Microwave ablation with a single small-gauge triaxial antenna: in vivo porcine liver model

Determining the Relationship between Delivery Parameters and Ablation Distribution for Novel Gel Ethanol Percutaneous Therapy in Ex Vivo Swine Liver

Ethyl cellulose-ethanol (ECE) is emerging as a promising formulation for ablative injections, with more controllable injection distributions than those from traditional liquid ethanol. This study evaluates the influence of salient injection parameters on forces needed for infusion, depot volume, retention, and shape in a large animal model relevant to human applications. Experiments were conducted to investigate how infusion volume (0.5 mL to 2.5 mL), ECE concentration (6% or 12%), needle gauge (22 G or 27 G), and infusion rate (10 mL/h) impacted the force of infusion into air using a load cell. These parameters, with the addition of manual infusion, were investigated to elucidate their influence on depot volume, retention, and shape (aspect ratio), measured using CT imaging, in an ex vivo swine liver model. Force during injection increased significantly for 12% compared to 6% ECE and for 27 G needles compared to 22 G. Force variability increased with higher ECE concentration and smaller needle diameter. As infusion volume increased, 12% ECE achieved superior depot volume compared to 6% ECE. For all infusion volumes, 12% ECE achieved superior retention compared to 6% ECE. Needle gauge and infusion rate had little influence on the observed depot volume or retention; however, the smaller needles resulted in higher variability in depot shape for 12% ECE. These results help us understand the multivariate nature of injection performance, informing injection protocol designs for ablations using gel ethanol and infusion, with volumes relevant to human applications.

Advancements in Microwave Ablation Techniques for Managing Pancreatic Lesions

Thermal ablation, including microwave ablation, has become increasingly important in the management of many solid tumors, including primary and metastatic tumors of the liver, kidney, and lung. However, its adoption to treat pancreatic lesions has been slowed due to concerns about potential adverse events. The success of radiofrequency ablation (RFA) in inoperable pancreatic cancers paved the way for its use in pancreatic neuroendocrine tumors and pancreatic cystic neoplasms (PCLs). In the last decade, other thermal ablation techniques, like microwave ablation, have emerged as alternatives to RFA. Microwaves, with frequencies ranging from 900 to 2450 MHz, generate heat by rapidly oscillating water molecules. Microwave ablation's advantage lies in its ability to achieve higher intra-lesion temperatures and uniform heating compared with RFA. Microwave ablation's application in pancreatic cancer and pancreatic neuroendocrine tumors has demonstrated promise with similar technical success to RFA. Yet, concern for peri-procedure complications, as well as a dearth of studies comparing RFA and microwave ablation, emphasize the need for further research. No studies have evaluated microwave ablation in PCLs. We herein review thermal ablation's potential to treat pancreatic lesions.

The combination of transcatheter arterial chemoembolisation (TACE) and thermal ablation versus TACE alone for hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma is the sixth most common cancer worldwide. Hepatic resection is regarded as the curative therapy for hepatocellular carcinoma. However, only about 20% of people with hepatocellular carcinoma are candidates for resection, which highlights the importance of effective nonsurgical therapies. Until now, transcatheter arterial chemoembolisation (TACE) is the most common palliative therapy for hepatocellular carcinoma, but its clinical benefits remain unsatisfactory. During recent years, some studies have reported that the combination of TACE plus thermal ablation can confer a more favourable prognosis than TACE alone. However, clear and compelling evidence to prove the beneficial or harmful effects of the combination of TACE and thermal ablation therapy is lacking.

OBJECTIVES

To assess the beneficial and harmful effects of the combination of thermal ablation with TACE versus TACE alone in people with hepatocellular carcinoma.

SEARCH METHODS

We performed searches in the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials in the Cochrane Library, MEDLINE, Embase, LILACS, Science Citation Index Expanded, and Conference Proceedings Citation Index-Science. We endeavoured to identify relevant randomised clinical trials also in the China National Knowledge Infrastructure (CNKI) and Wanfang databases. We searched trial registration websites for ongoing studies. We also handsearched grey literature sources. The date of last search was 22 December 2020.

SELECTION CRITERIA

We planned to include all randomised clinical trials comparing the combination of TACE plus thermal ablation versus TACE alone for hepatocellular carcinoma, no matter the language, year of publication, publication status, and reported outcomes.

