Irreversible Electroporation Zones Research Articles

Abstract No. 51 Differentiation of Irreversible Electroporation Regions in Normal and Tumor Tissues Using MRI Textures

Irreversible electroporation (IRE) is a promising tissue ablation technique for liver cancer patients unsuitable for surgical resection or liver transplantation. The main clinical challenge in IRE ablation is differentiating IRE ablation zones for immediate assessment. Here, we investigated the reproducibility of radiomic analysis of conventional T1w MRI data acquired from liver tumors and normal liver tissues for assessment of IRE outcomes. IRE ablation was performed on twenty-six rabbits' normal liver or tumors. Anatomical and perfusion MRI data were acquired immediately after the completion of the procedure. IRE and RE zones were outlined on perfusion MRI data with histology validation and mask images were translated to T1w images. T1w MRI data were normalized using three levels to examine the effects of different image specificity (8, 16, and 32) while determining the characteristic patterns related to IRE ablation. At each specificity level, quantitative imaging features were computed by analyzing intensity distribution and textural patterns. The relevant variables were identified by following a multi-step feature selection framework that integrates pairwise likelihood, analysis, and LASSO. Multiple classification models were generated using logistic regression, nonlinear support vector machines, and random forest (RF) with a five-fold cross-validation approach. The accuracy, sensitivity, specificity, and receiver operating characteristic (ROC) curves were employed for the evaluation of the developed classification methods. Random forest classification models outperformed logistic regression and support vector machine models. In terms of image specificity levels, the images sampled with sixteen intensity levels facilitated the most accurate and robust performance compared with images with lower and higher details. The random forest classifier equipped with features computed from images with sixteen levels obtained a training accuracy of 90.86% and a validation accuracy of 81.09% for T1w images. The model sensitivity was 92.33% and 81.33%, and specificity was 89.33% and 80.67% for training and validation sets, respectively. Moreover, we recorded the area under the ROC curve as 97.86% for training and 89.47% for the validation cohort. T1w MRI radiomic features reveal IRE ablation-related effects performed on normal liver and tumor tissues, which demonstrates the potential benefit of quantitative analysis of conventional MRI data for immediate assessment of IRE ablation zones in other solid cancers.

Abstract No. 267 TRIP-MRI detects immediate response to irreversible electroporation ablation in rabbit VX2 liver tumor

Irreversible electroporation (IRE) represents a promising treatment option for unresectable liver tumors. The effectively treated zone cannot be reliably predicted. We investigate the potential benefit of transcatheter intra-arterial perfusion (TRIP) -MRI for the early noninvasive differentiation of the IRE zone from the surrounding reversibly electroporated (RE) zone.

Early Differentiation of Irreversible Electroporation Ablation Regions With Radiomics Features of Conventional MRI

Irreversible electroporation (IRE) is a promising non-thermal ablation technique for the treatment of patients with hepatocellular carcinoma. Early differentiation of the IRE zone from surrounding reversibly electroporated (RE) penumbra is vital for the evaluation of treatment response. In this study, an advanced statistical learning framework was developed by evaluating standard MRI data to differentiate IRE ablation zones, and to correlate with histological tumor biomarkers. Fourteen rabbits with VX2 liver tumors were scanned following IRE ablation and forty-six features were extracted from T1w and T2w MRI. Following identification of key imaging variables through two-step feature analysis, multivariable classification and regression models were generated for differentiation of IRE ablation zones, and correlation with histological markers reflecting viable tumor cells, microvessel density, and apoptosis rate. The performance of the multivariable models was assessed by measuring accuracy, receiver operating characteristics curve analysis, and Spearman correlation coefficients. The classifiers integrating four radiomics features of T1w, T2w, and T1w+T2w MRI data distinguished IRE from RE zones with an accuracy of 97%, 80%, and 97%, respectively. Also, pixelwise classification models of T1w, T2w, and T1w+T2w MRI labeled each voxel with an accuracy of 82.8%, 66.5%, and 82.9%, respectively. Regression models obtained a strong correlation with behavior of viable tumor cells (0.62 ≤ r2 ≤ 0.85, p < 0.01), apoptosis (0.40 ≤ r2 ≤ 0.82, p < 0.01), and microvessel density (0.48 ≤ r2 ≤ 0.58, p < 0.01). MRI radiomics features provide descriptive power for early differentiation of IRE and RE zones while observing strong correlations among multivariable MRI regression models and histological tumor biomarkers.

