Impact of Liver Vasculature on Electric Field Distribution during Electroporation Treatments: An Anatomically Realistic Numerical Study

Abstract

Abstract-Electroporation is the phenomenon in which cell membrane permeability is increased by exposing the cell to high intensity electric fields. In living tissues, such permeabilization boost can be used in order to enhance the penetration of drugs or DNA plasmids or to destroy undesirable cells and it is typically performed by applying pulsed high voltages across needle electrodes. When used for ablation, and particularly in the context of liver tumors, it is often claimed that in contrast with thermal ablation techniques, electroporation is not severely impacted by the presence of large blood vessels because the heat sinking characteristic of those is not relevant for the electric field distribution. However, blood vessels do distort the electric field distribution because of their high inner conductivity. The goal of the study presented here is to numerically analyze the relevance of such distortion in a clinical scenario. An anatomically realistic model of the liver and its vasculature within an abdominal section was implemented. The blood vessels ranged from 0.3 to 6.3 mm in diameter and from 24 to 68.56 mm in length. A series of simulations with plausible random locations and depths (needle tips from 10 to 25mm within the liver) for the electrode pairs was conducted. Locations and depths were carefully verified so that the electrodes did not penetrate the vessels. The results were compared to those assuming that liver tissue is homogeneous. These comparisons indicate that volume error caused by neglecting the presence of vessels is less than 3%, which can be considered negligible if compared to other error sources. However, it was noticed that if the treated region comprises vessels or is very close to them, undertreated and over treated spots will appear around the vessels. Since undertreated spots may imply that tumor cells remain viable after treatment, caution is advised.

Incorporation of the Blood Vessel Wall into Electroporation Simulations

“…In a past numerical study focused on liver ablation by irreversible electroporation (IRE), we noticed that, although the presence of large blood vessels does not distort very significantly the treated volume, sub-lethal regions (i.e. too low electric field magnitude) can appear around the blood vessels [2]. The presence of such sub-lethal regions has also been reported recently in another numerical study [3].…”

“…Interestingly, the differences are larger where the sublethal regions appeared around the blood vessels in the IRE study reported in [2]. That is, at the vessel poles perpendicular to the electric field (axis defined by the two electrodes).…”

“…By modeling the wall it appears that those regions of depressed electric field magnitude are less intense. However, it must be noted that the electric field magnitude is still significantly lower at those regions and the cautionary remark in [2] still remains in effect. That is, clinicians performing IRE should look for signs of tumor recurrence around the vessels because under-treatment may have occurred there.…”

“…Last, the conductivity of blood is set at 0.6S/m as mean value of what can be encountered in the literature [2,12].…”

“…In the numerical study reported in [2], the vessels were simply modeled as homogeneous regions with a conductivity equal to that of the blood (this model is referred to as the "blood model" in the following sections). However, blood vessels are not just blood filled cavities within parenchyma; blood vessels contain a wall that separates blood from the parenchyma.…”