First-in-human demonstration of floating EMG sensors and stimulators wirelessly powered and operated by volume conduction

BACKGROUND

Recently we reported the design and evaluation of floating semi-implantable devices that receive power from and bidirectionally communicate with an external system using coupling by volume conduction. The approach, of which the semi-implantable devices are proof-of-concept prototypes, may overcome some limitations presented by existing neuroprostheses, especially those related to implant size and deployment, as the implants avoid bulky components and can be developed as threadlike devices. Here, it is reported the first-in-human acute demonstration of these devices for electromyography (EMG) sensing and electrical stimulation.

METHODS

A proof-of-concept device, consisting of implantable thin-film electrodes and a nonimplantable miniature electronic circuit connected to them, was deployed in the upper or lower limb of six healthy participants. Two external electrodes were strapped around the limb and were connected to the external system which delivered high frequency current bursts. Within these bursts, 13 commands were modulated to communicate with the implant.

RESULTS

Four devices were deployed in the biceps brachii and the gastrocnemius medialis muscles, and the external system was able to power and communicate with them. Limitations regarding insertion and communication speed are reported. Sensing and stimulation parameters were configured from the external system. In one participant, electrical stimulation and EMG acquisition assays were performed, demonstrating the feasibility of the approach to power and communicate with the floating device.

CONCLUSIONS

This is the first-in-human demonstration of EMG sensors and electrical stimulators powered and operated by volume conduction. These proof-of-concept devices can be miniaturized using current microelectronic technologies, enabling fully implantable networked neuroprosthetics.

Effects of Contact Force on Lesion Size During Pulsed Field Catheter Ablation: Histochemical Characterization of Ventricular Lesion Boundaries

BACKGROUND

Effects of contact force (CF) on lesion formation during pulsed field ablation (PFA) have not been well validated. The purpose of this study was to determine the relationship between average CF and lesion size during PFA using a swine-beating heart model.

METHODS

A 7F catheter with a 3.5-mm ablation electrode and CF sensor (TactiCath SE, Abbott) was connected to a PFA system (CENTAURI, Galvanize Therapeutics). In 5 closed-chest swine, biphasic PFA current was delivered between the ablation electrode and a skin patch at 40 separate sites in right ventricle (28 Amp) and 55 separate sites in left ventricle (35 Amp) with 4 different levels of CF: (1) low (CF range of 4-13 g; median, 9.5 g); (2) moderate (15-30 g; median, 21.5 g); (3) high (34-55 g; median, 40 g); and (4) no electrode contact, 2 mm away from the endocardium. Swine were sacrificed at 2 hours after ablation, and lesion size was measured using triphenyl tetrazolium chloride staining. In 1 additional swine, COX (cytochrome c oxidase) staining was performed to examine mitochondrial activity to delineate reversible and irreversible lesion boundaries. Histological examination was performed with hematoxylin and eosin and Masson trichrome staining.

RESULTS

Ablation lesions were well demarcated with triphenyl tetrazolium chloride staining, showing (1) a dark central zone (contraction band necrosis and hemorrhage); (2) a pale zone (no mitochondrial activity and nuclear pyknosis, indicating apoptosis zone); and a hyperstained zone by triphenyl tetrazolium chloride and COX staining (unaffected normal myocardium with preserved mitochondrial activity, consistent with reversible zone). At constant PFA current intensity, lesion depth increased significantly with increasing CF. There were no detectable lesions resulting from ablation without electrode contact.

CONCLUSIONS

Acute PFA ventricular lesions show irreversible and reversible lesion boundaries by triphenyl tetrazolium chloride staining. Electrode-tissue contact is required for effective lesion formation during PFA. At the same PFA dose, lesion depth increases significantly with increasing CF.

Dynamics of High-Density Unipolar Epicardial Electrograms During PFA

BACKGROUND

Pulsed field ablation (PFA) is a novel nonthermal cardiac ablation technology based on irreversible electroporation (IRE). While areas of IRE lead to durable lesions, the surrounding regions, where reversible electroporation occurs, recover. The behavior of local electrograms in areas of different electroporation levels remains unknown. The goal of this study is to characterize electrogram dynamics after PFA in IRE and reversible electroporation areas.

METHODS

A total of 6 domestic swine were used. PFA was applied in the epicardium of the right and left ventricles using a focal monopolar catheter. Additional radiofrequency ablations were performed. Epicardial unipolar electrograms were acquired at baseline and for 60 minutes post PFA/radiofrequency ablation using a high-density electrode matrix attached to the epicardium. Electrogram dynamics were analyzed in areas corresponding to different levels of electroporation. Acute lesion formation was assessed after 3 to 5 hours by triphenyl tetrazolium chloride staining.

RESULTS

Electrogram analysis demonstrated a clear association between electrogram changes and the level of electroporation. Immediately after PFA, electrograms displayed the following: a significant decrease in R/S-wave amplitude; a large elevation of the ST-segment; and a large decrease in their |(dV/dt)|max. Marked changes in electrograms were observed beyond the lesion area. Thereafter, a gradual recovery was observed. The evolution of all the electrogram parameters throughout the 60 minutes after PFA was significantly different (P<0.05) between the IRE and reversible electroporation areas. Acute lesion staining showed significantly larger depth for PFA lesions compared with radiofrequency ablation.

CONCLUSIONS

This study shows that unipolar electrograms can differentiate between reversible electroporation and IRE areas during the first 30 minutes post ablation. Differences after the first 30 minutes are less evident. Our findings could result useful for immediate lesion assessment after PFA and warrant further investigation.

PIRET-A Platform for Treatment Planning in Electroporation-Based Therapies

Tissue electroporation is the basis of several therapies. Electroporation is performed by briefly exposing tissues to high electric fields. It is generally accepted that electroporation is effective where an electric field magnitude threshold is overreached. However, it is difficult to preoperatively estimate the field distribution because it is highly dependent on anatomy and treatment parameters.

OBJECTIVE

We developed PIRET, a platform to predict the treatment volume in electroporation-based therapies.

METHODS

The platform seamlessly integrates tools to build patient-specific models where the electric field is simulated to predict the treatment volume. Patient anatomy is segmented from medical images and 3D reconstruction aids in placing the electrodes and setting up treatment parameters.

