Hepatic Microwave Ablation Research Articles

Impact of Power and Time in Hepatic Microwave Ablation: Effect of Different Energy Delivery Schemes.

Microwave ablation often involves the use of continuous energy-delivery protocols with a fixed power and time. To achieve larger ablation zones, a range of protocols and power levels have been studied in experimental studies. The objective of the present study was to develop and experimentally evaluate the performance of a coupled computational electromagnetic-bioheat transfer model of 2.45 GHz microwave ablation under a variety of continuous and pulsed power delivery schemes. The main aim was to obtain an in-depth knowledge of the influence of energy delivery settings on ablation zone profiles and thermal damage in the peri-ablation zone. In addition to the theoretical model, we evaluated the power delivery schemes using ex vivo experiments and compared them to previously published data from in vivo experiments. The results showed slight differences in terms of the ablation zone size for different power delivery schemes under ex vivo conditions, with the applied energy level being the most important factor that determines ablation zone size; however, under in vivo conditions, applying a high-power pulse prior to and following a longer constant power application (BOOKEND 95 W protocol) presented the most favorable ablation zones. Moreover, the modeling and experimental studies identified threshold applied power and ablation times beyond which increases did not yield substantive increases in ablation zone extents.

Safety and Effectiveness of Triple-Antenna Hepatic Microwave Ablation.

Microwave ablation is becoming a standard procedure for treating tumors based on heat generation, causing an elevation in the tissue temperature level from 50 to 60 °C, causing tissue death. Microwave ablation is associated with uniform cell killing within ablation zones, multiple-antenna capability, low complication rates, and long-term survival. Several reports have demonstrated that multiple-antenna microwave ablation is a promising strategy for safely, rapidly, and effectively treating large tumors. The key advantage of multi-antenna tumor microwave ablation is the creation of a large, well-defined ablation zone without excessively long treatment times or high power that can damage healthy tissue. The strategic positioning of multiple probes provides a fully ablated volume, even in regions where individual probe damage is incomplete. Accurate modeling of the complex thermal and electromagnetic behaviors of tissue is critical for optimizing microwave ablation because material parameters and tissue responses can change significantly during the procedure. In the case of multi-antenna microwave ablation, the calculation complexity increases significantly, requiring significant computational resources and time. This study aimed to evaluate the efficacy and safety of liver percutaneous microwave ablation using the simultaneous activation of three antennas for the treatment of lesions larger than 3 cm. Based on the known results from a single-probe setup, researchers can estimate and evaluate various spatial configurations of the three-probe array to identify the optimal arrangement. Due to the synergistic effects of the combined radiation from the three antennas, the resulting ablation zone can be significantly larger, leading to better outcomes in terms of treatment time and effectiveness. The obtained results revealed that volumetric damage and the amount of damaged healthy tissue are smaller for a three-antenna configuration than for microwave ablation using a single-antenna and two-antenna configurations.

Morphometric characterization and temporal temperature measurements during hepatic microwave ablation in swine.

Heat-induced destruction of cancer cells via microwave ablation (MWA) is emerging as a viable treatment of primary and metastatic liver cancer. Prediction of the impacted zone where cell death occurs, especially in the presence of vasculature, is challenging but may be achieved via biophysical modeling. To advance and characterize thermal MWA for focal cancer treatment, an in vivo method and experimental dataset were created for assessment of biophysical models designed to dynamically predict ablation zone parameters, given the delivery device, power, location, and proximity to vessels. MWA zone size, shape, and temperature were characterized and monitored in the absence of perfusion in ex vivo liver and a tissue-mimicking thermochromic phantom (TMTCP) at two power settings. Temperature was monitored over time using implanted thermocouples with their locations defined by CT. TMTCPs were used to identify the location of the ablation zone relative to the probe. In 6 swine, contrast-enhanced CTs were additionally acquired to visualize vasculature and absence of perfusion along with corresponding post-mortem gross pathology. Bench studies demonstrated average ablation zone sizes of 4.13±1.56cm2 and 8.51±3.92cm2, solidity of 0.96±0.06 and 0.99±0.01, ablations centered 3.75cm and 3.5cm proximal to the probe tip, and temperatures of 50 ºC at 14.5±13.4s and 2.5±2.1s for 40W and 90W ablations, respectively. In vivo imaging showed average volumes of 9.8±4.8cm3 and 33.2±28.4cm3 and 3D solidity of 0.87±0.02 and 0.75±0.15, and gross pathology showed a hemorrhagic halo area of 3.1±1.2cm2 and 9.1±3.0cm2 for 40W and 90W ablations, respectfully. Temperatures reached 50ºC at 19.5±9.2s and 13.0±8.3s for 40W and 90W ablations, respectively. MWA results are challenging to predict and are more variable than manufacturer-provided and bench predictions due to vascular stasis, heat-induced tissue changes, and probe operating conditions. Accurate prediction of MWA zones and temperature in vivo requires comprehensive thermal validation sets.

