Nonthermal Irreversible Electroporation Research Articles

Neurosurgical Techniques for Disruption of the Blood-Brain Barrier for Glioblastoma Treatment.

The blood–brain barrier remains a main hurdle to drug delivery to the brain. The prognosis of glioblastoma remains grim despite current multimodal medical management. We review neurosurgical technologies that disrupt the blood–brain barrier (BBB). We will review superselective intra-arterial mannitol infusion, focused ultrasound, laser interstitial thermotherapy, and non-thermal irreversible electroporation (NTIRE). These technologies can lead to transient BBB and blood–brain tumor barrier disruption and allow for the potential of more effective local drug delivery. Animal studies and preliminary clinical trials show promise for achieving this goal.

The effect of small intestine heterogeneity on irreversible electroporation treatment planning.

Nonthermal irreversible electroporation (NTIRE) is an ablation modality that utilizes microsecond electric fields to produce nanoscale defects in the cell membrane. This results in selective cell death while preserving all other molecules, including the extracellular matrix. Here, finite element analysis and experimental results are utilized to examine the effect of NTIRE on the small intestine due to concern over collateral damage to this organ during NTIRE treatment of abdominal cancers. During previous studies, the electrical treatment parameters were chosen based on a simplified homogeneous tissue model. The small intestine, however, has very distinct layers, and a more realistic model is needed to further develop this technology for precise clinical applications. This study uses a two-dimensional finite element solution of the Laplace and heat conduction equations to investigate how small intestine heterogeneities affect the electric field and temperature distribution. Experimental results obtained by applying NTIRE to the rat small intestine in vivo support the heterogeneous effect of NTIRE on the tissue. The numerical modeling indicates that the electroporation parameters chosen for this study avoid thermal damage to the tissue. This is supported by histology obtained from the in vivo study, which showed preservation of extracellular structures. The finite element model also indicates that the heterogeneous structure of the small intestine has a significant effect on the electric field and volume of cell ablation during electroporation and could have a large impact on the extent of treatment. The heterogeneous nature of the tissue should be accounted for in clinical treatment planning.

Predicting electroporation of cells in an inhomogeneous electric field based on mathematical modeling and experimental CHO-cell permeabilization to propidium iodide determination

High voltage electric pulses cause electroporation of the cell membrane. Consequently, flow of the molecules across the membrane increases. In our study we investigated possibility to predict the percentage of the electroporated cells in an inhomogeneous electric field on the basis of the experimental results obtained when cells were exposed to a homogeneous electric field. We compared and evaluated different mathematical models previously suggested by other authors for interpolation of the results (symmetric sigmoid, asymmetric sigmoid, hyperbolic tangent and Gompertz curve). We investigated the density of the cells and observed that it has the most significant effect on the electroporation of the cells while all four of the mathematical models yielded similar results. We were able to predict electroporation of cells exposed to an inhomogeneous electric field based on mathematical modeling and using mathematical formulations of electroporation probability obtained experimentally using exposure to the homogeneous field of the same density of cells. Models describing cell electroporation probability can be useful for development and presentation of treatment planning for electrochemotherapy and non-thermal irreversible electroporation.

In vivo characterization and numerical simulation of prostate properties for non-thermal irreversible electroporation ablation

Irreversible electroporation (IRE) delivers brief electric pulses to attain non-thermal focal ablation that spares vasculature and other sensitive systems. It is a promising prostate cancer treatment due to sparing of the tissues associated with morbidity risk from conventional therapies. IRE effects depend on electric field strength and tissue properties. These characteristics are organ-dependent, affecting IRE treatment outcomes. This study characterizes the relevant properties to improve treatment planning and outcome predictions for IRE prostate cancer treatment. Clinically relevant IRE pulse protocols were delivered to a healthy canine and two human cancerous prostates while measuring electrical parameters to determine tissue characteristics for predictive treatment simulations. Prostates were resected 5 hr, 3 weeks, and 4 weeks post-IRE. Lesions were correlated with numerical simulations to determine an effective prostate lethal IRE electric field threshold. Lesions were produced in all subjects. Tissue electrical conductivity increased from 0.284 to 0.927 S/m due to IRE pulses. Numerical simulations show an average effective prostate electric field threshold of 1072 ± 119 V/cm, significantly higher than previously characterized tissues. Histological findings in the human cases show instances of complete tissue necrosis centrally with variable tissue effects beyond the margin. Preliminary experimental IRE trials safely ablated healthy canine and cancerous human prostates, as examined in the short- and medium-term. IRE-relevant prostate properties are now experimentally and numerically defined. Importantly, the electric field required to kill healthy prostate tissue is substantially higher than previously characterized tissues. These findings can be applied to optimize IRE prostate cancer treatment protocols.