Comparison between high-frequency irreversible electroporation and irreversible electroporation ablation of small swine liver: follow-up of DCE-MRI and pathological observations.

Background:High-frequency irreversible electroporation (H-FIRE) is a novel, next-generation nanoknife technology with the advantage of relieving irreversible electroporation (IRE)-induced muscle contractions. However, the difference between IRE and H-FIRE with distinct ablation parameters was not clearly defined. This study aimed to compare the efficacy of the two treatments in vivo.Methods:Ten Bama miniature swine were divided into two group: five in the 1-day group and five in the 7-day group. The efficacy of IRE and H-FIRE ablation was compared by volume transfer constant (Krans), rate constant (Kep) and extravascular extracellular volume fraction (Ve) value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), size of the ablation zone, and histologic analysis. Each animal underwent the IRE and H-FIRE. Temperatures of the electrodes were measured during ablation. DCE-MRI images were obtained 1, 4, and 7 days after ablation in the 7-day group. All animals in the two groups were euthanized 1 day or 7 days after ablation, and subsequently, IRE and H-FIRE treated liver tissues were collected for histological examination. Student's t test or Mann-Whitney U test was applied for comparing any two groups. One-way analysis of variance (ANOVA) test and Welch's ANOVA test followed by Holm-Sidak's multiple comparisons test, one-way ANOVA with repeated measures followed by Bonferroni test, or Kruskal-Wallis H test followed by Dunn's multiple comparison test was used for multiple group comparisons and post hoc analyses. Pearson correlation coefficient test was conducted to analyze the relationship between two variables.Results:Higher Ve was seen in IRE zone than in H-FIRE zone (0.14 ± 0.02 vs. 0.08 ± 0.05, t = 2.408, P = 0.043) on day 4, but no significant difference was seen in Ktrans or Kep between IRE and H-FIRE zones at all time points (all P > 0.05). For IRE zone, the greatest Ktrans was seen on day 7, which was significantly higher than that on day 1 (P = 0.033). The ablation zone size of H-FIRE was significantly larger than IRE 1 day (4.74 ± 0.88 cm2vs. 3.20 ± 0.77 cm2, t = 3.241, P = 0.009) and 4 days (2.22 ± 0.83 cm2vs. 1.30 ± 0.50 cm2, t = 2.343, P = 0.041) after treatment. Apoptotic index (0.05 ± 0.02 vs. 0.73 ± 0.06 vs. 0.68 ± 0.07, F = 241.300, P < 0.001) and heat shock protein 70 (HSP70) (0.03 ± 0.01 vs. 0.46 ± 0.09 vs. and 0.42 ± 0.07, F = 64.490, P < 0.001) were significantly different between the untreated, IRE and H-FIRE zones, but no significant difference was seen in apoptotic index or HSP70 between IRE and H-FIRE zone (both P > 0.05). Electrode temperature variations were not significantly different between the two zones (18.00 ± 3.77°C vs. 16.20 ± 7.45°C, t = 0.682, P = 0.504). The Ktrans value (r = 0.940, P = 0.017) and the Kep value (r = 0.895, P = 0.040) of the H-FIRE zone were positively correlated with the number of hepatocytes in the ablation zone.Conclusions:H-FIRE showed a comparable ablation effect to IRE. DCE-MRI has the potential to monitor the changes of H-FIRE ablation zone.