Correction of heat-induced susceptibility changes in respiratory-triggered 2D-PRF-based thermometry for monitoring of magnetic resonance-guided hepatic microwave ablation in a human-like in vivo porcine model

Purpose To develop and evaluate susceptibility corrected 2D proton resonance frequency (PRF)-based magnetic resonance (MR)-thermometry for the accurate assessment of the ablation zone of hepatic microwave ablation (MWA). Methods and materials Twelve hepatic MWA were performed in five LEWE minipigs with human-like fissure-free liver. Temperature maps during ablation of PRF-based MR-thermometry were corrected by modeling heat induced susceptibility changes. Ablation zones were determined using cumulative equivalent minutes at 43 °C (CEM43) as tissue damage model. T1 weighted (w) post-ablation contrast-enhanced (CE) MR-imaging and manually segmented postmortem histology were used for validation. The agreement of uncorrected (raw) and susceptibility corrected (corr) MR-thermometry with T1w post-ablation CE MR-imaging and histology was evaluated. The Wilcoxon-signed rank test and Bland–Altman analysis were applied. Results With the susceptibility corrected MR-thermometry a significantly increased dice coefficient (raw: 77% vs. corr: 83%, p < 0.01) and sensitivity (raw: 72% vs. corr: 82%, p < 0.01) was found for the comparison to T1w-CE imaging as well as histopathology (dice coefficients: raw: 76% vs. corr: 79%, p < 0.001; sensitivity: raw: 72% vs. corr: 74%, p < 0.001). While major axis length was significantly increased (7.1 mm, p < 0.001) and minor axis length significantly decreased (2.2 mm, p < 0.001) in uncorrected MR-thermometry compared to T1w-CE MR-imaging, no significant bias was found after susceptibility correction. Conclusion Using susceptibility corrected 2D PRF-based MR-thermometry to predict the ablation zones of hepatic MWA provided a good agreement in comparison to T1w post-ablation CE MR-imaging and histopathology.

Three-dimensional assessment of vascular cooling effects on hepatic microwave ablation in a standardized ex vivo model

The aim of this study was a three-dimensional analysis of vascular cooling effects on microwave ablation (MWA) in an ex vivo porcine model. A glass tube, placed in parallel to the microwave antenna at distances of 2.5, 5.0 and 10.0 mm (A–V distance), simulated a natural liver vessel. Seven flow rates (0, 1, 2, 5, 10, 100, 500 ml/min) were evaluated. Ablations were segmented into 2 mm slices for a 3D-reconstruction. A qualitative and quantitative analysis was performed. 126 experiments were carried out. Cooling effects occurred in all test series with flow rates ≥ 2 ml/min in the ablation periphery. These cooling effects had no impact on the total ablation volume (p > 0.05) but led to changes in ablation shape at A–V distances of 5.0 mm and 10.0 mm. Contrary, at a A–V distance of 2.5 mm only flow rates of ≥ 10 ml/min led to relevant cooling effects in the ablation centre. These cooling effects influenced the ablation shape, whereas the total ablation volume was reduced only at a maximal flow rate of 500 ml/min (p = 0.002). Relevant cooling effects exist in MWA. They mainly depend on the distance of the vessel to the ablation centre.

Cooling Effects Occur in Hepatic Microwave Ablation At Low Vascular Flow Rates and in Close Proximity to Liver Vessels - Ex Vivo.

