Ablation Diameter Research Articles

Ablation characteristics of picosecond laser single point drilling of Si3N4 under dry and water medium

Single point laser ablation of Si3N4 under dry and water medium is investigated and analysed. The experiments were conducted based on the one-factor-at-a-time strategy considering various input parameters such as piercing time, focus point position and water layer thickness. The effects of process inputs on the ablated hole’s geometrical features including the ablation depth and diameter, hole taper, and hole edge roundness under presence and absence of water as an intermediate medium are studied. The laser focus point position was determined and varied during the investigation. It was found that, compared to the dry condition, the maximum ablation depth under wet condition is much more sensitive to the position of the laser focus point. It was also observed that the ablation depth is directly influenced by the piercing time in both dry and under water conditions. Picosecond laser single point ablation under a water layer with a thickness of 0.6 mm could increase the ablation depth up to 23%, compared to the dry condition. However, the ablation depth was significantly decreased by increasing the water layer thickness. Additionally, the hole entrance edge was rounded with increasing the water layer thickness. The hole taper was significantly influenced by the water layer thickness.

Effect of Water-Cooled Loop Monopole Antenna on Microwave Ablation Efficiency

This work compares the effect of a monopole antenna without cooling unit on a biological tissue and a monopole antenna with cooling unit. Computer simulation was done using a computer software named COMSOL MultiphysicsTM, input power was varied from 10W to 120W, with an interval of 10W, at different times, from 60s to 120s at an interval of 60s. It was observed that the diameter of the lowest power (20W) decreased by -17.2% at 5mins, the length decreased by -32.9% and aspect ratio for the two antennas increased by 23.40%. For medium power (60W), at 5mins, the diameter decreased by -9.89%, length decreased by -37.9%, and aspect ratio decreased by 45.24%. The p-value obtained from diameter for low power showed no significant difference for ablation without water cool (p > 0.005), but showed significant difference with water cool (p < 0.005), diameter for medium power showed no significant difference, p > 0.005 in both simulations, there was no statistically significant difference in the diameter for high power (110W and 120W) for both simulations, p-value > 0.005. The result showed that inclusion of cooling unit reduced backward heating of microwave antenna, ablation length, and ablation diameter of simulated tissue.

Computer modeling and in vitro experimental study of water-cooled microwave ablation array

Introduction Microwaves (MWs) quickly deliver relatively high temperatures into tumors and cover a large ablation zone. We present a research protocol for using water-cooled double-needle MW ablation arrays for tumor ablation here. Material and methods Our research program includes computer modeling, tissue-mimicking phantom experiments, and in vitro swine liver experiments. The computer modeling is based on the finite element method (FEM) to evaluate ablation temperature distributions. In tissue-mimicking phantom and in vitro swine liver ablation experiments, the performances of the new device and the single-needle MW device currently used in clinical practice are compared. Results FEM shows that the maximum transverse ablation diameter (MTAD) is 4.2 cm at 100 W output and 300 s (assessed at the 50 °C isotherm). In the tissue-mimicking phantom, the MTDA is 2.6 cm at 50 W and 300 s in single-needle MW ablation, and 4 cm in double needle MW ablation array. In in vitro swine liver experiments, the MTAD is 2.820 ± 0.127 cm at 100 W and 300 s in single-needle MW ablation, and 3.847 ± 0.103 cm in MW ablation array. Conclusion A new type of water-cooled MW ablation array is designed and tested, and has potential advantages over currently used devices.

