US findings after irreversible electroporation ablation: radiologic-pathologic correlation

Efficacy of a surgical cardiac ablation clamp using nanosecond pulsed electric fields: An acute porcine model

OBJECTIVE

To examine the effectiveness of a recently developed nonthermal technology, nanosecond pulse-field ablation (nsPFA), for surgical ablation of the atria in a beating heart porcine model.

METHODS

Six pigs underwent sternotomy and ablation using an nsPFA parallel clamp. The ablation electrodes (53 mm long) were embedded in the jaws of the clamp. Nine lesions per pig were created in locations chosen to be representative of the Cox-maze procedure. Four lesions were intended to electrically isolate parts of the atrium: the right atrial appendage, left atrial appendage, right pulmonary veins, and left pulmonary veins. For these lesions, exit block testing was performed both after ablation and before euthanasia; the time between the 2 tests was 3.3 ± 0.5 hours (range, 2-4 hours). Using purse string sutures, 5 more lesions were created up to the superior vena cava, down to the inferior vena cava, across the right atrial free wall, and at 2 distinct locations on the left atrial free wall. The clamp delivered a train of nanosecond duration pulses, with a total duration of 2.5 seconds, independent of tissue thickness. The heart tissue was stained with 1% triphenyltetrazolium chloride after a dwelling period of 2 hours. Subsequently, each lesion was cross sectioned at 5-mm intervals to assess the ablation depth and transmurality. In some sections, transmurality could not be established on the basis of triphenyltetrazolium chloride staining alone; for these lesions, Gomori-trichrome stains were used, and the histologic sections were evaluated for transmurality.

RESULTS

The ablation time was 2.5 seconds per lesion, for a total of only 22.5 seconds ablation time to create 9 lesions. A total of 53 lesions were created, resulting in 388 separate histologic sections. Transmurality was established in 386 sections (99.5%). Mean tissue thickness was 3.1 ± 1.5 mm (range, 0.2-8.6 mm). Exit block was confirmed in 23 of the 24 lesions (96%) postablation and 23 of 24 (96%) before the animals were humanely killed. Over the course of the procedure, neither pulse-induced arrhythmias nor any other complications were noted.

CONCLUSIONS

The novel nsPFA clamp device was effective in creating acute conduction block and transmural lesions in both the right and left atria in an acute porcine model. This nonthermal energy source has great potential to both shorten procedural time and enable effective ablation in the beating heart.

Electrolysis products, reactive oxygen species and ATP loss contribute to cell death following irreversible electroporation with microsecond-long pulsed electric fields

Membrane permeabilization and thermal injury are the major cause of cell death during irreversible electroporation (IRE) performed using high electric field strength (EFS) and small number of pulses. In this study, we explored cell death under conditions of reduced EFS and prolonged pulse application, identifying the contributions of electrolysis, reactive oxygen species (ROS) and ATP loss. We performed ablations with conventional high-voltage low pulse (HV-LP) and low-voltage high pulse (LV-HP) conditions in a 3D tumor mimic, finding equivalent ablation volumes when using 2000 V/cm 90 pulses or 1000 V/cm 900 pulses respectively. These results were confirmed by performing ablations in swine liver. In LV-HP treatment, ablation volume was found to increase proportionally with pulse numbers, without the substantial temperature increase seen with HV-LP parameters. Peri-electrode pH changes, ATP loss and ROS production were seen in both conditions, but LV-HP treatments were more sensitive to blocking of these forms of cell injury. Increases in current drawn during HV-LP was not observed during LV-HP condition where the total ablation volume correlated to the charge delivered into the tissue which was greater than HV-LP treatment. LV-HP treatment provides a new paradigm in using pulsed electric fields for tissue ablation with clinically relevant volumes.

Irreversible electroporation: Beyond the limits of tumor ablation

Irreversible Electroporation (IRE) is a non-thermal tumor ablation technique. High-voltage electrical pulses are applied between pairs of electrodes inserted around and/or inside a tumor. The generated electric current induces the creation of nanopores in the cell membrane, triggering apoptosis. As a result, IRE can be safely used in areas near delicate vascular structures where other thermal ablation methods are contraindicated. Currently, IRE has demonstrated to be a successful ablation technique for pancreatic, renal, and liver tumors and is widely used as a focal therapeutic option for prostate cancer. The need for specific anesthetic management and accurate parallel placement of multiple electrodes entails a high level of complexity and great expertise from the interventional team is required. Nevertheless, IRE is a very promising technique with a remarkable systemic immunological capability and may impact on distant metastases (abscopal effect).

Characteristics of pulsed electric field cardiac ablation porcine treatment zones with a focal catheter

OBJECTIVES

Pulsed electric field (PEF) therapies employ punctuated energy delivery to kill cells in a volume of tissue through mechanisms that are not dependent on thermal processes. A key component to successful cardiac ablation procedures is ensuring the generation of transmural, contiguous ablation zones, which requires in-depth knowledge regarding treatment sizes for a given therapeutic application.

METHODS

In this study, a series of acute treatments were delivered to porcine ventricles, where triphenyl tetrazolium chloride (TTC) vitality stain was used to identify treatment effect sizes for the three focal monopolar CENTAURI PEF cardiac ablation energy settings.

RESULTS

Treatment depths were 5.7, 7.2, and 8.2 mm for the 19, 22, and 25 A energy settings, respectively. Gross pathology indicated umbral zones of hemorrhage surrounded by pale avital TTC-negative-negative tissue, which contrasted significantly from radiofrequency ablation (RF) controls. Histologically, treatment zones are identified by regions of contraction band necrosis and cardiomyocytolysis, which contrasted with RF control lesions composed primarily of coagulation necrosis.

CONCLUSIONS

Together, these data indicate the ability for focal monopolar PEF treatments to generate deep treatment zones in cardiac ablation without incurring the gross or histological coagulative characteristics of RF thermal lesions.

Histological Response to 5 kHz Irreversible Electroporation in a Porcine Liver Model

Unlike necrosis by thermal ablation, irreversible electroporation (IRE) is known to induce apoptosis by disrupting plasma membrane integrity with electric pulses while preserving the structure of blood vessels and bile ducts in liver tissue without a heat sink effect. This study aimed to investigate thermal damage and histopathological effects in the porcine liver by high-frequency electric pulses (5 kHz) which is much higher than the widely used 1 Hz. The electric field and thermal distributions of 5 kHz electric pulses were compared with those of 1 Hz in numerical simulations. 5 kHz-IRE was applied on pigs under ultrasound imaging to guide the electrode placement. The animals underwent computed tomography (CT) examination immediately and 1 day after IRE. After CT, IRE-treated tissues were taken and analyzed histologically. CT revealed that hepatic veins were intact for 1-day post-IRE. Histopathologically, the structure of the portal vein was intact, but endothelial cells were partially removed. In addition, the hepatic artery structure from which endothelial cells were removed were not damaged, while the bile duct structure and cholangiocytes were intact. The thermal injury was observed only in the vicinity of the electrodes as simulated in silico. 5 kHz-IRE generated high heat due to its short pulse interval, but the thermal damage was limited to the tissue around the electrodes. The histopathological damage caused by 5 kHz-IRE was close to that caused by 1 Hz-IRE. If a short-time treatment is required for reasons such as anesthesia, high-frequency IRE treatment is worth considering. Our observations will contribute to a better understanding of the IRE phenomena and search for advanced therapeutic conditions.

