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Background and objectives Adrenocortical neoplasms are the main causes of secondary hypertension and related comorbidities including hypokalemia and cardiovascular diseases. Conventional techniques for the management of this condition are often invasive and not resolutive. Recent studies proposed microwave thermal ablation (MWA) to eradicate adrenocortical adenomas arising in proximity to sensitive structures. This study explores a new MWA approach to selectively direct the electromagnetic energy into the target and shield the surrounding tissues. The new solution relies on the anatomical and dielectric characteristics of the adrenal gland and the surrounding fat capsule.Methods A 3 D model of the adrenal gland is developed, and a cooled microwave applicator is placed parallel to the interface between the fat and adrenal tissue. Numerical simulations are conducted at 2.45 GHz accounting for two energy delivery settings, two orientations of the applicator and blood perfusion of the tissues. Ex vivo and in vivo ablation procedures are conducted on ovine adrenal glands. Histology analysis completes the experimental studies.Results Numerical results show asymmetric ablation profiles in ex vivo and in vivo conditions. The asymmetry ratio is influenced by the procedure settings and orientation of the applicator. Ablation zones obtained experimentally agree with those predicted by the numerical simulations. Histology analysis confirms irreversible cellular changes only in the adrenal tissue close to the applicator.Conclusions The outcomes show that the dielectric contrast between the fat layer and tissue target can be a tool in MWA to shape ablation zones to protect the surrounding structures from excessive temperature increases.

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This study presents the design and the experimental validation of a slot-loaded antipodal Vivaldi antenna. The intended use is in an array configuration for monitoring liver microwave thermal ablation by way of microwave imaging (MWI). To optimize electromagnetic power transfer to the human abdomen, the antenna was designed to operate in a coupling medium. The final design has overall dimensions of $40\text{mm} \times 65 \text{mm}$ , and the working bandwidth goes from 600 MHz up to 3 GHz, with the possibility to operate at higher frequencies, also. The antenna proposed in this study shows the most compact aperture dimension, as compared with other antennas designed for biomedical applications, working within the same bandwidth. To experimentally evaluate the antenna performances, the coupling medium was realized, proposing a recipe made by low cost, and easy to provide and use, materials. In particular, a mixture of water, oil, dishwashing detergent, and guar gum was used. The realized material showed dielectric properties close to the target ones, proved stability on a 1-week time, and reproducibility against different realizations. The antenna’s measured S-parameters well agreed with the simulation result. When locating two antennas in close proximity, as in the MWI array configuration, the results showed good performances towards mutual coupling.

Background and objectives: Adrenocortical neoplasms are the main causes of secondary hypertension and related comorbidities including hypokalemia and cardiovascular diseases. Conventional techniques for the management of this condition are often invasive and not resolutive. Recent studies proposed microwave thermal ablation (MWA) to eradicate adrenocortical adenomas arising in proximity to sensitive structures. This study explores a new MWA approach to selectively direct the electromagnetic energy into the target and shield the surrounding tissues. The new solution relies on the anatomical and dielectric characteristics of the adrenal gland and the surrounding fat capsule. Methods: A 3 D model of the adrenal gland is developed, and a cooled microwave applicator is placed parallel to the interface between the fat and adrenal tissue. Numerical simulations are conducted at 2.45 GHz accounting for two energy delivery settings, two orientations of the applicator and blood perfusion of the tissues. Ex vivo and in vivo ablation procedures are conducted on ovine adrenal glands. Histology analysis completes the experimental studies. Results: Numerical results show asymmetric ablation profiles in ex vivo and in vivo conditions. The asymmetry ratio is influenced by the procedure settings and orientation of the applicator. Ablation zones obtained experimentally agree with those predicted by the numerical simulations. Histology analysis confirms irreversible cellular changes only in the adrenal tissue close to the applicator. Conclusions: The outcomes show that the dielectric contrast between the fat layer and tissue target can be a tool in MWA to shape ablation zones to protect the surrounding structures from excessive temperature increases. [ABSTRACT FROM AUTHOR]