RESULTS

Four canine patients that had been treated with high-frequency irreversible electroporation were retrospectively planned with PIRET and with a workflow commonly used in previous studies, which uses different general-purpose segmentation (3D Slicer) and modeling software (3Matic and COMSOL Multiphysics). PIRET outperformed the other workflow by 65 minutes (× 1.7 faster), thanks to the improved user experience during treatment setup and model building. Both approaches computed similarly accurate electric field distributions, with average Dice scores higher than 0.93.

CONCLUSION

A platform which integrates all the required tools for electroporation treatment planning is presented. Treatment plan can be performed rapidly with minimal user interaction in a stand-alone platform.

SIGNIFICANCE

This platform is, to the best of our knowledge, the most complete software for treatment planning of irreversible electroporation. It can potentially be used for other electroporation applications.

MRI-based numerical modeling of cardiac pulsed field ablation (PFA) with sub-microsecond pulses

Background

The use of irreversible electroporation (IRE) for cardiac ablation in the management of cardiac arrhythmias, known as Pulsed Field Ablation (PFA), has gained the attention of many researchers, physicians and companies. Despite the demonstrated efficacy and safety profiles of the technique, there are still many open questions. One of them deals with the effective electric field thresholds necessary for cardiac tissue ablation.

Contrary to radiofrequency (RF) ablation, where the thermotemporal thresholds for tissue damage are well established, the electric field thresholds for effective IRE are uncertain and depend on the tissue type and the waveform characteristics of the delivered electric field.

Purpose

The use of numerical models to understand the electric field distribution and the corresponding lesion for a specific electrode geometry are widely used in IRE for cancer treatment. Models can predict ablation volumes when the field thresholds are known or can be used to estimate the field thresholds when the lesion geometry is established post-treatment. The goal of the present study was to build a subject-specific realistic 3D numerical model to assess the ability of modeling to predict PFA lesions.

Methods

PFA experiments were performed in male mongrel dogs following a protocol approved by the Mayo Clinic Institutional Animal Care and Use Committee. Briefly, animals were sedated and intubated, and two non-irrigated deflectable catheters with an 8-mm tip were positioned on both sides of the interventricular septum under fluoroscopy guidance. Submicrosecond pulses were delivered in a bipolar fashion across both catheters. Sequences of pulses of 300 ns duration (or other durations in that range) were repetitively applied with voltage levels in the kV range. 30 days after the procedure, MRI with late gadolinium enhancement (LGE) were acquired to assess the presence of ablation lesions in the treated tissue. Ventricular areas were segmented from MRI images and 3D volumes were created. The generated 3D geometries were imported into software COMSOL Multiphysics. Realistic 3D geometries of the catheters were placed in the same positions than during the experiments, fluoroscopy videos recorded during the procedures were used as a guidance.

The computed electric field intensity distributions were compared to the LGE areas to extract the range of electric field thresholds where the predicted lesion size was compatible with the real size of the LGE areas for each application site and pulsing protocol.

Results and conclusions

Our results show how the numerical model is able to reproduce the shape of the LGE fibrotic lesion areas observed 30 days after the procedure. Additionally, the model clearly confirms the dose-dependent lesion sizes observed experimentally. This study supports that numerical modeling is a valuable tool for understanding PFA treatments and that it could be used as patient-specific treatment planning tool.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie

Parametric Study of Pulsed Field Ablation With Biphasic Waveforms in an In Vivo Heart Model: The Role of Frequency

BACKGROUND

Pulsed field ablation (PFA) is a novel nonthermal cardiac ablation technology based on irreversible electroporation. Unfortunately, the characteristics of the electric field waveforms used in clinical and experimental PFA are not typically reported. This study examines the effect of the frequency of biphasic waveforms and compares biphasic to monophasic waveforms.

METHODS

A total of 29 Sprague-Dawley rats were treated with PFA using an epicardial monopolar electrode. Biphasic waveforms with three different frequencies, 90, 260, and 450 kHz (10 bursts of 100 µs duration at 500 V or 800 V) and monophasic waveforms (10 pulses of 100 µs duration at 500 V) were studied. Collateral neuromuscular stimulation and temperature increase in the point of application were directly measured. Lesion formation was assessed 3 weeks after treatment by histopathologic analysis. Computer simulations were used to estimate the electric field lethal threshold for each condition. A previous in vitro study was performed to draw a complete characterization of the studied dependencies.

RESULTS

Morphometric analysis demonstrated a significant association between chronic lesion size and waveform characteristics. For the same voltage level, monophasic waveforms yielded the largest lesions compared with any of the biphasic protocols (P<0.05). Increasing PFA frequency was associated with reduced neuromuscular stimulation but also with reduced ablation efficacy. Maximum absolute temperature increase recorded along a complete treatment was 3 °C. Vascular structures inside the lesions were preserved for all conditions. Computer simulation-based analysis showed that waveform frequency had a graded effect on the lethal electric field threshold, with threshold of 600 V/cm for monophasic waveforms versus 2000 V/cm for biphasic waveforms with a frequency of 450 kHz.

CONCLUSIONS

Frequency is a major determinant of efficacy in biphasic PFA. Our results highlight the critical need of disclosing waveform characteristics when reporting the results of different PFA systems.

Wireless networks of injectable microelectronic stimulators based on rectification of volume conducted high frequency currents

OBJECTIVE

To develop and in vivo demonstrate threadlike wireless implantable neuromuscular microstimulators that are digitally addressable.

APPROACH

These devices perform, through its two electrodes, electronic rectification of innocuous high frequency current bursts delivered by volume conduction via epidermal textile electrodes. By avoiding the need of large components to obtain electrical energy, this approach allows the development of thin devices that can be intramuscularly implanted by minimally invasive procedures such as injection. For compliance with electrical safety standards, this approach requires a minimum distance, in the order of millimeters or a very few centimeters, between the implant electrodes. Additionally, the devices must cause minimal mechanical damage to tissues, avoid dislocation and be adequate for long-term implantation. Considering these requirements, the implants were conceived as tubular and flexible devices with two electrodes at opposite ends and, at the middle section, a hermetic metallic capsule housing the electronics.

MAIN RESULTS

The developed implants have a submillimetric diameter (0.97 mm diameter, 35 mm length) and consist of a microcircuit, which contains a single custom-developed integrated circuit, housed within a titanium capsule (0.7 mm diameter, 6.5 mm length), and two platinum-iridium coils that form two electrodes (3 mm length) located at opposite ends of a silicone body. These neuromuscular stimulators are addressable, allowing to establish a network of microstimulators that can be controlled independently. Their operation was demonstrated in an acute study by injecting a few of them in the hind limb of anesthetized rabbits and inducing controlled and independent contractions.

