Ablation Diameter Research Articles

The research of sorafenib in combination with microwave ablation on rabbit orthotopic VX2 liver tumor model

Objective To evaluate the value of sorafenib as an adjuvant therapy in combination with microwave (MW) ablation on rabbit VX2 liver tumor model. Methods Thirty-seven rabbits with orthotic VX2 liver tumors were randomly divided into MW group (n=11), combination treatment group (n=14) and control group (n=12). MW therapy was performed with an output power of 20 W for one minute, achieving a maxim ablation diameter of about 1 cm. Sorafenib was given with a dosage of 30 mg/kg per day, while saline were given to the control group and the MW group. Tumor growth-curve in each group was drawn according to tumor volumes before and after treatment. The therapeutic efficacy was evaluated by contrast enhanced ultrasound (CEUS), magnetic resonance imaging (MRI), pathological and immunohistochemical examinations. The independent samples t-test and One-way ANOVA test were used to analyze the quantitative data. Chi-square test and fisher exact test were used to analyze the classified data. Two-tailed P<0.05 was considered statistically significant. Results The tumor growth was accelerated in MW group compared with control group and combination treatment group. The mean tumor volume in MW group at 3 d, 7 d and 14 d was significantly larger than those in two other groups (P=0.007, 0.001, 0.001), whereas no significant differences were found in tumor volume between control group and combination treatment group (P=0.381, 0.069, 0.328). A low metastases rate was shown in combination treatment group compared with other two groups. In combination treatment group, CEUS showed short rod-like and rim-like hypo-enhancement mainly detected in the periphery of lesion. However, conglomerate and latticed hyper-enhancement were the most patterns in MW group, with enhanced areas both in peripheral and internal of tumors. The apparent diffusion coefficient (ADC) value on diffused weighted image (DWI) was higher compared with that of the control and MW group, with statistical significance (1.845±0.503 vs. 1.102±0.149, 0.979±0.235). With adjuvant therapy of sorafenib after insufficient ablation, the microvessel density (MVD) was lower than that of control group (5.33±3.11 vs. 12.63±6.88), whereas in MW group the MVD was higher than that of control group (18.20±2.30 vs. 12.63±6.88), with statistical significance. Conclusion Insufficient thermal ablation promotes residual tumor progression. While the adjuvant therapy of sorafenib serves as an effective way to suppress the overgrowth and neovasculation of residual tumor after insufficient thermal ablation. Key words: Microwave ablation; Sorafenib; Orthotopic VX2 liver tumor model; Contrast enhanced ultrasound; Microvessel density; Apparent diffusion coefficient

IR-MALDESI Mass Spectrometry Imaging at 50 Micron Spatial Resolution.

High spatial resolution in mass spectrometry imaging (MSI) is crucial to understanding the biology dictated by molecular distributions in complex tissue systems. Here, we present MSI using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) at 50 μm resolution. An adjustable iris, beam expander, and an aspherical focusing lens were used to reduce tissue ablation diameters for MSI at high resolution. The laser beam caustic was modeled using laser ablation paper to calculate relevant laser beam characteristics. The minimum laser spot diameter on the tissue was determined using tissue staining and microscopy. Finally, the newly constructed optical system was used to image hen ovarian tissue with and without oversampling, detailing tissue features at 50 μm resolution. Graphical Abstract ᅟ.

Right atrial diameter and outcome of catheter ablation of atrial fibrillation.