Objective: To investigate the feasibility and efficacy of localized, subtotal, cortical-sparing microwave thermal ablation (MTA) as a potential curative management for primary aldosteronism. The study investigated with equal importance the selected ablation of small volumes of adrenal cortex while sparing adjacent cortex. Method: An in-vivo study was carried out in swine (n = 8) where MTA was applied under direct visualization, to the adrenal glands at 45 W or 70 W for 60 s, using a lateral, side-firing probe and a non-penetrative approach. Animals were survived for 48 h post-procedurally. Animals were investigated for markers of histological, immunohistochemical and biochemical evidence of adrenal function and adrenal damage by assessing samples drawn intra-operatively and at the time of euthanasia. Results: Selected MTA (70 W for 60 s) successfully ablated small adrenocortical volumes (∼0.8 cm3) characterized by coagulative necrosis and abnormal expression of functional markers (CYP11B1 and CYP17). Non-ablated, adjacent cortex was not affected and preserved normal expression of functional markers, without increased expression of markers of heat damage (HSP-70 and HMGB-1). Limited adrenal medullary damage was demonstrated histologically, clinically and biochemically. Conclusion: MTA offers potential as an efficient methodology for delivering targeted subtotal cortical-sparing adrenal ablation. Image-guided targeted MTA may also represent a safe future modality for curative management of PA, in the setting of both unilateral and bilateral disease.

Background: 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. Purpose: 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). Material and Methods: 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. Results: 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. Conclusion: 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. [ABSTRACT FROM AUTHOR]

Renal cell carcinoma (RCC) local recurrence after radical nephrectomy is uncommon. When feasible, surgical removal remains the primary treatment strategy; nevertheless, local RCC relapse management is controversial, and less invasive procedures may represent an attractive option to achieve oncologic control. The aim of our study was to assess the feasibility, safety, and clinical outcomes of image-guided percutaneous microwave ablation (MWA) for RCC local recurrence in patients initially treated with nephrectomy with curative intent. 10 consecutive patients underwent CT-guided percutaneous MWA of a total of 10 retroperitoneal nodules. Inclusion criteria were: histologically verified retroperitoneal metastases, previous radical nephrectomy, lesion no larger than 3 cm, no other metastatic site elsewhere. All the procedures were performed under moderate sedation choosing the most favorable patient decubitus. If deemed necessary, pneumodissection was induced before ablation. After the antenna placement inside the target lesion, thermal ablation was achieved by maintenance of a power of 100 W for a total time between 2 and 4 min. All patients were observed overnight and discharged the following day if clinically stable. Technical success was obtained in 100% of patients. One patient was re-treated to complete oncologic response with repeat MWA. No major complications were observed. No patients demonstrated local recurrence at a mean follow-up of 26 months. MWA is a safe and effective treatment strategy for loco-regional relapse of RCC following radical nephrectomy. This technique may represent a valuable approach for patients who are not eligible for surgery. [ABSTRACT FROM AUTHOR]

Highlights • A validation of a microwave thermal ablation simulation in ex vivo pig liver. • The simulation model used different flow coefficients. • The results showed a significant agreement with a flow coefficient of 90,000 W/(K*m3). Abstract The purpose of the study was to validate the simulation model for a microwave thermal ablation in ex vivo liver tissue. The study aims to show that heat transfer due to the flow of tissue water during ablation in ex vivo tissue is not negligible. Ablation experiments were performed in ex vivo porcine liver with microwave powers of 60 W to 100 W. During the procedure, the temperature was recorded in the liver sample at different distances to the applicator using a fiber-optic thermometer. The position of the probes was identified by CT imaging and transferred to the simulation. The simulation of the heat distribution in the liver tissue was carried out with the software CST Studio Suite. The results of the simulation with different flow coefficients were compared with the results of the ablation experiments using the Bland–Altman analysis. The analysis showed that the flow coefficient of 90,000 W/(K*m3) can be considered as the most suitable value for clinically used powers. The presented simulation model can be used to calculate the temperature distribution for microwave ablation in ex vivo liver tissue. [ABSTRACT FROM AUTHOR]

Bones are a frequent site of metastases that cause intolerable cancer-related pain in 90% of patients, making their quality of life poor. In this scenario, being able to treat bone oncology patients by means of minimally invasive techniques can be crucial to avoid surgery-related risks and decrease hospitalization times. The use of microwave ablation (MWA) is gaining broad clinical acceptance to treat bone tumors. It is worth investigating temperature variations in bone tissue undergoing MWA because the clinical outcomes can be inferred from this parameter. Several feasibility studies have been performed, but an experimental analysis of the temperature trends reached into the bone during the MWA has not yet been assessed. In this work, a multi-point temperature study along the bone structure during such treatment is presented. The study has been carried out on ex vivo bovine femur and tibia, subjected to MWA. An overall of 40 measurement points covering a large sensing area was obtained for each configuration. Temperature monitoring was performed by using 40 fiber Bragg grating (FBGs) sensors (four arrays each housing 10 FBGs), inserted into the bones at specific distances to the microwave antenna. As result, the ability of this experimental multi-point monitoring approach in tracking temperature variations within bone tissue during MWA treatments was shown. This study lays the foundations for the design of a novel approach to study the effects of MWA on bone tumors. As consequence, the MWA treatment settings could be optimized in order to maximize the treatment effects of such a promising clinical application, but also customized for the specific tumor and patient.