SIGNIFICANCE

These results show the feasibility of manufacturing threadlike wireless addressable neuromuscular stimulators by using fabrication techniques and materials well established for chronic electronic implants. Although long-term operation still must be demonstrated, the obtained results pave the way to the clinical development of advanced motor neuroprostheses formed by dense networks of such wireless devices.

Powering Electronic Implants by High Frequency Volume Conduction: In Human Validation

OBJECTIVE

Wireless power transfer (WPT) is used as an alternative to batteries to accomplish miniaturization in electronic medical implants. However, established WPT methods require bulky parts within the implant or cumbersome external systems, hindering minimally invasive deployments and the development of networks of implants. As an alternative, we propose a WPT approach based on volume conduction of high frequency (HF) current bursts. These currents are applied through external electrodes and are collected by the implants through two electrodes at their opposite ends. This approach avoids bulky components, enabling the development of flexible threadlike implants.

METHODS

We study in humans if HF (6.78 MHz) current bursts complying with safety standards and applied through two textile electrodes strapped around a limb can provide substantial powers from pairs of implanted electrodes.

RESULTS

Time averaged electric powers obtained from needle electrodes (diameter = 0.4 mm, length = 3 mm, separation = 30 mm) inserted into arms and lower legs of five healthy participants were 5.9 ± 0.7 mW and 2.4 ± 0.3 mW respectively. We also characterize the coupling between the external system and the implants using personalized two-port impedance models generated from medical images.

CONCLUSIONS

The results demonstrate that innocuous and imperceptible HF current bursts that flow through the tissues by volume conduction can be used to wirelessly power threadlike implants.

SIGNIFICANCE

This is the first time that WPT based on volume conduction is demonstrated in humans. This method overcomes the limitations of existing WPT methods in terms of minimal invasiveness and usability.

Floating EMG sensors and stimulators wirelessly powered and operated by volume conduction for networked neuroprosthetics

Background

Implantable neuroprostheses consisting of a central electronic unit wired to electrodes benefit thousands of patients worldwide. However, they present limitations that restrict their use. Those limitations, which are more adverse in motor neuroprostheses, mostly arise from their bulkiness and the need to perform complex surgical implantation procedures. Alternatively, it has been proposed the development of distributed networks of intramuscular wireless microsensors and microstimulators that communicate with external systems for analyzing neuromuscular activity and performing stimulation or controlling external devices. This paradigm requires the development of miniaturized implants that can be wirelessly powered and operated by an external system. To accomplish this, we propose a wireless power transfer (WPT) and communications approach based on volume conduction of innocuous high frequency (HF) current bursts. The currents are applied through external textile electrodes and are collected by the wireless devices through two electrodes for powering and bidirectional digital communications. As these devices do not require bulky components for obtaining power, they may have a flexible threadlike conformation, facilitating deep implantation by injection.

Methods

We report the design and evaluation of advanced prototypes based on the above approach. The system consists of an external unit, floating semi-implantable devices for sensing and stimulation, and a bidirectional communications protocol. The devices are intended for their future use in acute human trials to demonstrate the distributed paradigm. The technology is assayed in vitro using an agar phantom, and in vivo in hindlimbs of anesthetized rabbits.

Results

The semi-implantable devices were able to power and bidirectionally communicate with the external unit. Using 13 commands modulated in innocuous 3 MHz HF current bursts, the external unit configured the sensing and stimulation parameters, and controlled their execution. Raw EMG was successfully acquired by the wireless devices at 1 ksps.

Conclusions

The demonstrated approach overcomes key limitations of existing neuroprostheses, paving the way to the development of distributed flexible threadlike sensors and stimulators. To the best of our knowledge, these devices are the first based on WPT by volume conduction that can work as EMG sensors and as electrical stimulators in a network of wireless devices.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-01033-3.

Auricular Transcutaneous Vagus Nerve Stimulation Acutely Modulates Brain Connectivity in Mice

Brain electrical stimulation techniques take advantage of the intrinsic plasticity of the nervous system, opening a wide range of therapeutic applications. Vagus nerve stimulation (VNS) is an approved adjuvant for drug-resistant epilepsy and depression. Its non-invasive form, auricular transcutaneous VNS (atVNS), is under investigation for applications, including cognitive improvement. We aimed to study the effects of atVNS on brain connectivity, under conditions that improved memory persistence in CD-1 male mice. Acute atVNS in the cymba conchae of the left ear was performed using a standard stimulation protocol under light isoflurane anesthesia, immediately or 3 h after the training/familiarization phase of the novel object-recognition memory test (NORT). Another cohort of mice was used for bilateral c-Fos analysis after atVNS administration. Spearman correlation of c-Fos density between each pair of the thirty brain regions analyzed allowed obtaining the network of significant functional connections in stimulated and non-stimulated control brains. NORT performance was enhanced when atVNS was delivered just after, but not 3 h after, the familiarization phase of the task. No alterations in c-Fos density were associated with electrostimulation, but a significant effect of atVNS was observed on c-Fos-based functional connectivity. atVNS induced a clear reorganization of the network, increasing the inter-hemisphere connections and the connectivity of locus coeruleus. Our results provide new insights into the effects of atVNS on memory performance and brain connectivity extending our knowledge of the biological mechanisms of bioelectronics in medicine.

Modeling methods for treatment planning in overlapping electroporation treatments

OBJECTIVE

Irreversible electroporation (IRE) is a non thermal tissue ablation therapy which is induced by applying high voltage waveforms across electrode pairs. When multiple electrode pairs are sequentially used, the treatment volume (TV) is typically computed as the geometric union of the TVs of individual pairs. However, this method neglects that some regions are exposed to overlapping treatments. Recently, a model describing cell survival probability was introduced which effectively predicted TV with overlapping fields in vivo. However, treatment overlap has yet to be quantified. This study characterizes TV overlap in a controlled in vitro setup with the two existing methods which are compared to an adapted logistic model proposed here.

METHODS

CHO cells were immobilized in agarose gel. Initially, we characterized the electric field threshold and the cell survival probability for overlapping treatments. Subsequently, we created a 2D setup where we compared and validated the accuracy of the different methods in predicting the TV.

RESULTS

Overlap can reduce the electric field threshold required to induce cell death, particularly for treatments with low pulse number. However, it does not have a major impact on TV in the models assayed here, and all the studied methods predict TV with similar accuracy.