The Effect of Blood Flow on Magnetic Resonance Imaging of Non Thermal Irreversible Electroporation

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

The Effects of Metallic Implants on Electroporation Therapies: Feasibility of Irreversible Electroporation for Brachytherapy Salvage

Electroporation-based therapies deliver brief electric pulses into a targeted volume to destabilize cellular membranes. Nonthermal irreversible electroporation (IRE) provides focal ablation with effects dependent on the electric field distribution, which changes in heterogeneous environments. It should be determined if highly conductive metallic implants in targeted regions, such as radiotherapy brachytherapy seeds in prostate tissue, will alter treatment outcomes. Theoretical and experimental models determine the impact of prostate brachytherapy seeds on IRE treatments. This study delivered IRE pulses in nonanimal, as well as in ex vivo and in vivo tissue, with and in the absence of expired radiotherapy seeds. Electrical current was measured and lesion dimensions were examined macroscopically and with magnetic resonance imaging. Finite-element treatment simulations predicted the effects of brachytherapy seeds in the targeted region on electrical current, electric field, and temperature distributions. There was no significant difference in electrical behavior in tissue containing a grid of expired radiotherapy seeds relative to those without seeds for nonanimal, ex vivo, and in vivo experiments (all p > 0.1). Numerical simulations predict no significant alteration of electric field or thermal effects (all p > 0.1). Histology showed cellular necrosis in the region near the electrodes and seeds within the ablation region; however, there were no seeds beyond the ablation margins. This study suggests that electroporation therapies can be implemented in regions containing small metallic implants without significant changes to electrical and thermal effects relative to use in tissue without the implants. This supports the ability to use IRE as a salvage therapy option for brachytherapy.

Planning of Electroporation-Based Treatments Using Web-Based Treatment-Planning Software

Electroporation-based treatment combining high-voltage electric pulses and poorly permanent cytotoxic drugs, i.e., electrochemotherapy (ECT), is currently used for treating superficial tumor nodules by following standard operating procedures. Besides ECT, another electroporation-based treatment, nonthermal irreversible electroporation (N-TIRE), is also efficient at ablating deep-seated tumors. To perform ECT or N-TIRE of deep-seated tumors, following standard operating procedures is not sufficient and patient-specific treatment planning is required for successful treatment. Treatment planning is required because of the use of individual long-needle electrodes and the diverse shape, size and location of deep-seated tumors. Many institutions that already perform ECT of superficial metastases could benefit from treatment-planning software that would enable the preparation of patient-specific treatment plans. To this end, we have developed a Web-based treatment-planning software for planning electroporation-based treatments that does not require prior engineering knowledge from the user (e.g., the clinician). The software includes algorithms for automatic tissue segmentation and, after segmentation, generation of a 3D model of the tissue. The procedure allows the user to define how the electrodes will be inserted. Finally, electric field distribution is computed, the position of electrodes and the voltage to be applied are optimized using the 3D model and a downloadable treatment plan is made available to the user.