While AF is considered more like a left atrial (LA) disease, to what extent the right atrium contributes to the pathogenesis and ablation outcome of AF remains unclear. This study aimed to identify if right atrial diameter (RAD) could predict arrhythmia recurrence after catheter ablation of atrial fibrillation (AF). Four hundred and seventy patients with drug-resistant AF [paroxysmal AF (PAF) 196; non-PAF 274] who underwent primary catheter ablation were enrolled. Ablation strategy included complete bilateral pulmonary vein isolation (PVI) in all patients and additional linear ablation across mitral isthmus, LA roof, and tricuspid isthmus in non-PAF cases. Risk factors associated with recurrence were determined by a Cox regression model, and the predictive power was evaluated by using receiver operating characteristic curve. After 24.3±18.0months, 284 patients (60.6%) experienced atrial tachyarrhythmia recurrence (111 in PAF, 173 in non-PAF). RAD was moderately associated with LA diameter (r=0.371, P<0.001), left ventricular ejection fraction (r=-0.205, P<0.001), and left ventricular end-diastolic diameter (r=0.319, P<0.001). Multivariate Cox regression analysis demonstrated that RAD was an independent predictor for recurrence only in PAF patients with LAD ≥35mm (HR 1.044, 95% CI 1.007-1.082, P=0.021). The RAD cutoff value of 35.5mm predicts atrial tachyarrhythmia recurrence with 85.4% sensitivity and 29.2% specificity. Kaplan-Meier analysis indicated that RAD over 35.5mm is associated with more recurrence after PAF ablation (log-rank P=0.034), comparing to those with RAD <35.5mm. RAD predicts outcome of ablation only in patients with PAF and concurrent LA enlargement. Under this condition, RAD <35.5mm is associated with a more favorable recurrence-free survival at over 2-year follow-up.

Finding Optimal Ablation Parameters for Multipolar Radiofrequency Ablation.

Radiofrequency ablation (RFA) for primary liver tumors and liver metastases is restricted by a limited ablation size. Multipolar RFA is a technical advancement of RFA, which is able to achieve larger ablations. The aim of this ex vivo study was to determine optimal ablation parameters for multipolar RFA depending on applicator distance and energy input. RFA was carried out ex vivo in porcine livers with three internally cooled, bipolar applicators in multipolar ablation mode. Three different applicator distances were used and five different energy inputs were examined. Ablation zones were sliced along the cross-sectional area at the largest ablation diameter, orthogonally to the applicators. These slices were digitally measured and analyzed. Sixty RFA were carried out. A limited growth of ablation area was seen in all test series. This increase was dependent on ablation time, but not on applicator distance. A steady state between energy input and energy loss was not observed. A saturation of the minimum radius of the ablation zone was reached. Differences in ablation radius between the three test series were seen for lowest and highest energy input ( P < .05). No differences were seen for medium amounts of energy ( P > .05). The ablation parameters applicator distance and energy input can be chosen in such a way, that minor deviations of the preplanned ablation parameters have no influence on the size of the ablation area.

A comparison of the DPSS UV laser ablation characteristic of 1024 and H10F WC-Co

An investigation on ablation characteristics of 1024 and H10F cobalt cemented tungsten carbide (WC-Co) with a DPSS nanosecond UV laser (50ns pulse width, 355nm wavelength, 90W average power and 10kHz repetition rate) is presented. The ablation characteristic parameters such as ablation threshold, incubation effect and optical penetration depth were evaluated based on the spot ablation diameter and depth. It was observed that the ablation threshold is significantly influenced by the number of pulses (NOP) and it decreases with increase NOP which is attributed to the incubation effect. Only one ablation region is observed at low laser fluence and an additional molten ablation region is observed at high laser fluence accompanied with cracks. The cracks formation is due to the thermal induced stress and changes in WC microstructure during laser beam irradiation. The crack depth is proportional to the thickness of the molten WC region. The ablation threshold of 1024 WC-Co and H10F WC-Co were found to be Fth1 =4.32J/cm2 and Fth1 =4.26J/cm2 respectively. The difference in chemical composition has insignificant effect on the ablation threshold value of the material. The incubation factor and optical penetration depth values of 1024 WC-Co and H10F WC-Co were found to be ξ=0.73, α−1 =411nm and ξ=0.75, α−1 =397nm respectively.

Microwave ablation of ex vivo bovine tissues using a dual slot antenna with a floating metallic sleeve

