Advanced hepatic ablation technique for creating complete cell death: irreversible electroporation

Advances in managing hepatocellular carcinoma

Multiple modalities for treatment of hepatocellular carcinoma are available, depending on tumor size and number. Surgical resection remains the gold standard, so long as the residual liver function reserve is sufficient. In patients with advanced cirrhosis, liver transplantation is the preferred option, as these patients may not have adequate hepatic reserve after resection. Salvage liver transplantation has also become an option for a select few patients who recur after surgical resection. Ablative techniques have been used for palliation as well as to either completely destroy the tumor, act as an adjunct to resection, or downstage the tumor to meet Milan criteria such that a patient may be a candidate for liver transplantation. Radiofrequency ablation, microwave ablation, chemoembolization, radioembolization, and irreversible electroporation have all been used in this capacity. Currently, sorafenib is the only US Food and Drug Administration-approved chemotherapeutic for hepatocellular carcinoma. The efficacy of sorafenib, in combination with other agents, transarterial chemoembolization, and surgical resection is currently being investigated. Sunitinib and brivanib, tyrosine kinase inhibitors, have failed as potential first- or second-line options for chemotherapy. Bevacizumab in combination with erlotinib is also currently being studied. Final analysis for ramucirumab and axitinib are pending. Tivantinib, a selective mesenchymal-epithelial transition factor (MET) inhibitor, is also undergoing clinical trials for efficacy in MET-high tumors. This review serves to emphasize the current and new technologies emerging in the treatment of hepatocellular carcinoma.

Irreversible electroporation for nonthermal tumor ablation in the clinical setting: a systematic review of safety and efficacy

PURPOSE

To provide an overview of current clinical results of irreversible electroporation (IRE), a novel, nonthermal tumor ablation technique that uses electric pulses to induce cell death, while preserving structural integrity of bile ducts and vessels.

METHODS

All in-human literature on IRE reporting safety or efficacy or both was included. All adverse events were recorded. Tumor response on follow-up imaging from 3 months onward was evaluated.

RESULTS

In 16 studies, 221 patients had 325 tumors treated in liver (n = 129), pancreas (n = 69), kidney (n = 14), lung (n = 6), lesser pelvis (n = 1), and lymph node (n = 2). No major adverse events during IRE were reported. IRE caused only minor complications in the liver; however, three major complications were reported in the pancreas (bile leak [n = 2], portal vein thrombosis [n = 1]). Complete response at 3 months was 67%-100% for hepatic tumors (93%-100% for tumors o 3 cm). Pancreatic IRE combined with surgery led to prolonged survival compared with control patients (20 mo vs 13 mo) and significant pain reduction.

CONCLUSIONS

In cases where other techniques are unsuitable, IRE is a promising modality for the ablation of tumors near bile ducts and blood vessels. This articles gives an extensive overview of the available evidence, which is limited in terms of quality and quantity. With the limitations of the evidence in mind, IRE of central liver tumors seems relatively safe without major complications, whereas complications after pancreatic IRE appear more severe. The available limited results for tumor control are generally good. Overall, the future of IRE for difficult-to-reach tumors appears promising.

Multimodality imaging to assess immediate response to irreversible electroporation in a rat liver tumor model

PURPOSE

To compare changes on ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) images after irreversible electroporation (IRE) ablation of liver and tumor tissues in a rodent hepatoma model.

MATERIALS AND METHODS

Studies received approval from the institutional animal care and use committee. Forty-eight rats were used, and N1-S1 tumors were implanted in 24. Rats were divided into groups and allocated for studies with each modality. Imaging was performed in normal liver tissues and tumors before and after IRE. MR imaging was performed in one group before and after IRE after hepatic vessel ligation. US images were graded to determine echogenicity changes, CT attenuation was measured (in Hounsfield units), and MR imaging signal-to-noise ratio (SNR) was measured before and after IRE. Student t test was used to compare attenuation and SNR measurements before and after IRE (P < .05 indicated a significant difference).

RESULTS

IRE ablation produced greater alterations to echogenicity in normal tissues than in tumors. Attenuation in ablated liver tissues was reduced compared with that in control tissues (P < .001), while small attenuation differences between ablated (42.11 HU ± 2.11) and control (45.14 HU ± 2.64) tumors trended toward significance (P = .052). SNR in ablated normal tissues was significantly altered after IRE (T1-weighted images: pre-IRE, 145.95 ± 24.32; post-IRE, 97.80 ± 18.03; P = .004; T2-weighted images, pre-IRE, 47.37 ± 18.31; post-IRE, 90.88 ± 37.15; P = .023). In tumors, SNR differences before and after IRE were not significant. No post-IRE signal changes were observed after hepatic vessel ligation.

CONCLUSION

IRE induces rapid changes on gray-scale US, unenhanced CT, and MR images. These changes are readily visible and may assist a performing physician to delineate ablation zones from the unablated surrounding parenchyma.

Molecular bioluminescence imaging as a noninvasive tool for monitoring tumor growth and therapeutic response to MRI-guided laser ablation in a rat model of hepatocellular carcinoma

OBJECTIVES

The objective of this study was to quantitatively compare tumor imaging by magnetic resonance imaging (MRI) and molecular bioluminescence imaging (BLI) and test the feasibility of monitoring the effect of MRI-guided laser ablation on tumor viability by 2-dimensional BLI and 3-dimensional diffuse luminescence tomography (3D DLIT) in an orthotopic rat model of hepatocellular carcinoma.

MATERIALS AND METHODS

This study was approved by the animal care committee. Rats underwent injection of N1S1 cells stably transfected with an empty vector (n = 3) or a heat shock element luciferase reporter (HSE-luc; n = 4) into the liver. All rats underwent MRI to assess tumor establishment and volume and 2-dimensional BLI to assess tumor luminescence at day 7 with subsequent MRI and 2D BLI and 3D DLIT in select animals at days 14 and 21. Magnetic resonance imaging-guided laser ablation of the tumor was performed with preablation and postablation 2D BLI and/or 3D DLIT (n = 2). The tumors underwent histopathologic analysis to assess tumor viability.