Background: Microwave ablation (MWA) is a relatively new technique which has been used to achieve hemostasis at surgical field. However, few publications have reported MWA for epistaxis. Objectives: Our objectives were to identify the bleeding sites/points in instances of posterior epistaxis and to evaluate the efficacy of MWA for controlling bleeding. Material and methods: Patients with posterior epistaxis who met the inclusion criteria were examined and treated endoscopically using MWA. Recurrent bleeding and complications were evaluated at 1 and 3 months after treatment. Results: Of the 71 patients, the bleeding site/point was identified in 67 patients while 4 patients was unknown. Of the 67 patients with known bleeding sites, the olfactory cleft was in 44 patients, the middle meatus in 5 patients, and the inferior meatus in 18 patients. Only the bleeding point was coagulated in the 67 patients while prophylactic MWA in the 4 patients. No side effects or complications (including recurrent bleeding, crusting, nasal discomfort, and nasal septal perforation) were seen at 3-month follow-up. Conclusions: MWA may effectively control posterior epistaxis with a low cost and without complications. [ABSTRACT FROM AUTHOR]

Background: Microwave ablation (MWA) is a relatively new technique which has been used to achieve hemostasis at surgical field. However, few publications have reported MWA for epistaxis. Objectives: Our objectives were to identify the bleeding sites/points in instances of posterior epistaxis and to evaluate the efficacy of MWA for controlling bleeding. Material and methods: Patients with posterior epistaxis who met the inclusion criteria were examined and treated endoscopically using MWA. Recurrent bleeding and complications were evaluated at 1 and 3 months after treatment. Results: Of the 71 patients, the bleeding site/point was identified in 67 patients while 4 patients was unknown. Of the 67 patients with known bleeding sites, the olfactory cleft was in 44 patients, the middle meatus in 5 patients, and the inferior meatus in 18 patients. Only the bleeding point was coagulated in the 67 patients while prophylactic MWA in the 4 patients. No side effects or complications (including recurrent bleeding, crusting, nasal discomfort, and nasal septal perforation) were seen at 3- month follow-up. Conclusions: MWA may effectively control posterior epistaxis with a low cost and without complications. [ABSTRACT FROM AUTHOR]

According to the American Cancer Society the number of patients with bone tumors is growing up. The extremities of the long bones are the most affected by this disease. The common treatments are surgery (amputation), radio and chemotherapy. However, their high cost and side-effects show the necessity of new treatments. These should not only eradicate the tumor but also offer a major control over the treated area. In this sense, the microwave ablation plays an important role. A micro-coaxial slot antenna to generated thermal ablation in bone tumors is proposed. The antenna was modeled, constructed and evaluated in pig tissue. A parametric study to evaluate the effect of the blood perfusion in the thermal distributions was done. Values of bone blood perfusion among 30-1171 ml/min/kg were included in this study. Subsequently, temperature profiles and thermal distributions generated in pig bones were obtained and compared with those obtained in the model. This evaluation shows a high level of concordance; in the best cases, a difference between simulation and measurement of 0.13°C-3.83°C and 0.08°C-0.41°C was found. This study corroborates the efficiency of the models to predict the antenna behavior and the efficiency of the proposed antenna to generated thermal ablation in bone tissue. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate, characterise and compare the extent of tissue shrinkage induced from three different commercial microwave ablation devices, and to elucidate the mechanism behind the distinctive performances obtained. Materials and methods: Microwave ablation (N = 152) was conducted with three different commercial devices on cubes of ex vivo liver (10-40 ± 2 mm/side) embedded in agar phantoms. 50-60 W was applied for 1-10 min duration. Pre- and post-ablation dimensions of the samples, as well as the extent of carbonisation and coagulation were measured and correlated. ANOVA was performed to evaluate statistical significance. Results: For all devices, logarithmic correlations with time were observed for both tissue shrinkage (R2 = 0.84-1.00) and induced carbonisation (R2 = 0.73-0.99) radially to the antenna axis. Along the longitudinal axis of the antenna, for two of the devices shrinkage did not appreciably change with time (p > 0.05), yet carbonisation increased linearly (R2 = 0.57-0.94). For the third fully internally-cooled device, both carbonisation and shrinkage showed logarithmic trends (R2 = 0.85-0.98 and R2 = 0.78-0.94, respectively) based upon delayed carbonisation appearing only 5 min into ablation and onward. For all devices, non-uniform shrinkage was noted within the coagulated area increasing from the boundary of the ablated area (14%) to the limit of carbonisation (39%) in a linear fashion (R2 = 0.88) Conclusions: Microwave ablation device construction can alter the extent of post-ablation coagulation and tissue shrinkage. Given that tissue shrinkage in the coagulated area shows non-uniform behaviour, observed differences can be attributed in part to the applicator cooling system that alters the ablation temperature profile. [ABSTRACT FROM AUTHOR]