DATA COLLECTION AND ANALYSIS

We planned to use standard methodological procedures expected by Cochrane. We planned to calculate risk ratios (RRs) with the corresponding 95% confidence intervals (CIs). For time-to-event variables, we planned to use the methods of survival analysis and express the intervention effect as a hazard ratio (HR) with 95% Cl. If the log HR and the variance were not directly reported in reports, we planned to calculate them indirectly, following methods for incorporating summary time-to-event data into meta-analysis. We planned to assess the risk of bias of the included studies using the RoB 2 tool. We planned to assess the certainty of evidence with GRADE and present the evidence in a summary of findings table.

MAIN RESULTS

Out of 2224 records retrieved with the searches, we considered 135 records eligible for full-text screening. We excluded 21 of these records because the interventions used were outside the scope of our review or the studies were not randomised clinical trials. We listed the remaining 114 records, reporting on 114 studies, under studies awaiting classification because we could not be sure that these were randomised clinical trials from the information in the study paper. We could not obtain information on the registration of the study protocol for any of the 114 studies. We could not obtain information on study approval by regional research ethics committees, either from the study authors or through our own searches of trial registries. Corresponding authors did not respond to our enquiries about the design and conduct of the studies, except for one from whom we did not receive a satisfactory response. We also raised awareness of our concerns to editors of the journals that published the 114 studies, and we did not hear back with useful information. Moreover, there seemed to be inappropriate inclusion of trial participants, based on cancer stage and severity of liver disease, who should have obtained other interventions according to guidelines from learned societies. Accordingly, we found no confirmed randomised clinical trials evaluating the combination of TACE plus thermal ablation versus TACE alone for people with hepatocellular carcinoma for inclusion in our review. We identified five ongoing trials, by handsearching in clinical trial websites.

AUTHORS' CONCLUSIONS

We could not find for inclusion any confirmed randomised clinical trials assessing the beneficial or harmful effects of the combination of TACE plus thermal ablation versus TACE alone in people with hepatocellular carcinoma. Therefore, our results did not show or reject the efficiency of the combination of TACE plus thermal ablation versus TACE alone for people with hepatocellular carcinoma. We need trials that compare the beneficial and harmful effects of the combination of TACE plus thermal ablation versus TACE alone in people with hepatocellular carcinoma, not eligible for treatments with curative intent (liver transplantation, ablation surgical resection) and who have sufficient liver reserve, as assessed by the Child Pugh score, and who do not have extrahepatic metastases. Therefore, future trial participants must be classified at Barcelona Clinic Liver Cancer Stage B (intermediate stage) (BCLC-B) or an equivalent, with other staging systems.

Finite Element Analysis of the Microwave Ablation Method for Enhanced Lung Cancer Treatment

Simple Summary

Microwave ablation is a promising modality for treating cancerous tumor cells in patients with localized lung cancer who are non-surgical candidates. Microwave ablation requires the control of the elevation of temperature, ensuring the destruction of cancer cells without damaging healthy tissue. Despite the unquestionable benefits, such as enlarged ablation zones and reduced procedure times, the respiratory movement of the lungs may affect the development and evolution of the necrotic tissue. Apart from the experimental methods, computer modeling has proven to be a powerful approach to improving the ablative treatment’s performance. This study aims to provide a step forward in patient safety by delivering optimal conditions necessary for microwave ablation to be as effective as possible for curing lung cancer with minimized invasiveness and collateral damage. The primary goal is to transfer the treatment plan based on simulation outputs into a reliable and safe microwave ablation procedure.