Combination of natural killer cell-based immunotherapy and irreversible electroporation for the treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is among the most lethal cancer types despite great advancement in overall survival of the patients over the last decades. Surgical resection or partial hepatectomy has been approved as the curative treatment for early-stage HCC patients however only up to 30% of them are eligible for the procedures. Natural killer (NK) cells are cytotoxic lymphocytes recognized for killing virally infected cells and improving immune functions for defending the body against malignant cells. Although autologous NK cells failed to demonstrate significant clinical benefit, transfer of allogeneic adoptive NK cells arises as a promising approach for the treatment of solid tumors. The immunosuppressive tumor microenvironment and inadequate homing efficiency of NK cells to tumors can inhibit adoptive transfer immunotherapy (ATI) efficacy. However, potential of the NK cells is challenged by the transfection efficiency. The local ablation techniques that employ thermal or chemical energy have been investigated for the destruction of solid tumors for three decades and demonstrated promising benefits for individuals not eligible for surgical resection or partial hepatectomy. Irreversible electroporation (IRE) is one of the most recent minimally invasive ablation methods that destruct the cell within the targeted region through non-thermal energy. IRE destroys the tumor cell membrane by delivering high-frequency electrical energy in short pulses and overcomes tumor immunosuppression. The previous studies demonstrated that IRE can induce immune changes which can facilitate activation of specific immune responses and improve transfection efficiency. In this review paper, we have discussed the mechanism of NK cell immunotherapy and IRE ablation methods for the treatment of HCC patients and the combinatorial benefits of NK cell immunotherapy and IRE ablation.

A Systematic Review about Imaging and Histopathological Findings for Detecting and Evaluating Electroporation Based Treatments Response

BACKGROUND

Imaging methods and the most appropriate criteria to be used for detecting and evaluating response to oncological treatments depend on the pathology and anatomical site to be treated and on the treatment to be performed. This document provides a general overview of the main imaging and histopathological findings of electroporation-based treatments (Electrochemotherapy-ECT and Irreversible electroporation-IRE) compared to thermal approach, such as radiofrequency ablation (RFA), in deep-seated cancers with a particular attention to pancreatic and liver cancer.

METHODS

Numerous electronic datasets were examined: PubMed, Scopus, Web of Science and Google Scholar. The research covered the years from January 1990 to April 2021. All titles and abstracts were analyzed. The inclusion criteria were the following: studies that report imaging or histopathological findings after ablative thermal and not thermal loco-regional treatments (ECT, IRE, RFA) in deep-seated cancers including pancreatic and liver cancer and articles published in the English language. Exclusion criteria were unavailability of full text and congress abstracts or posters and different topic respect to inclusion criteria.

RESULTS

558 potentially relevant references through electronic searches were identified. A total of 38 articles met the inclusion criteria: 20 studies report imaging findings after RFA or ECT or IRE in pancreatic and liver cancer; 17 studies report histopathological findings after RFA or ECT or IRE; 1 study reports both imaging and histopathological findings after RFA or ECT or IRE.

CONCLUSIONS

Imaging features are related to the type of therapy administrated, to the timing of re-assessment post therapy and to the imaging technique being used to observe the effects. Histological findings after both ECT and IRE show that the treated area becomes necrotic and encapsulated in fibrous tissue, suggesting that the size of the treated lesion cannot be measured as an endpoint to detect response. Moreover, histology frequently reported signs of apoptosis and reduced vital tissue, implying that imaging criteria, which take into account the viability and not the size of the lesion, are more appropriate to evaluate response to treatment.

Irreversible electroporation in patients with liver tumours: treated-area patterns with contrast-enhanced ultrasound

BACKGROUND

Familiarity with post-IRE imaging interpretation is of considerable importance in determining ablation success and detecting recurrence. CEUS can be used to assess the tumour response and characteristics of the ablation zone. It is of clinical interest to describe the ultrasonographic findings of liver tumours after irreversible electroporation (IRE) percutaneous ablation.

METHODS

A prospective study of 24 cases of malignant liver tumours (22 cases of primary liver tumours and 2 cases of liver metastases) treated by IRE ablation was conducted. Two inspectors evaluated the ablation zone in a consensus reading performed immediately, 1 day, and 1 month after IRE ablation. The gold standard method, magnetic resonance imaging (MRI), was used to evaluate the effectiveness of the treatment at 1 month.

RESULTS

Immediately after IRE ablation and up to 1 month later, the ablation zones gradually changed from hypo-echogenicity to hyper-echogenicity on conventional ultrasound and showed non-enhancement on contrast-enhanced ultrasound (CEUS). One month after IRE ablation, CEUS and MRI results were highly consistent (κ = 0.78, p < 0.05).

CONCLUSIONS

We conclude that CEUS may be an effective tool for assessing post-IRE ablation changes after 1 month. CEUS enables the depiction of tumour vascularity in real time and serves as an easy, repeatable method.

Predictors of Occlusion of Hepatic Blood Vessels after Irreversible Electroporation of Liver Tumors

PURPOSE

To examine predictors of midterm occlusion in portal and hepatic veins within or adjacent to the ablation zone after irreversible electroporation (IRE) of liver tumors.

MATERIALS AND METHODS

This retrospective cohort analysis included 39 patients who underwent CT-guided IRE of liver tumors. Vessels within or adjacent to the ablation zone were identified on CT images acquired immediately after the procedure, and the positional relationships with the ablation zone (within/adjacent), locations (proximal/distal), and diameters (< 4 mm or ≥ 4 mm) were evaluated. Using contrast-enhanced follow-up scans, each vessel was classified as patent, stenosed, or occluded. Associations between vessel occlusion and each variable were investigated.

RESULTS

Overall, 33 portal veins and 64 hepatic veins were analyzed. Follow-up scans showed occlusion in 12/33 (36.7%) portal veins and 17/64 (26.6%) hepatic veins. Vessels within the ablation zone were occluded significantly more frequently than vessels adjacent to the ablation zone (portal: 55.6% [10/18] vs 13.3% [2/15], P = .04; hepatic: 45.4% [15/33] vs 6.4% [2/31], P = .011). Vessels with a diameter < 4 mm were also occluded significantly more frequently than vessels with a diameter ≥ 4 mm (portal: 72.7% [8/11] vs 18.1% [4/22], P = .011; hepatic: 54.8% [17/31] vs 0% [0/33], P < .001). The respective positive and negative predictive values for occlusion of vessels categorized as both within and < 4 mm were 88% (7/8) and 82% (20/25) for portal veins and 79% (15/19) and 96% (43/45) for hepatic veins.

CONCLUSIONS

Midterm vessel occlusion after liver IRE could be predicted with relatively high accuracy by assessing ablation location and vessel diameter.

Recent progress in pulsed electric field ablation for liver cancer

The number of liver cancer patients is likely to continue to increase in the coming decades due to the aging of the population and changing risk factors. Traditional treatments cannot meet the needs of all patients. New treatment methods evolved from pulsed electric field ablation are expected to lead to breakthroughs in the treatment of liver cancer. This paper reviews the safety and efficacy of irreversible electroporation in clinical studies, the methods to detect and evaluate its ablation effect, the improvements in equipment and its antitumor effect, and animal and clinical trials on electrochemotherapy. We also summarize studies on the most novel nanosecond pulsed electric field ablation techniques in vitro and in vivo. These research results are certain to promote the progress of pulsed electric field in the treatment of liver cancer.

A numerical study on the effect of conductivity change in cell kill distribution in irreversible electroporation

Introduction: irreversible electroporation (IRE) is a tissue ablation technique and physical process used to kill the undesirable cells. In the IRE process by mathematical modelling we can calculate the cell kill probability and distribution inside the tissue. The purpose of the study is to determine the influence of electric conductivity change in the IRE process into the cell kill probability and distribution.