RESULTS

The MRI scans demonstrated hyperintense T2-weighted lesions at 3 of 3 and 4 of 4 sites in the empty vector and HSE-luc rats, respectively. Two-dimensional BLI quantitation demonstrated 23.0-fold higher radiance in the HSE-luc group compared with the empty vector group at day 7 (P < 0.01) and a significant correlation with tumor volume by MRI (r = 0.86; P < 0.03). Tumor dimensions by 3D DLIT and MRI demonstrated good agreement. Three-dimensional DLIT quantitation demonstrated better agreement with the percentage of nonviable tumor by histopathology than did 2D BLI quantitation after the MRI-guided laser ablation.

CONCLUSIONS

Bioluminescence imaging is feasible as a noninvasive, quantitative tool for monitoring tumor growth and therapeutic response to thermal ablation in a rat model of hepatocellular carcinoma.

Percutaneous ablation of peribiliary tumors with irreversible electroporation

PURPOSE

To assess biliary complications after irreversible electroporation (IRE) ablation of hepatic tumors located < 1 cm from major bile ducts.

MATERIALS AND METHODS

A retrospective review was conducted of all percutaneous IRE ablations of hepatic tumors within 1 cm of the common, left, or right hepatic ducts at a single institution from January 2011 to September 2012. Computed tomography imaging performed before and after treatment was examined for evidence of bile duct dilatation, stricture, or leakage. Serum bilirubin and alkaline phosphatase levels were analyzed for evidence of biliary injury.

RESULTS

There were 22 hepatic metastases in 11 patients with at least one tumor within 1 cm of the common, left, or right hepatic duct that were treated with IRE ablations in 15 sessions. Median tumor size treated was 3.0 cm (mean, 2.8 cm ± 1.2, range, 1.0-4.7 cm). Laboratory values obtained after IRE were considered abnormal after four treatment sessions in three patients (bilirubin, 2.6-17.6 mg/dL; alkaline phosphatase, 130-1,035 U/L); these abnormal values were transient in two sessions. Two patients had prolonged elevation of values, and one required stent placement; both of these conditions appeared to be secondary to tumor progression rather than bile duct injury.

CONCLUSIONS

This clinical experience suggests that IRE may be a treatment option for centrally located liver tumors with margins adjacent to major bile ducts where thermal ablation techniques are contraindicated. Further studies with extended follow-up periods are necessary to establish the safety profile of IRE in this setting.

The effect of blood flow on magnetic resonance imaging of non thermal irreversible electroporation

To generate an understanding of the physiological significance of MR images of Non-Thermal Irreversible Electroporation (NTIRE) we compared the following MR imaging sequences: T1W, T2W, PD, GE, and T2 SPAIR acquired after NTIRE treatment in a rodent liver model. The parameters that were studied included the presence or absence of a Gd-based contrast agent, and in vivo and ex-vivo NTIRE treatments in the same liver. NTIRE is a new minimally invasive tissue ablation modality in which pulsed electric fields cause molecularly selective cell death while, the extracellular matrix and large blood vessels remain patent. This attribute of NTIRE is of major clinical importance as it allows treatment of undesirable tissues near critical blood vessels. The presented study results suggest that MR images acquired following NTIRE treatment are all directly related to the unique pattern of blood flow after NTIRE treatment and are not produced in the absence of blood flow.

Irreversible electroporation facilitates gene transfer of a GM-CSF plasmid with a local and systemic response

BACKGROUND

Electroporation uses an electric field to induce pores in the cell membrane that can transfer macromolecules into target cells. Modulation of electrical parameters leads to irreversible electroporation (IRE), which is being developed for tissue ablation. We sought to evaluate whether the application of IRE may induce a lesser electric field in the periphery where reversible electroporation may occur, facilitating gene transfer of a granulocyte macrophage colony-stimulating factor (GM-CSF) plasmid to produce its biologic response.

METHODS

Yorkshire pigs underwent laparotomy, and IRE of the liver was performed during hepatic arterial infusion of 1 or 7 mg of a naked human GM-CSF plasmid. The serum, liver, lymph nodes, and bone marrow were harvested for analysis.

RESULTS

Human GM-CSF level rose from undetectable to 131 pg/mL in the serum at 24 hours after IRE and plasmid infusion. The liver demonstrated an ablation zone surrounded by an immune infiltrate that had greater macrophage intensity than when treated with IRE or plasmid infusion alone. This dominance of macrophages was dose dependent. Distant effects of GM-CSF were found in the bone marrow, where proliferating myeloid cells increased from 14% to 25%.

CONCLUSION

IRE facilitated gene transfer of the GM-CSF plasmid and brought about a local and systemic biologic response. This technique holds potential for tumor eradication and immunotherapy of residual cancer.

Irreversible electroporation ablation: creation of large-volume ablation zones in in vivo porcine liver with four-electrode arrays

PURPOSE

To prospectively determine optimal parameters with which to achieve defined large target zones of coagulation by using irreversible electroporation (IRE) with four-electrode arrays and the time needed to achieve this treatment effect in an in vivo animal model.

MATERIALS AND METHODS

This study was approved by the animal care and use committee. Ultrasonography (US)-guided IRE ablation (n = 90) was performed in vivo in 69 pig livers with an array of four electrodes (18 gauge) and an electroporation generator. Cardiac-gated 100-µsec IRE pulses were applied sequentially between the six sets of electrode pairs at 2250-3000 V. Multiple algorithms of energy deposition and electrode configuration were studied, including interelectrode spacing (1.5-2.5 cm), number of IRE pulses applied consecutively to each electrode pair (10, 20, 50, and 100), and number of times per cycle each electrode pair was activated (one to 10). Resultant zones of treatment were measured with US 1.5-3 hours after IRE and confirmed at gross and histopathologic examination. Data and ablation times were compared to determine the optimal algorithms with which to achieve 4-7-cm areas of treatment effect in the shortest time possible. In addition, the IRE current applied was correlated with ablation size. Data were analyzed by using analysis of variance with multiple comparisons, t tests, or nonparametric statistics.