Purpose: To study the efficiency of a dual slot antenna with a floating metallic sleeve on the ablation of different ex vivo bovine tissues.Materials and methods: COMSOL Multiphysics® version 4.4 (Stockholm, Sweden), which is based on finite element methods (FEM), was used to design and simulate monopole and dual slot with sleeve antennas. Power, specific absorption rate (SAR), temperature and necrosis distributions in the selected tissues were determined using these antennas. Monopole and dual slot with sleeve antennas were designed, simulated, constructed and applied in this study based on a semi-rigid coaxial cable. Ex vivo experiments were performed on liver, lung, muscle and heart of bovine obtained from a public animal slaughter house. The microwave energy was delivered using a 2.45 GHz solid-state microwave generator at 40 W for 3, 5 and 10 min. Aspect ratio, ablation length and ablation diameter were also determined on ablated tissues and compared with simulated results. Student’s t-test was used to compare the statistically significant difference between the performance of the two antennas.Results: The dual slot antenna with sleeve produces localised microwave energy better than the monopole antenna in all ablated tissues using simulation and experimental validation methods. There were significant differences in ablation diameter and aspect ratio between the sleeve antenna and monopole antenna. Additionally, there were no significant differences between the simulation and experimental results.Conclusions: This study demonstrated that the dual slot antenna with sleeve produced larger ablation zones and higher sphericity index in ex vivo bovine tissues with minimal backward heating when compared with the monopole antenna.

Microwave ablation of primary and secondary liver tumours: ex vivo, in vivo, and clinical characterisation

Purpose: The aim of this study was to compare the performance of a microwave ablation (MWA) apparatus in preclinical and clinical settings.Materials and method: The same commercial 2.45 GHz MWA apparatus was used throughout this study. In total 108 ablations at powers ranging from 20 to 130 W and lasting from 3 to 30 min were obtained on ex vivo bovine liver; 28 ablations at 60 W, 80 W and 100 W lasting 5 and 10 min were then obtained in an in vivo swine model. Finally, 32 hepatocellular carcinomas (HCCs) and 19 liver metastases in 46 patients were treated percutaneously by administering 60 W for either 5 or 10 min. The treatment outcome was characterised in terms of maximum longitudinal and transversal axis of the induced ablation zone.Results: Ex vivo ablation volumes increased linearly with deposited energy (r2 = 0.97), with higher sphericity obtained at lower power for longer ablation times. Larger ablations were obtained on liver metastases compared to HCCs treated with 60 W for 10 min (p < 0.003), as ablation diameters were 4.1 ± 0.6 cm for metastases and 3.7 ± 0.3 cm for HCC, with an average sphericity index of 0.70 ± 0.04. The results on the in vivo swine model at 60 W were substantially smaller than the ex vivo and clinical results (either populations). No statistically significant difference was observed between ex vivo results at 60 W and HCC results (p > 0.08).Conclusions: For the selected MW ablation device, ex vivo data on bovine liver was more predictive of the actual clinical performance on liver malignancies than an in vivo porcine model. Equivalent MW treatments yielded a significantly different response for HCC and metastases at higher deposited energy, suggesting that outcomes are not only device-specific but must also be characterised on a tissue-by-tissue basis.

Analysis of iodinated contrast delivered during thermal ablation: is material trapped in the ablation zone?

Intra-procedural contrast-enhanced CT (CECT) has been proposed to evaluate treatment efficacy of thermal ablation. We hypothesized that contrast material delivered concurrently with thermal ablation may become trapped in the ablation zone, and set out to determine whether such an effect would impact ablation visualization. CECT images were acquired during microwave ablation in normal porcine liver with: (A) normal blood perfusion and no iodinated contrast, (B) normal perfusion and iodinated contrast infusion or (C) no blood perfusion and residual iodinated contrast. Changes in CT attenuation were analyzed from before, during and after ablation to evaluate whether contrast was trapped inside of the ablation zone. Visualization was compared between groups using post-ablation contrast-to-noise ratio (CNR). Attenuation gradients were calculated at the ablation boundary and background to quantitate ablation conspicuity. In Group A, attenuation decreased during ablation due to thermal expansion of tissue water and water vaporization. The ablation zone was difficult to visualize (CNR = 1.57 ± 0.73, boundary gradient = 0.7 ± 0.4 HU mm−1), leading to ablation diameter underestimation compared to gross pathology. Group B ablations saw attenuation increase, suggesting that iodine was trapped inside the ablation zone. However, because the normally perfused liver increased even more, Group B ablations were more visible than Group A (CNR = 2.04 ± 0.84, boundary gradient = 6.3 ± 1.1 HU mm−1) and allowed accurate estimation of the ablation zone dimensions compared to gross pathology. Substantial water vaporization led to substantial attenuation changes in Group C, though the ablation zone boundary was not highly visible (boundary gradient = 3.9 ± 1.1 HU mm−1). Our results demonstrate that despite iodinated contrast being trapped in the ablation zone, ablation visibility was highest when contrast is delivered intra-procedurally. Therefore, CECT may be feasible for real-time thermal ablation monitoring.