Abstract: In this study, microwave thermal ablation is numerically evaluated in the context of a treatment for Conn's Syndrome. This condition is caused by a benign shallow tumor in the cortex of adrenal gland. The modeling and design of microwave applicator to deliver thermal ablation to the adrenal gland requires accurate tissue characterization. Measuring the dielectric properties of the constituent tissues in the adrenal gland, that is cortex and medulla, enables more accurate numerical modeling for electromagnetic and thermal simulations. This study presents an anatomically and dielectrically realistic numerical model of the adrenal gland, and investigates the feasibility of applying controlled heating to small targets in the adrenal cortex. In addition, the use of dielectric contrast between the fat and the cortex of the adrenal gland to focus the thermal energy in the gland has also been studied. Being conscious of limitations of numerical simulation of complex multi‐physics problems like the microwave ablative treatment, calculated results provide a preliminary description of the electromagnetic and thermal phenomena involved. [ABSTRACT FROM AUTHOR]

Background and objectives: Microwave thermal ablation (MWT) is one of the treatment options for kidney cancer. However, for patients over 70 years old the safety and oncological efficacy of this treatment is still controversial. The goal of this study was to compare MWT with open partial nephrectomy (OPN) and to find out whether MWT is preferable in maintaining patient renal function and reducing the risk of postoperative complications. Materials and Methods: Depending on the treatment choice, all patients were divided into two groups: an MWT group and an open kidney resection (OPN) group. Data have been retrospectively collected for 7 years, starting with January 2012 up to January 2019. A total number of 33 patients with exophytic, single small renal masses were treated with either OPN (n = 18) or MWT (n = 15). All patients had histologically proven T1 kidney cancer. MWT was performed for patients who refused to have OPN or in those cases where the collecting system, renal calyx, and great vessels were free from tumor margins of more than 1 cm. Results: In the MWT group a median (IQR) patients’ age was 75 years (71−79) years, in the OPN group—71.5 (70−75) years, p = 0.005. A median (IQR) Charleston comorbidity index in the MWT group was 7.5 (5−10) and in the same way in the OPN group it was 5.22 (5−6), p = 0.005. A median (IQR) estimated glomerular filtration rate (eGFR) before surgery was higher in the MWT group 59.9 (49.5−73.8) mL/min/1.73 m2 vs. 46.2 (42.7−65.8) mL/min/1.73 m2 in the OPN group, p = 0.12. Three days following the surgery a median (IQR) eGFR was 56.45 (46.6−71.9) in MWT group mL/min/1.73 m2 vs. 43.45 (38.3−65) mL/min/1.73 m2) in the OPN group, p = 0.30. A median (IQR) of primary hemoglobin level was lower in the MWT group compared with the OPN group (134.5 (124−140) g/L vs. 125 (108−138) g/L), p = 0.41. However, after the surgery a median (IQR) lower hemoglobin level was detected in the OPN group (123.5 (111−134) g/L vs. 126 (112−135)), p = 0.53. The median (IQR) duration of the procedure in MWT group was shorter compared with the OPN group (26 (25−30) min vs. 67.5 (55−90) min), p < 0.0001. A median (IQR) hospitalization time was shorter in MWT group (3 (2−3) days vs. 89 (7−11.5) days), p < 0.0001. Pain by the visual analogue scale (VAS) scale the first day after surgery was significantly lower—median (IQR) in the MWT group was 2 (1−3) vs. 4 (3−6)), p = 0.008. Treatment failure rate was numerically higher in MWT (1/15 vs. 0/18, p = 0.56). Conclusions: Pain level on the next day after surgery, mean number of hospitalization and operation time were significantly lower in the MWT group than in the OPN group. The blood loss estimated glomerular filtration rate and oncologic data between the two groups was not statistically significant.