Nonthermal Irreversible Electroporation: Fundamentals, Applications, and Challenges

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

Irreversible Electroporation: Evaluation of Nonthermal and Thermal Ablative Capabilities in the Porcine Kidney

To compare the renal ablative capabilities of nonthermal irreversible electroporation (NT-IRE) with those of thermal irreversible electroporation (T-IRE) in a porcine model. A total of 24 laparoscopic renal ablations were performed in 12 pigs using a novel generator capable of alternately delivering NT-IRE and T-IRE. Each pig underwent unilateral interpolar ablation straddling the renal pelvis and lower pole ablation, using a single modality. The pigs were killed at 24 hours and 7 and 21 days. Basic serum laboratory tests, cardiac enzyme levels, and retrograde pyelograms were obtained before and immediately after ablation and at death. Ablation adequacy and lesion size were assessed by histologic examination. All procedures were successfully completed without complications. For NT-IRE vs T-IRE, the median lesion size (long axis) at 24 hours, 7 days and 21 days was 3.0 vs 3.3 cm (P = 1.0), 2.5 vs 3.9 cm (P = .04), and 1.2 vs 2.8 cm (P = .03), respectively. Prolonged urinary extravasation and collecting system scarring were observed only for T-IRE. Both NT-IRE and T-IRE ablated the renal tissue adequately. NT-IRE was characterized by acute hemorrhagic necrosis, sparing the large blood vessels and extracellular matrix, and T-IRE by coagulation necrosis with associated moderate inflammation. NT-IRE and T-IRE both safe and effectively ablate normal porcine kidneys. NT-IRE created smaller lesions with unique histologic characteristics. Significant collecting system injury occurred with T-IRE. Additional preclinical evaluation aimed at optimizing the ablation protocols is needed.

Pathology of non-thermal irreversible electroporation (N-TIRE)-induced ablation of the canine brain

This study describes the neuropathologic features of normal canine brain ablated with non-thermal irreversible electroporation (N-TIRE). The parietal cerebral cortices of four dogs were treated with N-TIRE using a dose-escalation protocol with an additional dog receiving sham treatment. Animals were allowed to recover following N-TIRE ablation and the effects of treatment were monitored with clinical and magnetic resonance imaging examinations. Brains were subjected to histopathologic and ultrastructural assessment along with Bcl-2, caspase-3, and caspase-9 immunohistochemical staining following sacrifice 72 h post-treatment. Adverse clinical effects of N-TIRE were only observed in the dog treated at the upper energy tier. MRI and neuropathologic examinations indicated that N-TIRE ablation resulted in focal regions of severe cytoarchitectural and blood-brain-barrier disruption. Lesion size correlated to the intensity of the applied electrical field. N-TIRE-induced lesions were characterized by parenchymal necrosis and hemorrhage; however, large blood vessels were preserved. A transition zone containing parenchymal edema, perivascular inflammatory cuffs, and reactive gliosis was interspersed between the necrotic focus and normal neuropil. Apoptotic labeling indices were not different between the N-TIRE-treated and control brains. This study identified N-TIRE pulse parameters that can be used to safely create circumscribed foci of brain necrosis while selectively preserving major vascular structures.

Educational application for visualization and analysis of electric field strength in multiple electrode electroporation

BackgroundElectrochemotherapy is a local treatment that utilizes electric pulses in order to achieve local increase in cytotoxicity of some anticancer drugs. The success of this treatment is highly dependent on parameters such as tissue electrical properties, applied voltages and spatial relations in placement of electrodes that are used to establish a cell-permeabilizing electric field in target tissue. Non-thermal irreversible electroporation techniques for ablation of tissue depend similarly on these parameters. In the treatment planning stage, if oversimplified approximations for evaluation of electric field are used, such as U/d (voltage-to-distance ratio), sufficient field strength may not be reached within the entire target (tumor) area, potentially resulting in treatment failure.ResultsIn order to provide an aid in education of medical personnel performing electrochemotherapy and non-thermal irreversible electroporation for tissue ablation, assist in visualizing the electric field in needle electrode electroporation and the effects of changes in electrode placement, an application has been developed both as a desktop- and a web-based solution. It enables users to position up to twelve electrodes in a plane of adjustable dimensions representing a two-dimensional slice of tissue. By means of manipulation of electrode placement, i.e. repositioning, and the changes in electrical parameters, the users interact with the system and observe the resulting electrical field strength established by the inserted electrodes in real time. The field strength is calculated and visualized online and instantaneously reflects the desired changes, dramatically improving the user friendliness and educational value, especially compared to approaches utilizing general-purpose numerical modeling software, such as finite element modeling packages.ConclusionIn this paper we outline the need and offer a solution in medical education in the field of electroporation-based treatments, e.g. primarily electrochemotherapy and non-thermal irreversible tissue ablation. We present the background, the means of implementation and the fully functional application, which is the first of its kind. While the initial feedback from students that have evaluated this application as part of an e-learning course is positive, a formal study is planned to thoroughly evaluate the current version and identify possible future improvements and modifications.