Elemental Fractionation Studies of 193 nm ArF Excimer Laser Ablation System at High Spatial Resolution Mode

Abstract The limit of detection (LOD), ICP mass load effect, downhole induced fractionation and matrix effect of 193 nm ArF excimer laser ablation system at high spatial resolution were systematically investigated. Trace elements in GSD-1G, StHs6/80-G and NIST612 were measured at 10 μm spot size. The results showed that the LOD decreased with the increasing ablation diameter. In addition, the LOD of part of trace elements was in a range of 1–10 μg g −1 at 7 μm spot size. Mass load effect was negatively correlated with the corresponding oxide melting temperature, while positively correlated with the elemental 1 st ionization potential. Downhole fractionation was negligible when the ratio of ablation depth to spot size was smaller than 1:1. Matrix effect between NIST610, GSD-1G, ATHO-G and StHs6/80-G did not change in the spot size ranged from 10 μm to 50 μm. The analytical results of GSD-1G, StHs6/80-G and NIST612 at 10 μm spot size matched well with the reference values. Generally, 10 μm spatial resolution could satisfy the requirements of trace elements analysis.

Temperature monitoring during microwave ablation in ex vivo porcine livers

ObjectiveThe aim of the present study was to assess the temperature map and its reproducibility while applying two different MWA systems (915 MHz vs 2.45 GHz) in ex vivo porcine livers. Materials and methodsFifteen fresh pig livers were treated using the two antennae at three different settings: treatment time of 10 min and power of 45 W for both systems; 4 min and 100 W for the 2.45 GHz system.Trends of temperature were recorded during all procedures by means of fiber optic-based probes located at five fixed distances from the antenna, ranging between 10 mm and 30 mm. Each trial was repeated twice to assess the reproducibility of temperature distribution. ResultsTemperature as function of distance from the antenna can be modeled by a decreasing exponential trend. At the same settings, temperature obtained with the 2.45 GHz system was higher than that obtained with the 915 MHz thus resulting into a wider area of ablation (diameter 17 mm vs 15 mm). Both systems showed good reproducibility in terms of temperature distribution (root mean squared difference for both systems ranged between 2.8 °C and 3.4 °C). ConclusionsWhen both MWA systems are applied, a decreasing exponential model can predict the temperature map. The 2.45 GHz antenna causes higher temperatures as compared to the 915 MHz thus, resulting into larger areas of ablation. Both systems showed good reproducibility although better results were achieved with the 2.45 GHz antenna.

Optimization of dual slot antenna using floating metallic sleeve for microwave ablation

Backward heating reduction is vital in power distribution optimization in microwave thermal ablation. In this study, we optimized dual slot antenna to yield reduction in backward heating pattern along the antenna shaft with the application of floating metallic sleeve. Finite element methods were used to generate the electromagnetic (EM) field and thermal distribution in liver tissue. The position of the sleeve from the tip of the probe (z = 0 mm) was varied within the range 14 ≤ z ≤ 22 mm while sleeve length was varied within 16 ≤ z ≤ 48 mm at 2 mm interval using operating frequency of 2.45 GHz. The best optimized design has reflection coefficient of −20.87 dB and axial ratio of 0.41 when the sleeve position was at 17 mm and sleeve length was 18 mm. Experimental validation shows that inclusion of a floating metallic sleeve on dual slot antenna for hepatic microwave ablation averagely increased ablation diameter and aspect ratio by 17.8% and 33.9% respectively and decreased ablation length by 11.2%. Reduction in backward heating and increase in power deposition into liver tissue could be achieved by using this antenna to provide greater efficiency and localization of specific absorption rate in delivering microwave energy for hepatic ablation.

