RF Electrode Research Articles

Synthesis of core–shell nanoparticles with liquid core using magnetron sputtering and capacitively coupled dusty plasmas

We succeeded in depositing amorphous carbon films around tin nanodroplets retained in a capacitively coupled plasma (CCP). High-pressure magnetron sputtering was used for synthesizing tin nanoparticles at the top of a vacuum chamber. Tin nanoparticles were transported to CCP at the bottom of the chamber, and they were trapped in the sheath above an rf electrode. Tin nanoparticles were heated above the mp by ion bombardment in CCP. We introduced methane into CCP to deposit amorphous carbon films around melted tin nanoparticles. The transmission electron microscope (TEM) images of core–shell nanoparticles showed completely spherical cores. We observed the melting of cores at the melting point of metal tin when we heated core–shell nanoparticles in TEM, suggesting that the amorphous carbon films protected cores from the oxidation. In addition, the amorphous carbon films were robust against the volume expansion of the cores due to melting.

Innovative Cesiation Deriving Incredible 145 mA Beam from J-PARC Cesiated RF-Driven H− Ion Source

In NIBS2022, the stable 8 hours operation of the J-PARC cesiated RF-driven H− ion source (IS) in a test-stand with a 69.9 keV 120 mA beam and a beam duty factor of 4 % (1 ms x 40 Hz) was reported. However, the Cesiation condition was produced after many times and rather large amount of Cs and H2Os injections. The fluctuation of the H− ion beam intensity (IH −) in a pulse and the transverse emittances were rather larger than those for the previous 65 keV 110 mA operation. The plasma electrode temperature (TPE) of 254 °C much higher than that not only for the usual J-PARC IS (about 70 °C) but also for the standard cesiated H− ion sources (180 ∼ 200 °C) suggested the existence of novel H2O mediated cesiation surviving against the high TPE. In this paper, the J-PARC IS improvements based upon a hypothesis of the best cesiation constituted of sub monolayer H2O (chemically bound with Mo) mediated cesiation and Cs half monolayer on remaining surface are presented. The innovative cesiation derived a 76.5 keV 145 mA beam stably with the small beam fluctuation and transverse emittances suitable for Radio Frequency Quadrupole LINACs of high energy LINACs. The measured results of the 145 mA / 83 mA beam, extraction electrode current and RF waveforms, parameter trends of an 8 hours 145 mA operation and the transverse emittances are presented. The optimum TPE was increased from 70 °C to 230 °C. Furthermore, the beam intensity for the J-PARC IS operation energy of 52.5 keV was increased from 72 mA to 83 mA, which was consistent with the 1.5 power perveance law on the beam energy compared with 145 mA for 76.5 keV.