Abstract

Knowledge of the frequency dependence of the dielectric properties of the lung tissues and temperature profiles are essential characteristics associated with the effective performance of microwave ablation. In microwave ablation, the electromagnetic wave propagates into the biological tissue, resulting in energy absorption and providing the destruction of cancer cells without damaging the healthy tissue. As a consequence of the respiratory movement of the lungs, however, the accurate prediction of the microwave ablation zone has become an exceptionally demanding task. For that purpose, numerical modeling remains a primordial tool for carrying out a parametric study, evaluating the importance of the inherent phenomena, and leading to better optimization of the medical procedure. This paper reports on simulation studies on the effect of the breathing process on power dissipation, temperature distribution, the fraction of damage, and the specific absorption rate during microwave ablation. The simulation results obtained from the relative permittivity and conductivity for inflated and deflated lungs are compared with those obtained regardless of respiration. It is shown that differences in the dielectric properties of inflated and deflated lungs significantly affect the time evolution of the temperature and its maximum value, the time, the fraction of damage, and the specific absorption rate. The fraction of damage determined from the degree of tissue injury reveals that the microwave ablation zone is significantly larger under dynamic physical parameters. At the end of expiration, the ablation lesion area is more concentrated around the tip and slot of the antenna, and the backward heating effect is smaller. The diffuse increase in temperature should reach a certain level to destroy cancer cells without damaging the surrounding tissue. The obtained results can be used as a guideline for determining the optimal conditions to improve the overall success of microwave ablation.

Transcostal Histotripsy Ablation in an In Vivo Acute Hepatic Porcine Model

PURPOSE

To determine whether histotripsy can create human-scale transcostal ablations in porcine liver without causing severe thermal wall injuries along the beam path.

MATERIALS AND METHODS

Histotripsy was applied to the liver using a preclinical prototype robotic system through a transcostal window in six female swine. A 3.0 cm spherical ablation zone was prescribed. Duration of treatment (75 min) was longer than a prior subcostal treatment study (24 min, 15 s) to minimize beam path heating. Animals then underwent contrast-enhanced MRI, necropsy, and histopathology. Images and tissue were analyzed for ablation zone size, shape, completeness of necrosis, and off-target effects.

RESULTS

Ablation zones demonstrated complete necrosis with no viable tissue remaining in 6/6 animals by histopathology. Ablation zone volume was close to prescribed (13.8 ± 1.8 cm³ vs. prescribed 14.1 cm³). Edema was noted in the body wall overlying the ablation on T2 MRI in 5/5 (one animal did not receive MRI), though there was no gross or histologic evidence of injury to the chest wall at necropsy. At gross inspection, lung discoloration in the right lower lobe was present in 5/6 animals (mean size: 1 × 2 × 4 cm) with alveolar hemorrhage, preservation of blood vessels and bronchioles, and minor injuries to pneumocytes noted at histology.

CONCLUSION

Transcostal hepatic histotripsy ablation appears feasible, effective, and no severe injuries were identified in an acute porcine model when prolonged cooling time is added to minimize body wall heating.

Image guided thermal ablation in lung cancer treatment

Lung ablation has been introduced into lung cancer treatment for about two decades. Currently, 3 main choices of thermal energy for lung ablation are radiofrequency ablation (RFA), microwave ablation (MWA), and cryoablation. As a mostly palliative, occasionally curative intent local treatment, the feasibility and safety of lung ablation have been validated in small size lung cancer treatment, especially in lung tumor ≤3 cm. Improved techniques and experience in recent years help render outcomes much better than before for lung cancer patients who are medically inoperable with early stage primary lung cancer, and patients with oligometastasis or local recurrence. For stage IA non-small cell lung cancer (NSCLC) patients underwent RFA, 1- and 2-year overall survival rate were reported as 86.3% and 69.8%. And 1- and 2-year local recurrence rate were reported as 68.9% and 59.8%. Limitations, including heat sink, skin burn, and inconsistent heat conduction, are observed in the first applied ablation technique, RFA. MWA and cryoablation are developed to overcome these limitations and achieve the goal of less morbidity. Generally, imaged guided thermal ablation has a good safety profile, with pneumothorax as the most common morbidity. This article will mainly discuss the current features and application of these ablation techniques in lung cancer treatment.