Influence of the target tissue size on the shape of ex vivo microwave ablation zones

Purpose: The aim of this study was to numerically and experimentally characterise the influence of tissues dimensions on the size and shape of microwave-induced ablation zones. Materials and methods: A 2.45 GHz interstitial antenna was introduced into ex vivo bovine liver samples, delivering 60 W for 10 min; then the dimensions of the coagulated area were measured. Ablations were performed both in large samples (termed unrestricted tissue) for characterising the tissue response, and in thin samples, whose dimensions in the plane perpendicular to the antenna were smaller than the short axis of the ablated area obtained in unrestricted samples. In the numerical study the electromagnetic field emitted from the antenna and the corresponding temperature increase were evaluated in both unrestricted and thin tissue samples. Results: When the height of the tissue was smaller than the ablation diameter measured in unrestricted samples, a 7.5% increase in length of the ablated zone was experimentally observed. When both the height and width were lower than the diameter measured in unrestricted samples, an elongation of about 23.4% was experimentally obtained. The numerical study showed that the boundary conditions between the target tissue and the surrounding materials are critical. Conclusions: The ex vivo performances of microwave ablation devices are notably influenced by the shape and dimension of the tissues where the procedure takes place. Accordingly, dedicated interventional protocols should be developed for treatment planning on targets of different shape and size.

Characterization of In Vivo Ablation Zones Following Percutaneous Microwave Ablation of the Liver with Two Commercially Available Devices: Are Manufacturer Published Reference Values Useful?

PurposeTo analyze in vivo ablation properties of microwave ablation antennae in tumor-bearing human livers by performing retrospective analysis of ablation zones following treatment with two microwave ablation systems. Materials and MethodsPercutaneous microwave ablations performed in the liver between February 2011 and February 2013 with use of the AMICA and Certus PR ablation antennae were included. Immediate postablation computed tomography images were evaluated retrospectively for ablation length, diameter, and volume. Ablation length, diameter, and volume indices were calculated and compared between in vivo results and references provided from each device manufacturer. The two microwave antenna models were then also compared versus each other. ResultsTwenty-five ablations were performed in 20 patients with the AMICA antenna, and 11 ablations were performed in eight patients with the Certus PR antenna. The AMICA and Certus PR antennae showed significant differences in ablation length (P = .013 and P = .009), diameter (P = .001 and P = .009), and volume (P = .003 and P = .009). The AMICA ablation indices were significantly higher than the Certus PR ablation indices in length (P = .026) and volume (P = .002), but there was no significant difference in ablation diameter indices (P = .110). ConclusionsIn vivo ablation indices of human tumors are significantly smaller than reference ex vivo ablation indices, and there are significant differences in ablation indices and sphericity between devices.

Abstract 4303: Bioimaging of multiple elements by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in penile carcinomas

Abstract Background: Penile cancer (PeCa) is a rare disease associated with a high mortality and morbidity rate. Surgery is usually the clinical procedure used for the local control of this disease, which results in the partial or complete amputation of the organ and consequently in the causation of psychosexual morbidities. The imbalance of trace elements has been shown to contribute to several cancer related mechanisms, including cell proliferation, tumor progression and apoptosis. The laser ablation imaging-ICP-MS (LA(i)-ICP-MS) is a high sensitive method used as a new tool to detect trace elements associated with human cancer. Aim: The main aim of our study is to develop a biometal imaging technique to map the spatial distribution of selected metals in cryosections of PeCa tissues in comparison to the ones in adjacent non-neoplastic and normal penile tissues. Methods: Fresh frozen specimens of PeCa (n=3), paired adjacent non-neoplastic tissue (n=1) and normal penile tissues (obtained from autopsy; n=2) were selected and evaluated using LA-ICP-MS, for the identification of the selected trace elements: 23Na, 44Ca, 43Ca, 39K, 24Mg, 31P and 13C (reference element). The instrumental parameters of the method were optimized for the quantification of plasma energy and optimal reaction cell conditions. Experimental parameters were optimized for the speed ablation (µm s-1) and laser beam diameter (mm), energy (mJ) and frequency (Hz). Results: The tissues were ablated using a spot size of 55µm and a scan speed of 60 µm s-1, which proved to be efficient laser parameters. The mapping of the trace elements revealed both decreased and increased levels of the different traces analyzed in the PeCa tumor cells when compared to the adjacent non-neoplastic and normal penile tissues. The same pattern of elements distribution and counts was observed in the three PeCa specimens analyzed. A lower average of element counts (43Ca/13C ratio=0.085; 44Ca/13C ratio=1.63; 23Na/13C ratio=188.91) was detected in the PeCa tissue when compared to the normal tissues (43Ca/13C ratio=0.48; 44Ca/13C ratio=6.7; 23Na/13C ratio= 336.2). In addition, PeCa presented considerably higher average counts of 24Mg, 39K and 31P (24Mg/13C ratio=18.56; 39K/13C ratio=189.12; 31P/13C ratio=18.27) compared to the normal tissues (24Mg/13C ratio=8.15; 39K/13C ratio=13.23; 31P/13C ratio=4.54). Conclusions: LA-ICP-MS mapping is a powerful and useful method to provide novel information regarding the spatial distribution of elements in penile tumors and their implication in tumorigenesis. Note: This abstract was not presented at the meeting. Citation Format: Juan José Augusto Moyano Muñoz, Sandra A. Drigo, Fabio Marchi, Gustavo Pessoa, Cristovam S. Neto, Gustavo Guimaraes, Marco A Z Arruda, Silvia R. Rogatto. Bioimaging of multiple elements by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in penile carcinomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4303. doi:10.1158/1538-7445.AM2014-4303