RESULTS

For 2.5-cm spacing, ablation diameter was increased by increasing either the overall time of energy application or the number of cycles of 20 pulses (P < .01 for both). IRE application of less than four cycles (or continuous IRE application of 100 pulses) did not result in contiguous ablation. However, sequentially increasing the number of cycles of IRE from four to 10 increased both the electrical current applied (from 14.4 A ± 0.4 to 17.6 A ± 0.7, P = .0004) and ablation diameter (from 5.6 cm ± 0.3 to 6.6 cm ± 0.3, P = .001). Although division of application into cycles did not alter coagulation at 2.0- and 1.5-cm spacing, application of energy to diagonal electrode pairs increased coagulation. Thus, one 100-pulse cycle (11.0 minutes ± 1.4) produced 4.8 cm ± 0.3 of ablation for 2.0-cm spacing with diagonal pairs but only 4.1 cm ± 0.3 of ablation without diagonal pairs (7.5 minutes ± 1.0, P < .03 for both).

CONCLUSION

With four-electrode arrays, IRE can create large contiguous zones of treatment effect in clinically acceptable ablation times; parameters can be tailored to achieve a wide range of ablation sizes. Cyclical deposition of IRE application is beneficial, particularly for larger interprobe spacing, most likely owing to alterations of electrical conductivity that occur after successive applications of IRE energy.

Irreversible electroporation: treatment effect is susceptible to local environment and tissue properties

PURPOSE

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.

MATERIALS AND 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.

CONCLUSION

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.

Alternative to surgery in early stage NSCLC-interventional radiologic approaches

Interventional radiologists have a variety of techniques in their armamentarium to treat pulmonary tumors. While most therapies are targeted to metastasis or palliation, percutaneous thermal ablation represents a potential therapy for not only palliation, but to treat inoperable early stage disease. Although radiofrequency ablation (RFA) is the most studied of these ablative techniques, newer technologies of thermal ablation, such as microwave and cryoablation have emerged as additional options. In this article, we will review the three different thermal ablative modalities, including patient selection, technique, outcomes, complications, and imaging follow-up. A brief discussion of state of the art techniques such as irreversible electroporation (IRE) and catheter directed therapies will also be included.

Rapid dramatic alterations to the tumor microstructure in pancreatic cancer following irreversible electroporation ablation

AIM

NanoKnife(®) (Angiodynamics, Inc., NY, USA) or irreversible electroporation (IRE) is a newly available ablation technique to induce the formation of nanoscale pores within the cell membrane in targeted tissues. The purpose of this study was to elucidate morphological alterations following 30 min of IRE ablation in a mouse model of pancreatic cancer.

MATERIALS & METHODS

Immunohistochemistry markers were compared with diffusion-weighted MRI apparent diffusion coefficient measurements before and after IRE ablation.

RESULTS

Immunohistochemistry apoptosis index measurements were significantly higher in IRE-treated tumors than in controls. Rapid tissue alterations after 30 min of IRE ablation procedures (structural and morphological alterations along with significantly elevated apoptosis markers) were consistently observed and well correlated to apparent diffusion coefficient measurements.

DISCUSSION

This imaging assay offers the potential to serve as an in vivo biomarker for noninvasive detection of tumor response following IRE ablation.

Cancer concepts and principles: primer for the interventional oncologist-part II

This is the second of a two-part overview of the fundamentals of oncology for interventional radiologists. The first part focused on clinical trials, basic statistics, assessment of response, and overall concepts in oncology. This second part aims to review the methods of tumor characterization; principles of the oncology specialties, including medical, surgical, radiation, and interventional oncology; and current treatment paradigms for the most common cancers encountered in interventional oncology, along with the levels of evidence that guide these treatments.

Improved local and systemic anti-tumor efficacy for irreversible electroporation in immunocompetent versus immunodeficient mice

Irreversible electroporation (IRE) is a non-thermal focal ablation technique that uses a series of brief but intense electric pulses delivered into a targeted region of tissue, killing the cells by irrecoverably disrupting cellular membrane integrity. This study investigates if there is an improved local anti-tumor response in immunocompetent (IC) BALB/c versus immunodeficient (ID) nude mice, including the potential for a systemic protective effect against rechallenge. Subcutaneous murine renal carcinoma tumors were treated with an IRE pulsing protocol that used 60% of the predicted voltage required to invoke complete regressions in the ID mice. Tumors were followed for 34 days following treatment for 11 treated mice from each strain, and 7 controls from each strain. Mouse survival based on tumor burden and the progression-free disease period was substantially longer in the treated IC mice relative to the treated ID mice and sham controls for both strains. Treated IC mice were rechallenged with the same cell line 18 days after treatment, where growth of the second tumors was shown to be significantly reduced or prevented entirely. There was robust CD3+ cell infiltration in some treated BALB/C mice, with immunocytes focused at the transition between viable and dead tumor. There was no difference in the low immunocyte presence for untreated tumors, nude mice, and matrigel-only injections in both strains. These findings suggest IRE therapy may have greater therapeutic efficacy in immunocompetent patients than what has been suggested by immunodeficient models, and that IRE may invoke a systemic response beyond the targeted ablation region.

A three-dimensional in vitro tumor platform for modeling therapeutic irreversible electroporation

Irreversible electroporation (IRE) is emerging as a powerful tool for tumor ablation that utilizes pulsed electric fields to destabilize the plasma membrane of cancer cells past the point of recovery. The ablated region is dictated primarily by the electric field distribution in the tissue, which forms the basis of current treatment planning algorithms. To generate data for refinement of these algorithms, there is a need to develop a physiologically accurate and reproducible platform on which to study IRE in vitro. Here, IRE was performed on a 3D in vitro tumor model consisting of cancer cells cultured within dense collagen I hydrogels, which have been shown to acquire phenotypes and respond to therapeutic stimuli in a manner analogous to that observed in in vivo pathological systems. Electrical and thermal fluctuations were monitored during treatment, and this information was incorporated into a numerical model for predicting the electric field distribution in the tumors. When correlated with Live/Dead staining of the tumors, an electric field threshold for cell death (500 V/cm) comparable to values reported in vivo was generated. In addition, submillimeter resolution was observed at the boundary between the treated and untreated regions, which is characteristic of in vivo IRE. Overall, these results illustrate the advantages of using 3D cancer cell culture models to improve IRE-treatment planning and facilitate widespread clinical use of the technology.

