas and coagulation around the electrode. Increasing the voltage from 2250-3000 V for 70 pulses of 70 microseconds increased coagulation to 3.1±0.4×2.0±0.2 cm (p<0.01 for depth). Greater coagulation width of 3.9±0.5 cm (p<0.01) was achieved at 2-cm interelectrode spacing (with similar depth of 1.9±0.4 cm). However, consistent results required 90 repetitions and a 100-microsecond pulse width; 2.5-cm spacing resulted in two separate zones of ablation. Although electrode exposure did not influence width or depth, a linear correlation (r2=0.77) was noted for height, which ranged from 2.0±0.2-5.0±0.8 cm (for 1- and 3-cm exposures, respectively).
Conclusion: Predictable zones of tissue destruction can be achieved for irreversible electroporation. Ablation dimensions are sensitive to multiple parameters, suggesting that precise technique and attention to detail will be particularly important when using this modality.