Optimization and characterization of a novel internally-cooled radiofrequency ablation system with optimized pulsing algorithm in an ex-vivo bovine liver

Purpose: To prospectively characterize and optimize radiofrequency energy deposition to determine ideal parameters for achieving large ablation zones.Materials and methods: An internally-cooled RF system was used to perform 214 ablations in 72 ex-vivo bovine livers. Tip exposure (1–5 cm), electrode current (400–2500 mA), and application duration (3–15 min) were systematically varied. A pulsing algorithm optimized efficiency of RF deposition, including initial automatic ramping followed by adjustment in current, in response to changes in tissue impedance. Following the procedure ablation diameter and length were measured, sphericity calculated, and correlated with parameters of energy deposition and tissue temperatures.Results: Increasing electrode exposure from 1–5 cm produced linear increases in ablation diameter from 1.4 ± 0.1 to 5.3 ± 0.1 cm (y = 1.1x–0.5; R2 = 0.93), and length (y = 1.18x + 0.34; R2 = 0.92). A sphericity index >0.85 was noted at optimal energy setting for electrode exposures of 1–4 cm. Maximum temperatures post-ablation increased with active tip length from 68.5 ± 4.9 °C to 91.3 ± 1.5 °C in a logarithmic (y = 0.94ln(x)−2.75; R2 = 0.90) or power relationship between temperature and the resultant ablation diameter (y = 0.27e0.0295x; R2 = 0.76). A tight exponential relationship (y = 0.28x0.38; R2 = 0.97) was also observed between total energy deposition and ablation diameter. Finally, a multifactor relationship of the diameter of ablation to electrode tip exposure and the time to first impedance rise was successfully modeled, with a root mean squared error of 1.9 mm and R2 = 0.95.Conclusion: Large, reproducible, and spherical ablation areas can be achieved with the novel system described, with efficient delivery of RF energy deposited into tissue. These findings may have important clinical relevance in regards to the clinical utility of RF ablation compared to other competitive forms of thermal tumor ablation.

Numerical simulation on nanosecond laser ablation of titanium considering plasma shield and evaporation-affected surface thermocapillary convection

Nanosecond laser ablation of metal is a complicated process, which consists of many strongly coupled physical phenomena, including material heating, melting, evaporation, vapour dynamics, and plasma shield. In this work, the nanosecond laser ablation process of titanium is investigated at 1064 nm wavelength. A multi-physics axisymmetric two-dimensional (2D) model is presented. The evolution and the distribution of titanium target’s temperature were solved using governing equations and the vapour dynamics was determined using the Knudsen relations. The maximum temperature of titanium grown slower with the increase in laser fluence and the maximum flow velocity of liquid materials reached 121 m/s with the laser fluence of 12 J/cm2. In addition, the plasma shield effect was taken into account to correct the energy distribution of the incident laser. As the laser fluence increases, the energy efficiency decreases. At the laser fluence of 12 J/cm only 55.9% of the energy was absorbed at the centre of titanium. Furthermore, the surface morphology profiles were analysed after the laser ablation on different laser fluences lying within the range of 2 - 12 J/cm2. The results showed that the surface morphology after ablation has a crater-like form and the increment of laser fluence leads to a slower non-linear increment in ablation depth and diameter of melt zone. The calculated results are in good agreement with the experimental results. The study provides useful information for nanosecond laser precision fabrication.

Sequential and Simultaneous 4-Antenna Microwave Ablation in an Ex Vivo Bovine Liver Model.

To determine the sizes and shapes of ablation zones in 4-antenna microwave ablation in ex vivo bovine liver model under different conditions of power delivery patterns, antenna spacings, and ablation durations, for further using of multi-antenna MWA strategies in the treatment of large hepatocellular carcinoma. We tested protocols of eight ablations each on ex vivo bovine livers, involving simultaneous or sequential activation of four microwave antennas, spaced either 3 cm, 4 cm, or 5 cm apart, for either 10 or 15min, at 60-W power. We determined the diameters, shapes, and temperatures of the ablation zones. Compared to sequential power delivery, simultaneous power delivery resulted in significantly larger ablation zone diameters (P < .001). The temperatures in ablation zones were significantly higher for simultaneous than for sequential power delivery. The largest ablation diameter (7.45 ± 0.06cm) resulted from simultaneous delivery for 15min using 4-cm antenna spacing. Simultaneous 4-antenna microwave ablation results in larger ablation zones than sequential ablation, and 4-cm antenna spacing with a 15-minute ablation duration creates the largest ablation zone. This information may provide multi-antenna MWA strategies for large HCC in the further clinical practice.