Changes of apoptosis in tumor tissues with time after irreversible electroporation

Irreversible electroporation is a novel method of ablating living tissues through its non-thermal effects, unlike radiofrequency ablation which has a severe problem of heat sink. It is due to high-energy direct current which leads to permanent disruption of lipid bilayer integrity in terms of exchanges between intra- and extracellular components via nano-sized pores. That finally causes irreversible damage to cellular homeostasis. Irreversibly damaged cells may undergo apoptosis followed by necrosis with time after electroporation. This damage can make it possible to monitor the ablated area with time post-IRE through MR imaging and an ultrasound system. Most previous studies have investigated the immediate response of undesired tissue to IRE. In our study, we showed changes of tumor tissues with time post-IRE by histological analysis and MR imaging. Tissues under IRE ablation showed a peak apoptotic rate at 24 h after IRE ablation with viable tissues at the peripheral rim of treated tissues in histological analysis. This phenomenon was also observed with no enhancement on contrast-enhanced MR images due to devascularization of IRE ablated zones.

Palliative treatment of presacral recurrence of endometrial cancer using irreversible electroporation: a case report

INTRODUCTION

Irreversible electroporation (IRE) is a new minimally invasive tumor ablation technique which induces irreversible disruption of cell membrane integrity by changing the transmembrane potential resulting in cell death. Irreversible electroporation is currently undergoing clinical investigation as local tumor therapy for malignant liver and lung lesions. This is the first case report to describe the successful palliative ablation of a presacral recurrence of an endometrial cancer to achieve locoregional tumor control and pain relief.

CASE PRESENTATION

A 56-year-old Caucasian woman was referred for interventional treatment of an advanced local recurrence of endometrial cancer (11.9 × 11.6 × 14.9cm) with infiltration of the sacral bone and nerve plexus. Due to the immediate proximity to the sacral plexus, the patient could neither undergo surgical therapy nor a second radiation therapy. Due to its ablation mechanism irreversible electroporation was deemed to be the best therapy option.

CONCLUSION

We showed in this case that a large tumor mass adjacent to a bundle of neural structures, the sacral plexus, can be widely ablated by irreversible electroporation with only minor temporary impairment of the neural function, even though a large infiltrating tissue volume (941cm3) was ablated.

Intense picosecond pulsed electric fields inhibit proliferation and induce apoptosis of HeLa cells

A picosecond pulsed electric field (psPEF) is a localized physical therapy for tumors that has been developed in recent years, and that may in the future be utilized as a targeted non‑invasive treatment. However, there are limited studies regarding the biological effects of psPEF on cells. Electric field amplitude and pulse number are the main parameters of psPEF that influence its biological effects. In this study, we exposed HeLa cells to a psPEF with a variety of electric field amplitudes, from 100 to 600 kV/cm, and various pulse numbers, from 1,000 to 3,000. An MTT assay was used to detect the growth inhibition, while flow cytometry was used to determine the occurrence of apoptosis and the cell cycle of the HeLa cells following treatment. The morphological changes during cell apoptosis were observed using transmission electron microscopy (TEM). The results demonstrated that the cell growth inhibition rate gradually increased, in correlation with the increasing electric field amplitude and pulse number, and achieved a plateau of maximum cell inhibition 12 h following the pulses. In addition, typical characteristics of HeLa cell apoptosis in the experimental groups were observed by TEM. The results demonstrated that the rate of apoptosis in the experimental groups was significantly elevated in comparison with the untreated group. In the treatment groups, the rate of apoptosis was greater in the higher amplitude groups than in the lower amplitude groups. The same results were obtained when the variable was the pulse number. Flow cytometric analysis indicated that the cell cycle of the HeLa cells was arrested at the G2/M phase following psPEF treatment. Overall, our results indicated that psPEF inhibited cell proliferation and induced cell apoptosis, and that these effects occurred in a dose-dependent manner. In addition, the results demonstrated that the growth of the HeLa cells was arrested at the G2/M phase following treatment. This study may provide a foundation for further in vivo experiments, and for the potential clinical application of psPEF in the treatment of cervical cancer.

Safety and early efficacy of irreversible electroporation for hepatic tumors in proximity to vital structures

INTRODUCTION

Irreversible electroporation (IRE) has shown promise for ablation of lesions in proximity to vital structures in the preclinical setting. This study aims to evaluate the safety and efficacy of IRE for hepatic tumors in the clinical setting.

METHODS

An IRB approved prospective registry of patients undergoing IRE for hepatic tumors over a 2-year period. Factors analyzed included patient and tumor characteristics, treatment related complications, and local recurrence free survival (LRFS) for ablated lesions. LRFS was calculated according to Kaplan-Meier, with secondary analyses stratified by procedural approach (laparotomy, laparoscopy, and percutaneous) and tumor histology.

RESULTS

There were 44 patients undergoing 48 total IRE procedures, 20 colorectal mets, 14 hepatocellular, and 10 other metastatsis. Initial success was achieved in 46 (100%) treatments. Five patients had 9 adverse events, with all complications resolving within 30 days. LRFS at 3, 6, and 12 months was 97.4%, 94.6%, and 59.5%. There was a trend toward higher recurrence rates for tumors over 4 cm (HR 3.236, 95% CI: 0.585-17.891; P = 0.178).

CONCLUSIONS

IRE appears to be a safe treatment for hepatic tumors in proximity to vital structures. Further prospective evaluation is needed to determine the optimal effectiveness of IRE in relation to size and technique for IRE of the liver.

Irreversible electroporation ablation of the liver can be detected with ultrasound B-mode and elastography

BACKGROUND

Irreversible electroporation (IRE) is a novel ablation technique that induces permanent membrane permeability and cell death. We are interested in ultrasound B-mode and elastography to monitor IRE ablation in the liver.

METHODS

Yorkshire pigs underwent IRE ablation of the liver and were imaged with ultrasound B-mode and elastography. Histologic evaluation of cell death by triphenyltetrazolium chloride and hematoxylin and eosin staining was performed.

RESULTS

Elastography showed that liver ablated by IRE exhibited increased tissue stiffness with a peak strain ratio of 2.22. The IRE lesion had a discrete border without bubble artifact, and the lesion size significantly correlated with area of cell death on histology. IRE ablation was unaffected by presence of large blood vessels or bile ducts.

CONCLUSION

IRE ablation led to increased tissue stiffness that was detectable by elastography and indicative of cell death. Elastography may complement B-mode ultrasonography to monitor IRE ablation of the liver.