Accelerated Stress Tests to Project PEM Fuel Cell Durability

One of the major degradation mechanisms limiting the long-term durability of proton exchange membrane fuel cells (PEMFCs) is the loss of platinum electrochemically active surface area (ECSA) of the carbon-supported platinum (Pt/C) cathode catalyst, caused by Pt dissolution that is followed by both Ostwald ripening of the Pt nanoparticles and loss of Pt into the ionomer phase [1]. The Pt ECSA loss is accelerated when subjecting PEMFCs to extended load-cycling inducing concomitant cycling of the cathode potential. To this end, accelerated stress tests (ASTs) can be conducted either by controlling the cell/stack current (“load-cycling” AST) under H2/air (anode/cathode) or the potential (“voltage-cycling” AST) under H2/N2 (anode/cathode).Most of the experiments studying the effect of load-cycling on catalyst durability have been based on voltage-cycling in a H2/N2 configuration, showing that Pt ECSA loss is aggravated with increasing upper potential limit (UPL), temperature, and relative humidity (RH) [2, 3, 4]. Comparing voltage-cycling induced degradation under H2/N2 versus H2/air, a recent study has found an essentially identical Pt ECSA loss, but a slightly higher H2/air performance decay when cycling under H2/N2 [4]. This study by General Motors Corporation indicates that Pt ECSA loss may not be a unique descriptor for H2/air performance loss, contrary to what was observed in recent work by Toyota Motor Corporation and Kyushu University [5] as well as in our own studies [6].In this talk, we will discuss the correlation between H2/air performance loss and Pt ECSA loss during voltage-cycling ASTs at different conditions (UPL, RH, and gas-feed) conducted in 5 cm2 active area single-cell PEMFCs, complemented by a voltage-loss analysis to deconvolute oxygen reduction reaction (ORR) activity losses and mass transport losses (due to oxygen mass transport and proton conduction in the cathode catalyst layer). We will also discuss whether the H2/air performance loss is governed by the Pt ECSA loss (independent of catalyst loading) or, as we had proposed previously, by the cathode electrode roughness factor (rf) loss (in cm2 Pt/cm2 cathode, i.e., the product of ECSA and Pt loading) [7]. As roughly 100,000 [8] or even more voltage-cycles are expected for heavy-duty applications, requiring very long measurement times, an approach to relate the degradation under harsh AST conditions with those under application-relevant conditions will be discussed. Experiments are conducted with cathode catalysts based on different carbon supports (Vulcan, Ketjenblack, or so-called accessible carbon supports [9, 10]), on catalysts with different initial Pt ECSAs (i.e., different Pt nanoparticle sizes) and with different initial Pt-loadings (i.e. different initial rf). Finally, exploratory experiments to evaluate the effect of start-up/shut-down on the correlation between electrode rf and H2/air performance decay will be discussed.

A Conjoined Rectilinear Collision Cell and Pulsed Extraction Ion Trap with Auxiliary DC Electrodes.

Ion traps are routinely directly coupled to mass analyzers, where they serve to suitably cool and shape an ion population prior to pulsed extraction into the analyzer proper. Such devices benefit from high duty cycle and transmission but suffer slow ion processing times caused by a compromise in the buffer gas pressure range that suitably dampens the ion kinetic energy without causing excessive scatter during extraction or within the analyzer. A rectilinear RF quadrupole ion trap has been characterized, conjoining a pressurized collision region with a pumped extraction region, and an unbroken RF interface for seamless ion transfer between them. Auxiliary electrodes mounted between the RF electrodes provide DC voltage gradients that serve to both guide ions through the device and position them at the extraction slot. The influence of the auxiliary DC upon the trapping RF field was measured, and suitable parameters were defined. A mode of operation was developed that allowed parallel processing of ions in both regions, enabling a repetition rate of 200 Hz when the device was coupled to a high-resolution accurate-mass analyzer.

Conversion of the bronchial tree into a conforming electrode to ablate the lung nodule in a porcine model

BackgroundRadiofrequency ablation (RFA) is one of the treatment options for lung nodules. However, the need for exact delivery of the rigid metal electrode into the center of the target mass often leads to complications or suboptimal results. To overcome these limitations, a concept of conforming electrodes using a flexible material has been tested in this study.MethodsA bronchoscopy-guided RFA (CAROL) under a temperature-controlled mode was tested in in-vivo and ex-vivo porcine lungs. Gallium-based liquid metal was used for turning the bronchial tree into temporary RF electrodes. A customized bronchoscopy-guided balloon-tipped guiding catheter (CAROL catheter) was used to make the procedure feasible under fluoroscopy imaging guidance. The computer simulation was also performed to gain further insight into the ablation results. Safety was also assessed including the liquid metal remaining in the body.ResultsThe bronchial electrode injected from the CAROL catheter was able to turn the target site bronchial air pipe into a temporally multi-tined RF electrode. The mean volume of Gallium for each effective CAROL was 0.46 ± 0.47 ml. The ablation results showed highly efficacious and consistent results, especially in the peripheral lung. Most bronchial electrodes were also retrieved by either bronchoscopic suction immediately after the procedure or by natural expectoration thereafter. The liquid metal used in these experiments did not have any significant safety issues. Computer simulation also supports these results.ConclusionThe CAROL ablation was very effective and safe in porcine lungs showing encouraging potential to overcome the conventional approaches.