Intraprocedural Transcatheter Intraarterial Perfusion (TRIP)-MRI for Evaluation of Irreversible Electroporation Therapy Response in a Rabbit Liver Tumor Model.

PurposeIrreversible electroporation (IRE) is a promising new ablation method for hepatocellular carcinoma (HCC) treatment with few side-effects; however, tissue perfusion and differentiation between treatment zones have not been sufficiently studied. In this project, we analyzed HCC tumor perfusion changes immediately after IRE treatment using transcatheter intraarterial perfusion (TRIP)-MRI to monitor treatment zone margins.Materials and MethodsAll protocols were approved by the institutional animal care and use committee. A total of 34 rabbits were used for this prospective study: tumor liver group (n=17), normal liver group (n=14), and 3 for growing VX2 tumors. All procedures and imaging were performed under anesthesia. VX2 tumors were grown by injection of VX2 cells into rabbit hindlimbs. Liver tumors were induced by percutaneous US-guided injection of VX2 tumor fragments into liver. For digital subtraction angiography (DSA), a 2F catheter was advanced through left hepatic artery via femoral artery access, followed by contrast injection. All rabbits underwent baseline anatomic MRI, then IRE procedure or IRE probe placement only, and lastly post-procedure anatomic and TRIP-MRI. Liver tissues were dissected immediately after imaging for histology. All statistical analyses were performed on GraphPad Prism, with P<0.05 considered significant.ResultsIRE generated central IRE zone and peripheral reversible electroporation (RE) zone on anatomic MRI for both normal liver and liver tumor tissues. The semiquantitative analysis showed that IRE zone had the lowest AUC, PE, WIS, Ktrans, ve, and vp as well as the highest TTP, followed by RE zone, then untreated tissues. Receiver operating characteristic analysis showed that WIS and AUC60 had the highest AUCROC. Histologic analysis showed a positive correlation in viable area fraction between MRI and histologic measurements. IRE zone had the highest %apoptosis and lowest CD31+ staining.ConclusionOur results demonstrated that intraprocedural TRIP-MRI can effectively differentiate IRE and RE zones after IRE ablation in normal liver and liver tumor tissues.

Intra-arterial Injection of Lidocaine as a Cell Sensitizer during Irreversible Electroporation

PurposeTo investigate whether intra-arterial injection of lidocaine enhances irreversible electroporation (IRE) in a liver model. Materials and MethodsConventional IRE (C-IRE) and lidocaine-enhanced IRE (L-IRE) were performed in 8 pig livers. Protocol 1 (tip exposure and electrode distance of 2.0 cm each) and protocol 2 (increased tip exposure and electrode distance 2.5 cm each) were used. Animals were sacrificed 3 hours after IRE. Study goals included electrical tissue properties (eg, current, conductivity) during IRE, geometry of IRE zones analyzed using computed tomography and magnetic resonance imaging (eg, volume and sphericity index), degree of acute liver damage, and irreversible cell death analyzed using microscopy (hematoxylin and eosin staining and terminal deoxynucleotidyl transferase deoxyuridine 5-triphosphate nick end labeling). Statistical comparisons were performed using the paired t test and Wilcoxon test. ResultsAll treatments were performed without adverse events. Electrical tissue properties were not significantly different between C-IRE and L-IRE. For protocol 1, the diameter of the largest sphere within the IRE zone was significantly larger for L-IRE than for C-IRE (25.0 ± 4.7 mm vs 18.4 ± 3.1 mm [P = .013]). For protocol 2, the volume of IRE zone was significantly larger for L-IRE compared with C-IRE (46.0 ± 5.4 cm3 vs 22.6 ± 6.4 cm3 [P = .018]), as well as the diameter of the largest sphere within the IRE zone (27.1 ± 2.2 mm vs 19.8 ± 2.3 mm [P = .020]). For protocol 1, a significantly higher degree of irreversible cell death was noted for L-IRE than for C-IRE (1.8 ± 1.0 vs 0.8 ± 1.0 [P = .046]). ConclusionsIntra-arterial injection of lidocaine can enhance IRE in terms of larger IRE zones and an increase of irreversible cell death.