CONCLUSION

Treatment overlap has a minor influence in the TV for typical protocols found in IRE therapies.

SIGNIFICANCE

This study provides evidence that the modeling method used in most pre-clinical and clinical studies seems adequate.

Comparing High-Frequency With Monophasic Electroporation Protocols in an In Vivo Beating Heart Model

This study compared monophasic 100-μs pulses with high-frequency electroporation (HF-EP) bursts using an in vivo animal model. Myocardial damage was evaluated by histologic analysis. Compared with 10 monophasic pulses, 20 bursts of HF-EP at 100 and 150 kHz were associated with less damage. However, when the number of HF-EP bursts was increased to 60, myocardial damage was comparable to that of the monophasic group. HF-EP protocols were associated with attenuated collateral muscle contractions. This study shows that HF-EP is feasible and effective and that pulse frequency has a significant effect on extent of ablation.

EView: An electric field visualization web platform for electroporation-based therapies

BACKGROUND AND OBJECTIVES

Electroporation is the phenomenon by which cell membrane permeability to ions and macromolecules is increased when the cell is briefly exposed to high electric fields. In electroporation-based treatments, such exposure is typically performed by delivering high voltage pulses across needle electrodes in tissue. For a given tissue and pulsing protocol, an electric field magnitude threshold exists that must be overreached for treatment efficacy. However, it is hard to preoperatively infer the treatment volume because the electric field distribution intricately depends on the electrodes' positioning and length, the applied voltage, and the electric conductivity of the treated tissues. For illustrating such dependencies, we have created EView (https://eview.upf.edu), a web platform that estimates the electric field distribution for arbitrary needle electrode locations and orientations and overlays it on 3D medical images.

METHODS

A client-server approach has been implemented to let the user set the electrode configuration easily on the web browser, whereas the simulation is computed on a dedicated server. By means of the finite element method, the electric field is solved in a 3D volume. For the sake of simplicity, only a homogeneous tissue is modeled, assuming the same properties for healthy and pathologic tissues. The non-linear dependence of tissue conductivity on the electric field due to the electroporation effect is modeled. The implemented model has been validated against a state of the art finite element solver, and the server has undergone a heavy load test to ensure reliability and to report execution times.

RESULTS

The electric field is rapidly computed for any electrode and tissue configuration, and alternative setups can be easily compared. The platform provides the same results as the state of the art finite element solver (Dice = 98.3 ± 0.4%). During the high load test, the server remained responsive. Simulations are computed in less than 2 min for simple cases consisting of two electrodes and take up to 40 min for complex scenarios consisting of 6 electrodes.

CONCLUSIONS

With this free platform we provide expert and non-expert electroporation users a way to rapidly model the electric field distribution for arbitrary electrode configurations.

Interleaved intramuscular stimulation with minimally overlapping electrodes evokes smooth and fatigue resistant forces

OBJECTIVE

It is known that multi-site interleaved stimulation generates less muscle fatigue compared to single-site synchronous stimulation. However, in the limited number of studies in which intramuscular electrodes were used, the fatigue reduction associated with interleaved stimulation could not consistently be achieved. We hypothesize that this could be due to the inability to place the intramuscular electrodes used in interleaved stimulation in locations that minimize overlap amongst the motor units activated by the electrodes. Our objective in the present study was to use independent intramuscular electrodes to compare fatigue induced by interleaved stimulation with that generated by synchronous stimulation at the same initial force and ripple.

APPROACH

In the medial gastrocnemius muscle of an anesthetized rabbit (n = 3), ten intramuscular hook wire electrodes were inserted at different distances from the nerve entry. Overlap was measured using the refractory technique and only three electrodes were found to be highly independent. After ensuring that forces obtained by both stimulation modalities had the same ripple and magnitude, fatigue induced during interleaved stimulation across three independent distal electrodes was compared to that obtained by synchronously delivering pulses to a single proximal electrode.

MAIN RESULTS

Contractions evoked by interleaved stimulation exhibited less fatigue than those evoked by synchronous stimulation. Twitch force recruitment curves collected from each of the ten intramuscular electrodes showed frequent intermediate plateaus and the force value at these plateaus decreased as the distance between the electrode and nerve entry increased.

SIGNIFICANCE

The results indicate that interleaved intramuscular stimulation is preferred over synchronous intramuscular stimulation when fatigue-resistant and smooth forces are desired. In addition, the results suggest that the large muscle compartments innervated by the primary intramuscular nerve branches give rise to progressively smaller independent compartments in subsequent nerve divisions.

Injectable Sensors Based on Passive Rectification of Volume-Conducted Currents

Sensing implants that can be deployed by catheterization or by injection are preferable over implants requiring invasive surgery. However, present powering methods for active implants and present interrogation methods for passive implants require bulky parts within the implants that hinder the development of such minimally invasive devices. In this article, we propose a novel approach that potentially enables the development of passive sensing systems overcoming the limitations of previous implantable sensing systems in terms of miniaturization. In this approach implants are shaped as thread-like devices suitable for implantation by injection. Their basic structure consists of a thin elongated body with two electrodes at opposite ends and a simple and small circuit made up of a diode, a capacitor and a resistor. The interrogation method to obtain measurements from the implants consists in applying innocuous bursts of high frequency (≥1 MHz) alternating current that reach the implants by volume conduction and in capturing and processing the voltage signals that the implants produce after the bursts. As proof-of-concept, and for illustrating how to put in practice this novel approach, here we describe the development and characterization of a system for measuring the conductivity of tissues surrounding the implant. We also describe the implementation and the in vitro validation of a 0.95 mm-thick, flexible injectable implant made of off-the-shelf components. For conductivities ranging from about 0.2 to 0.8 S/m, when compared to a commercial conductivity meter, the accuracy of the implemented system was about ±10%.

Pulsed radiofrequency for chronic pain: In vitro evidence of an electroporation mediated calcium uptake

Pulsed radiofrequency (PRF) treatments for chronic pain consist in the delivery of a train of sinusoidal electric bursts to the targeted nerve. Despite numerous clinical evidence of its efficiency, the mechanism of action of PRF remains unclear. Since most of the reported biological effects of PRF can be initiated by a calcium influx into the neurons, we hypothesized that PRF may induce a mild electroporation effect causing a calcium uptake. To test this hypothesis, HEK-293 cells were exposed to PRF bursts and cytosolic calcium and Yo-Pro-1 uptake were monitored. After a single burst, calcium peaks were observed for electric fields above 480 V/cm while the uptake of Yo-pro-1 was insignificant. After a train of 120 bursts, the electric fields required to induce a calcium and Yo-pro-1 uptake decreased to 330 V/cm and 880 V/cm respectively. Calcium peaks were not detected when cells were treated in calcium free media. The temperature increase during the treatments was lower than 5 °C in all cases. Finally, the cell response for different burst frequencies and extracellular media conductivities correlated with the induced transmembrane voltage calculated with a numerical model. Our results support the hypothesis of an electroporation mediated calcium influx.