Methods: cell death probability and electric conductivity were calculated with COMSOL Multiphysics software package. 8 pulses with a frequency of 1 Hz, pulse width of 100 µs and electric field intensity from 1000 to 3000 V/Cm with steps of 500 V/Cm used as electric pulses.

Results: significantly, the electrical conductivity of tissue will increase during the time of pulse delivery. According to our results, electrical conductivity increased with an electric field intensity of pulses. By considering the effect of conductivity change on cell kill probability, the cell kill probability and distribution will change.

Conclusion: we believe that considering the impact of electric conductivity change on the cell kill probability will improve the accuracy of treatment outcome in the clinic for treatment with IRE.

Irreversible electroporation of hepatocellular carcinoma: the role of ultrasonography

Irreversible electroporation (IRE) is a novel form of soft tissue ablation therapy that uses high-current electrical pulses to induce the formation of pores in the cell membrane, leading to cell death. Although outcome data for the ablation of hepatocellular carcinoma (HCC) by IRE are limited, early results are encouraging and may suggest equivalency to the outcomes achieved by thermal ablation methods such as radiofrequency ablation (RFA) and microwave ablation (MWA). However, IRE can be a challenging and very time-consuming procedure compared to RFA and MWA. In this review article, we not only evaluate the efficacy and safety of IRE for the treatment of HCC, but also discuss imaging guidance, ablation monitoring, and endpoint assessment, with a particular focus on ultrasonography.

High-Voltage Electrical Pulses in Oncology: Irreversible Electroporation, Electrochemotherapy, Gene Electrotransfer, Electrofusion, and Electroimmunotherapy

This review summarizes the use of high-voltage electrical pulses (HVEPs) in clinical oncology to treat solid tumors with irreversible electroporation (IRE) and electrochemotherapy (ECT). HVEPs increase the membrane permeability of cells, a phenomenon known as electroporation. Unlike alternative ablative therapies, electroporation does not affect the structural integrity of surrounding tissue, thereby enabling tumors in the vicinity of vital structures to be treated. IRE uses HVEPs to cause cell death by inducing membrane disruption, and it is primarily used as a radical ablative therapy in the treatment of soft-tissue tumors in the liver, kidney, prostate, and pancreas. ECT uses HVEPs to transiently increase membrane permeability, enhancing cellular cytotoxic drug uptake in tumors. IRE and ECT show immunogenic effects that could be augmented when combined with immunomodulatory drugs, a combination therapy the authors term electroimmunotherapy. Additional electroporation-based technologies that may reach clinical importance, such as gene electrotransfer, electrofusion, and electroimmunotherapy, are concisely reviewed. HVEPs represent a substantial advancement in cancer research, and continued improvement and implementation of these presented technologies will require close collaboration between engineers, interventional radiologists, medical oncologists, and immuno-oncologists.

Ultrasound and Contrast-enhanced Ultrasound Findings after Percutaneous Irreversible Electroporation of Hepatic Malignant Tumors

The aim of this study was to describe ultrasound (US) and contrast-enhanced ultrasound (CEUS) findings immediately and 1 d after percutaneous irreversible electroporation (IRE) of hepatic malignant tumors. Immediately after IRE, the ablation zone was shown to be a gradually expanding hypo-echoic area around the electrodes. The microcirculation of the ablation zone was markedly reduced on CEUS (before vs. immediately after, p < 0.001), and the macrocirculation within the ablation zone was preserved. At 1 d after IRE, the ablation zones lost their hypo-echogenicity to become iso-echoic or hyper-echoic (before vs. 1 d after, p = 0.004; immediately after vs. 1 d after, p = 0.002). At this time, further elimination of microcirculation was confirmed on CEUS (before vs. 1 d after, p < 0.001; immediately after vs. 1 d after, p = 0.003). The size of the ablation zone, which measured by US, was strongly correlated with that measured by CEUS (length: r: = 0.929, width: r = 0.940, p < 0.001), was significantly enlarged immediately after IRE and shrunk 1 d after IRE.

Incidence and evolution of venous thrombosis during the first 3 months after irreversible electroporation of malignant hepatic tumours

The incidence and evolution of venous thrombosis adjacent to the ablation zone after percutaneous irreversible electroporation (IRE) were evaluated to identify potential risk factors in patients with hepatic malignancies. 205 venous structures (in 87 patients) within a ≤1.0 cm radius of the ablation zone were assessed after IRE of 112 hepatic lesions (74 primary, 38 secondary hepatic malignancies) by pre-interventional and post-interventional (1–3 days, 6 weeks and 3 months after IRE) contrast-enhanced magnetic resonance imaging. The relationships between venous thrombosis and clinical features were analysed using a binary logistic regression model. In 27 of 87 patients (31%), a total of 67 venous complications were noted during the 3 months follow-up. Thrombosis represented the most frequently observed complication (n = 47; 70.1%), followed by vessel narrowing (n = 20; 29.9%). 5 (10.6%) of 47 thromboses showed spontaneous regression 3 months after IRE. A small vessel diameter (p = 0.011) and post-interventional vessel narrowing (p = 0.006) were independently associated with delayed post-ablative thrombosis. Delayed venous thrombosis frequently occurs after IRE of hepatic malignancies. Pre-existing vessel narrowing and a small vessel diameter represent significant risk factors that require further surveillance and potentially therapeutic intervention.

Radiological findings of porcine liver after electrochemotherapy with bleomycin

Background

Radiologic findings after electrochemotherapy of large hepatic blood vessels and healthy hepatic parenchyma have not yet been described.

Materials and methods

We performed a prospective animal model study with regulatory approval, including nine grower pigs. In each animal, four ultrasound-guided electroporated regions were created; in three regions, electrodes were inserted into the lumen of large hepatic vessels. Two types of electrodes were tested; variable linear- and fixed hexagonal-geometry electrodes. Ultrasonographic examinations were performed immediately and up to 20 minutes after the procedure. Dynamic computed tomography was performed before and at 60 to 90 minutes and one week after the procedure.

Results

Radiologic examinations of the treated areas showed intact vessel walls and patency; no hemorrhage or thrombi were noted. Ultrasonographic findings were dynamic and evolved from hyperechogenic microbubbles along electrode tracks to hypoechogenicity of treated parenchyma, diffusion of hyperechogenic microbubbles, and hypoechogenicity fading. Contrast-enhanced ultrasound showed decreased perfusion of the treated area. Dynamic computed tomography at 60 to 90 minutes after the procedure showed hypoenhancing areas. The total hypoenhancing area was smaller after treatment with fixed hexagonal electrodes than after treatment with variable linear geometry electrodes.

Conclusions

Radiologic findings of porcine liver after electrochemotherapy with bleomycin did not show clinically significant damage to the liver, even if a hazardous treatment strategy, such as large vessel intraluminal electrode insertion, was employed, and thus further support safety and clinical use of electrochemotherapy for treatment of hepatic neoplasia.

Diffusion-Weighted MR Imaging to Evaluate Immediate Response to Irreversible Electroporation in a Rabbit VX2 Liver Tumor Model

PURPOSE

To evaluate the feasibility of diffusion-weighted imaging (DWI) in magnetic resonance imaging for quantitative measurement of responses following irreversible electroporation (IRE) in a rabbit liver tumor model.