Application of Artificial Neural Networks for Accurate Determination of the Complex Permittivity of Biological Tissue

Medical devices making use of radio frequency (RF) and microwave (MW) fields have been studied as alternatives to existing diagnostic and therapeutic modalities since they offer several advantages. However, the lack of accurate knowledge of the complex permittivity of different biological tissues continues to hinder progress in of these technologies. The most convenient and popular measurement method used to determine the complex permittivity of biological tissues is the open-ended coaxial line, in combination with a vector network analyser (VNA) to measure the reflection coefficient (S11) which is then converted to the corresponding tissue permittivity using either full-wave analysis or through the use of equivalent circuit models. This paper proposes an innovative method of using artificial neural networks (ANN) to convert measured S11 to tissue permittivity, circumventing the requirement of extending the VNA measurement plane to the coaxial line open end. The conventional three-step calibration technique used with coaxial open-ended probes lacks repeatability, unless applied with extreme care by experienced persons, and is not adaptable to alternative sensor antenna configurations necessitated by many potential diagnostic and monitoring applications. The method being proposed does not require calibration at the tip of the probe, thus simplifying the measurement procedure while allowing arbitrary sensor design, and was experimentally validated using S11 measurements and the corresponding complex permittivity of 60 standard liquid and 42 porcine tissue samples. Following ANN training, validation and testing, we obtained a prediction accuracy of 5% for the complex permittivity.

Microwave ablation: How we do it?

Minimally invasive techniques such as Image guided thermal ablation are now widely used in the treatment of tumors. Microwave ablation (MWA) is one of the newer modality of thermal ablation and has proven its safety and efficacy in the management of the tumors amenable for ablation for primary and metastatic diseases. It is used in the treatment of primary and secondary liver malignancies, primary and secondary lung malignancies, renal and adrenal tumors and bone metastases. We wanted to share our initial experience with this newer modality. In this article we will describe the mechanism and technique of MWA, comparison done with RFA, advantages and disadvantages of MWA along with pre procedure workup, post procedure follow-up and review of literature.

A Shifting Paradigm in Diagnosis and Management of Hepatic Adenoma

BACKGROUND

New insights into molecular pathogenesis of hepatocellular adenomas (HCA) have allowed sub-classification based on distinct genetic alterations and a fresh look at characterizations of natural history. Clinically, this is important in understanding risk factors for two feared complications: malignant transformation and hemorrhage.

METHODS

PubMed literature search for hepatocellular adenoma over all years, excluding case reports and articles focusing on multiple adenomas or adenomatosis.

RESULTS

The β-catenin exon 3 mutated HCA accounts for about 10% of all HCAs and is associated with the highest risk of malignant transformation. The HF1α subtype accounts for 30-40% of all HCAs and has the lowest risk of malignant transformation. Gender has also emerged as an increasingly important risk factor and males with HCA are at considerably higher risk of malignant transformation, regardless of tumor size. The increasing use of gadoxetic-enhanced MRI has allowed for improved differentiation of HCAs from focal nodular hyperplasia, as well as the identification of specific radiologic features of some subtypes, particularly the inflammatory and HF1α HCAs.

CONCLUSIONS

Classification of HCA by subtype has important implications for patient counseling and treatment given variable risks of malignant transformation and hemorrhage. Males and those with β-catenin exon 3 mutated HCAs are two groups who should always be counselled to undergo surgical resection. On the other hand, in the lower risk HF1α subtype observation is appropriate in lesions < 5 cm and may even be considered in larger lesions as longer follow-up data is aggregated and tumorigenesis is better understood.

Ablative therapies for hepatic and biliary tumors: endohepatology coming of age

Ablative therapies refer to minimally invasive procedures performed to destroy abnormal tissue that may arise with many conditions, and can be achieved clinically using chemical, thermal, and other techniques. In this review article, we explore the different ablative therapies used in the management of hepatic and biliary malignancies, namely hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), with a particular focus on radiofrequency ablation (RFA) and photodynamic therapy (PDT) techniques.

Curative-Intent Therapies in Localized Hepatocellular Carcinoma

PURPOSE OF REVIEW

The high mortality rate for hepatocellular carcinoma (HCC) relative to its prevalence underscores the need for curative-intent therapies. Image-guided therapies such as ablation and embolization have an established role as primary or neoadjuvants preparing patients for curative treatment.