In vitro study on the mechanisms of action of electrolytic electroporation (E2)

Electrolytic Electroporation (E2) is the combination of reversible electroporation and electrolysis. It has been proposed as a novel treatment option to ablate tissue percutaneously. The present in vitro study in cells in suspension was performed to investigate the underlying mechanisms of action of E2. Different types of experiments were performed to isolate the effects of the electrolysis and the electroporation components of the treatment. Additionally, thermal simulations were performed to determine whether significant temperature increase contributes to the effect. The results indicate that E2's cell killing efficacy is due to a combinational effect of electrolysis and reversible electroporation that takes place within the first two minutes after E2 application. The results further show that cell death after E2 treatment is significantly delayed. These observations suggest that cell death is induced in permeabilized cells due to the uptake of electrolysis species. Thermal simulations revealed a significant but innocuous temperature increase.

The combination of electroporation and electrolysis (E2) employing different electrode arrays for ablation of large tissue volumes

Background

The combination of electroporation with electrolysis (E2) has previously been introduced as a novel tissue ablation technique. E2 allows the utilization of a wide parameter range and may therefore be a suitable technology for development of tissue-specific application protocols. Previous studies have implied that it is possible to achieve big lesions in liver in a very short time. The goal of this study was to test a variety of electrode configurations for the E2 application to ablate large tissue volumes.

Materials and methods

27 lesions were performed in healthy porcine liver of five female pigs. Four, two and bipolar electrode-arrays were used to deliver various E2 treatment protocols. Liver was harvested approx. 20h after treatment and examined with H&E and Masson’s trichrome staining, and via TUNEL staining for selective specimen.

Results

All animals survived the treatments without complications. With four electrodes, a lesion of up to 35x35x35mm volume can be achieved in less than 30s. The prototype bipolar electrode created lesions of 50x18x18mm volume in less than 10s. Parameters for two-electrode ablations with large exposures encompassing large veins were found to be good in terms of vessel preservation, but not optimal to reliably close the gap between the electrodes.

Conclusion

This study demonstrates the ability to produce large lesions in liver within seconds at lower limits of the E2 parameter space at different electrode configurations. The applicability of E2 for single electrode ablations was demonstrated with bipolar electrodes. Parameters for large 4-electrode ablation volumes were found suitable, while parameters for two electrodes still need optimization. However, since the parameter space of E2 is large, it is possible that for all electrode geometries optimal waveforms and application protocols for specific tissues will emerge with continuing research.

Design, Construction and Validation of an Electrical Impedance Probe with Contact Force and Temperature Sensors Suitable for in-vivo Measurements

Bioimpedance spectroscopy measurements can be used for tissue characterization. These measurements can be performed in soft tissues by direct contact of a non-invasive probe consisting of two or four electrodes. The amount of force applied by users can be quite different, and the measurements can vary as a result. To compensate for this, we have built an electrical impedance probe (diameter 3.2 mm) with fibre optic contact-force and temperature sensors built in it. The different sensors of the probe were tested individually. The errors in magnitude and phase angle of the probe are <0.9% and <4°, respectively, for a 0.9% NaCl solution. The linear dynamic range of the force sensor was from 0 to 100 grams. An ex-vivo experiment on a section of proximal colon from a guinea-pig was performed. Twenty bioimpedance measurements were taken in a frequency range of 5 kHz to 1 MHz, while simultaneously recording the force applied. For an increase in contact pressure applied to tissue from 0 to 15.4 kPa, the maximum change in resistivity was 33% at 5 kHz and the minimum was 6.6% at 142 kHz. The probe is small enough to be introduced via the instrument port of an endoscope.

Monitoring the Effect of Contact Pressure on Bioimpedance Measurements

This paper presents preliminary results on the effect of contact pressure on bioimpedance measurements in an excised section of human colon tissue. The impedance measurements were performed with a small diameter probe suitable for in-vivo use, which is capable of measuring contact force. Force measurements are performed by fiber optic sensor which consisted of a Fiber Bragg Grating. The obtained results highlight the importance on limiting the applied pressure during bioimpedance measurements.

Impedance spectroscopy measurements as a tool for distinguishing different luminal content during bolus transit studies

BACKGROUND

Intraluminal electrical impedance is a well-known diagnostic tool used to study bolus movement in the human esophagus. However, it is use in the human colon it is hindered by the fact that the content cannot be controlled and may include liquid, gas, solid, or a mixture of these at any one time. This article investigates the use of complex impedance spectroscopy to study different luminal content (liquid and gas).

METHODS

An excised section of guinea pig proximal colon was placed in an organ bath with Krebs solution at 37°C and a custom built bioimpedance catheter was placed in the lumen. Liquid (Krebs) and gas (air) content was pumped through the lumen and the intraluminal impedance was measured at five different frequencies (1, 5.6, 31.6, 177.18 kHz and 1 MHz) at 10 samples per second. A numerical model was created to model the passage of bolus with different content and compared to the experimental data.

KEY RESULTS

Differences in mean impedance magnitude and phase angle were found (from 1 to 177.18 kHz) for different contents. The numerical results qualitatively agreed with those in the experimental study. Conductivities of bolus had an effect on detecting its passage.

CONCLUSIONS & INFERENCES

Complex impedance spectroscopy can distinguish between different luminal content within a range of measuring frequencies. The numerical model showed the importance of bolus conductivities for bolus transit studies in those where the bolus is controlled.

