Introduction

Electroporation is a phenomenon where cells exposed to a strong external electric field develop nano-scale pores in their plasma membrane. Typically, the pores reseal once the external electric field is removed and the cell continues functioning normally. However, if the number or size of pores formed in the membrane exceeds a certain threshold, the cell is unable to repair the pores, even after removal of the external electric field. This effect has been termed irreversible electroporation (IRE). IRE may be considered a non-thermal ablation technique, as cell death is largely due to electroporation-related factors and is not contingent on sustained changes in temperature. However, this does not completely preclude heating of the treated tissue, as Joule heating-induced damage to tissue during IRE has been seen to occur within a 2–3-mm zone adjacent to the probes. The largely non-thermal mechanism of cell lysis makes IRE an attractive option for the treatment of tumors that are contraindicated for established thermal ablation techniques. As IRE ablation seems unaffected by variations in tissue perfusion and biological heat-sink effects, it has been used to treat hypervascular tumors and lesions adjacent to large blood vessels (Figure 3.1). Unlike thermal ablation techniques, which can denature proteins and completely destroy collagenous structures within the ablation zone, ablation with IRE has been observed to spare the extracellular matrix within the treated regions. This has allowed the safe application of IRE to treat tumors abutting the bile duct or the rectum in patients (Figure 3.1).

IRE presents a new clinical paradigm for the planning and delivery of image-guided ablations. Unlike thermal ablation techniques, where the ablation zone is centered on a single ablation probe, treatment delivery using IRE is typically planned between two monopolar needle electrodes (Figure 3.2). Small variations in the geometry of probe placement can significantly affect the size and shape of the resulting effective ablation zone, affecting the volume of tissue that undergoes destruction (Figure 3.3). The strong electric fields used for IRE ablation can induce neuromuscular activation and affect physiological functions that are sensitive to electrical energy. Therefore, use of IRE in patients has special anesthesia requirements, including the use of a deep paralytic agent to reduce current-induced neuromuscular stimulation.