Background. The impact of vascular cooling effects in hepatic microwave ablation (MWA) is controversially discussed. The objective of this study was a systematic assessment of vascular cooling effects in hepatic MWA ex vivo. Methods. Microwave ablations were performed in fresh porcine liver ex vivo with a temperature-controlled MWA generator (902-928MHz) and a non-cooled 14-G-antenna. Energy input was set to 9.0kJ. Hepatic vessels were simulated by glass tubes. Three different vessel diameters (3.0, 5.0, 8.0mm) and vessel to antenna distances (5, 10, 20mm) were examined. Vessels were perfused with saline solution at nine different flow rates (0-500mL/min). Vascular cooling effects were assessed at the largest cross-sectional ablation area. A quantitative and semi-quantitative/morphologic analysis was carried out. Results. 228 ablations were performed. Vascular cooling effects were observed at close (5mm) and medium (10mm) antenna to vessel distances (P < .05). Vascular cooling effects occurred around vessels with flow rates ≥1.0mL/min (P < .05) and a vessel diameter ≥3mm (P < .05). Higher flow rates did not result in more distinct cooling effects (P > .05). No cooling effects were measured at large (20mm) antenna to vessel distances (P > .05). Conclusion. Vascular cooling effects occur in hepatic MWA and should be considered in treatment planning. The vascular cooling effect was mainly affected by antenna to vessel distance. Vessel diameter and vascular flow rate played a minor role in vascular cooling effects.

Study of Single- and Dual-Frequency Microwave Ablation Antennas Based on Shorted Helical Slot

We present single- and dual-frequency antennas based on the shorted helical slot in hepatic microwave ablation. The single-frequency antenna is designed by lathing a helical slot on shorted traditional semirigid coaxial cable, which is expected to be operated at the frequency of 2450 MHz, and the dual-frequency antenna is designed with the combination of an annular slot and a helical slot, which can be operated at 915 and 2450 MHz. We use full-wave electromagnetic simulation and transient thermal simulation to analyze the performance of the proposed ablation antennas. Both the proposed antennas are fabricated and used in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex vivo</i> ablation experiments at different frequencies with a power level of 23 W for 2 or 5 min. We observe that the proposed single-frequency antenna with helical slot has more concentrated specific absorption rate (SAR) pattern than those antennas with conventional slots does at 2450 MHz, and the dual-frequency one has the capability to control the roundness of ablation zone from 0.34 to 0.63 under the different combination of frequencies and operation times. The proposed microwave ablation antennas are expected to lead to a potential solution of curing the liver cancers with various characteristics.

Design of a closed dual‐slot antenna for spherical hepatic microwave ablation

Microwave ablation has been considered as a promising therapy for the treatment of liver tumors. However, many antennas proposed in previous literature generated ellipsoidal ablation and also were not suitable for percutaneous intervention due to the lack of mechanical properties. To address these problems, a closed dual-slot antenna was investigated to generate spherical ablation and designed with zirconia tip, which facilitated its ability to puncture into tissues, and metal tube, which provided mechanical strength for percutaneous puncture. A numerical model was constructed to optimize antenna geometry and analyze antenna performance. The reflection coefficient, specific absorption rate, and temperature distribution of the closed and conventional dual-slot antennas were all simulated by using finite element method. The two antennas were also validated with ex vivo porcine livers, finding a great agreement between simulated and experimental results. The closed dual-slot antenna generated a more spherical ablation zone (34.0 mm × 37.2 mm vs. 29.1 mm × 48.5 mm at 50 W for 10 min) with a lower reflection coefficient (−30.3 vs. −9.5 dB) than did conventional dual-slot antenna, and showed qualified mechanical properties for clinical application, which may be further applied to clinical percutaneous intervention to treat liver tumors effectively.

Advanced CT techniques for hepatic microwave ablation zone monitoring and follow-up.