RECENT FINDINGS

For HCC < 3 cm, percutaneous thermal ablation provides oncologic outcomes similar to surgical resection and is now a recommended first-line therapy in the EASL guidelines. Both ablation and embolization are recommended as bridging therapies for HCC patients awaiting liver transplantation. T3 HCC can be downstaged by embolization to T2, allowing liver transplantation with similar outcomes to patients transplanted within Milan criteria. New and evolving techniques such as SBRT, radiation segmentectomy and lobectomy, and combination therapies show promise but require further prospective data before they can be integrated into treatment algorithms. Combinations of embolic, ablative, and extirpative therapies can increase access to curative-intent treatment of HCC. Multidisciplinary treatment decisions are required to craft optimal treatment strategies considering tumor size, location, and underlying liver cirrhosis.

Thermal Ablation of Metastatic Colon Cancer to the Liver

Colorectal cancer (CRC) is responsible for approximately 10% of cancer-related deaths in the Western world. Liver metastases are frequently seen at the time of diagnosis and throughout the course of the disease. Surgical resection is often considered as it provides long-term survival; however, few patients are candidates for resection. Percutaneous ablative therapies are also used in the management of this patient population. Different thermal ablation (TA) technologies are available including radiofrequency ablation, microwave ablation (MWA), laser, and cryoablation. There is growing evidence about the role of interventional oncology and image-guided percutaneous ablation in the management of metastatic colorectal liver disease. This article aims to outline the technical considerations, outcomes, and rational of TA in the management of patients with CRC liver metastases, focusing on the emerging role of MWA.

Factors predicting ablation site recurrence following percutaneous microwave ablation of colorectal hepatic metastases

BACKGROUND

Microwave ablation (MWA) is a recognised treatment option for liver metastases. The size of the tumour is a well-established factor that influences the success of MWA. However, the effect of "heat sink" on the success of MWA for hepatic metastases is unclear. The aim of this study was to determine whether heat sink effect is a factor that contributes to ablation site recurrence (ASR).

METHODS

A prospectively maintained database of patients who underwent percutaneous MWA for treatment of colorectal liver metastases was analysed. Imaging and demographic characteristics were compared between metastases that recurred following ablation and those that did not. Proximity to a large hepatic vein was defined as <10 mm.

RESULTS

126 ablations in 87 patients met the inclusion criteria and were studied over a median follow-up period of 28 (12-75) months. ASR was detected in 43 ablations (34%) and was associated with clinical risk score (CRS) ≥2 (OR 2.2 95% CI 1.3-3.3, p = 0.029), metastasis size (OR 0.953 95% CI (0.929-0.978), p < 0.001) and proximity to a large hepatic vein (OR 7.5 95%CI 2.4-22.8, p < 0.001). Proximity to a large hepatic vein was not associated with reduced overall survival (OS) but was associated with liver-specific recurrence (HR 4.7 95%CI 1.7-12.5, p = 0.004).

CONCLUSIONS

In addition to tumour size proximity to large hepatic venous structures is an independent predictor of ASR and liver-specific recurrence following MWA. However, this was not associated with overall survival.

Veterinary Clinics: Tumor Ablation

Over the past decade, interventional oncology techniques have become integrated into the treatment plans of companion animals with cancer on a regular basis. Although procedures such as stenting are performed commonly, other less frequently utilized techniques for locoregional therapy, such as embolization and ablation, are emerging and demonstrating promise. Tumor ablation techniques are categorized into two subgroups: chemical ablation and energy-based ablation. Increased utilization of ablation will allow for the determination of specific indications and evaluation of outcomes for these techniques.

Local treatment of oligometastatic disease: current role

The presence of distant metastases has long been a predictor of poor outcome in solid cancer. However, in an oncologic situation called oligometastatic disease (OMD), multiple studies have revealed a survival benefit with aggressive treatment of these metastases. Besides surgery and radiation therapy, local thermal therapies have developed into a treatment option for OMD. Most studies concerning local therapy of OMD are available for colorectal cancer, which is therefore the focus of this article. Furthermore, this review gives a basic overview of the most popular ablation techniques for treatment of OMD.

Monitoring Thermal Ablation via Microwave Tomography: An Ex Vivo Experimental Assessment

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances.

Percutaneous thermal ablation combined with TACE versus TACE monotherapy in the treatment for liver cancer with hepatic vein tumor thrombus: A retrospective study

Purpose

To investigate the efficacy of percutaneous thermal ablation combined with transarterial chemoembolization (TACE) versus TACE monotherapy in treating primary liver cancer with hepatic vein tumor thrombus (HVTT), and to identify potential factors of overall survival after combination therapy.