Treatment of Uveal Melanoma by Nonthermal Irreversible Electroporation: Electrical and Bioheat Finite Element Model of the Human Eye

Nonthermal irreversible electroporation (NTIRE) is an new minimally invasive tissue ablation modality that uses high electric field pulses to produce irreversible permeation of the cell membrane (irreversible electroporation) while avoiding thermal damage and is applied to treat malignant tumors. This paper describes efforts to develop NTIRE as a new minimally invasive treatment modality for uveal melanoma, the most common primary intraocular malignancy in adults, and other ocular malignancies. The paper deals with a 3D mathematical simulation model of the eye that employs the simultaneous solution to the electric field equation and to the Pennes bioheat equation to predict the electric field in the eye as well as the rise in eye temperature in response to the application of a high power electric pulse. Treatment efficacy was defined as the fraction of tumor volume in which the electric field exceeded a predefined target field and treatment safety was calculated by the ratio of the electric field in the tumor to the electric field in the vitreous humor or in the macula. Results show that treatment efficacy and safety are criteria that can be used to optimize the NTIRE treatment protocol.

Irreversible electroporation on the small intestine.

Background:Non-thermal irreversible electroporation (NTIRE) has recently been conceived as a new minimally invasive ablation method, using microsecond electric fields to produce nanoscale defects in the cell membrane bilayer and induce cell death while keeping all other molecules, including the extracellular matrix, intact. Here, we present the first in vivo study that examines the effects of NTIRE on the small intestine, an organ whose collateral damage is of particular concern in the anticipated use of NTIRE for treatment of abdominal cancers.Methods:A typical NTIRE electrical protocol was applied directly to the rat small intestine and histological analysis was used to examine the effect of NTIRE over time.Results:The application of NTIRE led to complete cell ablation in the targeted tissue, but the animal did not show any physiological effects of the procedure and the intestine showed signs of recovery, developing an epithelial layer 3 days post treatment and regenerating its distinct layers within a week.Conclusion:Our results indicate that this novel procedure can be used for abdominal cancer treatment while minimising collateral damage to adjacent tissues because of the unique ability of the NTIRE ablation method to target the cell membrane.

High-frequency irreversible electroporation (H-FIRE) for non-thermal ablation without muscle contraction

BackgroundTherapeutic irreversible electroporation (IRE) is an emerging technology for the non-thermal ablation of tumors. The technique involves delivering a series of unipolar electric pulses to permanently destabilize the plasma membrane of cancer cells through an increase in transmembrane potential, which leads to the development of a tissue lesion. Clinically, IRE requires the administration of paralytic agents to prevent muscle contractions during treatment that are associated with the delivery of electric pulses. This study shows that by applying high-frequency, bipolar bursts, muscle contractions can be eliminated during IRE without compromising the non-thermal mechanism of cell death.MethodsA combination of analytical, numerical, and experimental techniques were performed to investigate high-frequency irreversible electroporation (H-FIRE). A theoretical model for determining transmembrane potential in response to arbitrary electric fields was used to identify optimal burst frequencies and amplitudes for in vivo treatments. A finite element model for predicting thermal damage based on the electric field distribution was used to design non-thermal protocols for in vivo experiments. H-FIRE was applied to the brain of rats, and muscle contractions were quantified via accelerometers placed at the cervicothoracic junction. MRI and histological evaluation was performed post-operatively to assess ablation.ResultsNo visual or tactile evidence of muscle contraction was seen during H-FIRE at 250 kHz or 500 kHz, while all IRE protocols resulted in detectable muscle contractions at the cervicothoracic junction. H-FIRE produced ablative lesions in brain tissue that were characteristic in cellular morphology of non-thermal IRE treatments. Specifically, there was complete uniformity of tissue death within targeted areas, and a sharp transition zone was present between lesioned and normal brain.ConclusionsH-FIRE is a feasible technique for non-thermal tissue ablation that eliminates muscle contractions seen in IRE treatments performed with unipolar electric pulses. Therefore, it has the potential to be performed clinically without the administration of paralytic agents.