MATERIALS AND METHODS

Twelve rabbits underwent ultrasound-guided VX2 tumor implantation in the left medial and left lateral liver lobes. The tumors in the left medial lobe were treated with IRE, whereas those in the left lateral lobe served as internal controls. DWI was performed before and immediately after IRE. Tumors were then harvested for histopathologic staining. The apparent diffusion coefficient (ADC) and change in ADC (ΔADC) were calculated based on DWI. Tumor apoptosis index (AI) was assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling. These measurements from DWI and histopathology were compared between untreated and treated tumors.

RESULTS

The ADC values, ΔADC, and AI showed statistically significant differences between treated and untreated tumors (P < .05 for all). ADC values were higher in treated tumors than in untreated tumors (1.08 × 10^-3 mm²/s ± 0.15 vs 0.88 × 10^-3 mm²/s ± 0.19; P = .042).

CONCLUSIONS

DWI can be used to quantitatively evaluate treatment response in liver tumors immediately after IRE.

Histopathological and Ultrastructural Changes after Electroporation in Pig Liver Using Parallel-Plate Electrodes and High-Performance Generator

Irreversible electroporation (IRE) has gained attention as a new non-thermal therapy for ablation with important benefits in terms of homogeneous treatment and fast recovery. In this study, a new concept of high voltage generator is used, enabling irreversible electroporation treatment in large tissue volume using parallel plates. Unlike currently available generators, the proposed versatile structure enables delivering high-voltage high-current pulses. To obtain homogeneous results, 3-cm parallel-plates electrodes have also been designed and implemented. IRE ablation was performed on six female pigs at 2000 V/cm electric field, and the results were analysed after sacrifice three hours, three days and seven days after ablation. Histopathological and ultrastructural studies, including transmission and scanning electron microscopy, were carried out. The developed high-voltage generator has proved to be effective for homogeneous IRE treatment using parallel plates. The destruction of the membrane of the hepatocytes and the alterations of the membranes of the cellular organelles seem incompatible with cell death by apoptosis. Although endothelial cells also die with electroporation, the maintenance of vascular scaffold allows repairing processes to begin from the third day after IRE as long as the blood flow has not been interrupted. This study has opened new direction for IRE using high performance generators and highlighted the importance of taking into account ultrastructural changes after IRE by using electron microscopy analysis.

Does Drug-Eluting Bead TACE Enhance the Local Effect of IRE? Imaging and Histopathological Evaluation in a Porcine Model

OBJECTIVES

We conducted an in vivo trial on swine to compare the ablation volumes of irreversible electroporation (IRE) followed by drug-eluting beads transarterial chemoembolization (DEB-TACE) versus IRE only.

MATERIALS AND METHODS

Nine swine underwent CT-guided IRE in one liver lobe and IRE immediately followed by DEB-TACE in a different liver lobe. For DEB-TACE, 100-300 µm beads (DC-Beads^®) were loaded with 50 mg doxorubicin. For IRE, the NanoKnife^® was used employing two electrodes according to the vendor's protocol. Imaging follow-up was performed including CT-based lesion volume assessment using contrast-enhanced CT (venous phase) on days 1, 3, and 7 after the procedure. Three animals were killed for histopathological analysis after each follow-up.

RESULTS

Ablation volumes in CT in the IRE + DEB-TACE group were 15.4 ± 10.5 ml on day 1, 8.7 ± 5.6 ml on day 3, and 1.6 ± 0.7 ml on day 7. In the IRE group, the corresponding values were 5.2 ± 5.2 ml on day 1, 1.0 ± 1.2 ml on day 3, and 0.1 ± 0.1 ml on day 7. On day 1 and day 3, ablation volumes of IRE + TACE group were significantly larger than in the IRE group (p < 0.05). 96% of beads were depicted in or around ablative lesions. 69% of these beads were found in the surrounding hemorrhagic infiltration and 31% within the ablative lesion itself.

CONCLUSIONS

Combination of IRE immediately followed by DEB-TACE resulted in larger ablation volumes compared to IRE alone, suggesting that local efficacy of IRE can be enhanced by post-IRE DEB-TACE.

Histological analysis of human pancreatic carcinoma following irreversible electroporation in a nude mouse model

AIM

To determine changes in the morphology and function of pancreatic cancer cells after irreversible electroporation (IRE) treatment, and to explore the clinical significance of IRE treatment for pancreatic cancer providing an experimental basis for the clinical application of IRE treatment.

METHODS

IRE was carried out in an athymic nude mouse model of pancreatic carcinoma generated with human pancreatic cancer cells 1. In therapy groups, IRE electrodes were inserted with 90 pulses per second at 800 V/cm applied to ablate the targeted tumor tissues. Histological assessment of the affected tissue was performed by hematoxylin and eosin staining (HE). Quantification of cell proliferation and apoptosis was performed by evaluating Ki67 and caspase-3 levels, respectively. Flow cytometry was used to assess cell apoptosis. Ultrasound imaging was carried out to evaluate IRE treatment results. Pathological correlation studies showed IRE is effective for the targeted ablation of pancreatic tumors in an orthotopic mouse model.

RESULTS

IRE was efficacious in removing tumors in the orthotopic mouse model. The IRE-ablated zone displays characteristics of nude mouse models at different time-points as assessed by hematoxylin and eosin staining. Immunohistochemical analysis of samples from the pancreatic cancer models showed significantly enhanced caspase-3 cleavage and Ki67. Flow cytometry data corroborated the above findings that apoptosis in tumor cells was observed immediately on the first postoperative day, and with time the middle and late stages of apoptosis were observed. For ultrasound imaging studies, the IRE ablation zone became a hyperechoic area due to increasing inflammatory and immunologic cellular contents.

CONCLUSION

IRE is a promising new approach for pancreatic cancer, with many potential advantages over conventional ablation techniques.

Ultrasonographic changes in the liver tumors as indicators of adequate tumor coverage with electric field for effective electrochemotherapy

Background

The aim of the study was to characterize ultrasonographic (US) findings during and after electrochem-otherapy of liver tumors to determine the actual ablation zone and to verify the coverage of the treated tumor with a sufficiently strong electric field for effective electrochemotherapy.

Patients and methods

US findings from two representative patients that describe immediate and delayed tumor changes after electrochemotherapy of colorectal liver metastases are presented.

Results

The US findings were interrelated with magnetic resonance imaging (MRI). Electrochemotherapy-treated tumors were exposed to electric pulses based on computational treatment planning. The US findings indicate immediate appearance of hyperechogenic microbubbles along the electrode tracks. Within minutes, the tumors became evenly hyperechogenic, and simultaneously, an oedematous rim was formed presenting as a hypoechogenic formation which persisted for several hours after treatment. The US findings overlapped with computed electric field distribution in the treated tissue, indicating adequate coverage of tumors with sufficiently strong electric field, which may predict an effective treatment outcome.

Conclusions

US provides a tool for assessment of appropriate electrode insertion for intraoperative electrochemo-therapy of liver tumors and assessment of the appropriate coverage of a tumor with a sufficiently strong electric field and can serve as predictor of the response of tumors.