Materials and methods

Patients with primary liver cancer and HVTT from 2011 to 2016 at our institute were retrospectively identified. They were divided into two groups (group A and group B). Patients in group A underwent TACE with subsequent percutaneous thermal ablation, while patients in group B who were unsuitable for ablation received TACE monotherapy. Characteristics and survival data of the two groups were analyzed and compared. Relevant factors for overall survival (OS) of group A were explored by univariate analysis.

Results

Twenty-six patients were included and analyzed. The median OS for group A (n = 13) was 18 months, while the 1-, 2- and 3-year survival rates were 58.6%, 46.9% and 46.9%, respectively. The median OS for group B (n = 13) was 6.5 months and the 1-year survival rate was 10.9%. The survival of group A was significantly better than group B (P = 0.02). The following factors were related with overall survival of group A: ablation technique, complete response of tumor and HVTT, Child-pugh grade, pre-operative extrahepatic metastases and lymph node metastases. In group A, patients who achieved complete response had the longest average survival time (42.1 months).

Conclusion

For patients with primary liver cancer and HVTT, percutaneous thermal ablation and TACE present better efficacy than TACE monotherapy. Long-term survival could be achieved in selected patients.

Percutaneous Ablation for Hepatocellular Carcinoma: Comparison of Various Ablation Techniques and Surgery

Image-guided percutaneous ablation is considered best in the treatment of early-stage hepatocellular carcinoma (HCC). Ablation is potentially curative, minimally invasive, and easily repeatable for recurrence. Ethanol injection used to be the standard in ablation. However, radiofrequency ablation has recently been the most prevailing ablation method for HCC. Many investigators have reported that radiofrequency ablation is superior to ethanol injection, from the viewpoints of treatment response, local tumor curativity, and overall survival. New-generation microwave ablation can create a larger ablation volume in a shorter time period. Further comparison studies are, however, mandatory between radiofrequency ablation and microwave ablation, especially in terms of complications and long-term survival. Irreversible electroporation, which is a non-thermal ablation method that delivers short electric pulses to induce cell death due to apoptosis, requires further studies, especially in terms of long-term outcomes. It is considerably difficult to compare outcomes in ablation with those in surgical resection. However, radiofrequency ablation seems to be a satisfactory alternative to resection for HCC 3 cm or smaller in Child-Pugh class A or B cirrhosis. Furthermore, radiofrequency ablation may be a first-line treatment in HCC 2 cm or smaller in Child-Pugh class A or B cirrhosis. Various innovations would further improve outcomes in ablation. Training programs may be effective in providing an excellent opportunity to understand basic concepts and learn cardinal skills for successful ablation. Sophisticated ablation would be more than an adequate alternative of surgery for small- and possibly middle-sized HCC.

The Performance of Higher Frequency Microwave Ablation in the Presence of Perfusion

OBJECTIVE

In this paper, we investigate the impact of perfusion on the performance of microwave ablation across a large frequency range.

METHODS

We designed multiple microwave ablation antennas to operate in liver tissue at discrete frequencies in the range 1.9-18 GHz. We performed electromagnetic simulations to calculate microwave power absorption patterns. Five-minute, 25 W ablation experiments were performed at each frequency in perfused and nonperfused ex vivo porcine livers, and thermal lesion dimensions were measured.

RESULTS

The volume of greatest microwave power absorption shrinks by two orders of magnitude as the frequency is increased from 1.9 to 18 GHz. Mean thermal lesion volumes are consistent across the frequency range for a given perfusion state and are about three times smaller under active perfusion. Typical thermal lesion diameters (perpendicular to the antenna axis) were 24 mm and 16 mm for nonperfused and perfused ablations, respectively. No significant differences in axial ratio were observed among different frequency groups in active-perfusion experiments.

CONCLUSION

Higher-frequency microwave ablation produces thermal lesions with volumes comparable to those achieved at lower frequencies, even in strongly perfused environments.