Experimental investigation on ablation characteristics of coated and uncoated steel under 30/80 μs impulse current

The ablation tests on coated and uncoated Q235B steel sheets were conducted under 30/80 μs impulse current simulating the lightning first return stroke current, aimed at further understanding the ablation characteristics of steel and investigating the impact of anti-corrosion coating on these characteristics. Ablation characteristics were investigated through the macroscopic morphology and x-ray diffraction patterns on the surface of damaged zones, the microstructure and micro Vickers hardness on the cross-section of damaged zones, and the maximum rear-face temperature of sample sheets. It can be concluded that the ablation areas of uncoated sheet consist of the melted layer and the heat-affect layer. These ablation areas include not only the area ablated directly by the arc root, of which the depth is deeper, but also the area forming due to the splashing of molten steel, of which the depth is shallower and decreases when the area’s distance from the arc attachment point increases. For coated sheet, coating materials have decomposed and evaporated forming an ablation pit on the sheet surface, in which the steel surface is exposed, and zinc filler of coating primer has infused into the exposed surface. The ablation diameter of uncoated sheet relates to the amplitude of the 30/80 μs impulse current in quadratic function, while for coated sheet, the relation is linear. In general, under the 30/80 μs impulse current, the coating can decrease the energy injected from the arc to the steel sheet and reduce the melting and splashing of steel. As a result, the ablation severity of uncoated sheet is severer than that of coated sheet.

03:36 PM Abstract No. 367 An ex vivo bench and perfused liver assessment and extension of the ablation zone by “EdgeBoost” with IR-Circle: a new bipolar ablation device

The InCircle bipolar ablation device has allowed for the ablation of tumours >3 cm (3-7cm), using a no-touch, ‘outside in’ approach. A limitation of this device is its relative unsuitability for interventional radiology use as the diameter of the probe needle is >2mm in the larger devices. The aim of this study was to create ablations via a rotational technique using a new minimally invasive probe whilst maintaining ablation size and sphericity. The new device entails deployable coils on one side of the probe with a reduced probe needle diameter of 1.6mm. The device ablates using the ‘outside in’ approach larger ablations are created using a rotational technique (e.g., retracting the coils, rotating 180° and redeploying). The devices used had 3×2cm or 3×1.5cm diameter overlapping coils on one side of a 1.6mm diameter probe needle. EdgeBoost was created via multi-dimensional redeployment of the bipolar coils in the same tract by rotating the device’s orientation and deploying coils lateral to the initial ablation area. Ex vivo bovine liver was used for all experiments. Multiple set deployment angles (0°, 180°, 90/270°, 45/315°, 135/225°) were used to test which rotation sequence would yield constant size and sphericity. Grey zone was measured to calculate ablation size. Perfused experiments were performed. Power mode generator was used until impedance was reached and the ablated liver was examined. A total of 37 ablations were performed. An ablation size of 7.5×6×7cm was achieved in 3 consecutive ablations using the 3x2cm diameter coils with a 1.6mm probe needle in an outside in approach via multi-dimensional EdgeBoost at 0/180° and 90/270° placements. Using the 0°, 180°, 45/315°, 135/225° dimensions, the mean ablation size for the 3x1.5cm probe ex-vivo was 4.5x4.2x5cm. When repeated in the perfused liver model, the mean ablation size was 5.1x5.1x5cm with a mean ablation time of 13.2 minutes. Using the 3x2cm probe in the perfused liver model, the mean ablation size was 5.8x5.4x5.7cm. The new probe shows promising potential to produce large ablations. Additionally, the EdgeBoost increases the ablation diameter by over 1 cm whilst maintaining relative sphericity.