Irreversible electroporation for unresectable hepatocellular carcinoma: initial experience and review of safety and outcomes

The aims of this study were to evaluate the safety, feasibility and tumour response of _irreversible electroporation, a non-thermal ablation technique, for the treatment of unresectable hepatocellular carcinoma. The endpoints were safety and local treatment efficacy. Patients with unresectable tumours and tumours not amenable for radiofrequency _ablation because of their vicinity to organs vulnerable to thermal damage such as the bowel or because they were close to large blood vessels that would limit efficacy of ablation due to the heat sink effect were treated with irreversible electroporation using percutaneous _ultrasound and/or computed tomography guided electrode placement between November 2008 and _December 2009. Early, late, minor and major complications were recorded. Tumour response was determined on triphasic helical computed tomography follow-up at one month, then every three months post-procedure. Eleven patients received IRE therapy to 18 HCC lesions (Mean diameter 2.44 ± 0.99 cm; range 1.0-6.1 cm) with five patients having more than one treated HCC. Mean follow-up was 18 months (range 14-24 months). Six patients required repeat treatments for local residual or recurrent disease; two of these also had IRE for distant intrahepatic recurrence. No serious complications were observed despite seven lesions lying adjacent to important structures or organs. Four patients developed transient urinary retention and seven developed transient local post-procedure pain. After IRE therapy, 13 (72%) lesions were completely ablated with 93% success for lesions ≤ 3 cm (13/14). The local recurrence-free period was 18 ± 4 months and the distance recurrence free period was 14 ± 6 months. These preliminary results suggest that IRE is a safe and feasible technique for local ablation of HCC, particularly for lesions less than 3 cm. No major complications were encountered during this study even for tumours close to essential structures or organs.

Nonthermal irreversible electroporation: fundamentals, applications, and challenges

Tissue ablation is an essential procedure for the treatment of many diseases. In the last decade, a nonthermal tissue ablation using intensive pulsed electric fields, called nonthermal irreversible electroporation (NTIRE), has rapidly emerged. The exact mechanisms responsible for cell death by NTIRE, however, are currently unknown. Nevertheless, the technique's remarkable ability to ablate tissue in the proximity of larger blood vessels, to preserve tissue architecture, short procedure duration, and shortened postoperative recovery period rapidly moved NTIRE from bench to bed side. This work provides an overview on the development of NTIRE, its current state-of-the-art, challenges, and future needs.

Irreversible electroporation ablation: is all the damage nonthermal?

PURPOSE

To determine whether high-dose irreversible electroporation (IRE) ablation induces thermal effects in normal liver tissue.

MATERIALS AND METHODS

Animal care and use committee approval was obtained prior to the experiments. IRE ablation (n = 78) was performed by a single four-person team in vivo in 22 porcine livers by applying electric current to two 1.3-cm-diameter circular flat-plate electrodes spaced 1 cm apart. Cardiac-gated IRE pulses (n = 40-360) were systematically applied at varying voltages (1500-2900 V). End temperatures at the ablation zone center were measured and were correlated with ablation time, energy parameters, and resultant treatment effect as determined at gross pathologic and histopathologic examination. Temperatures were then monitored at the center and periphery of four ablations created by using a four-electrode IRE array (3000 V, 90 pulses per electrode pair). Data were analyzed by using multivariate analysis of variance with multiple comparisons and/or paired t tests and regression analysis, as appropriate.

RESULTS

Temperature rose above the 34°C baseline after IRE in all flat-plate experiments and correlated linearly (R(2) = 0.39) with IRE "energy dose" (product of voltage and number of pulses) and more tightly in univariate analysis with both voltage and number of pulses. Thus, mean temperatures as high as 86°C ± 3 (standard deviation) were seen for 2500 V and 270 pulses. Ablations of 90 pulses or more at 2500 V produced temperatures of 50°C or greater and classic gross and histopathologic findings of thermal coagulation (pyknotic nuclei and streaming cytoplasm). For lower IRE doses (ie, 2100 V, 90 pulses), temperatures remained below 45°C, and only IRE-associated pathologic findings (ie, swollen sinusoids, dehydrated cells, and hemorrhagic infiltrate) were seen. For the four-electrode arrays, temperatures measured 54.2°C ± 6.1 at the electrode surfaces and 38.6°C ± 3.2 at the ablation zone margin.

CONCLUSION

In some conditions of high intensity, IRE can produce sufficient heating to induce "white zone" thermal coagulation. While this can be useful in some settings to increase tumor destruction, further characterization of the thermal profile created with clinical electrodes and energy parameters is therefore needed to better understand the best ways to avoid unintended damage when ablating near thermally sensitive critical structures.

Immunologic response to tumor ablation with irreversible electroporation

Background

Irreversible electroporation (IRE) is a promising technique for the focal treatment of pathologic tissues, which involves placing minimally invasive electrodes within the targeted region. However, the knowledge about the therapeutic efficacy and immune reactions in response to IRE remains in its infancy.

Methods

In this work, to detect whether tumor ablation with IRE could trigger the immunologic response, we developed an osteosarcoma rat model and applied IRE directly to ablate the tumor. In the experiment, 118 SD rats were randomized into 4 groups: the control, sham operation, surgical resection, and IRE groups. Another 28 rats without tumor cell implantation served as the normal non-tumor-bearing group. We analyzed the changes in T lymphocyte subsets, sIL-2R and IL-10 levels in the peripheral blood one day before operation, as well as at 1, 3, 7,14 and 21 days after the operation. Moreover, splenocytes were assayed for IFN-γ and IL-4 production using intracellular cytokine staining one day before the operation, as well as at 7 and 21 days after operation.

Results

We found that direct IRE completely ablated the tumor cells. A significant increase in peripheral lymphocytes, especially CD3⁺ and CD4⁺ cells, as well as an increased ratio of CD4⁺/CD8⁺ were detectable 7 days after operation in both the IRE and surgical resection groups. Compared with the surgical resection group, the IRE group exhibited a stronger cellular immune response. The sIL-2R level of the peripheral blood in the IRE group decreased with time and was significantly different from that in the surgical resection group. Moreover, ablation with IRE significantly increased the percentage of IFN-γ-positive splenocytes.