Non-enhanced Pattern on Contrast-Enhanced Ultrasound in the Local Efficacy Assessment of Irreversible Electroporation Ablation of Pancreatic Adenocarcinoma

The objective was to evaluate the diagnostic value of contrast-enhanced ultrasound in the assessment of the local efficacy after irreversible electroporation (IRE) ablation of pancreatic adenocarcinoma 1 mo after ablation. Fifteen patients with pancreatic adenocarcinoma were treated with IRE and then examined by contrast-enhanced ultrasound 1 mo after ablation. The contrast agent was SonoVue. Technical efficacy was assessed at 3 mo after IRE and classified as technical efficiency (TE) and technical inefficiency (TIE). Diagnostic performance was analyzed using a receiver operating characteristic curve. Ten patients were considered as having TE, and five, TIE. Complete non-enhancement was observed in seven ablation zones (70.0%) in the TE group, and peripheral heterogeneous enhancement, in all five ablation zones (100.0%) in the TIE group. The non-enhancement pattern differed significantly between the TE and TIE groups (p = 0.026), with significant correlation with technical efficacy (p = 0.007). The area under the receiver operating characteristic curve was 0.85 (p = 0.008, 95% confidence interval: 0.65-1.05). A non-enhancement pattern using contrast-enhanced ultrasound was useful in the assessment of local efficacy after IRE ablation of pancreatic adenocarcinoma.

18F-FDG PET Biomarkers Help Detect Early Metabolic Response to Irreversible Electroporation and Predict Therapeutic Outcomes in a Rat Liver Tumor Model

Purpose To test the hypothesis that biomarkers of fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) positron emission tomography (PET) can be used for the early detection of therapeutic response to irreversible electroporation (IRE) of liver tumor in a rodent liver tumor model. Materials and Methods The institutional animal care and use committee approved this study. Rats were inoculated with McA-RH7777 liver tumor cells in the left median and left lateral lobes. Tumors were allowed to grow for 7 days to reach a size typically at least 5 mm in longest diameter, as verified with magnetic resonance (MR) imaging. IRE electrodes were inserted, and eight 100-μsec, 2000-V pulses were applied to ablate the tumor tissue in the left median lobe. Tumor in the left lateral lobe served as a control in each animal. PET/computed tomography (CT) and MR imaging measurements were performed at baseline and 3 days after IRE for each animal. Additional MR imaging measurements were obtained 14 days after IRE. After 14-day follow-up MR imaging, rats were euthanized and tumors harvested for hematoxylin-eosin, CD34, and caspase-3 staining. Change in the maximum standardized uptake value (ΔSUV_max) was calculated 3 days after IRE. The maximum lesion diameter change (ΔD_max) was measured 14 days after IRE by using axial T2-weighted imaging. ΔSUV_max and ΔD_max were compared. The apoptosis index was calculated by using caspase-3-stained slices of apoptotic tumor cells. Pearson correlation coefficients were calculated to assess the relationship between ΔSUV_max at 3 days and ΔD_max (or apoptosis index) at 14 days after IRE treatment. Results ΔSUV_max, ΔD_max, and apoptosis index significantly differed between treated and untreated tumors (P < .001 for all). In treated tumors, there was a strong correlation between ΔSUV_max 3 days after IRE and ΔD_max 14 days after IRE (R = 0.66, P = .01) and between ΔSUV_max 3 days after IRE and apoptosis index 14 days after IRE (R = 0.57, P = .04). Conclusion ¹⁸F-FDG PET imaging biomarkers can be used for the early detection of therapeutic response to IRE treatment of liver tumors in a rodent model. ^© RSNA, 2017.

MR and CT imaging characteristics and ablation zone volumetry of locally advanced pancreatic cancer treated with irreversible electroporation

OBJECTIVES

To assess specific imaging characteristics after irreversible electroporation (IRE) for locally advanced pancreatic carcinoma (LAPC) with contrast-enhanced (ce)MRI and ceCT, and to explore the correlation of these characteristics with the development of recurrence.

METHODS

Qualitative and quantitative analyses of imaging data were performed on 25 patients treated with percutaneous IRE for LAPC. Imaging characteristics of the ablation zone on ceCT and ceMRI were assessed over a 6-month follow-up period. Contrast ratio scores between pre- and post-treatment were compared. To detect early imaging markers for treatment failure, attenuation characteristics at 6 weeks were linked to the area of recurrence within 6 months.

RESULTS

Post-IRE, diffusion-weighted imaging (DWI)-b800 signal intensities decreased in all cases (p < 0.05). Both ceMRI and ceCT revealed absent or decreased contrast enhancement, with a hyperintense rim on ceMRI. Ablation zone volume increase was noted on both modalities in the first 6 weeks, followed by a decrease (p < 0.05). In the patients developing tumour recurrence (5/25), a focal DWI-b800 hyperintense spot at 6 weeks predated unequivocal recurrence on CT.

CONCLUSION

The most remarkable signal alterations after pancreatic IRE were shown by DWI-b800 and ceMRI. These early imaging characteristics may be useful to establish technical success and predict treatment outcome.

KEY POINTS

• This study describes imaging characteristics after irreversible electroporation (IRE) for pancreatic adenocarcinoma. • Familiarity with typical post-IRE imaging characteristics helps to interpret ablation zones. • Post-IRE, no central and variable rim enhancement are visible on contrast-enhanced imaging. • DWI-b800 may prove useful to predict early tumour recurrence. • Post-IRE examinations reveal an initial volume increase followed by a decrease.

The local liver ablation with pulsed electric field stimulate systemic immune reaction against hepatocellular carcinoma (HCC) with time-dependent cytokine profile

AIM

How irreversible electroporation (IRE) affect immune status is still kept unknown. This preclinical study is to investigate its local and systemic immune reaction both on tumor-bearing and tumor free animals.

METHODS

Liver ablation was performed by a standard IRE instrument and proposal. Altogether 57 tumor bearing mice and 10 tumor-free porcine livers were ablated. The reaction of survival, radiology image, pathologically and immunologically were followed up. The detailed cytokines and chemokines responses were recorded dynamically post IRE ablation.

RESULTS

IRE ablation induced coagulation and necrosis in liver. It caused macrophages infiltration, in ablation zone. IRE ablation caused cellular inflammation. It, corrected the abnormal drifted Th2 in HCC back to Th1 status, promoting tumor eradication and host survival. The quantified cytokines and chemokines indicate IRE can stimulate both local immune reaction and systemic immune reaction.

CONCLUSION

Local IRE ablation changes the abnormal drifted Th2 in HCC back to Th1 status, facilitating tumor eradication and host survival.

Magnetic Resonance Imaging Findings After Percutaneous Irreversible Electroporation of Liver Metastases: A Systematic Longitudinal Study

Objective

The aim of this study was to systematically investigate the course of magnetic resonance (MR) signal intensity (SI) changes that occur in noncirrhotic livers after irreversible electroporation (IRE) of liver metastases.

Methods

This study is an institutional review board–approved prospective longitudinal follow-up study on 27 patients with 37 liver metastases who underwent computed tomography–guided percutaneous IRE and a standardized follow-up protocol by serial hepatic MR imaging studies that consisted of a gadobutrol-enhanced dynamic series, axial T2-weighted (T2w) turbo spin echo, and diffusion-weighted imaging (b = 0/50/800), acquired before, within 2, and at 24 hours after IRE; at 1, 2, 4, 6, 8, and 12 weeks after IRE; and every 3 months thereafter for a follow-up of at least 12 months.

Results

The ablated target lesion remained visible within the ablation zone in 23 (62%) of 37 of cases for a mean time of 21 ± 20 weeks (median, 12 weeks). The ablation zone appeared homogeneously hyperintense on T2w turbo spin echo images on the day of IRE in 37 of 37 cases. By 24 hours after IRE, the ablation zone inverted its SI in 35 of 37 cases to intermediately hypointense, with a rim of T2w bright SI that exhibited arterial phase enhancement; this persisted for 7 ± 5 weeks (median, 4 weeks). The rim resolved in 35 (95%) of 37 cases within 3 months. The ablation zone increased slightly over the first 48 hours, then shrank progressively. Complete healing of the ablation zone was observed in 57% (21/37) after an average of 14 ± 15 (median, 8 weeks).