Microwave thermal ablation (MTA) therapy for cancer treatments relies on the absorption of electromagnetic energy at microwave frequencies to induce a very high and localized temperature increase, which causes an irreversible thermal damage in the target zone. Treatment planning in MTA is based on experimental observations of ablation zones in ex vivo tissue, while predicting the treatment outcomes could be greatly improved by reliable numerical models. In this work, a fully dynamical simulation model is exploited to look at effects of temperature-dependent variations in the dielectric and thermal properties of the targeted tissue on the prediction of the temperature increase and the extension of the thermally coagulated zone. In particular, the influence of measurement uncertainty of tissue parameters on the numerical results is investigated. Numerical data were compared with data from MTA experiments performed on ex vivo bovine liver tissue at 2.45 GHz, with a power of 60 W applied for 10 min. By including in the simulation model an uncertainty budget (CI = 95%) of ±25% in the properties of the tissue due to inaccuracy of measurements, numerical results were achieved in the range of experimental data. Obtained results also showed that the specific heat especially influences the extension of the thermally coagulated zone, with an increase of 27% in length and 7% in diameter when a variation of −25% is considered with respect to the value of the reference simulation model. [ABSTRACT FROM AUTHOR]

Interventional radiology plays a major role in the modern management of liver cancers, in primary hepatic malignancies or metastases and in palliative or curative situations. Radiological treatments are divided in two categories based on their approach: endovascular treatment and direct transcapsular access. Endovascular treatments include mainly three applications: transarterial chemoembolization (TACE), transarterial radioembolization (TARE) and portal vein embolization (PVE). TACE and TARE share an endovascular arterial approach, consisting of a selective catheterization of the hepatic artery or its branches. Subsequently, either a chemotherapy (TACE) or radioembolic (TARE) agent is injected in the target vessel to act on the tumor. PVE raises the volume of the future liver remnant in extended hepatectomy by embolizing a portal vein territory which results in hepatic regeneration. Direct transcapsular access treatments involve mainly three techniques: radiofrequency thermal ablation (RFA), microwave thermal ablation (MWA) and percutaneous ethanol injection (PEI). RFA and MWA procedures are almost identical, their clinical applications are similar. A probe is deployed directly into the tumor to generate heat and coagulation necrosis. PEI has known implications based on the chemical toxicity of intra-tumoral injection with highly concentrated alcohol by a thin needle. [ABSTRACT FROM AUTHOR]

Background: The surgical therapy of choice for hepatocellular carcinoma (HCC) is liver transplantation (LT) or hepatic resection, although only a small percentage of patients can undergo these procedures. Microwave thermal ablation (MWTA) can be an effective alternative treatment for HCC that complicates a cirrhotic liver disease, either as a final procedure or for downstaging patients on the waiting list for LT, or in combination with resective surgery to achieve oncological radicality.Objective: The purpose of this retrospective study was to evaluate experience with the laparoscopic approach of MWTA at our center.Materials and Methods: In a cohort of 35 consecutive patients undergoing MWTA with laparoscopic approach between January, 2013 and May, 2016, we reviewed the demographic data, the Barcelona clinic liver cancer stage, the severity of cirrhotic liver disease, the size of the ablated lesion, the duration of the procedure, and complications occurring within 90 days of surgery.Results: MWTA was performed by applying one to three hepatic parenchymal insertions (mean 1.8) per patient. The mean duration of surgery was 163 ± 18 minutes. There was no blood loss in any of the procedures. Complete necrosis on CT scan was achieved in 26/35 patients (75%). The mean hospital stay was 4.6 (range 2-7) days; major complications were postablation syndrome in 2/35 (5.7%), peritoneal fluid in 4/35 (11.4%), and transient jaundice in 1/35 (2.8%) patients. There was no mortality.Conclusions: Laparoscopic MTWA is a safe and effective treatment for unresectable HCC and when a percutaneous procedure is not feasible. [ABSTRACT FROM AUTHOR]