To evaluate utility of advanced CT techniques including HighlY constrained back-projection and dual-energy CT for intra- and post-procedure hepatic microwave ablation zone monitoring. 8 hepatic microwave ablations were performed in 4 adult swine (5min/65W). Low-dose routine CECT and dual-energy CT images were obtained every 1min during ablation. Images were reconstructed ± HYPR. Image quality and dose metrics were collected. 21 MWA were performed in 4 adult swine. Immediate post-procedure CECT was performed in the arterial, portal venous, and delayed phases using both routine and DECT imaging with full-dose weight-based IV contrast dosing. An additional 16 MWA were subsequently performed in 2 adult swine. Immediate post-procedure CT was performed with half-dose IV contrast using routine and DECT. 12 patients (10M/2F, mean age 62.4 yrs) with 14 hepatic tumors (4 HCC, 10 metastatic lesions) treated with MWA were prospectively imaged with DECT 1month post-procedure. 120kV equivalent images were compared to DECT [51keV, iodine material density]. Image quality and dose metrics were collected. Gas created during MWA led to high CNR in all intraprocedural CT datasets. Optimal CNRs were noted at 4min with CNR 6.7, 15.5,15.9, and 21.5 on LD-CECT, LD-CECT + HYPR, DECT, and DECT + HYPR, respectively (p < 0.001). Image quality scores at 4min were 1.8, 2.8, 2.4, and 3, respectively (p < 0.001). Mean radiation dose (CTDIvol) was eightfold higher for the DECT series. For swine, post-procedural DECT images (IMD/51keV) showed improved CNR compared to routine CT at all time points with full and with reduced dose contrast (CNR 4.6, 3.2, and 1.5, respectively, at half-contrast dose, p < 0.001). For human subjects, the 51keV and IMD images showed higher CNRs (5.8, 4.8 vs 4.0, p < 0.001) and SNRs (3.7, 5.9 vs 2.8). Ablation zone sharpness was improved with DECT (routine 3.0 ± 0.7, DECT 3.5 ± 0.5). Diagnostic confidence was higher with DECT (routine 2.3 ± 0.9, DECT 2.6 ± 0.8). Mean DLP for DECT was 905.7 ± 606mGy-cm, CTDIvol 37.5 ± 21.2mGy, and effective dose 13.6 ± 9.1mSv, slightly higher than conventional CT series. Advanced CT techniques can improve CT image quality in peri-procedural hepatic microwave ablation zone evaluation.

Abstract No. 447 Quality improvement: creation and sustainability of an enhanced recovery after procedure initiative for hepatic microwave ablation

The purpose of this quality improvement project (QI) was to establish a novel and sustainable enhanced recovery after procedure (ERAP) pathway utilizing a computerized physician order entry (CPOE) set to improve periprocedural pain for patients undergoing hepatic microwave ablation (MWA). An enhanced recovery after procedure (ERAP) pathway was formulated and included evidence-based interventions shown to decrease periprocedural procedural pain. These included pre-procedure analgesics (PA): acetaminophen, celecoxib, oxycodone as well as preprocedure bilateral paravertebral blocks (PVB). A dedicated regional anesthesia team from the OR was recruited to perform the PVB. The pathway was implemented in October 2017. IR fellows, nurses, and anesthesia providers were educated with lectures on acute pain management. Initially, daily email reminders were sent for PA and PVB. Subsequently, the CPOE order set was developed for IR physician use, which included choices and recommendations for PAs. This was implemented in June 2018, and emails stopped. Acute pain management lectures were given to incoming IR fellows. A QI retrospective cohort analysis was then conducted from May 2016 through March 2020 on over 300 consecutive patients undergoing CT-guided liver microwave ablations (MWA). Adherence to PA and PVB performance was compared prior to ERAP (May 2016-September 2017) and after ERAP (October 2017 - March 2020). Initial goals were that 80% of eligible patients would receive at least 1 PA, and 50%of eligible patients would receive PVB. Process control charts were utilized to analyze month to month compliance to the ERAP pathway. Statistical process control charts demonstrated that after initiation of the ERAP protocol PA administration increased from 12% to 93%, and PVB increased from 15% to 78% on average from May 2016 to March 2020. After implementation of the CPOE order set and discontinuation of daily email reminders, there was a sustained adherence to utilizing the ERAP protocol over time with month-to-month adherence of > 80% for PA and > 50% for PVB (eligible patients). Acute pain management programs such as ERAP are a viable option for many patients presenting to IR for microwave ablations as well as for other painful ablative procedures. This initiative represents stresses that education and CPOE are effective elements to facilitate implementation of and adherence to ERAP pathways.

Triple Coaxial-Half-Slot Antenna Scheme With Deep Learning-Based Temperature Prediction for Hepatic Microwave Ablation: Finite Element Analysis and In Vitro Experiment