Radiofrequency ablation of atypical cartilaginous tumors in long bones: a retrospective study

Purpose: To determine the size of the ablation zone after radiofrequency ablation (RFA) of atypical cartilaginous bone tumors (ACT) using temperature-controlled 20 and 30 mm RFA straight non-cooled electrodes.Materials and methods: Sixteen patients with ACT in their long bones, who had undergone a single-session single-application CT-guided temperature-controlled RFA, were included retrospectively in the study. Tumors with a diameter of 10–25 mm were treated with 20 mm electrodes (n = 10), and tumors of 25–35 mm, with 30 mm electrodes (n = 6). The ablated zone was measured after three months on MRI images.Results: All the tumors were within the ablated zone on the 3-month follow-up MRI scan. The mean ablation time with the electrode, at a target temperature of 90 °C, was 7.6 minutes (range 6–10). The median of the largest ablation diameters, on applying the 20 and 30 mm electrodes, were 42 mm (IQR 8.5, range 30–51 mm) and 44.5 mm (IQR 4.5, range 42–63 mm), respectively.Conclusions: All the retrospectively viewed tumors in the long bones of ACT patients treated with RFA were completely ablated. The ablation zone diameters in the bones were larger than expected, when compared to other tissues, such as the liver.

Comparison of temperature change and resulting ablation size induced by a 902–928 MHz and a 2450 MHz microwave ablation system in in-vivo porcine kidneys

Introduction: Microwave ablation (MWA) uses heat to ablate undesired tissue. Development of pre-planning algorithms for MWA of small renal masses requires understanding of microwave-tissue interactions at different operating parameters. The objective of this study was to compare the performance of two MWA systems in in-vivo porcine kidneys.Methods: Five ablations were performed using a 902–928 MHz system (24 W, 5 min) and a 2450 MHz system (180 W, 2 min). Nonlinear regression analysis of temperature changes measured 5 mm from the antenna axis was completed for the initial 10 s of ablation using the power equation and after the inflection point using an exponential equation. Thermal damage was calculated using the Arrhenius equation. Long and short axis ablation diameters were measured.Results: The average ‘a’ varied significantly between systems (902–928 MHz: 0.0299 ± 0.027, 2450 MHz: 0.1598 ± 0.158), indicating proportionality to the heat source, but ‘b’ did not (902–928 MHz: 1.910 ± 0.372, 2450 MHz: 2.039 ± 0.366), signifying tissue type dependence. Past the inflection point, average steady-state temperature increases were similar between systems but reached more quickly with the 2450 MHz system. Complete damage was reached at 5 mm for both systems. The 2450 MHz system produced significantly larger short axis ablations (902–928 MHz: 2.40 ± 0.54 cm, 2450 MHz: 3.32 ± 0.41cm).Conclusion: The 2450 MHz system achieved similar steady state temperature increases compared to the 902–928 MHz system, but more quickly due to higher output power. Further investigations using various treatment parameters and precise thermal sensor placement are warranted to refine equation parameters for the development of an ablation model.

Nanosecond laser ablation of Si(111) under an aqueous medium

Nanosecond laser ablation of p-type Si(111) wafer is presented under an ambient, a water and a glycerin conditions. Effects of pulse energy, number of pulses and type of environment are systematically analyzed with an Optical Profilometer, a Scanning Electron Microscope and an Atomic Force Microscope. Obtained results are compared with Zemax∘-EE simulations. Self-assembly nano-ripple formation has been observed in an ambient condition. However, these ripples and heat affected zone (HAZ) area disappeared in aqueous medium which enhances the quality of ablation. Moreover, no remarkable oxidation was obtained in ablation zone even in an ambient condition based on the SEM-EDX analysis. Ablation profiles and their depths for different environments are compared with false color technique. Although ablation diameters are comparable each other, their depths are small enough in aqueous medium to control depth profile of damaged area. According to our results, best ablation profiles (precise edges without HAZ) are achieved under an aqueous medium especially in glycerin conditions both in low and high pulse energy regime.