Transcatheter Intraarterial Perfusion MRI Approaches to Differentiate Reversibly Electroporated Penumbra From Irreversibly Electroporated Zones in Rabbit Liver

To investigate whether transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) can differentiate reversible electroporation (RE) zones from irreversible electroporation (IRE) zones immediately after IRE procedure in the rabbit liver. All studies were approved by the institutional animal care and use committee and performed in accordance with institutional guidelines. A total of 13 healthy New Zealand White rabbits were used. After selective catheterization of the hepatic artery under X-ray fluoroscopy, we acquired TRIP-MRI at 20 minutes post-IRE using 3 mL of 5% intraarterial gadopentetate dimeglumine. Semi-quantitative (peak enhancement, PE; time to peak, TTP; wash-in slope, WIS; areas under the time-intensity curve, AUT, over 30, 60, 90, 120, 150, and 180 seconds after the initiation of enhancement) and quantitative (Ktrans, ve, and vp) TRIP-MRI parameters were calculated. The relationships between TRIP-MRI parameters and histological measurements and the differential ability of TRIP-MRI parameters was assessed. PE, AUT60, AUT90, AUT120, AUT150, AUT180, Ktrans, and ve were significantly higher in RE zones than in IRE zones (all P < 0.05), and AUC for these parameters ranged from 0.91(95% CI, 0.80, 1.00) to 0.99 (95% CI, 0.98, 1.00). There was no significant difference in AUC between any two parameters (Z, 0-1.47; P, 0.14-1.00). Hepatocyte apoptosis strongly correlated with PE, AUT60, AUT90, AUT120, AUT150, AUT180, Ktrans, and vp (the absolute value r, 0.6-0.7, all P < 0.0001). AUT150 or AUT180 could be a potential imaging biomarker to differentiate RE from IRE zones, and TRIP-MRI permits to differentiate RE from IRE zones immediately after IRE procedure in the rabbit liver.

Transcatheter intra-arterial perfusion (TRIP)-MRI biomarkers help detect immediate response to irreversible electroporation of rabbit VX2 liver tumor.

Irreversible electroporation (IRE) is a nonthermal tissue ablation technique that represents a promising treatment option for unresectable liver tumors, but the effectively treated zone cannot be reliably predicted. We investigate the potential benefit of transcatheter intra-arterial perfusion (TRIP) -MRI for the early noninvasive differentiation of IRE zone from surrounding reversibly electroporated (RE) zone. Seventeen rabbits with VX2 liver tumors were scanned with morphological and contrast-enhanced MRI sequences approximately 30 min after IRE tumor ablation. Quantitative TRIP-MRI perfusion parameters were evaluated in IRE zone and RE zone, defined according to histology. MRI and histology results were compared among zones using Wilcoxon rank-sum tests and correlations were evaluated by Pearson's correlation coefficient. There were significant differences in area under the curve, time to peak, maximum and late enhancement, wash-in and wash-out rates in the tumor IRE zones compared with the boundary tumor RE zones and untreated tumors. Histology showed significantly fewer tumor cells, microvessels and significantly more apoptosis in tumor IRE zones compared with tumor RE zones (-51%, -66% and +185%, respectively) and untreated tumors (-60%, -67%, and +228%, respectively). A strong correlation was observed between MRI and histology measurements of IRE zones (r = 0.948) and RE zones (r = 0.951). TRIP-MRI demonstrated the potential to detect immediate perfusion changes following IRE liver tumor ablation and effectively differentiate the IRE zone from the surrounding tumor RE zone.

The Accumulation and Effects of Liposomal Doxorubicin in Tissues Treated by Radiofrequency Ablation and Irreversible Electroporation in Liver: In Vivo Experimental Study on Porcine Models.