Purpose: This paper compares the results obtained with numerical simulations andex vivoexperiments involving a dual applicator microwave thermal ablation system operating at a 2.45 GHz frequency, both in synchronous and asynchronous modes. Our purpose was to demonstrate that at this frequency an asynchronous or switched-mode system performs essentially as well as the synchronous one, in spite of the prevailing belief that coherence would assure better thermal (TH) synergy.Numerical analysis: The calculations of temperature fields were based on the Pennes bioheat equation, taking into account the effects of blood perfusion by means of a full-wave 3D simulator that allows numerical electromagnetic (EM) and TH analyses.Materials and methods: Experiments were done using a 100 W microwave (MW) power generator and a fast switched-mode sequential ‘active’ power splitter. By adding a further passive power splitter we arranged a test bed for an accurate experimental comparison of synchronous versus switched-mode TH ablations.Results: The experimental ablation zones produced by a dual applicator array onex vivoswine tissue corresponded well with the simulated ones, confirming that the simplifications assumed in the full-wave analysis were compatible with the aim of our work.Conclusions: Numerical simulations and experiments show that at a 2.45 GHz industrial, scientific and medical (ISM) frequency, synchronous, asynchronous and switched-mode multi-probe systems are substantially equivalent in terms of ablative performance. Moreover, the switched-mode solution offers simpler operation along with lesser sensitivity to the placement of applicators in the tissue. [ABSTRACT FROM PUBLISHER]

Purpose: To study the planar strain effects in liver during microwave (MW) thermal ablation as a means for tracking tissue expansion and contraction as a method for improving ablation monitoring. Methods: 1.4 mm circular metallic markers were inserted into 16 ex-vivo bovine fresh liver specimens, that were subsequently ablated (with the markers inside the specimen) by 40 W of microwave energy, for 1, 2, 3, 6, and 10 min. The markers were tracked during the ablation using an x-ray CT scanner. Images were acquired every 5-10 s enabling determination of the markers' coordinates over time. The 2D principal strains were calculated for triangles formed by subgroups of three markers, and their planar strain index, Ω, was plotted vs time. In addition, the radial distance of the markers from the antenna was measured at the end of each ablation. Subsequently, the tissue was sliced parallel to the imaged planes and the ablation zone was traced and digitized. The average ablation radius was then computed and compared to the radial distance. Results: The planar strain, Ω(t), profile demonstrated an ascending pattern until reaching a maximum at about 180 s, with a mean peak value (Ω = 1.31 ± 0.04) indicating tissue expansion. Thereafter, Ω progressively declined over the remaining duration of the ablation treatment, indicating tissue contraction. Furthermore, when plotting the ablation size vs time and the markers' mean radial distance vs time, it was found that the two curves intercepted at a time corresponding to the time of peak planar strain. Conclusions: By detecting the point of maximal planar strain in tissues during MW application, it is possible to noninvasively identify the location of the ablation zone front. The fact that the liver tissue proximal to the ablated zone expands during the first part of the treatment and then contracts when the ablation front reaches it, may serve as an index for monitoring the thermal treatment. [ABSTRACT FROM AUTHOR]