The value of protection device in microwave ablation at canine liver risk area

Objective To explore the application value of protective device in microwave ablation at canine liver risk area, and the role of the device in reducing complications during ablation. Methods Six healthy mongrel dogs were randomly divided into two groups: group A, used protective devices; group B, unprotected. Conventional gray-scale ultrasound and contrast-enhanced ultrasound (CEUS) were performed before treatment to identify the ablation area (the right lobe of the liver near diaphragm, 1 cm from the surface of the liver). The two groups were treated percutaneous puncture liver microwave ablation under real time ultrasound-guided with the same ablation power (50 W) and equivalent ablation time (600 s). Liver specimens were evaluated histological examination to evaluate the necrotic area of ablation and the degree of diaphragm′s injury. Results ①There was no significance difference in the ablation range between two groups[ (3.3±0.1)cm vs (3.5±0.1)cm, P=0.184]; ②The tolerance of group A was better than group B during ablation treatment; ③The mean maximum ablation diameter in group A was significantly lower than that in group B [(2.1±0.1)cm vs (5.3±0.2)cm, P=0.001]. Meanwhile the pathological results showed that the damage degree in group A was significantly lower than that in group B. Conclusions This protective device has an obvious protective effect for microwave ablation of the risk area in liver (adjacent diaphragm, hepatic envelope). Our experiment suggests that this protective can reduce the damage of adjacent organ and the complications during the ablation surgery. Key words: Microwave ablation; Liver; Diaphragm; Artificialascites; Dogs

Automated trajectory planning for laser interstitial thermal therapy in mesial temporal lobe epilepsy

SummaryObjectiveSurgical resection of the mesial temporal structures brings seizure remission in 65% of individuals with drug‐resistant mesial temporal lobe epilepsy (MTLE). Laser interstitial thermal therapy (LiTT) is a novel therapy that may provide a minimally invasive means of ablating the mesial temporal structures with similar outcomes, while minimizing damage to the neocortex. Systematic trajectory planning helps ensure safety and optimal seizure freedom through adequate ablation of the amygdalohippocampal complex (AHC). Previous studies have highlighted the relationship between the residual unablated mesial hippocampal head and failure to achieve seizure freedom. We aim to implement computer‐assisted planning (CAP) to improve the ablation volume and safety of LiTT trajectories.MethodsTwenty‐five patients who had previously undergone LiTT for MTLE were studied retrospectively. The EpiNav platform was used to automatically generate an optimal ablation trajectory, which was compared with the previous manually planned and implemented trajectory. Expected ablation volumes and safety profiles of each trajectory were modeled. The implemented laser trajectory and achieved ablation of mesial temporal lobe structures were quantified and correlated with seizure outcome.Results CAP automatically generated feasible trajectories with reduced overall risk metrics (P < .001) and intracerebral length (P = .007). There was a significant correlation between the actual and retrospective CAP‐anticipated ablation volumes, supporting a 15 mm diameter ablation zone model (P < .001). CAP trajectories would have provided significantly greater ablation of the amygdala (P = .0004) and AHC (P = .008), resulting in less residual unablated mesial hippocampal head (P = .001), and reduced ablation of the parahippocampal gyrus (P = .02).SignificanceCompared to manually planned trajectories CAP provides a better safety profile, with potentially improved seizure‐free outcome and reduced neuropsychological deficits, following LiTT for MTLE.

3:50 PM Abstract No. 347 Ex vivo liver model temperature is a significant factor in ablation zone dimensional reference values claimed by manufacturers