Avoiding neuromuscular stimulation in liver irreversible electroporation using radiofrequency electric fields

Electroporation-based treatments typically consist of the application of high-voltage dc pulses. As an undesired side effect, these dc pulses cause electrical stimulation of excitable tissues such as motor nerves. The present in vivo study explores the use of bursts of sinusoidal voltage in a frequency range from 50 kHz to 2 MHz, to induce irreversible electroporation (IRE) whilst avoiding neuromuscular stimulation. A series of 100 dc pulses or sinusoidal bursts, both with an individual duration of 100 µs, were delivered to rabbit liver through thin needles in a monopolar electrode configuration, and thoracic movements were recorded with an accelerometer. Tissue samples were harvested three hours after treatment and later post-processed to determine the dimensions of the IRE lesions. Thermal damage due to Joule heating was ruled out via computer simulations. Sinusoidal bursts with a frequency equal to or above 100 kHz did not cause thoracic movements and induced lesions equivalent to those obtained with conventional dc pulses when the applied voltage amplitude was sufficiently high. IRE efficacy dropped with increasing frequency. For 100 kHz bursts, it was estimated that the electric field threshold for IRE is about 1.4 kV cm^-1 whereas that of dc pulses is about 0.5 kV cm^-1.

Modeling liver electrical conductivity during hypertonic injection

Metastases in the liver frequently grow as scattered tumor nodules that neither can be removed by surgical resection nor focally ablated. Previously, we have proposed a novel technique based on irreversible electroporation that may be able to simultaneously treat all nodules in the liver while sparing healthy tissue. The proposed technique requires increasing the electrical conductivity of healthy liver by injecting a hypersaline solution through the portal vein. Aiming to assess the capability of increasing the global conductivity of the liver by means of hypersaline fluids, here, it is presented a mathematical model that estimates the NaCl distribution within the liver and the resulting conductivity change. The model fuses well-established compartmental pharmacokinetic models of the organ with saline injection models used for resuscitation treatments, and it considers changes in sinusoidal blood viscosity because of the hypertonicity of the solution. Here, it is also described a pilot experimental study in pigs in which different volumes of NaCl 20% (from 100 to 200 mL) were injected through the portal vein at different flow rates (from 53 to 171 mL/minute). The in vivo conductivity results fit those obtained by the model, both quantitatively and qualitatively, being able to predict the maximum conductivity with a 14.6% average relative error. The maximum conductivity value was 0.44 second/m, which corresponds to increasing 4 times the mean basal conductivity (0.11 second/m). The results suggest that the presented model is well suited for predicting on liver conductivity changes during hypertonic saline injection.

Focused Transhepatic Electroporation Mediated by Hypersaline Infusion through the Portal Vein in Rat Model. Preliminary Results on Differential Conductivity

Background

Spread hepatic tumours are not suitable for treatment either by surgery or conventional ablation methods. The aim of this study was to evaluate feasibility and safety of selectively increasing the healthy hepatic conductivity by the hypersaline infusion (HI) through the portal vein. We hypothesize this will allow simultaneous safe treatment of all nodules by irreversible electroporation (IRE) when applied in a transhepatic fashion.

Material and methods

Sprague Dawley (Group A, n = 10) and Athymic rats with implanted hepatic tumour (Group B, n = 8) were employed. HI was performed (NaCl 20%, 3.8 mL/Kg) by trans-splenic puncture. Deionized serum (40 mL/Kg) and furosemide (2 mL/Kg) were simultaneously infused through the jugular vein to compensate hypernatremia. Changes in conductivity were monitored in the hepatic and tumour tissue. The period in which hepatic conductivity was higher than tumour conductivity was defined as the therapeutic window (TW). Animals were monitored during 1-month follow-up. The animals were sacrificed and selective samples were used for histological analysis.

Results

The overall survival rate was 82.4% after the HI protocol. The mean maximum hepatic conductivity after HI was 2.7 and 3.5 times higher than the baseline value, in group A and B, respectively. The mean maximum hepatic conductivity after HI was 1.4 times higher than tumour tissue in group B creating a TW to implement selective IRE.

Conclusions

HI through the portal vein is safe when the hypersaline overload is compensated with deionized serum and it may provide a TW for focused IRE treatment on tumour nodules.

Avoiding nerve stimulation in irreversible electroporation: a numerical modeling study

Electroporation based treatments consist in applying one or multiple high voltage pulses to the tissues to be treated. As an undesired side effect, these pulses cause electrical stimulation of excitable tissues such as nerves and muscles. This increases the complexity of the treatments and may pose a risk to the patient. To minimize electrical stimulation during electroporation based treatments, it has been proposed to replace the commonly used monopolar pulses by bursts of short bipolar pulses. In the present study, we have numerically analyzed the rationale for such approach. We have compared different pulsing protocols in terms of their electroporation efficacy and their capability of triggering action potentials in nerves. For that, we have developed a modeling framework that combines numerical models of nerve fibers and experimental data on irreversible electroporation. Our results indicate that, by replacing the conventional relatively long monopolar pulses by bursts of short bipolar pulses, it is possible to ablate a large tissue region without triggering action potentials in a nearby nerve. Our models indicate that this is possible because, as the pulse length of these bipolar pulses is reduced, the stimulation thresholds raise faster than the irreversible electroporation thresholds. We propose that this different dependence on the pulse length is due to the fact that transmembrane charging for nerve fibers is much slower than that of cells treated by electroporation because of their geometrical differences.

Long-term effectiveness of irreversible electroporation in a murine model of colorectal liver metastasis

Irreversible electroporation (IRE) has recently gained in popularity as an ablative technique, however little is known about its oncological long-term outcomes. To determine the long-time survival of animals treated with a high dose of IRE and which histological changes it induces in tumoral tissue, IRE ablation was performed in forty-six athymic-nude mice with KM12C tumors implanted in the liver by applying electric current with different voltages (2000 V/cm, 1000 V/cm). The tumors were allowed to continue to grow until the animals reached the end-point criteria. Histology was harvested and the extent of tumor necrosis was semi-quantitatively assessed. IRE treatment with the 2000 V/cm protocol significantly prolonged median mouse survival from 74.3 ± 6.9 days in the sham group to 112.5 ± 15.2 days in the 2000 V/cm group. No differences were observed between the mean survival of the 1000 V/cm and the sham group (83.2 ± 16.4 days, p = 0.62). Histology revealed 63.05% ± 23.12 of tumor necrosis in animals of the 2000 V/cm group as compared to 17.50% ± 2.50 in the 1000 V/cm group and 25.6% ± 22.1 in the Sham group (p = 0.001). IRE prolonged the survival of animals treated with the highest electric field (2000 V/cm). The animals in this group showed significantly higher rate of tumoral necrosis.