A new J.E probe for measurement of spatial profiles of power absorption in RF produced plasma.

This paper reports an indigenously developed probe for the measurement of spatial profiles of the absorbed/generated RF power density Pabs (W/m3) in RF discharges. The technique utilizes a calibrated current (J) probe based on the Rogowski coil principle and an electric field (E) probe based on capacitive coupling, both integrated into a single probe called the J.E probe. Various aspects of the probe, such as its design, fabrication, calibration, and limitations, were resolved before it was used for obtaining axial profiles of RF power absorption/generation. Also presented are the first experimental results for the absorbed power density profiles at the fundamental (13.56MHz) and harmonic (27.12MHz) along the length of a capacitively coupled discharge. The axial scans between the powered and grounded electrode were taken at different argon gas pressures (10-800mTorr) at a fixed RF power of 10W. Detailed analysis of the results shows that even for systems with large electrode gaps, i.e., plasmas with long bulk plasma regions, practically all the fundamental power is absorbed in a narrow edge region near the powered electrode, irrespective of the pressure. Absorption is high near the RF electrode since the RF fields peak in this region. Another important conclusion is that stochastic absorption of the fundamental and harmonic generation proceeds fairly efficiently in the vicinity of the powered electrode even at high pressures. It may be mentioned that the probe technique introduced here is the first of its kind, and although there is considerable scope for miniaturization, it has, nonetheless, provided some key insights into the nature of RF power absorption in capacitive discharges.

Lesion formation in irrigated RF-ablation is not linear, but monoexponential

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency ablation remains one of the most important ablation techniques in the EP lab. Creating durable lesion is difficult, as progression of lesion formation cannot be observed directly. Surrogate parameters, as force-time-integral and indices, as the ablation index or lesion size index, help distinguishing the efficacy of a RF-application, but several deficiencies are known. The aim of this study was to further investigate dynamic changes in ablation parameters and lesion growth in RF-ablation. Methods RF-lesions were created using an ex vivo porcine cardiac model with a force and local impedance sensing catheter. A second catheter was used for lesions up to 70 Watts. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and electrode tissue coupling. RF power of 20W, 30W, 40W, and 50W was used in the local impedance sensing catheter, while RF power of 30W, 40W, 50W, 60W, and 70W were used in the second catheter. All parameters (power, temperature, global impedance, ETC, lesion diameter and lesion depth) were measured once per second during application of RF-current, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Results In total, 61 lesions were included in the analysis. Due to at least 60 measurements per lesion, 3321 data points with all ablation parameters (power, temperature, global impedance, lesion diameter and lesion depth) were collected and analyzed. Throughout the application, lesion progression was highest in the first seconds of RF application and showed a slowing approximation to a maximum (Figure 1 and 2). Potential maximum lesion size seems to be defined by selected power level (s. Figure 3). Interestingly, these findings were seen in all power levels from 20 – 70 W (s. Figure 3). 75 % of final lesion size was achieved after 12-25 seconds, depending on selected power levels (s. Figure 4). In high power ablation (> 50 W), 75% of final lesion size was reached significantly earlier compared to lower power levels (20-40 W, s. Figure 4). Conclusion In RF-ablation, lesion growth is not linear. A slowing approximation of lesion diameter and depth to a maximum is observed. This finding should be considered in clinical settings to avoid steam pops and collateral damage due to a long RF duration despite little changes in lesion size. Further investigation is needed for a surrogate parameter, which is able to assess declining lesion growth after the first seconds of RF-application.