The purpose of this study is to report how ex vivo model temperature can influence ablation zone dimensional performance claims. In this study, 72 microwave ablations were created in freshly harvested bovine livers using the Emprint™ ablation system at the 100 Watt generator setting. Bovine livers were submersed in a calibrated temperature controlled water bath prior to ablation testing to enable tight control (±2°C) of model background temperature across three model temperature groups (17°C, 25°C, 35°C). Within the 17°C liver model, ablations were performed for 60, 210, 510, 600, 900 and 1200 seconds. Within the 25°C liver model, ablations were performed for 300 and 600 seconds. Within the 35°C liver model, ablations were performed for 120, 240, 360 and 600 seconds. Immediately upon completion of each ablation sample, the ablation probe was removed and the ablation zone was bisected along the needle path. The ablation zone along the needle shaft (height) and in the cross-needle axis (width) was then grossly measured. Ablation zone cross-sections were photographed and data was statistically analyzed across temperature groupings. Within the 600 second ablation time grouping, the mean ablation width was 4.23 cm (17°C) vs 4.67 cm (25°C) vs 5.03 cm (35°C) (p<0.001), the mean ablation height was 4.15 cm (17°C) vs 4.50 cm (25°C) vs 4.75 cm (35°C) (p = 0.002), the mean ablation shape metric (minimum dimension/maximum dimension, 1.0 = sphere) was 0.96 (17°C) vs 0.96 (25°C) vs 0.93 (35°C) (p = 0.278), and the mean ablation volume (using ellipsoidal calculation) was 39.25 ml (17°C) vs 51.39 ml (25°C) vs 63.25 ml (35°C) (p<0.001). Ex-vivo background liver model temperature is a significant factor in microwave ablation dimensional performance. This study demonstrated a 61% increase in ablation volume by increasing model temperature from 17°C to 35°C. Manufacturers of microwave ablation systems utilize different model temperatures. When comparing ablation dimensional performance across microwave ablation systems, the model temperature used by each manufacturer is an important consideration.Tabled 1100 W Ablation Zone Dimension ResultsModel Temperature (ºC)Ablation Time (sec)NMean Ablation Diameter (cm)St Dev Ablation Diameter (cm)Mean Ablation Length (cm)St Dev Ablation Length (cm)Mean Ablation Volume (ml)St Dev Ablation Volume (ml)Mean Ablation ShapeSt Dev Ablation Shape176061.770.0822.480.1844.080.6360.710.0361721062.900.1792.920.40712.952.7700.900.0841751064.020.1944.030.25034.164.1200.950.0391760064.230.2424.150.35139.257.2000.960.0431790064.820.0754.780.23258.164.1200.970.01617120065.200.3745.050.32171.9911.9900.950.0522530063.650.2263.680.12225.874.6300.940.0352560064.670.1514.500.03751.394.0400.960.0253512063.050.1383.130.16315.281.4810.940.0443524063.780.1173.680.17227.611.9130.950.0333536064.280.1724.150.28140.004.9600.950.0363560065.030.2944.750.18763.258.5400.930.038 Open table in a new tab

3:27 PM Abstract No. 174 A retrospective comparison of ablation volumes, clinical response, and outcomes of overlapping versus simultaneous microwave ablation in patients with hepatocellular carcinoma

To compare the ablation volumes, clinical response, and outcomes after microwave ablation (MVA) with overlapping ablations (OA) vs. simultaneous ablations (SA) in patients with hepatocellular carcinoma (HCC). This retrospective study included 45 patients with 45 HCC who underwent MVA between 2013 and 2017. MVA was performed sequentially with one antenna in the OA group (n = 33; 23 M, 10 F; mean age: 61.9 y ± 9) and simultaneously with two antennae in the SA group (n = 12; 10 M, 2 F; mean age: 62.2 y ± 8.7). Patients were followed with CT or MR imaging for at least a year to identify tumor progression. Clinical and technical factors were reviewed. Ablation length, diameter, and volumes on first follow-up cross-sectional imaging were calculated. Tumor response, including complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD) were evaluated according to mRECIST. Local tumor progression (LTP), time to progression (TTP), progression-free survival (PFS), and overall survival (OS) were compared between groups. There were no significant differences between both groups in terms of tumor etiology, MELD, ECOG, Child-Pugh, BCLC scores, and median tumor size (OA: 2.45 cm; SA: 3 cm). The median wattage for OA and SA groups was not significantly different (66.8 W ± 16.7 vs. 58.3 W ± 11.6). Mean ablation time was longer in the OA group compared to the SA group (16.1 min ± 4.8 vs. 9.1 min ± 2.0, p<0.0001). Mean ablation volumes were larger in the SA group compared to the OA group (62.7 cm3 ± 20.9 vs. 36.2 cm3 ± 39.7, p<0.0001). There were no significant differences between OA and SA groups in terms of CR, PR, SD, or PD on follow-up imaging, as well as clinical outcomes, including LTP (median: 5 vs. 6.5 mo), TTP (median: 5 vs. 4 mo), and PFS (median: 13 vs. 17 mo). Overall survival was similar between groups at 12 mo (90.9% vs. 91.7%), but showed a decreased trend for the OA group at 24 mo (50% vs. 88.9%). SA leads to larger ablation volumes and shorter ablation times in patients with HCC but is not associated with improved clinical response, LTP, TTP, PFS, or OS when compared to patients undergoing OA.