To compare the accumulation and effect of liposomal doxorubicin in liver tissue treated by radiofrequency ablation (RFA) and irreversible electroporation (IRE) in in vivo porcine models. Sixteen RFA and 16 IRE procedures were performed in healthy liver of two groups of three pigs. Multi-tined RFA parameters included: 100W, target temperature 105°C for 7min. 100 IRE pulses were delivered using two monopolar electrodes at 2250V, 1Hz, for 100 µsec. For each group, two pigs received 50mg liposomal doxorubicin (0.5mg/kg) as a drip infusion during ablation procedure, with one pig serving as control. Samples were harvested from the central and peripheral zones of the ablation at 24 and 72h. Immunohistochemical analysis to evaluate the degree of cellular stress, DNA damage, and degree of apoptosis was performed. These and the ablation sizes were compared. Doxorubicin concentrations were also analyzed using fluorescence photometry of homogenized tissue. RFA treatment zones created with concomitant administration of doxorubicin at 24h were significantly larger than controls (2.5 ± 0.3cm vs. 2.2 ± 0.2cm; p = 0.04). By contrast, IRE treatment zones were negatively influenced by chemotherapy (2.2 ± 0.4cm vs. 2.6 ± 0.4cm; p = 0.05). At 24h, doxorubicin concentrations in peripheral and central zones of RFA were significantly increased in comparison with untreated parenchyma (0.431 ± 0.078µg/g and 0.314 ± 0.055µg/g vs. 0.18 ± 0.012µg/g; p < 0.05). Doxorubicin concentrations in IRE zones were not significantly different from untreated liver (0.191 ± 0.049µg/g and 0.210 ± 0.049µg/g vs. 0.18 ± 0.012µg/g). Whereas there is an increased accumulation of periprocedural doxorubicin and an associated increase in ablation zone following RFA, a contrary effect is noted with IRE. These discrepant findings suggest that different mechanisms and synergies will need to be considered in order to select optimal adjuvants for different classes of ablation devices.

Electrochemical Effects after Transarterial Chemoembolization in Combination with Percutaneous Irreversible Electroporation: Observations in an Acute Porcine Liver Model

PurposeTo evaluate the effects of combined use of transarterial chemoembolization and irreversible electroporation (IRE) for focal tissue ablation in an acute porcine liver model. Materials and MethodsTwo established interventional techniques were combined: IRE with zones of irreversible and reversible electroporation and chemoembolization with microspheres, iodized oil, and doxorubicin. IRE was performed before chemoembolization in two pigs (pigs 1 and 2; IRE/chemoembolization group), chemoembolization was performed before IRE in two pigs (pigs 3 and 4; chemoembolization/IRE group), and only IRE was performed in two pigs (pigs 5 and 6). Five study groups were defined: IRE/chemoembolization (pigs 1 and 2), chemoembolization/IRE (pigs 3 and 4), IRE only (pigs 5 and 6), chemoembolization only (tissue outside the IRE zones in pigs 1–4), and control (untreated liver tissue outside the IRE zones in pigs 5 and 6). Animals were euthanized 2 hours after intervention. Size and shape of IRE zones on contrast-enhanced computed tomography, cell death on light microscopy, and doxorubicin tissue concentrations on chromatography and fluorescence microscopy were analyzed. ResultsSize and shape of IRE zones were not significantly different (eg, P = .067 for volume). A histologic marker for irreversible cell death was positive in IRE/chemoembolization, chemoembolization/IRE, and IRE groups only in the macroscopically visible IRE zones. Doxorubicin tissue concentrations were not significantly different (P = .873). However, in the reversible electroporation (RE) zones, broad areas with intense intranuclear doxorubicin accumulation were observed in IRE/chemoembolization but not in chemoembolization/IRE and chemoembolization groups. ConclusionsIRE before chemoembolization enhances the intranuclear accumulation of doxorubicin in the RE zone.