Conclusion

These findings indicated that IRE could not only locally destroy the tumor but also change the status of cellular immunity in osteosarcoma-bearing rats. This provides experimental evidence for the clinical application of IRE in osteosarcoma treatment.

Therapeutic potential of irreversible electroporation in sarcoma

Irreversible electroporation is a newly developed nonthermal tissue ablation technique in which certain short-duration electrical fields are used to permanently permeabilize the cell membrane to disrupt cellular homeostasis. This disruption of cellular homeostasis initiates apoptosis, which leads to permanent cell death. Sarcomas are generally divided into soft-tissue and bone sarcomas based on their different mesenchymal origins and anatomical locations. Each of these sarcomas present in different ways, exhibit different behaviors and prognoses, and present unique therapeutic challenges. In this article, a series of recently conducted irreversible electroporation treatment for sarcomas based on local nonthermal ablation are summarized, and the therapeutic potential of this newly developed technique is assessed.

Irreversible electroporation of lung neoplasm: a case series

Background

Percutaneous irreversible electroporation (IRE) of lung tumors is a new minimally invasive technique which has recently been used in the treatment of soft tissue tumors.

Case Reports

The case histories are presented of two patients with unresectable malignancies in the lung, who underwent irreversible electroporation as a treatment attempt. The procedure was performed under CT guidance and was uneventful.

Conclusions

At follow up 6 months later, the tumors both appeared to have recurred. To our knowledge, no similar cases have previously been reported in the literature.

Ex vivo and in silico feasibility study of monitoring electric field distribution in tissue during electroporation based treatments

Magnetic resonance electrical impedance tomography (MREIT) was recently proposed for determining electric field distribution during electroporation in which cell membrane permeability is temporary increased by application of an external high electric field. The method was already successfully applied for reconstruction of electric field distribution in agar phantoms. Before the next step towards in vivo experiments is taken, monitoring of electric field distribution during electroporation of ex vivo tissue ex vivo and feasibility for its use in electroporation based treatments needed to be evaluated. Sequences of high voltage pulses were applied to chicken liver tissue in order to expose it to electric field which was measured by means of MREIT. MREIT was also evaluated for its use in electroporation based treatments by calculating electric field distribution for two regions, the tumor and the tumor-liver region, in a numerical model based on data obtained from clinical study on electrochemotherapy treatment of deep-seated tumors. Electric field distribution inside tissue was successfully measured ex vivo using MREIT and significant changes of tissue electrical conductivity were observed in the region of the highest electric field. A good agreement was obtained between the electric field distribution obtained by MREIT and the actual electric field distribution in evaluated regions of a numerical model, suggesting that implementation of MREIT could thus enable efficient detection of areas with insufficient electric field coverage during electroporation based treatments, thus assuring the effectiveness of the treatment.

Long term survival of mice with hepatocellular carcinoma after pulse power ablation with nanosecond pulsed electric fields

Novel therapies are needed for treating hepatocellular carcinoma (HCC) without recurrence in a single procedure. In this work we evaluated anti-neoplastic effects of a pulse power ablation (PPA) with nanosecond pulsed electric fields (nsPEFs), a non-thermal, non-drug, local, regional method and investigated its molecular mechanisms for hepatocellular carcinoma tumor ablation in vivo. An ectopic tumor model was established using C57BL/6 mice with Hepa1-6 hepatocellular carcinoma cells. Pulses with durations of 30 or 100 ns and fast rise times were delivered by a needle or ring electrode with different electric field strengths (33, 50 and 68 kV/cm), and 900 pulses in three treatment sessions (300 pulses each session) or a single 900 pulse treatment. Treated and control tumor volumes were monitored by ultrasound and apoptosis and angiogenesis markers were evaluated by immunohistochemistry. Seventy five percent of primary hepatocellular carcinoma tumors were eradicated with 900 hundred pulses at 100 ns pulses at 68 kV/cm in a single treatment or in three treatment sessions without recurrence within 9 months. Using quantitative analysis, tumors in treated animals showed nsPEF-mediated nuclear condensation (3 h post-pulse), cell shrinkage (1 h), increases in active executioner caspases (caspase-3 > -7 > -6) and terminal deoxynucleotidyl transferase dUTP nick-end-labeling (1 h) with decreases in vascular endothelial growth factor expression (7d) and micro-vessel density (14d). NsPEF ablation eliminated hepatocellular carcinoma tumors by targeting two therapeutic sites, apoptosis induction and inhibition of angiogenesis, both important cancer hallmarks. These data indicate that PPA with nsPEFs is not limited to treating skin cancers and provide a rationale for continuing to investigate pulse power ablation for hepatocellular carcinoma using other models in pre-clinical applications and ultimately in clinical trials. Based on present treatments for specific HCC stages, it is anticipated that nsPEFs could be substituted for or used in combination with ablation therapies using heat, cold or chemicals.

Image-guided tumor ablation: emerging technologies and future directions

As the trend continues toward the decreased invasiveness of medical procedures, image-guided percutaneous ablation has begun to supplant surgery for the local control of small tumors in the liver, kidney, and lung. New ablation technologies, and refinements of existing technologies, will enable treatment of larger and more complex tumors in these and other organs. At the same time, improvements in intraprocedural imaging promise to improve treatment accuracy and reduce complications. In this review, the latest advancements in clinical and experimental ablation technologies will be summarized, and new applications of image-guided tumor ablation will be discussed.

The delayed effects of irreversible electroporation ablation on nerves

OBJECTIVE

To evaluate the delayed effects of irreversible electroporation (IRE) ablation on nerves.

METHODS

The study was approved by the institutional animal care and use committee. CT-guided IRE-ablation (electric field per distance, 1,500 V/cm; pulse length, 70 μs; number of pulses, 90) of 6 sciatic nerves was performed in 6 pigs that were euthanized 2 months after ablation. The sciatic nerves were harvested immediately after euthanasia for histopathological evaluation. Sections from selected specimens were stained with haematoxylin and eosin (H&E), Masson's trichrome (MT) method for collagen, and immunohistochemistry was performed for S100 and neurofilaments (markers for Schwann cells and axons, respectively).

RESULTS

All nerves showed a preserved endoneural architecture and presence of numerous small calibre axons associated with Schwann cell hyperplasia, consistent with axonal regeneration. A fibrous scar was observed in the adjacent muscle tissue, confirming ablation at the site examined.