The purpose of this study was to provide a simulation therapy environment for microwave thermal ablation (MWA) under the guidance of ultrasound, and to present an inexpensive and portable simulator built on real patient-based pre-operative computed tomography (CT) data. We established an experimental simulation system for teaching MWA and present the results of a preliminary evaluation of the simulator's realism and utility for training. The system comprises physical elements of an electromagnetic tracking device and an abdominal phantom, and software elements providing three-dimensional (3D) image processing tools, real-time navigation functions and objective evaluation function module. Details of the novel aspects of this system are presented, including a portable electromagnetic tracking device, adoption of real patient-based pre-operative CT data of liver, operation simulation of MWA, and recording and playback of the operation simulation. Patients with liver cancer were selected for evaluation of the clinical application value of the experimental simulation system. A total of 50 consultant interventional radiologists and 20 specialist registrars in radiology rated the simulator's hardware reality and overall ergonomics. Results show that the simulator system we describe can be used as a training tool for MWA. It enables training with real patient cases prior to surgery, and it can provide a realistic simulation of the actual procedure. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to characterise changes in tissue volume during image-guided microwave ablation in order to arrive at a more precise determination of the true ablation zone. Materials and methods: The effect of power (20-80 W) and time (1-10 min) on microwave-induced tissue contraction was experimentally evaluated in various-sized cubes of ex vivo liver (10-40 mm ± 2 mm) and muscle (20 and 40 mm ± 2 mm) embedded in agar phantoms ( N = 119). Post-ablation linear and volumetric dimensions of the tissue cubes were measured and compared with pre-ablation dimensions. Subsequently, the process of tissue contraction was investigated dynamically during the ablation procedure through real-time X-ray CT scanning. Results: Overall, substantial shrinkage of 52-74% of initial tissue volume was noted. The shrinkage was non-uniform over time and space, with observed asymmetry favouring the radial (23-43 % range) over the longitudinal (21-29%) direction. Algorithmic relationships for the shrinkage as a function of time were demonstrated. Furthermore, the smallest cubes showed more substantial and faster contraction (28-40% after 1 min), with more considerable volumetric shrinkage (>10%) in muscle than in liver tissue. Additionally, CT imaging demonstrated initial expansion of the tissue volume, lasting in some cases up to 3 min during the microwave ablation procedure, prior to the contraction phenomenon. Conclusions: In addition to an asymmetric substantial shrinkage of the ablated tissue volume, an initial expansion phenomenon occurs during MW ablation. Thus, complex modifications of the tissue close to a radiating antenna will likely need to be taken into account for future methods of real-time ablation monitoring. [ABSTRACT FROM AUTHOR]

Purpose: This work focuses on the characterisation of the ablated area induced by a microwave thermal ablation (MTA) procedure. An experimental methodology for establishing a straightforward correlation between the temperature gradient and the changes in the dielectric properties of the tissue is presented and discussed. Materials and methods: Temperature measurements were performed during an ablation procedure in ex vivo bovine liver, at different distances from the antenna, whereas measurements of complex permittivity were conducted in sagittal sections of the ablated samples. The measured temperatures and dielectric properties were then correlated to obtain the dependence of the dielectric properties' spatial variation on the temperature gradient. The obtained correlation has been validated through comparison with previously obtained experimental data. A weighted cubic polynomial function and a weighted sigmoid function have been tested for best-fit interpolation of the measured data. Results: Temperatures in the range 23-105 °C were measured during the MTA procedure, while, after the end of the MTA trials, relative permittivities in the range 7-43 and electric conductivities in the range 0.3-1.8 S/m were measured according to the distance from the antenna's axis. The polynomial function showed better regression coefficients than the sigmoid one for both the relative permittivity (R2 = 0.9947 versus R2 = 0.9912, respectively) and the conductivity (R2 = 0.9919 versus R2 = 0.9866, respectively). However, the weighted cubic function showed an unrealistic behaviour for the relative permittivity at temperatures lower than 40 °C. Conclusions: According to the results obtained, information on the changes in the dielectric properties of the tissue under MTA treatment could be inferred from measured temperature data. Once validated by in vivo studies, the proposed methodology could be exploited to develop predictive tools for treatment planning. [ABSTRACT FROM AUTHOR]

Bones are a frequent site of metastases that cause intolerable cancer-related pain in 90% of patients, making their quality of life poor. In this scenario, being able to treat bone oncology patients by means of minimally invasive techniques can be crucial to avoid surgery-related risks and decrease hospitalization times. The use of microwave ablation (MWA) is gaining broad clinical acceptance to treat bone tumors. It is worth investigating temperature variations in bone tissue undergoing MWA because the clinical outcomes can be inferred from this parameter. Several feasibility studies have been performed, but an experimental analysis of the temperature trends reached into the bone during the MWA has not yet been assessed. In this work, a multi-point temperature study along the bone structure during such treatment is presented. The study has been carried out on ex vivo bovine femur and tibia, subjected to MWA. An overall of 40 measurement points covering a large sensing area was obtained for each configuration. Temperature monitoring was performed by using 40 fiber Bragg grating (FBGs) sensors (four arrays each housing 10 FBGs), inserted into the bones at specific distances to the microwave antenna. As result, the ability of this experimental multi-point monitoring approach in tracking temperature variations within bone tissue during MWA treatments was shown. This study lays the foundations for the design of a novel approach to study the effects of MWA on bone tumors. As consequence, the MWA treatment settings could be optimized in order to maximize the treatment effects of such a promising clinical application, but also customized for the specific tumor and patient. [ABSTRACT FROM AUTHOR]