Characterization of laser ablation of copper in the irradiance regime of laser-induced breakdown spectroscopy analysis

The LIBS signal depends both on the ablated mass and on the plasma excitation temperature. These fundamental parameters depend in a complex manner on laser ablation and on laser–plasma coupling. As several works in the literature suggest that laser ablation processes play a predominant role compared to plasma heating phenomena in the LIBS signal variations, this paper focuses on the study of laser ablation. The objective was to determine an interaction regime enabling to maximally control the laser ablation. Nanosecond laser ablation of copper at 266nm was characterized by scanning electron microscopy and optical profilometry analysis, in air at 1bar and in the vacuum. The laser beam spatial profile at the sample surface was characterized in order to give realistic values of the irradiance. The effect of the number of accumulated laser shots on the crater volume was studied. Then, the ablation crater morphology, volume, depth and diameter were measured as a function of irradiance between 0.35 and 96GW/cm². Results show that in the vacuum, a regular trend is observed over the whole irradiance range. In air at 1bar, below a certain irradiance, laser ablation is very similar to the vacuum case, and the ablation efficiency of copper was estimated at 0.15±0.03atom/photon. Beyond this irradiance, the laser beam propagation is strongly disrupted by the expansion of the dense plasma, and plasma shielding appears. The fraction of laser energy used for laser ablation and for plasma heating is estimated in the different irradiance regimes.

Effect of geometry measurements on characteristics of femtosecond laser ablation of HR4 nickel alloy

This paper presents an investigation on ablation characteristics of HR4 nickel cast alloy with a Ti:Sapphire femtosecond laser (100fs pulse width, 800nm wavelength and 1kHz repetition rate). The ablation characteristics including laser material interaction parameters, i.e. ablation threshold, optical penetration depth and incubation factor are estimated based on ablated geometries from two ablation methods, i.e. spot ablation and line ablation. The work shows that the single pulse ablation threshold is dependent on the laser fluence and the number of pulses (NOP). The ablation threshold decreases with the NOP, where it reaches an asymptotical value due to incubation effect. By varying the laser fluence, two ablation regimes are identified which are the low fluence ablation regime and the high fluence ablation regime. The former is governed by optical penetration depth; and the latter is governed by the energy penetration depth. It is also observed that the laser material interaction parameters obtained based on ablation diameters through the line ablation agree with the values obtained through the spot ablation but not with those obtained based on ablated depth through the line ablation. It is found that the evaluation of the laser material interaction parameters based on ablated diameters is more reliable compared to those based on ablated depth. The ablation threshold (low fluence ablation region) for the HR4 nickel alloy is estimated to be Fth1=0.39J/cm2 with the incubation factor, ξ=0.8 and optical penetration depth of 47.3nm.