Spatial structures of rf ring-shaped magnetized sputtering plasmas with two facing cylindrical ZnO/Al2O3 targets

Spatial structures of the ion flux to the substrate are measured in an rf ring-shaped magnetized sputtering plasma with two facing cylindrical ZnO/Al2O3 targets at various argon gas pressures of 0.13, 0.67, and 0.93 Pa. Spatial distributions of the Hall parameter and Larmor radius of electrons and ions are also discussed by using simulated values of the magnetic flux density. The magnitude of the ion flux for 0.13 and 0.67 Pa is of the order of 1020 m−2 s−1, while for 0.93 Pa it is of the order of 1021 m−2 s−1 at a fixed rf power of 20 W. The radial profile of the ion flux has a peak at the position of the ring-shaped groove near an rf electrode and then becomes uniform further away from the electrode at all gas pressures. It is found that the axial profile of the deviation from a uniform profile estimated from the radial profile of the ion flux has two decay characteristics (1st decay length of 13.9–17.5 mm and 2nd decay length of 52.6–66.7 mm) and their decay lengths decrease with increasing the gas pressure.

Влияние внешнего переменного электрического поля на эффективность сверхпроводникового однофотонного детектора

In this paper, model of a surface ion trap for a scalable quantum computer with an RF electrode and a superconducting single-photon detector was studied with an operating temperature of 4K. The amplitude range of the radio frequency signal varied from 10 to 800 mV at frequencies from 5 to 20 MHz. The effect of the induced external RF field of the trap on the dark and bright count rate of a single-photon detector is studied. The results of this work are important in the design of surface ion traps with planar single-photon detectors.

The Effect of Thermal and Electrical Conductivities on the Ablation Volume during Radiofrequency Ablation Process

Radiofrequency ablation (RFA) is the treatment of choice for certain types of cancers, especially liver cancer. However, the main issue with RFA is that the larger the tumor volume, the longer the ablation period. That causes more pain for the patient, so the surgeons perform a larger number of ablation sessions or surgeries. The current commonly used electrode material, nickel-titanium alloy, used in RFA is characterized by low thermal and electrical conductivities. Using an electrode material with higher electrical conductivity and thermal conductivity provides more thermal energy to tumors. In this paper, we design two models: a cool-tip RF electrode and a multi-hook RF electrode, which aim to study the effect of the thermal and electrical conductivities of the electrode material on ablation volume. Gold, silver, and platinum have higher thermal and electrical conductivity than nickel and titanium alloy, and therefore we studied the effect of these materials on the ablation volume using two different designs, which are the RF cooling tip electrode and the multi-hook electrode. The proposed model reduces the ablation time and damages healthy tissue while increasing the ablation volume with values ranging from 2.6 cm3 to 15.4 cm3. The results show ablation volume increasing with materials characterized by higher thermal and electrical conductivities and thus reducing patient pain.

The PSR effect of matching network in 8/100 MHz geometrically symmetrical capacitively coupled Ar plasma

The high-order harmonics caused by the self-excitation of nonlinear plasma series resonance (PSR) in a geometrically symmetric (8 + 100) MHz capacitively coupled argon plasma are studied by using a nonlinear global model. The voltage waveforms and current waveforms measured by oscilloscope between the two electrodes are used to observe the harmonics. The voltage waveforms are used as input parameters for the nonlinear global model to simulate harmonics of the sheath charges of low-frequency electrode, bias voltage, and plasma RF current. These discharged parameters considering coupling effect between these two frequencies and without considering coupling effect are compared in (8 + 100) MHz capacitively coupled plasma with the increasing low-frequency powers at a pressure of 30 mTorr. These results indicate that the theoretical discharge behavior without considering the coupling effect has big difference from the real experiment. The PSR effect of the matching network plays an important role in modulating the plasma homogeneity. Therefore, how to design a suitable matching network to enhance the PSR effect is more meaningful for the nonlinear dynamics of plasma.