Average apparent diffusion coefficient values of the ablation zone decreased from 0.74 ± 0.36 × 10⁻³ mm²/s pre-IRE to 0.63 ± 0.27 × 10⁻³ mm²/s within the first 24 hours (P < 0.05), followed by a progressive normalization to 0.91 ± 0.30 × 10⁻³ mm²/s at 2 months.

Conclusions

Knowledge of the broad spectrum of MR imaging findings after IRE is important to avoid diagnostic errors in the follow-up of patients after IRE.

Time-Dependent Impact of Irreversible Electroporation on Pancreas, Liver, Blood Vessels and Nerves: A Systematic Review of Experimental Studies

Introduction

Irreversible electroporation (IRE) is a novel ablation technique in the treatment of unresectable cancer. The non-thermal mechanism is thought to cause mostly apoptosis compared to necrosis in thermal techniques. Both in experimental and clinical studies, a waiting time between ablation and tissue or imaging analysis to allow for cell death through apoptosis, is often reported. However, the dynamics of the IRE effect over time remain unknown. Therefore, this study aims to summarize these effects in relation to the time between treatment and evaluation.

Methods

A systematic search was performed in Pubmed, Embase and the Cochrane Library for original articles using IRE on pancreas, liver or surrounding structures in animal or human studies. Data on pathology and time between IRE and evaluation were extracted.

Results

Of 2602 screened studies, 36 could be included, regarding IRE in liver (n = 24), pancreas (n = 4), blood vessels (n = 4) and nerves (n = 4) in over 440 animals (pig, rat, goat and rabbit). No eligible human studies were found. In liver and pancreas, the first signs of apoptosis and haemorrhage were observed 1–2 hours after treatment, and remained visible until 24 hours in liver and 7 days in pancreas after which the damaged tissue was replaced by fibrosis. In solitary blood vessels, the tunica media, intima and lumen remained unchanged for 24 hours. After 7 days, inflammation, fibrosis and loss of smooth muscle cells were demonstrated, which persisted until 35 days. In nerves, the median time until demonstrable histological changes was 7 days.

Conclusions

Tissue damage after IRE is a dynamic process with remarkable time differences between tissues in animals. Whereas pancreas and liver showed the first damages after 1–2 hours, this took 24 hours in blood vessels and 7 days in nerves.

Ultrasound and Contrast-Enhanced Ultrasound for Evaluation of Irreversible Electroporation Ablation: In Vivo Proof of Concept in Normal Porcine Liver

The objective of this study was to describe the performance of ultrasound (US) and contrast-enhanced ultrasound (CEUS) within 2 h after irreversible electroporation (IRE) ablation of porcine liver. Six IRE ablations were performed on porcine liver in vivo; ultrasound assessments were performed within 2 h after IRE ablation. On US images, the ablation zone appeared as a hypo-echoic area within 10 min after the ablation, and then the echo of the ablation zone gradually increased. On CEUS images, the ablation zone appeared as a non-enhanced area within 10 min after ablation and then was gradually centripetally filled by microbubbles. A hyper-echoic rim on US images and a hyper-enhanced rim on CEUS images appeared in the periphery of the ablation zone 60 min after the ablation. Characteristic and dynamic ultrasound images of the IRE ablation zone were obtained within 2 h after IRE ablation of in vivo porcine liver.

Optimizing Irreversible Electroporation Ablation with a Bipolar Electrode

PURPOSE

To optimize single-insertion bipolar irreversible electroporation (IRE) by characterizing effects of electric parameters and controlling tissue electric properties in a porcine model.

MATERIALS AND METHODS

Single-insertion electrode bipolar IRE was performed in 28 in vivo pig livers (78 ablations). First, effects of voltage (2,700-3,000 V), number of pulses, repeated cycles (1-6 cycles), and pulse width (70-100 µs) were studied. Next, electric conductivity was altered by instillation of hypertonic and hypotonic fluids. Finally, effects of thermal stabilization were assessed using internal electrode cooling. Treatment effect was evaluated 2-3 hours after IRE. Dimensions were compared and subjected to statistical analysis.

RESULTS

Delivering 3,000 V at 70 µs for a single 90-pulse cycle yielded 3.8 cm ± 0.4 × 2.0 cm ± 0.3 of ablation. Applying 6 cycles of energy increased ablation to 4.5 cm ± 0.4 × 2.6 cm ± 0.3 (P < .001). Further increasing pulse lengths to 100 µs (6 cycles) increased ablation to 5.0 cm ± 0.4 × 2.9 cm ± 0.3 (P < .001) but resulted in electric spikes and system crashes in 40%-50% of cases. Increasing tissue electric conductivity via hypertonic solution instillation in surrounding tissues increased frequency of generator crashes, whereas continuous instillation of distilled water eliminated this arcing phenomenon but reduced ablation to 2.3 cm ± 0.1. Controlled instillation of distilled water when electric arcing was suspected from audible popping produced ablations of 5.3 cm ± 0.6 × 3.1 cm ±0.3 without crashes. Finally, 3.1 cm ± 0.1 short-axis ablation was achieved without system crashes with internal electrode perfusion at 37°C versus 2.3 cm ± 0.1 with 4°C-10°C perfusion (P < .001).

CONCLUSIONS

Bipolar IRE ablation zones can be increased with repetitive high voltage and greater pulse widths accompanied by either judicious instillation of hypotonic fluids or internal electrode perfusion to minimize unwanted electric arcing.

Local Ablative Strategies for Ductal Pancreatic Cancer (Radiofrequency Ablation, Irreversible Electroporation): A Review

Pancreatic ductal adenocarcinoma (PDAC) has still a dismal prognosis. Locally advanced pancreatic cancer (LAPC) accounts for the 40% of the new diagnoses. Current treatment options are based on chemo- and radiotherapy regimens. Local ablative techniques seem to be the future therapeutic option for stage-III patients with PDAC. Radiofrequency Ablation (RFA) and Irreversible Electroporation (IRE) are actually the most emerging local ablative techniques used on LAPC. Initial clinical studies on the use of these techniques have already demonstrated encouraging results in terms of safety and feasibility. Unfortunately, few studies on their efficacy are currently available. Even though some reports on the overall survival are encouraging, randomized studies are still required to corroborate these findings. This study provides an up-to-date overview and a thematic summary of the current available evidence on the application of RFA and IRE on PDAC, together with a comparison of the two procedures.

Electric Ablation with Irreversible Electroporation (IRE) in Vital Hepatic Structures and Follow-up Investigation

Irreversible electroporation (IRE) with microsecond-pulsed electric fields (μsPEFs) can effectively ablate hepatocellular carcinomas in animal models. This preclinical study evaluates the feasibility and safety of IRE on porcine livers. Altogether, 10 pigs were included. Computed tomography (CT) was used to guide two-needle electrodes that were inserted near the hilus hepatis and gall bladder. Animals were followed-up at 2 hours and at 2, 7 and 14 days post-treatment. During and after μsPEF ablation, electrocardiographs found no cardiovascular events, and contrast CT found no portal vein thrombosis. There was necrosis in the ablation zone. Mild cystic oedema around the gall bladder was found 2 hours post-treatment. Pathological studies showed extensive cell death. There was no large vessel damage, but there was mild endothelial damage in some small vessels. Follow-up liver function tests and routine blood tests showed immediate liver function damage and recovery from the damage, which correlated to the pathological changes. These results indicate that μsPEF ablation affects liver tissue and is less effective in vessels, which enable μsPEFs to ablate central tumour lesions close to the hilus hepatis and near large vessels and bile ducts, removing some of the limitations and contraindications of conventional thermal ablation.