Analysis of Planned and Postoperatively Measured Flap Thickness After LASIK Using the LenSx Multifunctional Femtosecond Laser System

To evaluate LASIK corneal flaps using a multifunctional femtosecond laser suitable for cataract and corneal surgery (LenSx; Alcon Laboratories, Inc., Aliso Viejo, CA) and to compare the planned and postoperatively measured flap thickness using an anterior segment optical coherence tomography device (AS-OCT). Twenty patients (38 eyes) diagnosed as having myopia and myopic astigmatism were enrolled. LASlK was performed using the LenSx femtosecond laser for intracorneal flaps and the Wavelight Allegretto 400 excimer laser (Alcon Laboratories, Inc.) for intra- stromal photoablation. Desired flap thickness and diameter were 140.0 + 0.0 pm and 8.5 + 0.0 mm, respectively, whereas mean ablation depth and diameter of the excimer laser treatment were 67.9 ± 24.18 pm and 6.5 ± 0.08 mm, respectively. Entered data of the LenSx femtosecond laser were used to determine desired flap thickness, whereas AS-OCT (RTVue; Optovue, Inc., Fremont, CA) was used to measure flap thickness postoperatively. The Wilcoxon signed-rank test, dependent paired t test, and Friedman test were used for comparison of dependent and repeated measures. There was no statistically significant difference in the planned and postoperatively measured flap thickness (140.0 ± 0.0 vs 140.28 _ 8.0 pm; P = .4067). Interfaces of the flaps had even surfaces according to the images and calculations on the AS-OCT device (P = .058). Application of this multifunctional femtosecond laser performing LASIK proved to be a safe and effective method regarding predictability of flap thickness.

Comparison of four radiofrequency ablation systems at two target volumes in an ex vivo bovine liver model

We aimed to validate actually achieved macroscopic ablation volumes in relation to calculated target volumes using four different radiofrequency ablation (RFA) systems operated with default settings and protocols for 3 cm and 5 cm target volumes in ex vivo bovine liver. Sixty-four cuboid liver specimens were ablated with four commercially available RFA systems (Radionics Cool-tip, AngioDynamic 1500X, Boston Scientific RF 3000, Celon CelonPower LAB): 16 specimens for each system; eight for 3 cm, and eight for 5 cm. Ablation diameters were measured, volumes were calculated, and RFA times were recorded. For the 3 cm target ablation volume, all tested RFA systems exceeded the mathematically calculated volume of 14.14 cm3. For the 3 cm target ablation volume, mean ablation volume and mean ablation time for each RFA system were as follows: 28.5 ± 6.5 cm3, 12.0 ± 0.0 min for Radionics Cool-tip; 17.1 ± 4.9 cm3, 9.36 ± 0.63 min for AngioDynamic 1500X; 29.7 ± 11.7 cm3, 4.60 ± 0.50 min for Boston Scientific RF 3000; and 28.8 ± 7.0 cm3, 20.85 ± 0.86 min for Celon CelonPower LAB. For the 5 cm target ablation volume, Radionics Cool-tip (48.3 ± 9.9 cm3, 12.0 ± 0.0 min) and AngioDynamic 1500X (39.4 ± 16.2 cm3, 19.59 ± 1.13 min) did not reach the mathematically calculated target ablation volume (65.45 cm3), whereas Boston Scientific RF 3000 (71.8 ± 14.5 cm3, 9.15 ± 2.93 min) and Celon CelonPower LAB (93.9 ± 28.1 cm3, 40.21 ± 1.78 min) exceeded it. While all systems reached the 3 cm target ablation volume, results were variable for the 5 cm target ablation volume. Only Boston Scientific RF 3000 and Celon CelonPower LAB created volumes above the target, whereas Radionics Cool-tip and AngioDynamic 1500X remained below the target volume. For the 3 cm target ablation volume, AngioDynamic 1500X with 21% deviation was closest to the target volume. For the 5 cm target volume Boston Scientific RF 3000 with 10% deviation was closest.