Maskless interdigitated a-Si:H PECVD process on full M0 c-Si wafer: Homogeneity and passivation assessment

In this work, the use of a novel, large area, mask-less and contact-less patterning technique is demonstrated for the first time, showing the localized deposition of hydrogenated amorphous silicon (a-Si:H) in a desired pattern over the full surface of an M0 (156 mm × 156 mm) solar wafer. The patterning functionality is achieved through a custom-designed RF electrode possessing a series of “slits” and placed in close proximity to the substrate in a plasma enhanced chemical vapor deposition (PECVD) chamber. Under a certain set of process conditions, a plasma only ignites within these slits, and the localized plasma results in localized patterned deposition of a-Si:H with feature widths compatible with application in an interdigitated back contact (IBC) solar cell design (760 μm). The homogeneity of the finger width and thickness over the surface of the M0 wafer is evaluated, with a 37% variation in thickness (at very high deposition rate, ∼1 nm/s) but only a 4.7% variation in finger width (MSE). With this application in mind, the impact of the deposition of such “fingers” on an underlying “blanket” passivation layer is assessed. Passivation is maintained or improved up to a given finger/blanket thickness ratio, above which the passivation is degraded. It is shown that the acceptable process window contains suitable thickness values for heterojunction (HJT) IBC solar cells, and the physical processes at the origin of this phenomenological observation are discussed.

Analysis of Efficacy and Factors Associated with Reccurence After Radiofrequency Thermocoagulation in Patients with Postherpetic Neuralgia: a Long-Term Retrospective and Clinical Follow-Up Study.

IntroductionPostherpetic neuralgia (PHN) is a painful condition that persists for 1 month or more after herpes zoster rash has healed. Radiofrequency thermocoagulation (RF-TC) provides analgesia by destroying the dorsal root ganglion and blocking the pain upload pathway; nonetheless, the concomitant neurological-related side effects and recurrence remain a concern.MethodsIn this study, 228 patients with PHN in the thoracic segment treated with RF-TC of the dorsal root ganglion of the spinal nerve were included, and were followed up regularly after surgery. The numerical rating scale (NRS) scores, time to recurrence, and intraoperative and postoperative adverse events were recorded and analyzed. The Kaplan–Meier method was used to plot survival curves and calculate the cumulative effective rate and recurrence rate. Cox regression analyses were performed to identify factors associated with postoperative recurrence. Predictive models were built to assess the value of applications.ResultsThe NRS scores decreased in all postoperative periods compared with preoperative ones. At 10-year-follow-up, recurrence was observed in 34.6% (79/228) of patients that underwent PHN. The main postoperative complications were numbness and reduced abdominal muscle strength, which gradually decreased with time, while the abdominal muscle strength gradually recovered. No other adverse events occurred. Interval-censored multivariable Cox regression analysis demonstrated that disease course, complications, pain grade, and type of RF electrode were associated with a significantly higher risk of relapse. The main intraoperative adverse effect was a transient increase in pain during RF-TC.ConclusionCT-guided RF-TC of the dorsal root ganglion of the spinal nerve for PHN is a relatively safe and effective surgical option. Disease course, type of RF electrode, complications, and pain grade are risk factors for postoperative recurrence and can assist in clinical decision-making before the RF-CT procedure.

Electrode tissue coupling is a new main determinant of RF lesion creation, experience from a cardiac animal model