Anatomically Realistic Simulations of Liver Ablation by Irreversible Electroporation: Impact of Blood Vessels on Ablation Volumes and Undertreatment

Irreversible electroporation is a novel tissue ablation technique which entails delivering intense electrical pulses to target tissue, hence producing fatal defects in the cell membrane. The present study numerically analyzes the potential impact of liver blood vessels on ablation by irreversible electroporation because of their influence on the electric field distribution. An anatomically realistic computer model of the liver and its vasculature within an abdominal section was employed, and blood vessels down to 0.4 mm in diameter were considered. In this model, the electric field distribution was simulated in a large series of scenarios (N = 576) corresponding to plausible percutaneous irreversible electroporation treatments by needle electrode pairs. These modeled treatments were relatively superficial (maximum penetration depth of the electrode within the liver = 26 mm) and it was ensured that the electrodes did not penetrate the vessels nor were in contact with them. In terms of total ablation volume, the maximum deviation caused by the presence of the vessels was 6%, which could be considered negligible compared to the impact by other sources of uncertainty. Sublethal field magnitudes were noticed around vessels covering volumes of up to 228 mm³. If in this model the blood was substituted by a liquid with a low electrical conductivity (0.1 S/m), the maximum volume covered by sublethal field magnitudes was 3.7 mm³ and almost no sublethal regions were observable. We conclude that undertreatment around blood vessels may occur in current liver ablation procedures by irreversible electroporation. Infusion of isotonic low conductivity liquids into the liver vasculature could prevent this risk.

Irreversible electroporation of the liver: is there a safe limit to the ablation volume?

Irreversible electroporation is a fast-growing liver ablation technique. Although safety has been well documented in small ablations, our aim is to assess its safety and feasibility when a large portion of liver is ablated. Eighty-seven mice were subjected to high voltage pulses directly delivered across parallel plate electrodes comprising around 40% of mouse liver. One group consisted in 55 athymic-nude, in which a tumor from the KM12C cell line was grown and the other thirty-two C57-Bl6 non-tumoral mice. Both groups were subsequently divided into subsets according to the delivered field strength (1000 V/cm, 2000 V/cm) and whether or not they received anti-hyperkalemia therapy. Early mortality (less than 24 hours post-IRE) in the 2000 V/cm group was observed and revealed considerably higher mean potassium levels. In contrast, the animals subjected to a 2000 V/cm field treated with the anti-hyperkalemia therapy had higher survival rates (OR = 0.1, 95%CI = 0.02–0.32, p < 0.001). Early mortality also depended on the electric field magnitude of the IRE protocol, as mice given 1000 V/cm survived longer than those given 2000 V/cm (OR = 4.7, 95%CI = 1.8–11.8, p = 0.001). Our findings suggest that ionic disturbances, mainly due to potassium alterations, should be warned and envisioned when large volume ablations are performed by IRE.

In vivo demonstration of injectable microstimulators based on charge-balanced rectification of epidermically applied currents

OBJECTIVE

It is possible to develop implantable microstimulators whose actuation principle is based on rectification of high-frequency (HF) current bursts supplied through skin electrodes. This has been demonstrated previously by means of devices consisting of a single diode. However, previous single diode devices caused dc currents which made them impractical for clinical applications. Here flexible thread-like stimulation implants which perform charge balance are demonstrated in vivo.

APPROACH

The implants weigh 40.5 mg and they consist of a 3 cm long tubular silicone body with a diameter of 1 mm, two electrodes at opposite ends, and, within the central section of the body, an electronic circuit made up of a diode, two capacitors, and a resistor. In the present study, each implant was percutaneously introduced through a 14 G catheter into either the gastrocnemius muscle or the cranial tibial muscle of a rabbit hindlimb. Then stimulation was performed by delivering HF bursts (amplitude <60 V, frequency 1 MHz, burst repetition frequency from 10 Hz to 200 Hz, duration = 200 μs) through a pair of textile electrodes strapped around the hindlimb and either isometric plantarflexion or dorsiflexion forces were recorded. Stimulation was also assayed 1, 2 and 4 weeks after implantation.

MAIN RESULTS

The implants produced bursts of rectified current whose mean value was of a few mA and were capable of causing local neuromuscular stimulation. The implants were well-tolerated during the 4 weeks.

SIGNIFICANCE

Existing power supply methods, and, in particular inductive links, comprise stiff and bulky parts. This hinders the development of minimally invasive implantable devices for neuroprostheses based on electrical stimulation. The proposed methodology is intended to relieving such bottleneck. In terms of mass, thinness, and flexibility, the demonstrated implants appear to be unprecedented among the intramuscular stimulation implants ever assayed in vertebrates.

In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses

Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs) that will be flexible, thread-like (diameters < 0.5 mm) and not only with controlled stimulation capabilities but also with sensing capabilities for artificial proprioception. We in vivo demonstrate that neuroprostheses composed of addressable microstimulators based on this electrical stimulation method are feasible and can perform controlled charge-balanced electrical stimulation of muscles. We developed miniature external circuit prototypes connected to two bipolar probes that were percutaneously implanted in agonist and antagonist muscles of the hindlimb of an anesthetized rabbit. The electronic implant architecture was able to decode commands that were amplitude modulated on the high frequency (1 MHz) auxiliary current bursts. The devices were capable of independently stimulating the target tissues, accomplishing controlled dorsiflexion and plantarflexion joint movements. In addition, we numerically show that the high frequency current bursts comply with safety standards both in terms of tissue heating and unwanted electro-stimulation. We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible.

Tumor growth delay by adjuvant alternating electric fields which appears non-thermally mediated

Delivery of the so-called Tumor Treatment Fields (TTFields) has been proposed as a cancer therapy. These are low magnitude alternating electric fields at frequencies from 100 to 300 kHz which are applied continuously in a non-invasive manner. Electric field delivery may produce an increase in temperature which cannot be neglected. We hypothesized that the reported results obtained by applying TTFields in vivo could be due to heat rather than to electrical forces as previously suggested. Here, an in vivo study is presented in which pancreatic tumors subcutaneously implanted in nude mice were treated for a week either with mild hyperthermia (41 °C) or with TTFields (6 V/cm, 150 kHz) and tumor growth was assessed. Although the TTFields applied singly did not produce any significant effect, the combination with chemotherapy did show a delay in tumor growth in comparison to animals treated only with chemotherapy (median relative reduction=47%). We conclude that concomitant chemotherapy and TTFields delivery show a beneficial impact on pancreatic tumor growth. Contrary to our hypothesis, this impact is non-related with the induced temperature increase.