This research proposes a triple-antenna scheme of three coaxial half slot antennas (CHSA) for minimally invasive hepatic microwave ablation (MWA). In the MWA treatment, the antennas were positioned around the cancer tissue in equilateral triangle formation, with the half-slot side of the antennas directed at the triangle center to concentrate the microwave energy. Finite element (FE) simulations and in vitro experiments with swine liver were carried out to determine the temperatures and coagulation zone under different distances between the three antennas: 10, 20, and 30 mm. Besides, a regression-based deep learning algorithm was utilized to predict temperatures at the midpoint of the triple-CHSA arrangement without inserting a temperature sensor into the targeted tissue. The algorithm relied on temperatures at a site adjacent to the targeted cancer tissue to predict the midpoint temperatures. The triple-CHSA scheme could achieve a large coagulation zone with temperatures of 60 °C or higher. The FE simulation results showed that the largest coagulation volumes achieved were 18.425, 29.312, and 63.507 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for the between-antenna distances of 10, 20, and 30 mm, respectively. The largest coagulation volumes of in vitro experiments were 18.437, 29.317, and 63.504 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for the corresponding between-antenna distances. The prediction accuracy of the deep learning algorithm were 99.98 % for mean square error, 98.75 % for mean absolute error, and 99.22 % for mean absolute percentage error. The novelty of the research lies in the use of CHSA surrounding the cancer tissue in equilateral triangle formation for hepatic MWA, as opposed to the conventional hepatic MWA procedure which requires inserting antennas into the targeted tissue. Another research novelty is the use of regression-based deep learning algorithm to predict the temperature of liver tissue at the midpoint of the triple-CHSA arrangement.

Subregion Radiomics Analysis to Display Necrosis After Hepatic Microwave Ablation-A Proof of Concept Study.

The aim of this study was to improve the visualization of coagulation necrosis after computed tomography (CT)-guided microwave ablation (MWA) in routine postablational imaging. Ten MWAs were performed in 8 pigs under CT guidance. After each ablation, we obtained contrast-enhanced CT scans in venous phase. Ablations were then resected as a whole, and histologic slices were obtained orthogonally through the ablation center. Subsequently, a vital stain was applied to the sections for visualization of coagulation necrosis. Computed tomography images were reformatted to match the histologic slices. Afterwards, quantitative imaging features were extracted from the subregions of all images, and binary classifiers were used to predict the presence of coagulation necrosis for each subregion. From this, heatmaps could be created, which visually represented the extent of necrosis in each CT image. Two independent observers evaluated the extent of coagulative necrosis between the heat maps and histological sections. We applied 4 different classifiers, including a generalized linear mixed model (GLMM), a stochastic gradient boosting classifier, a random forest classifier, and a k-nearest neighbor classifier, out of which the GLMM showed the best performance to display coagulation necrosis. The GLMM resulted in an area under the curve of 0.84 and a Jaccard index of 0.6 between the generated heat map and the histologic reference standard as well as a good interobserver agreement with a Jaccard index of 0.9. Subregion radiomics analysis may improve visualization of coagulation necrosis after hepatic MWA in an in vivo porcine model.

Periportal fields cause stronger cooling effects than veins in hepatic microwave ablation: an in vivo porcine study.

Vascular cooling effects are a well-known source for tumor recurrence in thermal in situ ablation techniques for hepatic malignancies. Microwave ablation (MWA) is an ablation technique to be considered in the treatment of malignant liver tumors. The impact of vascular cooling in MWA is still controversial. To evaluate the influence of different intrahepatic vessel types, vessel sizes, and vessel-to-antenna-distances on MWA geometry in vivo. Five MWAs (902-928 MHz) were performed with an energy input of 24.0 kJ in three porcine livers in vivo. MWA lesions were cut into 2-mm slices. The minimum and maximum radius of the ablation area was measured for each slice. Distances were measured from ablation center toward all adjacent hepatic vessels with a diameter of ≥1 mm and within a perimeter of 20 mm around the antenna. The respective vascular cooling effect relative to the maximum ablation radius was calculated. In total, 707 vessels (489 veins, 218 portal fields) were detected; 370 (76%) hepatic veins and 185 (85%) portal fields caused a cooling effect. Portal fields resulted in higher cooling effects (37%) than hepatic veins (26%, P < 0.01). No cooling effect could be observed in close proximity of vessels within the central ablation zone. Hepatic vessels influenced MWA zones and caused a distinct cooling effect. Portal fields resulted in more pronounced cooling effect than hepatic veins. No cooling effect was observed around vessels situated within the central white zone.

CT-based quantification of short-term tissue shrinkage following hepatic microwave ablation in an in vivo porcine liver model.