Equivalent Pulse Parameters for Electroporation

Electroporation-based applications require the use of specific pulse parameters for a successful outcome. When recommended values of pulse parameters cannot be set, similar outcomes can be obtained by using equivalent pulse parameters. We determined the relations between the amplitude and duration/number of pulses resulting in the same fraction of electroporated cells. Pulse duration was varied from 150 ns to 100 ms, and the number of pulses from 1 to 128. Fura 2-AM was used to determine electroporation of cells to Ca(2+). With longer pulses or higher number of pulses, lower amplitudes are needed for the same fraction of electroporated cells. The expression derived from the model of electroporation could describe the measured data on the whole interval of pulse durations. In a narrower range (0.1-100 ms), less complex, logarithmic or power functions could be used instead. The relation between amplitude and number of pulses could best be described with a power function or an exponential function. We show that relatively simple two-parameter power or logarithmic functions are useful when equivalent pulse parameters for electroporation are sought. Such mathematical relations between pulse parameters can be important in planning of electroporation-based treatments, such as electrochemotherapy and nonthermal irreversible electroporation.

Urinary Tract Effects After Multifocal Nonthermal Irreversible Electroporation of the Kidney: Acute and Chronic Monitoring by Magnetic Resonance Imaging, Intravenous Urography and Urinary Cytology

The nonthermal irreversible electroporation (NTIRE) is a novel potential ablation modality for renal masses. The aim of this study was the first evaluation of NTIRE's effects on the renal urine-collecting system using intravenous urography (IVU) and urinary cytology in addition to histology and magnetic resonance imaging (MRI). Eight percutaneous NTIRE ablations of the renal parenchyma, including the calyxes or pelvis, were performed in three male swine. MRI, IVU, histology, and urinary cytology follow-ups were performed within the first 28 days after treatment. MRI and histological analysis demonstrated a localized necrosis 7 days and a localized scarification of the renal parenchyma with complete destruction 28 days after NTIRE. The urine-collecting system was preserved and showed urothelial regeneration. IVU and MRI showed an unaltered normal morphology of the renal calyxes, pelvis, and ureter. A new urinary cytology phenomenon featured a temporary degeneration by individual vacuolization of detached transitional epithelium cells within the first 3 days after NTIRE. This first urographical, urine-cytological, and MRI evaluation after porcine kidney NTIRE shows multifocal parenchyma destruction while protecting the involved urine-collecting system with regenerated urothelial tissue. NTIRE could be used as a targeted ablation method of centrally located renal masses.

Angiography in the Isolated Perfused Kidney: Radiological Evaluation of Vascular Protection in Tissue Ablation by Nonthermal Irreversible Electroporation

The nonthermal irreversible electroporation (NTIRE) is a novel nonthermal tissue ablation technique by local application of high-voltage current within microseconds leading to a delayed apoptosis. The purpose of this experimental study was the first angiographic evaluation of the acute damage of renal vascular structure in NTIRE. Results of conventional dynamic digital substraction angiography (DSA) and visualization of the terminal vascular bed of renal parenchyma by high-resolution X-ray in mammography technique were evaluated before, during, and after NTIRE of three isolated perfused porcine ex vivo kidneys. In the dedicated investigation, no acute vascular destruction of the renal parenchyma and no dysfunction of the kidney perfusion model were observed during or after NTIRE. Conspicuous were concentric wave-like fluctuations of the DSA contrast agent simultaneous to the NTIRE pulses resulting from NTIRE pulse shock wave. The NTIRE offers an ablation method with no acute collateral vascular damage in angiographic evaluation.