A Comparison of Internally Water-perfused and Cryogenically Cooled Monopolar and Bipolar Radiofrequency Applicators in Ex Vivo Liver Samples

To evaluate the ex vivo ablation zones created in hepatic tissue using monopolar and bipolar gas- and water-cooled radiofrequency (RF) applicators. RF ablations were performed on ex vivo bovine liver tissue using closed circuit water-cooled and closed circuit cryogenically cooled (via CO₂ enthalpy) 15-ga linear-needle applicators. Both monopolar and bipolar electrode applicators were used, with the electric current administered ranging in 50-mA increments from 1100 to 1300 mA for the monopolar case, and from 500 to 700 mA for the bipolar case. Total ablation time was 15 minutes. Six tissue samples were ablated per setting. The ablated volumes were assumed to have a three-dimensional ellipsoid shape, with one long major axis and two smaller minor axes. Gross histology was used to measure the dimensions of the ablated regions to quantify the ablated volume, the dimensions of the axis, and the ratio between the long axis and the smallest minor axis, which was termed the ellipticity index. The gas-cooled monopolar applicator achieved the largest short-axis ablation diameter (4.05 ± 0.4 cm), followed by the water-cooled monopolar applicator (3.18 ± 0.29 cm). With the bipolar applicator, the gas-cooled applicators also achieved larger short-axis ablation diameters (3.02 ± 0.15 cm) than the water-cooled applicators (2.72 ± 0.29 cm). The gas-cooled monopolar applicator also provided the largest ablation volume (42.7 ± 10.7 mL) and the most spherically shaped lesions (ellipticity index: 1.21 ± 0.10). Lesion size increased with injected current up to a threshold current of 1200/1250 mA (monopolar water-/gas-cooled) and 600/650 mA (bipolar water-/gas-cooled), but dropped at greater values. Gas-cooled monopolar applicators were superior to the other tested applicators in terms of both volume and sphericity of the ablation zone.

Abstract No. 303 - Volume comparison after radiofrequency ablation at two different target volumes by means of four different RF generators - MR volumetry in a 1.0 Tesla open MRI vs. macroscopic measurement

No. 303 Volume comparison after radiofrequency ablation at two different target volumes by means of four different RF generators—MR volumetry in a 1.0 Tesla open MRI vs. macroscopic measurement H. Rathke, F.V. Guettler, B. Schnackenburg, J. Rump, B. Hamm, U. Teichgraeber, M. de Bucourt; Department of Radiology, Charite University Medicine Berlin, Berlin, Germany; Department of Radiology, Jena University, Jena, Germany; Healthcare, Philips, Hamburg, Germany Purpose: In several studies radiofrequency ablation (RFA) was found to be safe and reliable for intervention of primary and secondary malignancies. The aim of this study was to evaluate MR volumetry directly after RFA in an open MRI and to validate the visualization of the produced necrosis volume. As the RF necrosis can be subdivided in three zones it was evaluated if the outer zone of the necrosis is detectable with the MR sequences used and whether or not there are differences with respect to lesion size and generator type. Materials and Methods: 64 liver specimens were ablated under constant simulated physiological conditions with four commercially available RF systems (A, B, C, D; n1⁄416 for each system; n1⁄48 for 3cm, and n1⁄48 for 5cm). Target volumes were set to 14.14cm (3cm lesion) and 65.45cm(5cm lesion). T1 and PD weighted TSE sequences were acquired in a 1.0 Tesla open MRI and MR-volumetry was performed by semi-automatic software. After manual dissection actual macroscopic ablation diameters were recorded and volumes calculated. Results: For system A with the 3cm lesion, the manual measured macroscopic volume was 28.2cm in comparison to 15.2cm/ 13.5cm (T1/PDW) using MR volumetry—with the 5cm lesion: 48.3cm vs. 19.3cm/15.6cm. System B: 3cm: 17.1cm vs. 6.5cm/ 6.0cm-5cm: 39.3cm vs. 16.7cm/15.2cm. System C: 3cm 29.7 cm vs. 12.9cm/11.5cm-5cm 71.8cm vs. 29.6cm/27.4cm. System D: 3cm 28.7cm vs. 11.3cm/12.8cm-5cm 93.9cm vs. 42.6cm/37.5cm. Conclusion: MR volumetry yielded smaller appearing volumes than manual measurement after dissection—irrespective of RF system used, target lesion size and MR sequence. Histopathological assessment showed an incomplete cellular damage in the transitional zone of the necrosis. As expected cellular apoptotic processes could not be detected immediately after RFA, probably also because of the ex vivo setting and missing blood perfusion.The exact transition from ablated to vital tissue could not be assessed directly after Intervention with the MR sequences investigated.