CT Findings of Patients Treated with Irreversible Electroporation for Locally Advanced Pancreatic Cancer

Introduction. In patients with locally advanced pancreatic cancer (LAPC), IRE has been shown to be safe for local disease control and palliation. As IRE continues to gain acceptance it is important to characterize the expected imaging findings. Materials and Methods. A review of our prospective soft tissue ablation registry from July 2010 to June 2013 was performed on patients who had undergone IRE for LAPC. Five masses treated with intraoperative IRE ablation for pancreatic tumors that underwent CT imaging before and after ablation were reviewed. Results and Discussion. Following IRE, the postablation bed is larger than the original ablated tumor. This ablation zone may get smaller in size (due to decreased edema and hyperemia) in the following months and more importantly remains stable provided there is no recurrence. In cases of recurrent disease there is increased size of the ablation bed, mass effect, and new or worsening vascular encasement or occlusion. Conclusion. CT imaging remains the best current imaging modality to assess post-IRE ablation changes. Serial imaging over at least 2-6 months must be employed to detect recurrence by comparing with prior studies in conjunction with clinical and serum studies. Larger imaging studies are underway to evaluate a more ideal imaging modality for this unique patient population.

Colorectal liver metastatic disease: efficacy of irreversible electroporation--a single-arm phase II clinical trial (COLDFIRE-2 trial)

Background

Irreversible electroporation (IRE) is a novel image-guided tumor ablation technique that has shown promise for the ablation of lesions in proximity to vital structures such as blood vessels and bile ducts. The primary aim of the COLDFIRE-2 trial is to investigate the efficacy of IRE for unresectable, centrally located colorectal liver metastases (CRLM). Secondary outcomes are safety, technical success, and the accuracy of contrast-enhanced (ce)CT and ¹⁸F-FDG PET-CT in the detection of local tumor progression (LTP).

Methods/design

In this single-arm, multicenter phase II clinical trial, twenty-nine patients with ¹⁸F-FDG PET-avid CRLM ≤ 3,5 cm will be prospectively included to undergo IRE of the respective lesion. All lesions must be unresectable and unsuitable for thermal ablation due to vicinity of vital structures. Technical success is based on ceMRI one day post-IRE. All complications related to the IRE procedure are registered. Follow-up consists of ¹⁸F-FDG PET-CT and 4-phase liver CT at 3-monthly intervals during the first year of follow-up. Treatment efficacy is defined as the percentage of tumors successfully eradicated 12 months after the initial IRE procedure based on clinical follow-up using both imaging modalities, tumor marker and (if available) histopathology. To determine the accuracy of ¹⁸F-FDG PET-CT and ceCT, both imaging modalities will be individually scored by two reviewers that are blinded for the final oncologic outcome.

Discussion

To date, patients with a central CRLM unsuitable for resection or thermal ablation have no curative treatment option and are given palliative chemotherapy. For these patients, IRE may prove a life-saving treatment option. The results of the proposed trial may represent an important step towards the implementation of IRE for central liver tumors in the clinical setting.

Trial registration

Trial registration number: NCT02082782.

Feasibility of a Modified Biopsy Needle for Irreversible Electroporation Ablation and Periprocedural Tissue Sampling

OBJECTIVES

To test the feasibility of modified biopsy needles as probes for irreversible electroporation ablation and periprocedural biopsy.

METHODS

Core biopsy needles of 16-G/9-cm were customized to serve as experimental ablation probes. Computed tomography-guided percutaneous irreversible electroporation was performed in in vivo porcine kidneys with pairs of experimental (n = 10) or standard probes (n = 10) using a single parameter set (1667 V/cm, ninety 100 µs pulses). Two biopsy samples were taken immediately following ablation using the experimental probes (n = 20). Ablation outcomes were compared using computed tomography, simulation, and histology. Biopsy and necropsy histology were compared.

RESULTS

Simulation-suggested ablations with experimental probes were smaller than that with standard electrodes (455.23 vs 543.16 mm²), although both exhibited similar shape. Computed tomography (standard: 556 ± 61 mm², experimental: 515 ± 67 mm²; P = .25) and histology (standard: 313 ± 77 mm², experimental: 275 ± 75 mm²; P = .29) indicated ablations with experimental probes were not significantly different from the standard. Histopathology indicated similar morphological changes in both groups. Biopsies from the ablation zone yielded at least 1 core with sufficient tissue for analysis (11 of the 20).

CONCLUSIONS

A combined probe for irreversible electroporation ablation and periprocedural tissue sampling from the ablation zone is feasible. Ablation outcomes are comparable to those of standard electrodes.

Assessment of various types of US findings after irreversible electroporation in porcine liver: comparison with radiofrequency ablation

PURPOSE

To assess various ultrasound (US) findings, including B-mode, shear-wave elastography (SWE), and contrast-enhanced US, in accurately assessing ablation margins after irreversible electroporation (IRE) based on radiologic-pathologic correlation, and to compare these findings between IRE and radiofrequency (RF) ablation.

MATERIALS AND METHODS

IRE (n = 9) and RF ablation (n = 3) were performed in vivo in three pig livers. Each ablation zone was imaged by each method immediately after the procedure and 90 minutes later. Ablation zones were evaluated based on gross pathologic and histopathologic findings in samples from animals euthanized 2 hours after the last ablation. The characteristics and dimensions of the histologic ablation zones were qualitatively and quantitatively compared against each US finding.

RESULTS

In B-mode US at 90 minutes after IRE, the ablation zones appeared as hyperechoic areas with a peripheral hyperechoic rim, showing excellent correlation (r(2) = 0.905, P < .0001) with gross pathologic findings. SWE showed that tissue stiffness in the IRE ablation zones increased over time. Contrast-enhanced US depicted the IRE ablation zones as hypovascular areas in the portal phase, and showed the highest correlation (r(2) = 0.923, P < .0001) with gross pathologic findings. The RF ablation zones were clearly visualized by B-mode US. SWE showed that tissue stiffness after RF ablation was higher than after IRE. Contrast-enhanced US depicted the RF ablation zones as avascular areas.

CONCLUSIONS

IRE and RF ablation zones can be most accurately predicted by portal-phase contrast-enhanced US measurements obtained immediately after ablation.

A review of basic to clinical studies of irreversible electroporation therapy

The use of irreversible electroporation (IRE) for cancer treatment has increased sharply over the past decade. As a nonthermal therapy, IRE offers several potential benefits over other focal therapies, which include 1) short treatment delivery time, 2) reduced collateral thermal injury, and 3) the ability to treat tumors adjacent to major blood vessels. These advantages have stimulated widespread interest in basic through clinical studies of IRE. For instance, many in vitro and in vivo studies now identify treatment planning protocols (IRE threshold, pulse parameters, etc.), electrode delivery (electrode design, placement, intraoperative imaging methods, etc.), injury evaluation (methods and timing), and treatment efficacy in different cancer models. Therefore, this study reviews the in vitro, translational, and clinical studies of IRE cancer therapy based on major experimental studies particularly within the past decade. Further, this study provides organized data and facts to assist further research, optimization, and clinical applications of IRE.

Irreversible Electroporation of Malignant Hepatic Tumors--Alterations in Venous Structures at Subacute Follow-Up and Evolution at Mid-Term Follow-Up

Purpose

To evaluate risk factors associated with alterations in venous structures adjacent to an ablation zone after percutaneous irreversible electroporation (IRE) of hepatic malignancies at subacute follow-up (1 to 3 days after IRE) and to describe evolution of these alterations at mid-term follow-up.