SIGNIFICANCE

Higher-frequency microwave ablation is appealing because it allows for more flexibility in antenna design. A critical issue concerning the feasibility of higher frequency microwave ablation, considering its strong dependence on heat diffusion to grow thermal lesions, is its performance in strongly perfused environments. This paper shows that higher frequency microwave ablation achieves thermal lesions comparable to those from microwave ablation performed at conventional frequencies in both non- and strongly perfused environments.

Effect of Change in Portal Venous Blood Flow Rates on the Performance of a 2.45-GHz Microwave Ablation Device

PURPOSE

To investigate the effect of change in portal venous blood flow rates on the size and shape of ablations created by a 2.45-GHz microwave ablation device.

MATERIALS AND METHODS

This study was exempt from review by the institutional animal care and use committee. An in vitro bovine liver model perfused with autologous blood via the portal vein at five flow rates (60, 70, 80, 90, and 100 mL/min per 100 g of liver) was used to evaluate the effect of change in flow rates on the size and shape of coagulation created by a 2.45-GHz, 140-W microwave ablation device operated for 5 and 10 minutes. Three ablations per ablation time were conducted in each of 10 livers, with two livers perfused at each flow rate. Short- and long-axis diameters were measured from gross specimens, and volume and sphericity index were calculated. General linear mixed models that accounted for correlations within the liver were used to evaluate the effects of lobe, flow, and ablation time on size and sphericity index of ablations.

RESULTS

Flow did not have a significant effect on the size or shape of coagulation created at 5 or 10 minutes (P > .05 for all tests). The mean short- and long-axis diameters and volume were 3.2 cm (95% confidence interval [CI]: 3.1, 3.3), 5.6 cm (95% CI: 5.4, 5.8), and 30.2 cm(3) (95% CI: 28.4, 32.1) for the 5-minute ablations and 3.8 cm (95% CI: 3.7, 3.9), 6.5 cm (95% CI: 6.3, 6.7), and 49.3 cm(3) (95% CI: 47.5, 51.2), for the 10-minute ablations, respectively. The mean sphericity index for both 5- and 10-minute ablations was 34.4% (95% CI: 32%, 36.7%).

CONCLUSION

Change in portal venous blood flow rates did not have an effect on the size and shape of ablations created by a 2.45-GHz microwave ablation device.

Ultrasound-guided percutaneous microwave ablation of sporadic renal angiomyolipoma: preliminary results

BACKGROUND

Microwave ablation (MWA) has been developed as one of the most commonly used local oncologic treatments. However, there is still a dearth of studies concerning MWA in the treatment of renal angiomyolipomas (AML).

PURPOSE

To evaluate the efficacy and safety of ultrasound (US)-guided percutaneous MWA when treating AML.

MATERIAL AND METHODS

Nineteen lesions with pathologically confirmed AML in 14 patients (5 men, 9 women; mean age, 49.2 ± 14 years) were treated with US-guided percutaneous MWA with one or two cooled-shaft needle antennae. A power output of 45 W or 50 W for 300-1140 s was emitted to achieve complete tumor necrosis. Contrast-enhanced ultrasound (CEUS) was performed to observe the treatment efficacy 3 days later. Patients were followed up with CEUS, computed tomography (CT), and/or magnetic resonance imaging (MRI) after 1, 3, and 6 months, and long-term ablation efficacy was evaluated every 6 months thereafter.

RESULTS

Among the 19 renal lesions, 17 achieved complete ablation as monitored by US after one session of MWA, and two patients required a second session of MWA. Postoperative evaluation with CEUS showed that complete ablation was obtained in 15 lesions; however, in four lesions, complete ablation could not be attained. During the follow-up period of 6-36 months (median, 10 months), a fistula to the descending colon was found in one patient and local infection around the ablation zone was found in another. Neither injury to the renal pelvis nor damage to renal function was observed. None of the patients exhibited hematuria or abnormalities in routine urine tests during the hospitalization period or during follow-up. Minor complications, such as subcapsular bleeding, mild to moderate pain, and fever were eliminated after appropriate treatment.

CONCLUSION

MWA is an effective and minimally invasive technique for the management of AML that can preserve renal function with acceptable complication rates.

Percutaneous microwave ablation of hepatocellular carcinoma with a gas-cooled system: initial clinical results with 107 tumors

PURPOSE

To retrospectively review the results of hepatocellular carcinoma (HCC) treatment with a high-power, gas-cooled, multiantenna-capable microwave device.