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency (RF) current is a classic ablation technology used in the EP lab. By now it is assumed that RF lesion size is mainly determined by RF power, duration and contact force. This ex vivo animal model study shows that a new parameter - "electrode tissue coupling" (ETC) - plays an additional major role in RF lesion creation. The ETC level describes the amount of electric contact between the RF electrode and cardiac tissue: In minor ETC levels, only the distal electrode connects to tissue. In full ETC levels, the whole RF electrode is embedded in cardiac tissue. Methods RF-lesions were created using an ex vivo porcine cardiac model. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. A RF power of 20W, 30W, 40W, and 50W was used. The ETC levels were systematically varied between minor and full coupling. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly during application of RF-current, enabling real-time correlation of RF parameters and lesion size. Results In total, 1923 measurements during application of RF-current were analyzed. In ETC III (full tissue coupling), lesions became significantly wider and deeper. In 20W ablations, lesion diameters were significantly (1.68 fold) larger when applying ETC III instead of ETC I. This relation was found in variations of RF parameters (Table 1). Interestingly, baseline local impedance and local impedance drop showed a high correlation with selected ETC levels. The average baseline local impedance in ETC I was 207.2 Ohm, compared to 267.3 Ohm in ETC III (p < 0.01). Discussion In addition to by now known parameters (power, duration, contact force), electrode tissue coupling is a main determinant of lesion size. Higher ETC levels result in higher amounts of RF current going into adjacent tissue instead of current dissipation into the blood pool. In clinical practice, the ETC level can be predicted by baseline local and global impedance. Observation of these parameters should become clinical practice during RF ablation.

Implementation of Ion Mobility Spectrometry-Based Separations in Structures for Lossless Ion Manipulations (SLIM).

Structures for Lossless Ion Manipulations (SLIM) is a powerful variant of traveling wave ion mobility spectrometry (TW-IMS) that uses a serpentine pattern of microelectrodes deposited onto printed circuit boards to achieve ultralong ion path lengths (13.5m). Ions are propelled through SLIM platforms via arrays of TW electrodes while RF and DC electrodes provide radial confinement, establishing near lossless transmission. The recent ability to cycle ions multiple times through a SLIM has allowed ion path lengths to exceed 1000m, providing unprecedented separation power and the ability to observe ion structural conformations unobtainable with other IMS technologies. The combination of high separation power, high signal intensity, and the ability to couple with mass spectrometry places SLIM in the unique position of being able to address longstanding proteomics and metabolomics challenges by allowing the characterization of isomeric mixtures containing low abundance analytes.

Angular distribution measurement of high-energy argon neutral and ion in a 13.56 MHz capacitively-coupled plasma

Angular distributions of high energy neutrals and ions, impinging on an RF-biased electrode in a 13.56 MHz capacitively-coupled argon plasma were investigated. Ions and neutrals were introduced into a drift chamber that was directly connected to the RF electrode. A two-dimensional beam image was measured by a micro-channel plate. Neutral and ion beams were separated by an electrostatic deflector in the drift chamber. Angular distribution widths for ion and neutral were less than 1° at self-bias voltages above 300 V and monotonically decreased with increasing the self-bias voltage. Neutral angular distribution width was larger than that of ion, irrespective of self-bias voltage.

Computational Modeling of Catheter-based Radiofrequency Renal Denervation with Patient-specific Model.

Renal sympathetic denervation (RDN) is an effective approach for uncontrolled hypertension. Although several studies have compared the ablation characteristics at various locations, there is no direct comparative study on the effect of ablation in main and branch renal artery (RAs) and different electrode materials. The study aims to investigate the effect of different electrode materials (copper, gold, and platinum) and positions (proximal, middle, or distal site) on ablation. A 3D patient-specific renal artery model and a unipolar model (470 kHz) were constructed to mimic RDN. Two therapeutic strategies, including main (site 1 and 2) and branch (site 3) ablations were simulated with three electrode materials. The finite element method was used to calculate the coupled electric-thermal-flow field. Maximum lesion depth, width, area, and lesion angle were analyzed. The results showed that the difference in lesion width and depth was no mere than 0.5 mm, and the maximum difference value in lesion area is 0.683 mm2 among three electrode materials. The lesion angle of proximal site 1 versus middle site 2 was 58.39 ° and 52.23 °, but the difference between distal site 3 and site 1, or site 2 was 29.19 ° and 35.35 ° respectively. There is no significant difference in the use of the three electrode materials, and ablation at the distal site of the artery is more effective.Clinical Relevance-This provides a reference for the selection of RF electrode materials and ablation locations.