Materials and Methods

43 patients (men/women, 32/11; mean age, 60.3 years) were identified in whom venous structures were located within a perimeter of 1.0 cm of the ablation zone at subacute follow-up after IRE of 84 hepatic lesions (primary/secondary hepatic tumors, 31/53). These vessels were retrospectively evaluated by means of pre-interventional and post-interventional contrast-enhanced magnetic resonance imaging or computed tomography or both. Any vascular changes in flow, patency, and diameter were documented. Correlations between vascular change (yes/no) and characteristics of patients, lesions, and ablation procedures were assessed by generalized linear models.

Results

191 venous structures were located within a perimeter of 1.0 cm of the ablation zone: 55 (29%) were encased by the ablation zone, 78 (41%) abutted the ablation zone, and 58 (30%) were located between 0.1 and 1.0 cm from the border of the ablation zone. At subacute follow-up, vascular changes were found in 19 of the 191 vessels (9.9%), with partial portal vein thrombosis in 2, complete portal vein thrombosis in 3, and lumen narrowing in 14 of 19. At follow-up of patients with subacute vessel alterations (mean, 5.7 months; range, 0 to 14 months) thrombosis had resolved in 2 of 5 cases; vessel narrowing had completely resolved in 8 of 14 cases, and partly resolved in 1 of 14 cases. The encasement of a vessel by ablation zone (OR = 6.36, p<0.001), ablation zone being adjacent to a portal vein (OR = 8.94, p<0.001), and the usage of more than 3 IRE probes (OR = 3.60, p = 0.035) were independently associated with post-IRE vessel alterations.

Conclusion

Venous structures located in close proximity to an IRE ablation zone remain largely unaffected by this procedure, and thrombosis is rare.

In vivo irreversible electroporation kidney ablation: experimentally correlated numerical models

Irreversible electroporation (IRE) ablation uses brief electric pulses to kill a volume of tissue without damaging the structures contraindicated for surgical resection or thermal ablation, including blood vessels and ureters. IRE offers a targeted nephron-sparing approach for treating kidney tumors, but the relevant organ-specific electrical properties and cellular susceptibility to IRE electric pulses remain to be characterized. Here, a pulse protocol of 100 electric pulses, each 100 μs long, is delivered at 1 pulse/s to canine kidneys at three different voltage-to-distance ratios while measuring intrapulse current, completed 6 h before humane euthanasia. Numerical models were correlated with lesions and electrical measurements to determine electrical conductivity behavior and lethal electric field threshold. Three methods for modeling tissue response to the pulses were investigated (static, linear dynamic, and asymmetrical sigmoid dynamic), where the asymmetrical sigmoid dynamic conductivity function most accurately and precisely matched lesion dimensions, with a lethal electric field threshold of 575 ± 67 V/cm for the protocols used. The linear dynamic model also attains accurate predictions with a simpler function. These findings can aid renal IRE treatment planning under varying electrode geometries and pulse strengths. Histology showed a wholly necrotic core lesion at the highest electric fields, surrounded by a transitional perimeter of differential tissue viability dependent on renal structure.

Image-guided tumor ablation: standardization of terminology and reporting criteria--a 10-year update

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes.

Irreversible electroporation ablation of malignant hepatic tumors: subacute and follow-up CT appearance of ablation zones

PURPOSE

To describe findings on contrast-enhanced computed tomography (CT) images of malignant hepatic tumors 24-72 hours after percutaneous ablation by irreversible electroporation (IRE) and at midterm follow-up.

MATERIALS AND METHODS

Retrospective analysis of 52 malignant liver tumors-30 primary hepatic tumors and 22 hepatic metastases-in 34 patients (28 men and 6 women, mean age 64 y) treated by IRE ablation was performed. Ablation zones were evaluated by two examiners in a consensus reading by means of a dual-phase CT scan (consisting of a hepatic arterial and portal venous phase) performed 24-72 hours after IRE ablation and at follow-up.

RESULTS

During the portal venous phase, ablation zones either were homogeneously hypoattenuating (n = 36) or contained heterogeneously isoattenuating or hyperattenuating (n = 16) foci, or both, in a hypoattenuating area. Of 52 lesions, 38 included gas pockets. Peripheral contrast enhancement of the ablation defect was evident in 23 tumors during the arterial phase and in 36 tumors during the portal venous phase. Four tumors showed intralesional abscesses after the intervention. At follow-up (mean, 4.7 mo), the mean volume of the ablation defects was reduced to 29% of their initial value.

CONCLUSIONS

Because normal findings on contrast-enhanced CT images after IRE ablation may be very similar to the typical characteristics of potential complications following ablation, such as liver abscesses, CT scans must be carefully analyzed to distinguish normal results after intervention from complications requiring further treatment.

A numerical investigation of the electric and thermal cell kill distributions in electroporation-based therapies in tissue

Electroporation-based therapies are powerful biotechnological tools for enhancing the delivery of exogeneous agents or killing tissue with pulsed electric fields (PEFs). Electrochemotherapy (ECT) and gene therapy based on gene electrotransfer (EGT) both use reversible electroporation to deliver chemotherapeutics or plasmid DNA into cells, respectively. In both ECT and EGT, the goal is to permeabilize the cell membrane while maintaining high cell viability in order to facilitate drug or gene transport into the cell cytoplasm and induce a therapeutic response. Irreversible electroporation (IRE) results in cell kill due to exposure to PEFs without drugs and is under clinical evaluation for treating otherwise unresectable tumors. These PEF therapies rely mainly on the electric field distributions and do not require changes in tissue temperature for their effectiveness. However, in immediate vicinity of the electrodes the treatment may results in cell kill due to thermal damage because of the inhomogeneous electric field distribution and high current density during the electroporation-based therapies. Therefore, the main objective of this numerical study is to evaluate the influence of pulse number and electrical conductivity in the predicted cell kill zone due to irreversible electroporation and thermal damage. Specifically, we simulated a typical IRE protocol that employs ninety 100-µs PEFs. Our results confirm that it is possible to achieve predominant cell kill due to electroporation if the PEF parameters are chosen carefully. However, if either the pulse number and/or the tissue conductivity are too high, there is also potential to achieve cell kill due to thermal damage in the immediate vicinity of the electrodes. Therefore, it is critical for physicians to be mindful of placement of electrodes with respect to critical tissue structures and treatment parameters in order to maintain the non-thermal benefits of electroporation and prevent unnecessary damage to surrounding healthy tissue, critical vascular structures, and/or adjacent organs.

Irreversible electroporation: ready for prime time?

Image-guided ablation has evolved rapidly in the past decade into a competitive technique for treating focal solid malignancies. However, as they rely mainly on thermal energy, such as radiofrequency or microwave, many tumors close to sensitive organs, such as ducts, bowel, and nerves, still remain nonablatable owing to the risk of thermal injury. Irreversible electroporation is a novel ablation modality that relies largely on a nonthermal mechanism to induce cell death, and therefore may overcome many of the shortcomings of thermal ablation. Emerging preclinical data as well as early clinical experience is showing promise for this technique in treating a variety of tumors including periportal liver masses, pancreatic cancer, perihilar renal tumors, prostate cancer, and other soft tissue tumors. However, practical limitations remain for irreversible electroporation, and its complete cancer and location-specific safety and efficacy profiles are still largely unknown. We therefore review what is known for this new ablation modality based on preclinical and preliminary clinical data, and discuss its emerging indications as well as technical challenges.