CONCLUSION

After IRE-ablation of nerves, the preservation of the architecture of the endoneurium and the proliferation of Schwann cells may enable axonal regeneration as demonstrated after 2 months in this study.

Pain analysis in patients with hepatocellular carcinoma: irreversible electroporation versus radiofrequency ablation-initial observations

PURPOSE

To retrospectively compare the postprocedure pain of hepatocellular carcinoma treated with irreversible electroporation (IRE) with radiofrequency ablation (RFA).

METHODS

This Health Insurance Portability and Accountability Act-compliant, institutional review board-approved study compared postprocedure pain in 21 patients (15 men, six women; mean age 61.5 years) who underwent IRE of 29 intrahepatic lesions (mean size 2.20 cm) in 28 IRE sessions with 22 patients (16 men, six women; mean age 60.2 years) who underwent RFA of 27 lesions (mean size 3.38 cm) in 25 RFA sessions. Pain was determined by patient-disclosed scores with an 11-point numerical rating scale and 24 h cumulative hydromorphone use from patient-controlled analgesia pump. Complications were noted. Statistical significance was evaluated by Fisher's exact test, the Chi-square test, and Student's t test.

RESULTS

There was no significant difference in the cumulative hydromorphone dose (1.54 mg (IRE) vs. 1.24 mg (RFA); P = 0.52) and in the mean pain score (1.96 (IRE) vs. 2.25 (RFA); P = 0.70). In nine (32.14 %) of 28 IRE sessions and 11 (44.0 %) of 25 RFA sessions, patients reported no pain. Complications occurred in three (10.7 %) of 28 IRE treatments and included pneumothorax (n = 1), pleural effusion (n = 1), and bleeding in the form of hemothorax (n = 1); one (4 %) of 25 RFA treatments included burn.

CONCLUSION

IRE is comparable to RFA in the amount of pain that patients experience and the amount of pain medication self-administered. Both modalities were well tolerated by patients. Prospective, randomized trials are necessary to further evaluate these findings.

Percutaneous ultrasound-guided irreversible electroporation: A goat liver study

Irreversible electroporation (IRE) is a new tumor ablation technique. Pulsed electric fields (PEFs) with permanent duration (100 μsec) permanently permeabilize the cell membrane, causing the formation of innumerable permanent nanopores in the cell membrane and leading to cell death. In this study, percutaneous IRE was performed on 24 goat livers under the guidance of ultrasonography (US). IRE-exposed tissues were pathologically examined and glucose-6-phosphatase (G-6-P) and succinodehydrogenase (SDH) staining were used to detect the activity and function of the endoplasmic reticulum and mitochondria of liver tissues at 0 and 24 h after IRE ablation. Tissue ablation responses were monitored in real-time with US in the percutaneous IRE group; the largest diameter of the ablation zones was measured immediately (D1) and after 24 h (D2). Following D2 measurement, the animals were sacrificed and the gross sections (D3) were measured. The pathological examination results showed complete tissue necrosis after 24 h instead of immediately following IRE. The largest long diameters measured by intraprocedural US immediately after IRE (D1, 39.58±2.13 mm) were larger than those measured by US after 24 h (D2, 37.07±3.51 mm) and in gross section measurements (D3, 36.44±2.04 mm; P<0.05). D1 showed a good linear correlation with D3 (r=0.949). We conclude from these studies that IRE is not an acute ablating effect which leads to cell death. If US-guided percutaneous IRE focused on the target liver areas accurately, physicians would be able to assess the extent of necrosis through the regression equation during the IRE ablation procedure, and evaluate whether sufficient electric field energy had been applied to the desired tissue. Assisted with US guiding and monitoring, the minimally invasive IRE procedure in intraperitoneal lesions may become an important tumor ablation technique.

Ablation of perivascular hepatic malignant tumors with irreversible electroporation

BACKGROUND

Ablation is increasingly used to treat primary and secondary liver cancer. Ablation near portal pedicles and hepatic veins is challenging. Irreversible electroporation (IRE) is a new ablation technique that does not rely on heat and, in animals, appears to be safe and effective when applied near hepatic veins and portal pedicles. This study evaluated the safety and short-term outcomes of IRE to ablate perivascular malignant liver tumors.

STUDY DESIGN

A retrospective review of patients treated with IRE between January 1, 2011 and November 2, 2011 was performed. Patients were selected for IRE when resection or thermal ablation was not indicated due to tumor location. Treatment outcomes were classified by local, regional, and systemic recurrence and complications. Local failure was defined as abnormal enhancement at the periphery of an ablation defect on post-procedure contrast imaging.

RESULTS

Twenty-eight patients had 65 tumors treated. Twenty-two patients (79%) were treated via an open approach and 6 (21%) were treated percutaneously. Median tumor size was 1 cm (range 0.5 to 5 cm). Twenty-five tumors were <1 cm from a major hepatic vein; 16 were <1 cm from a major portal pedicle. Complications included 1 intraoperative arrhythmia and 1 postoperative portal vein thrombosis. Overall morbidity was 3%. There were no treatment-associated mortalities. At median follow-up of 6 months, there was 1 tumor with persistent disease (1.9%) and 3 tumors recurred locally (5.7%).

CONCLUSIONS

This early analysis of IRE treatment of perivascular malignant hepatic tumors demonstrates safety for treating liver malignancies. Larger studies and longer follow-up are necessary to determine long-term efficacy.

BNNT-mediated irreversible electroporation: its potential on cancer cells

Irreversible lethal electroporation (IRE) is a new non-thermal ablation modality that uses short pulses of high amplitude static electric fields (up 1000 V/cm) to create irreversible pores in the cell membrane, thus, causing cell death. Recently, IRE has emerged as a promising clinical modality for cancer disease treatment. Here, we investigated the responses of tumour human HeLa cells when subjected to IRE in the presence of BNNTs. These consist of tiny tubes of B and N atoms (arranged in hexagons) with diameters ranging from a 1 to 3 nanometres and lengths < 2 μm. BNNTs have attracted wide attention because of their unique electrical properties. We speculate that BNNTs, when interacting with cells exposed to static electrical fields, amplify locally the electric field, leading to cell death. In this work, electroporation assays were performed with a commercial electroporator using the cell- specific protocol suggested by the supplier (exponential decay wave, time constant 20 ms) with the specific aim to compare IRE in absence and in presence of BNNTs. We observed that BNNTs have the capacity to decrease substantially the voltage required for IRE. When cells were pulsed at 800 V/cm, we observed a 2,2-fold reduction in cell survival in the presence of BNNTs compared to controls. We conclude that the death of the tumour cells exposed to IRE is strongly enhanced in the presence of BNNTs, indicating their potential therapeutic application.