Towards addressable wireless microstimulators based on electronic rectification of epidermically applied currents

Electrical stimulation has been explored to restore the capabilities of the nervous system in paralysis patients. This area of research and of clinical practice, known as Functional Electrical Stimulation, would greatly benefit from further miniaturization of implantable stimulators. To that end, we recently proposed and demonstrated an innovative electrical stimulation method in which implanted microstimulators operate as rectifiers of bursts of innocuous high frequency current supplied by skin electrodes, thus generating low frequency currents capable of stimulating excitable tissues. A diode could suffice in some applications but, in order to broaden the method's clinical applicability, we envision rectifiers with advanced capabilities such as current control and addressability. We plan flexible thread-like implants (diameters < 300 μm) containing ASICs. As an intermediate stage, we are developing macroscopic implants (diameters ~ 2 mm) made of off-the-shelf components. Here we present a circuit which responds to commands modulated within the high frequency bursts and which is able to deliver charge-balanced currents. We show that a number of these circuits can perform independent stimulation of segments of an anesthetized earthworm following commands from a computer.

Vascular smooth muscle cells ablation with endovascular nonthermal irreversible electroporation

PURPOSE

To evaluate the effect of endovascular nonthermal irreversible electroporation (NTIRE) on blood vessels.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Non-invasive assessment of corneal endothelial permeability by means of electrical impedance measurements

The permeability of the corneal endothelial layer has an important role in the correct function of the cornea. Since ionic permeability has a fundamental impact on the passive electrical properties of living tissues, here it is hypothesized that impedance methods can be employed for assessing the permeability of the endothelial layer in a minimally invasive fashion. Precisely, the main objective of the present study is to develop and to analyze a minimally invasive method for assessing the electrical properties of the corneal endothelium, as a possible diagnostic tool for the evaluation of patients with endothelial dysfunction. A bidimensional model consisting of the main corneal layers and a four-electrode impedance measurement setup placed on the epithelium has been implemented and analyzed by means of the finite elements method (FEM). In order to obtain a robust indicator of the permeability of the endothelium layer, the effect of the endothelium electrical properties on the measured impedance has been studied together with reasonable variations of the other model layers. Simulation results show that the impedance measurements by means of external electrodes are indeed sufficiently sensitive to the changes in the electrical properties of the endothelial layer. It is concluded that the method presented here can be employed as non-invasive method for assessing endothelial layer function.

Electrical impedance characterization of normal and cancerous human hepatic tissue

The four-electrode method was used to measure the ex vivo complex electrical impedance of tissues from 14 hepatic tumors and the surrounding normal liver from six patients. Measurements were done in the frequency range 1-400 kHz. It was found that the conductivity of the tumor tissue was much higher than that of the normal liver tissue in this frequency range (from 0.14 +/- 0.06 S m(-1) versus 0.03 +/- 0.01 S m(-1) at 1 kHz to 0.25 +/- 0.06 S m(-1) versus 0.15 +/- 0.03 S m(-1) at 400 kHz). The Cole-Cole models were estimated from the experimental data and the four parameters (rho(0), rho(infinity), alpha, f(c)) were obtained using a least-squares fit algorithm. The Cole-Cole parameters for the cancerous and normal liver are 9 +/- 4 Omega m(-1), 2.2 +/- 0.7 Omega m(-1), 0.5 +/- 0.2, 140 +/- 103 kHz and 50 +/- 28 Omega m(-1), 3.2 +/- 0.6 Omega m(-1), 0.64 +/- 0.04, 10 +/- 7 kHz, respectively. These data can contribute to developing bioelectric applications for tissue diagnostics and in tissue treatment planning with electrical fields such as radiofrequency tissue ablation, electrochemotherapy and gene therapy with reversible electroporation, nanoscale pulsing and irreversible electroporation.

Non thermal irreversible electroporation: novel technology for vascular smooth muscle cells ablation

Background

Non thermal Irreversible electroporation (NTIRE) is a new tissue ablation method that induces selective damage only to the cell membrane while sparing all other tissue components. Our group has recently showed that NTIRE attenuated neointimal formation in rodent model. The goal of this study was to determine optimal values of NTIRE for vascular smooth muscle cell (VSMC) ablation.

Methods and Results

33 Sprague-Dawley rats were used to compare NTIRE protocols. Each animal had NTIRE applied to its left common carotid artery using a custom-made electrodes. The right carotid artery was used as control. Electric pulses of 100 microseconds were used. Eight IRE protocols were compared: 1–4) 10 pulses at a frequency of 10 Hz with electric fields of 3500, 1750, 875 and 437.5 V/cm and 5–8) 45 and 90 pulses at a frequency of 1 Hz with electric fields of 1750 and 875 V/cm. Animals were euthanized after one week. Histological analysis included VSMC counting and morphometry of 152 sections. Selective slides were stained with elastic Van Gieson and Masson trichrome to evaluate extra-cellular structures. The most efficient protocols were 10 pulses of 3500 V/cm at a frequency of 10 Hz and 90 pulses of 1750 V/cm at a frequency of 1 Hz, with ablation efficiency of 89±16% and 94±9% respectively. Extra-cellular structures were not damaged and the endothelial layer recovered completely.

Conclusions

NTIRE is a promising, efficient and simple novel technology for VMSC ablation. It enables ablation within seconds without causing damage to extra-cellular structures, thus preserving the arterial scaffold and enabling endothelial regeneration. This study provides scientific information for future anti-restenosis experiments utilizing NTIRE.

Linear superposition electrical impedance tomography imaging with multiple electrical/biopsy probes

In medical diagnostics, tissue is often examined with multiple discrete biopsies taken under ultrasound placement. In a previous theoretical study, we have suggested that the linear nature of the equations used in electrical impedance tomography (EIT) can be employed with the conventional practice of biopsy sampling to produce an image of the tissue between the biopsy samplings. Specifically, the biopsy probes can be used to record EIT-type electrical data during the discrete tissue sampling. The location of the discrete biopsy needle insertions available from the ultrasound placement of the probes can be combined with the electrical measurement data and used with linear superposition to produce a complete EIT image of the tissue between the sampled sites. In this study, we explore the concept experimentally using gel phantoms to simulate tissue and heterogeneities in the tissue. The experiments are performed in 2-D and 3-D configurations, and data are taken discretely, one at a time, through single electrical probe insertions. In the 2-D configuration, we were able to produce images of reasonable quality for heterogeneities with a diameter larger than 3 mm (conductivity ratio 1:5) and with relative conductivity differences above 50% (diameter 5 mm).