In vivo non-thermal irreversible electroporation impact on rat liver galvanic apparent internal resistance

Non-thermal irreversible electroporation (NTIRE) is a biophysical phenomenon which involves application of electric field pulses to cells or tissues, causing certain rearrangements in the membrane structure leading to cell death. The treated tissue ac impedance changes induced by electroporation were shown to be the indicators for NTIRE efficiency. In a previous study we characterized in vitro tissue galvanic apparent internal resistance (GAIR) changes due to NTIRE. Here we describe an in vivo study in which we monitored the GAIR changes of a rat liver treated by NTIRE. Electrical pulses were delivered through the same Zn/Cu electrodes by which GAIR was measured. GAIR was measured before and for 3 h after the treatment at 15 min intervals. The results were compared to the established ac bioimpedance measurement method. A decrease of 33% was measured immediately after the NTIRE treatment and a 40% decrease was measured after 3 h in GAIR values; in the same time 40% and 47% decrease respectively were measured by ac bioimpedance analyses. The temperature increase due to the NTIRE was only 0.5 °C. The results open the way for an inexpensive, self-powered in vivo real-time NTIRE effectiveness measurement.

Towards the creation of decellularized organ constructs using irreversible electroporation and active mechanical perfusion.

BackgroundDespite advances in transplant surgery and general medicine, the number of patients awaiting transplant organs continues to grow, while the supply of organs does not. This work outlines a method of organ decellularization using non-thermal irreversible electroporation (N-TIRE) which, in combination with reseeding, may help supplement the supply of organs for transplant.MethodsIn our study, brief but intense electric pulses were applied to porcine livers while under active low temperature cardio-emulation perfusion. Histological analysis and lesion measurements were used to determine the effects of the pulses in decellularizing the livers as a first step towards the development of extracellular scaffolds that may be used with stem cell reseeding. A dynamic conductivity numerical model was developed to simulate the treatment parameters used and determine an irreversible electroporation threshold.ResultsNinety-nine individual 1000 V/cm 100-μs square pulses with repetition rates between 0.25 and 4 Hz were found to produce a lesion within 24 hours post-treatment. The livers maintained intact bile ducts and vascular structures while demonstrating hepatocytic cord disruption and cell delamination from cord basal laminae after 24 hours of perfusion. A numerical model found an electric field threshold of 423 V/cm under specific experimental conditions, which may be used in the future to plan treatments for the decellularization of entire organs. Analysis of the pulse repetition rate shows that the largest treated area and the lowest interstitial density score was achieved for a pulse frequency of 1 Hz. After 24 hours of perfusion, a maximum density score reduction of 58.5 percent had been achieved.ConclusionsThis method is the first effort towards creating decellularized tissue scaffolds that could be used for organ transplantation using N-TIRE. In addition, it provides a versatile platform to study the effects of pulse parameters such as pulse length, repetition rate, and field strength on whole organ structures.

Vascular Smooth Muscle Cells Ablation with Endovascular Nonthermal Irreversible Electroporation

To evaluate the effect of endovascular nonthermal irreversible electroporation (NTIRE) on blood vessels. Specially made endovascular devices with four electrodes on top of inflatable balloons were used to apply electroporation pulses. Finite element simulations were used to characterize NTIRE protocols that would not induce thermal damage to treated tissues. Right iliac arteries of eight rabbits were treated with 90 NTIRE pulses. Angiograms were performed before and after the procedures. Arterial specimens were harvested at 7 and 35 days. Evaluation included hematoxylin and eosin, elastic von Giessen, and Masson trichrome stains. Immunohistochemistry of selected slides included smooth muscle actin (SMA), proliferating cell nuclear antigen, von Willebrand factor (VWF), and S-100 antigen. At 7 days, all NTIRE-treated arterial segments displayed complete, transmural ablation of vascular smooth muscle cells (VSMC). At 35 days, similar damage to VSMC was noted. In most cases, the elastic lamina remained intact, and endothelial layer regenerated. Occasional mural inflammation and cartilaginous metaplasia were noted. After 5 weeks, there was no evidence of significant VSMC proliferation, with the dominant process being wall fibrosis with regenerated endothelium. NTIRE can be applied in an endovascular approach. It efficiently ablates vessel wall within seconds and with no damage to extracellular structures. NTIRE has possible applications in many fields of clinical cardiology, including arterial restenosis and cardiac arrhythmias.