Safety and effect on ablation size of hydrochloric acid-perfused radiofrequency ablation in animal livers

Purpose: Our objective was to determine the safety and ablation size of hydrochloric acid-perfused radiofrequency ablation (HCl-RFA) in liver tissues, prospectively using in vivo rabbit and ex vivo porcine liver models.Materials and methods: The livers in 30 rabbits were treated in vivo with perfusions of normal saline (controls) and HCl concentrations of 5%, 10%, 15%, and 20%, during RFA at 103 °C and 30 W for 3 min. For each experimental setting, six ablations were created. Safety was assessed by comparing baseline weight and selected laboratory values with those at 2, 7, and 14 days’ post-ablation, and by histopathological analysis. The livers in 25 pigs were treated ex vivo with the same five perfusions during RFA at 103 °C, at both 30 W and 60 W, for 30 min. Ablation diameters and volumes were measured by two examiners.Results: Rabbit weights and selected laboratory values did not differ significantly from baseline to 7 and 14 days’ post-ablation, liver tissues outside the ablation zones were normal histologically, and adjacent organs showed no macroscopic damage. The mean ablation volumes in the porcine livers treated with HCl-RFA were all larger than those treated with normal saline perfusion during RFA (NS-RFA), at both 30 W and 60 W (p < 0.001). The largest ablation volume and transverse diameter were observed in the porcine livers during 10% HCl-RFA at 60 W, measuring 179.22 (SD = 24.79) cm3 and 6.84 (SD = 0.36) cm, respectively.Conclusions: Based on our experiments, HCl-RFA in the liver appears to be as safe as NS-RFA while also resulting in larger ablation zones.

Analysis of efficiency of different antennas for microwave ablation using simulation and experimental methods

The objective of this study is to analyze the efficiency of different antennas proposed for microwave ablation therapy using numerical simulation and experimental approach. The simulation was done with COMSOL MULTIPHYSICS® software to design antenna prototypes and evaluate its reflection coefficient, power dissipation distribution, power dissipation density, specific absorption rate and temperature distribution in tissue. Antennas were fabricated from a 50 Ω RG405/U semi-rigid coaxial cable to match the geometric prototypes generated during simulation. Ex vivo bovine livers were ablated with the fabricated antennas using 50 W for 5 and 10 min. Ablation diameters, ablation lengths and aspect ratios were determined. Sleeved antenna produced lowest reflection coefficient, high power dissipation, low power dissipation density, high SAR and high temperature in the simulation. Sleeved antenna provides excellent localization, large ablative diameter, low backward heating and high aspect ratio than single slot, dual slot and monopole antennas.

Robotically Assisted Sonic Therapy as a Noninvasive Nonthermal Ablation Modality: Proof of Concept in a Porcine Liver Model.

Purpose To determine the feasibility of creating a clinically relevant hepatic ablation (ie, an ablation zone capable of treating a 2-cm liver tumor) by using robotically assisted sonic therapy (RAST), a noninvasive and nonthermal focused ultrasound therapy based on histotripsy. Materials and Methods This study was approved by the institutional animal use and care committee. Ten female pigs were treated with RAST in a single session with a prescribed 3-cm spherical treatment region and immediately underwent abdominal magnetic resonance (MR) imaging. Three pigs (acute group) were sacrificed immediately following MR imaging. Seven pigs (chronic group) were survived for approximately 4 weeks and were reimaged with MR imaging immediately before sacrifice. Animals underwent necropsy and harvesting of the liver for histologic evaluation of the ablation zone. RAST ablations were performed with a 700-kHz therapy transducer. Student t tests were performed to compare prescribed versus achieved ablation diameter, difference of sphericity from 1, and change in ablation zone volume from acute to chronic imaging. Results Ablation zones had a sphericity index of 0.99 ± 0.01 (standard deviation) (P < .001 vs sphericity index of 1). Anteroposterior and transverse dimensions were not significantly different from prescribed (3.4 ± 0.7; P = .08 and 3.2 ± 0.8; P = .29, respectively). The craniocaudal dimension was significantly larger than prescribed (3.8 ± 1.1; P = .04), likely because of respiratory motion. The central ablation zone demonstrated complete cell destruction and a zone of partial necrosis. A fibrous capsule surrounded the ablation zone by 4 weeks. On 4-week follow-up images, ablation zone volumes decreased by 64% (P < .001). Conclusion RAST is capable of producing clinically relevant ablation zones in a noninvasive manner in a porcine model. © RSNA, 2018.