Microwave ablation (MWA) is a minimally invasive treatment option for solid tumors and belongs to the local ablative therapeutic techniques, based on thermal tissue coagulation. So far there are mainly ex vivo studies that describe tissue shrinkage during MWA. To characterize short-term volume changes of the ablated zone following hepatic MWA in an in vivo porcine liver model using contrast-enhanced computer tomography (CECT). We performed multiple hepatic MWA with constant energy parameters in healthy, narcotized and laparotomized domestic pigs. The volumes of the ablated areas were calculated from venous phase CT scans, immediately after the ablation and in short-term courses of up to 2 h after MWA. In total, 19 thermally ablated areas in 10 porcine livers could be analyzed (n = 6 with two volume measurements during the measurement period and n = 13 with three measurements). Both groups showed a statistically significant but heterogeneous volume reduction of up to 12% (median 6%) of the ablated zones in CECT scans during the measurement period (P < 0.001 [n = 13] and P = 0.042 [n = 6]). However, the dimension and dynamics of volume changes were heterogenous both absolutely and relatively. We observed a significant short-term volume reduction of ablated liver tissue in vivo. This volume shrinkage must be considered in clinical practice for technically successful tumor treatment by MWA and therefore it should be further investigated in in vivo studies.

Improved MR-thermometry during hepatic microwave ablation by correcting for intermittent electromagnetic interference artifacts

MRI-guided microwave ablation (MWA) is a minimally invasive treatment for localized cancer. MR thermometry has been shown to be able to provide vital information for monitoring the procedure in real-time. However, MRI during active MWA can suffer from image quality degradation due to intermittent electromagnetic interference (EMI). A novel approach to correct for EMI-contaminated images is presented here to improve MR thermometry during clinical hepatic MWA. The method was applied to MR-thermometry images acquired during four MR-guided hepatic MWA treatments using a commercially available MRI-configured microwave generator system. During the treatments MR thermometry data acquisition was synchronized to respiratory cycle to minimize the impact of motion. EMI was detected and corrected using uncontaminated k-space data from nearby frames in k-space. Substantially improved temperature and thermal damage maps have been obtained and the treatment zone can be better visualized. Our ex vivo tissue sample study shows the correction introduced minimal errors to the temperature maps and thermal damage maps.

Exploring Patterns of Dynamic Size Changes of Lesions after Hepatic Microwave Ablation in an In Vivo Porcine Model

Microwave ablation (MWA) is a type of minimally invasive cancer therapy that uses heat to induce necrosis in solid tumours. Inter- and post-ablational size changes can influence the accuracy of control imaging, posing a risk of incomplete ablation. The present study aims to explore post-ablation 3D size dynamics in vivo using computed tomography (CT). Ten MWA datasets obtained in nine healthy pigs were used. Lesions were subdivided along the z-axis with an additional planar subdivision into eight subsections. The volume of the subsections was analysed over different time points, subsequently colour-coded and three-dimensionally visualized. A locally weighted polynomial regression model (LOESS) was applied to describe overall size changes, and Student’s t-tests were used to assess statistical significance of size changes. The 3D analysis showed heterogeneous volume changes with multiple small changes at the lesion margins over all time points. The changes were pronounced at the upper and lower lesion edges and characterized by initially eccentric, opposite swelling, followed by shrinkage. In the middle parts of the lesion, we observed less dimensional variations over the different time points. LOESS revealed a hyperbolic pattern for the volumetric changes with an initially significant volume increase of 11.6% (111.6% of the original volume) over the first 32 minutes, followed by a continuous decrease to 96% of the original volume (p < 0.05).

Immediate post-interventional contrast-enhanced computed tomography overestimates hepatic microwave ablation – an in vivo animal study

Objectives Contrast-enhanced computed tomography (CECT) is used to monitor technical success immediately after hepatic microwave ablation (MWA). However, it remains unclear, if CECT shows the exact extend of the thermal destruction zone, or if tissue changes such as peri-lesionary edema are depicted as well. The objective of this study was to correlate immediate post-interventional CECT with histological and macroscopic findings in hepatic MWA in porcine liver in vivo. Methods Eleven MWA were performed in porcine liver in vivo with a microwave generator (928 MHz; energy input 24 kJ). CECT was performed post-interventionally. Livers were explanted and ablations were bisected immediately after ablation. Samples were histologically analyzed after vital staining (NADH-diaphorase). Ablation zones were histologically and macroscopically outlined. We correlated histologic findings, macroscopic images and CECT. Results Three ablation zones were identified in histological and macroscopic findings. Only one ablation zone could be depicted in CECT. Close conformity was observed between histological and macroscopic findings. The ablation zone depicted in CECT overestimated the histological avital central zone and inner red zone (p < = .01). No differences were found between CECT and the histological outer red zone (p > .05). Conclusions Immediate post-interventional CECT overestimated the clinically relevant zone of complete cell ablation after MWA in porcine liver in vivo. This entails the risk of incomplete tumor ablation and could lead to tumor recurrence.