Irreversible electroporation for focal ablation at the porta hepatis

Patients with chemotherapy-refractory liver metastases who are not candidates for surgery may be treated with focal ablation techniques with established survival benefits. Irreversible electroporation is the newest of these and has the putative advantages of a nonthermal action, preventing damage to adjacent biliary structures and bowel. This report describes the use of irreversible electroporation in a 61-year-old man with a solitary chemoresistant liver metastasis unsuitable for radiofrequency ablation as a result of its proximity to the porta hepatis. At 3 months, tumor size was decreased on computed tomography from 28 × 19 to 20 × 17 mm, representing stable disease according to the response evaluation criteria in solid tumors. This corresponded to a decrease in tumor volume size from 5.25 to 3.16 cm(3). There were no early or late complications. Chemoresistant liver metastases in the proximity of the porta hepatis that are considered to be too high a risk for conventional surgery or thermal ablation may be considered for treatment by the novel ablation technique of irreversible electroporation.

Characterization of irreversible electroporation ablation in in vivo porcine liver

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.

Minimally invasive evaluation and treatment of colorectal liver metastases

Minimally invasive techniques used in the evaluation and treatment of colorectal liver metastases (CRLMs) include ultrasonography (US), computed tomography, magnetic resonance imaging, percutaneous and operative ablation therapy, standard laparoscopic techniques, robotic techniques, and experimental techniques of natural orifice endoscopic surgery. Laparoscopic techniques range from simple staging laparoscopy with or without laparoscopic intraoperative US, through intermediate techniques including simple liver resections (LRs), to advanced techniques such as major hepatectomies. Hereins, we review minimally invasive evaluation and treatment of CRLM, focusing on a comparison of open LR (OLR) and minimally invasive LR (MILR). Although there are no randomized trials comparing OLR and MILR, nonrandomized data suggest that MILR compares favorably with OLR regarding morbidity, mortality, LOS, and cost, although significant selection bias exists. The future of MILR will likely include expanding criteria for resectability of CRLM and should include both a patient registry and a formalized process for surgeon training and credentialing.

Real-time ultrasound imaging of irreversible electroporation in a porcine liver model adequately characterizes the zone of cellular necrosis

BACKGROUND

  Irreversible electroporation (IRE) is a largely non-thermal method for the ablation of solid tumours. The ability of ultrasound (US) to measure the size of the IRE ablation zone was studied in a porcine liver model.

METHODS

  Three normal pig livers were treated in vivo with a total of 22 ablations using IRE. Ultrasound was used within minutes after ablation and just prior to liver harvest at either 6 h or 24 h after the procedure. The area of cellular necrosis was measured after staining with nitroblue tetrazolium and the percentage of cell death determined by histomorphometry.

RESULTS

  Visible changes in the hepatic parenchyma were apparent by US after all 22 ablations using IRE. The mean maximum diameter of the ablation zone measured by US during the procedure was 20.1 ± 2.7 mm. This compared with a mean cellular necrosis zone maximum diameter of 20.3 ± 2.9 mm as measured histologically. The mean percentage of dead cells within the ablation zone was 77% at 6 h and 98% at 24 h after ablation.

CONCLUSIONS

  Ultrasound is a useful modality for measuring the ablation zone within minutes of applying IRE to normal liver tissue. The area of parenchymal change measured by US correlates with the area of cellular necrosis.

Electrode activation sequencing employing conductivity changes in irreversible electroporation tissue ablation

Irreversible electroporation (IRE) uses high-voltage pulses applied to tissue, which cause dielectric breakdown of cell membranes resulting in cell death. IRE is a promising technique for ablation of nonresectable tumors because it can be configured to spare critical structures such as blood vessels. A consequence of pulse application is an increase in tissue electrical conductivity due to current pathways being opened in cell membranes. We propose a novel IRE method introducing electrode switching and pulse sequencing in which tissue conductivity is first increased using preparatory pulses in order to form high-conductivity zones, which then helps provide higher electric field intensity within the targeted tissue as subsequent pulses are applied, and hence, enhances the efficiency and selectivity of the IRE treatment. We demonstrate the potential of this method using computational models on simple geometries.

Electron microscopic demonstration and evaluation of irreversible electroporation-induced nanopores on hepatocyte membranes

PURPOSE

To demonstrate, evaluate, and verify the existence of irreversible electroporation (IRE)-ablation induced nanopores on the plasma membrane of hepatocytes.

MATERIALS AND METHODS

On animal research committee approval, four New Zealand rabbits and two Yorkshire swine underwent IRE ablation of the liver (90 pulses, 100 μs per pulse at 2,500 V), and selected ablated liver tissues were harvested, fixed, and air-dried according to the electron microscopy (EM) protocol. A scanning electron microscope (SEM; Nova 230 NanoSEM [FEI, Hillsboro, Oregon] with 80 picoamperes and 10-kV acceleration) was used to visualize and verify IRE-created nanopores. Using NIH image (Bethesda, Maryland) and ImageScope (Aperio Inc., Vista, California), 21 ablated tissues (16 rabbit, 5 swine) were evaluated. Corresponding hematoxylin and eosin (H&E) evaluation was performed to verify IRE-induced cell death.

RESULTS

In all 21 IRE-ablated tissues, the SEM was able to show numerous, well-circumscribed, round, and concave-shaped pore defects disturbing the hepatocyte plasma membranes. These pores were not seen in normal liver. The size of the nanopores ranged from 80-490 nm with the greatest frequency of pores in bimodal distribution. The highest frequency of pore size was noted at the size range 340-360 nm.

CONCLUSIONS

IRE induces nanopores on hepatocyte membranes, as shown by SEM. The pore diameters are larger than nanopores created by reversible electroporation (RE), which may have implications for irreversibility or permanency.