Mathematical modeling of a new way of renal artery denervation

The aim of the work is to create a new design of electrodes for renal denervation. In standard RFA systems, monopolar heating is most often used, by introducing an RF electrode inside the vessel. This approach leads to the need to interrupt blood flow during the procedure. In addition, the monopolar mode of operation requires the contact of the inserted electrode with the vessel walls, which greatly complicates the design of the electrode system. Point contact of the electrode system with the vessel can damage the inner walls of the artery. It is proposed to use a multi-electrode structure for external stimulation by creating a hollow cylindrical thermal field for effective treatment. It has been established that external heating will create the required thermal field without direct contact with the walls of the artery. The external arrangement of the electrodes makes it possible to regulate the temperature on the external surface of the vessel. With such heating, it is not necessary to block the blood flow, and due to the symmetry of the arrangement, continuous heating can be obtained without moving the electrodes during the procedure. Mathematical modeling confirms the possibility of vascular denervation during external heating.

Computed tomography guided radiofrequency ablation of osteoid osteoma in children: a single center's experience.

To report a single center's experience evaluating the efficacy and safety of computed tomography-guided radiofrequency ablation for the treatment of osteoid osteoma in children. Institutional database research identified 33 symptomatic patients (≤ 18years of age; male/female ratio: 21/12, mean age 13.09 ± 3.66) with osteoid osteoma who were treated by CT-guided RFA. Technical and clinical success as well as complication rates were recorded. The duration of the procedure, the number of computed tomography scans and the results of the biopsy were assessed. Pain, prior, the following morning and 1week, 1/6/12months after the procedure were compared by means of a numeric visual scale (NVS) questionnaire. Mean lesion size was 8.28 ± 4.24mm. Mean follow-up was 23.33 ± 17.61months (range 12-62). Mean pain score prior to radiofrequency ablation was 9.06 ± 0.80 NVS units. On week 1 and 1/6/12months, all patients were pain-free reporting 0 NVS units (p < 0.05). The mean procedure time was 54min (range 51-59) and a mean of 7 CT scans were performed during the ablation session. RF electrode was successfully placed in the center of the nidus in all cases. In our study, none of our patient experienced recurrence of the pain, nor complications. The present study demonstrates that percutaneous CT-guided radiofrequency ablation constitutes a safe and effective technique for osteoid osteoma treatment in children.

Unidirectional ablation minimizes unwanted thermal damage and promotes better thermal ablation efficacy in time-based switching bipolar radiofrequency ablation

Switching bipolar radiofrequency ablation (bRFA) is a thermal treatment modality used for liver cancer treatment that is capable of producing larger, more confluent and more regular thermal coagulation. When implemented in the no-touch mode, switching bRFA can prevent tumour track seeding; a medical phenomenon defined by the deposition of cancer cells along the insertion track. Nevertheless, the no-touch mode was found to yield significant unwanted thermal damage as a result of the electrodes’ position outside the tumour. It is postulated that the unwanted thermal damage can be minimized if ablation can be directed such that it focuses only within the tumour domain. As it turns out, this can be achieved by partially insulating the active tip of the RF electrodes such that electric current flows in and out of the tissue only through the non-insulated section of the electrode. This concept is known as unidirectional ablation and has been shown to produce the desired effect in monopolar RFA. In this paper, computational models based on a well-established mathematical framework for modelling RFA was developed to investigate if unidirectional ablation can minimize unwanted thermal damage during time-based switching bRFA. From the numerical results, unidirectional ablation was shown to produce treatment efficacy of nearly 100%, while at the same time, minimizing the amount of unwanted thermal damage. Nevertheless, this effect was observed only when the switch interval of the time-based protocol was set to 50 s. An extended switch interval negated the benefits of unidirectional ablation.