Microwave ablation of pancreatic tumors

Objectives: To evaluate the clinical performance of percutaneous microwave ablation (MWA) for treatment of locally-advanced-pancreatic-cancer (LAPC).Material and methods: Twenty-two MWA sessions (August 2015–March 2017) in 20 patients with primary pancreatic cancer (13 men, 7 women, mean-age: 59.9 ± 8.6 years, range: 46–73 years), who had given informed consent, were retrospectively evaluated. All procedures were performed percutaneously under CT-guidance using the same high-frequency (2.45-GHz) MWA device. Tumor location and diameter, ablation diameter and volume, roundness, duration, technical success and efficacy, output energy, complications, and local tumor progression defined as a tumor focus connected to the edge of a previously technically efficient ablation zone were collected.Results: Seventeen pancreatic malignant tumors (77.3%) were located in the pancreatic head and five (22.7%) in the pancreatic tail. Initial Mean Tumor Diameter was 30 ± 6 mm. Technical success and efficacy were idem (100%). No major complications occurred. Two patients (9.1%) showed minor complications of severe local pain related to MWA. Post-ablation diameter was on average 34.4 ± 5.8 mm. Mean ablation volume was 7.8 ± 3.8 cm³. The mean transverse roundness index was 0.74 ± 0.14. Mean ablation time was 2.6 ± 0.96 min. The mean applied energy per treatment was 9627 ± 3953 J. Local tumor progression was documented in one case (10%) of the 10/22 available three-month follow-up imaging studies.Conclusion: High-frequency (2.45 GHz) microwave ablation (MWA) for treatment of unresectable and non-metastatic locally-advanced-pancreatic-cancer (LAPC) shows promising results regarding feasibility and safety of percutaneous approach after short-term follow-up and should be further evaluated.

Thermographic real-time-monitoring of surgical radiofrequency and microwave ablation in a perfused porcine liver model.

Radiofrequency ablation (RFA) and microwave ablation (MWA) are currently the dominant modalities to treat unresectable liver tumors. Monitoring the ablation process with b-mode-sonography is often hampered by artefacts. Furthermore, vessels may cause cooling in the adjacent tumor target (heat-sink-effect) with risk of local recurrence. The present study evaluated infrared-thermography to monitor surgical RFA/MWA and detect heat-sink-effects in real-time. RFA and MWA of perfused porcine livers was conducted at peripheral and central-vessel-adjacent locations, and monitored by real-time thermography. Ablation was measured and evaluated by gross pathology. The mean time for ablation was significantly longer in RFA compared with MWA (8 vs. 2 min). Although mean macroscopic ablation diameter was similar (RFA, 3.17 cm; MWA, 3.38 cm), RFA showed a significant heat-sink-effect compared with MWA. The surface temperature during central RFA near vessels was 1/3 lower compared with peripheral RFA (47.11±8.35°C vs. 68.72±12.70°C; P<0.001). There was no significant difference in MWA (50.52±8.35°C vs. 50.18±10.35°C; P=0.74). In conclusion, thermography is suitable to monitor the correct ablation with MWA and RFA. The results of the current study demonstrated a significant heat-sink-effect for RFA, but not MWA near vessels. MWA reaches consistent surface temperatures much faster than RFA. With further in vivo validation, thermography may be useful to ensure appropriate ablation particularly near vulnerable or vascular structures.