P0250 : Effect of irreversible electroporation (IRE) on the porcine liver: comparison with radiofrequency ablation

Background and Aims: Irreversible electroporation (IRE) is a promising, non-thermal ablation therapy for hepatocellular carcinoma, which, unlike radiofrequency thermal ablation (RFA), induces apoptosis through irreversible formation of nanoscale pores in the cell membrane with delivery of high-voltage electric current and is considered to improve safety in the vicinity of heat-sensitive blood vessel and bile duct. The aim of the present study is to clarify the acute pathological effect of IRE on the liver and also to compare with effect of RFA. Methods: Three pigs underwent ultrasound-guided IRE and RFA of normal liver under general anesthesia and at laparotomy. A total of 9 IRE ablated areas and 3 RFA ablated areas were created. We examined histopathologic findings of ablated areas at 4 hours after therapy with immunohistochemical methods. The pathologic findings according to IRE ablation conditions were compared with findings of RFA. Results: In IRE zones, various degree of congestion and hemorrhage, apoptotic change of hepatocytes, defluxion of portal endothelial cells and cholangitis were observed in hepatic lobules. With the increase in the total pulse number of IRE delivered, these pathological findings became remarkable. NADPH-diaphorase enzyme histochemistry performed in IRE zones demonstrated the stainability is very weak in the hepatic lobule, which reflecting defluxion of hepatocytes and reduced activity of viable hepatocytes in acute phase, while the stainability is lost in the central portion of RFA. Silver impregnation stain and collagen type 4 immunohistochemistry showed that reticular fibers and collagen fibers around the sinusoid remain well-preserved in IRE zones, on the other hand, those in RFA zones are very poorly stained. The vessels in IRE zones demonstrated a relatively intact configuration of positive smooth muscle cells for Caldesmon staining and endothelial cells for Factor 8 staining, with the minimal endothelial damage, while the vessels in RFA zones demonstrated a negative or weakened reaction. Bile duct epithelial cells showed a positive reaction for cytokeratin 7 staining in IRE zones with desquamated cells, while an entirely negative reaction in RFA zones, revealing protein denaturation. Conclusions: Unlike RFA, IRE induces apoptosis of hepatocytes, endothelium of the blood vessels and mucosal membrane of the bile ducts, whereas preservation of sinusoidal framework and vascular structure may have the potential for liver regeneration.

Assessment of Chronological Effects of Irreversible Electroporation on Hilar Bile Ducts in a Porcine Model

To evaluate the chronological effects of irreversible electroporation (IRE) on large hilar bile ducts in an in vivo porcine model correlated with computed tomography (CT) cholangiography and histopathology. Twelve IRE zones were made along hilar bile ducts intraoperatively under ultrasound (US)-guidance in 11 pigs. Paired electrodes were placed either on opposing sides of the bile duct (straddle [STR]) or both on one side of the bile duct (one-sided [OSD]). The shortest electrode-to-duct distance was classified as periductal (≤ 2 mm) or nonperiductal (>2 mm). CT cholangiography and laboratory tests were performed before IRE and again at 2 days, 4 weeks, and 8 weeks after IRE. Degree of bile duct injury were graded as follows: grade 0 = no narrowing; grade 1 = ≤ 50 % duct narrowing; grade 2 = >50 % narrowing without proximal duct dilatation; grade 3 = grade 2 with proximal duct dilatation; and grade 4 = grade 3 with enzyme elevation. Pigs were selected for killing and histopathology at 2 days, 4, and 8 weeks. Nonperiductal electrode placement produced no long-term strictures in 5 of 5 ducts. Periductal electrode placement produced mild narrowing in 6 of 7 ducts: 5 grade 1 and 1 grade 2. None showed increased enzymes. There was no significant difference between STR versus OSD electrode placement. Histopathology showed minor but relatively greater ductal mural changes in narrowed ducts. In the larger hilar ducts, long-term patency and mural integrity appear resistant to IRE damage with the energy deposition used, especially if the electrode is not immediately periductal in position.