Ablation zone geometry after CT-guided hepatic microwave ablation: evaluation of a semi-automatic software and comparison of two different ablation systems

Purpose The aims of this study were to evaluate a semi-automatic segmentation software for assessment of ablation zone geometry in computed tomography (CT)-guided microwave ablation (MWA) of liver tumors and to compare two different MWA systems. Material and Methods 27 patients with 40 hepatic tumors (primary liver tumor n = 20, metastases n = 20) referred for CT-guided MWA were included in this retrospective IRB-approved study. MWA was performed using two systems (system 1: 915 MHz; n = 20; system 2: 2.45 GHz; n = 20). Ablation zone segmentation and ellipticity index calculations were performed using SAFIR (Software Assistant for Interventional Radiology). To validate semi-automatic software calculations, results (2 perpendicular diameters, ellipticity index, volume) were compared with those of manual analysis (intraclass correlation, Pearson’s correlation, Mann–Whitney U test; p < 0.05 deemed significant. Results Manual measurements of mean maximum ablation zone diameters were 43 mm (system 1) and 34 mm (system 2), respectively. Correlations between manual and semi-automatic measurements were r = 0.72 and r = 0.66 (both p < 0.0001) for perpendicular diameters, and r = 0.98 (p < 0.001) for volume. Manual analysis demonstrated that ablation zones created with system 2 had a significantly lower ellipticity index compared to system 1 (mean 1.17 vs. 1.86, p < 0.0001). Results correlated significantly with semi-automatic software measurements (r = 0.71, p < 0.0001). Conclusion Semi-automatic assessment of ablation zone geometry using SAFIR is feasible. Software-assisted evaluation of ablation zones may prove beneficial with complex ablation procedures, especially for less experienced operators. The 2.45 GHz MWA system generated a significantly more spherical ablation zone compared to the 915 MHz system. The choice of a specific MWA system significantly influences ablation zone geometry.

Microwave ablation zones are larger than they macroscopically appear - Reevaluation based on NADH vitality staining ex vivo.

Animal liver is established as an ex vivo model for studies on hepatic microwave ablation (MWA). Macroscopically visible color changes in the ablation zone are used to assess cell destruction and confirm successful ablation ex vivo. Macroscopy and histology of MWA zones regarding cell viability in ex vivo porcine livers were compared in this study. Six MWA were performed in porcine livers post mortem. A 14-G antenna and microwave generator (928 MHz; 9.0 kJ) were used. MWA were cut at the maximum cross section in vertical alignment to the antenna. NADH-diaphorase staining determined cell vitality. Macroscopic and microscopic ablation zones were statistically analyzed. Histology showed two distinct ablation zones: central white zone (WZH) with no cell viability and peripheral red zone (RZH) with partial cell viability. However, the macroscopically visible WZM was significantly smaller than the microscopic WZH with an area difference of 43.1% (p < 0.05) and a radius difference of 21.2% (1.6 mm; p < 0.05). Macroscopy and histology showed a very high correlation for the complete lesion area (WZH/M+RZH/M; r = 0.9; p = 0.001). The avital central zone is significantly larger as the macroscopically visible WZ which is commonly used to assess successful ablation in MWA ex vivo studies. Irreversible cell destruction can be underestimated in macroscopic evaluation.

Hepatic Microwave Ablation in Challenging Locations.

In recent years, there has been increased utilization of microwave ablation (MWA) in the treatment of soft tissue tumors. MWA has several theoretical advantages over radiofrequency ablation (RFA) by achieving a more rapid and sustained heating of tissues, increased efficacy in tissues with poor thermal conductivity, and less susceptibility to heat sink effect. While its greater power output has led to appropriate caution when applying this energy to soft tissue tumors, many commonly held beliefs regarding contraindications to MWA are unsupported by data and have been passed along based on experience with RFA. The goal of this article is to review the use of MWA in challenging clinical situations along with the existing evidence for its use.