MATERIALS AND METHODS

A total of 107 HCCs in 75 patients (65 men) with a mean age of 61 years (range, 44-82 y) were treated via percutaneous approach. Combination microwave ablation and transarterial chemoembolization was performed for 22 tumors in 19 patients with tumors larger than 4 cm (n = 10), tumors larger than 3 cm with ill-defined margins (n = 7), or lesions not identified with ultrasonography (n = 5). Mean tumor size was 2.1 cm (range, 0.5-4.2 cm), with median follow-up of 14 months, for ablation alone; compared with 3.7 cm (range, 1.0-7.0 cm) and 12 months, respectively, for combination therapy. All procedures were performed with a single microwave system (Certus 140) with one to three 17-gauge antennas.

RESULTS

Mean ablation time was 5.3 minutes (range, 1-11.5 min). All treatments were considered technically successful in a single session. Primary technique effectiveness rates were 91.6% (98 of 107) overall, 93.7% (89 of 95) for tumors 4 cm or smaller, and 75.0% (nine of 12) for tumors larger than 4 cm; and 91.8% (78 of 85) for ablation alone and 90.9% (20 of 22) for combination therapy. There was no major complication or procedure-related mortality. The overall survival rate was 76.0% at a median 14-month clinical follow-up, with most deaths related to end-stage liver disease (n = 11) or multifocal HCC (n = 5).

CONCLUSIONS

Treating HCC with a gas-cooled, multiantenna-capable microwave ablation device is safe, with promising treatment effectiveness.

Creation of short microwave ablation zones: in vivo characterization of single and paired modified triaxial antennas

PURPOSE

To characterize modified triaxial microwave antennas configured to produce short ablation zones.

MATERIALS AND METHODS

Fifty single-antenna and 27 paired-antenna hepatic ablations were performed in domestic swine (N = 11) with 17-gauge gas-cooled modified triaxial antennas powered at 65 W from a 2.45-GHz generator. Single-antenna ablations were performed at 2 (n = 16), 5 (n = 21), and 10 (n = 13) minutes. Paired-antenna ablations were performed at 1-cm and 2-cm spacing for 5 (n = 7 and n = 8, respectively) and 10 minutes (n = 7 and n = 5, respectively). Mean transverse width, length, and aspect ratio of sectioned ablation zones were measured and compared.

RESULTS

For single antennas, mean ablation zone lengths were 2.9 cm ± 0.45, 3.5 cm ± 0.55, and 4.2 cm ± 0.40 at 2, 5, and 10 minutes, respectively. Mean widths were 1.8 cm ± 0.3, 2.0 cm ± 0.32, and 2.5 cm ± 0.25 at 2, 5, and 10 minutes, respectively. For paired antennas, mean length at 5 minutes with 1-cm and 2-cm spacing and 10 minutes with 1-cm and 2-cm spacing was 4.2 cm ± 0.9, 4.9 cm ± 1.0, 4.8 cm ± 0.5, and 4.8 cm ± 1.3, respectively. Mean width was 3.1 cm ± 1.0, 4.4 cm ± 0.7, 3.8 cm ± 0.4, and 4.5 cm ± 0.7, respectively. Paired-antenna ablations were more spherical (aspect ratios, 0.72-0.79 for 5-10 min) than single-antenna ablations (aspect ratios, 0.57-0.59). For paired-antenna ablations, 1-cm spacing appeared optimal, with improved circularity and decreased clefting compared with 2-cm spacing (circularity, 0.85 at 1 cm, 0.78 at 2 cm).

CONCLUSIONS

Modified triaxial antennas can generate relatively short, spherical ablation zones. Paired-antenna ablations were rounder and larger in transverse dimension than single antenna ablations, with 1-cm spacing optimal for confluence of the ablation zone.

Tumor ablation: common modalities and general practices

Tumor ablation is a minimally invasive technique that is commonly used in the treatment of tumors of the liver, kidney, bone, and lung. During tumor ablation, thermal energy is used to heat or cool tissue to cytotoxic levels (less than -40°C or more than 60°C). An additional technique is being developed that targets the permeability of the cell membrane and is ostensibly nonthermal. Within the classification of tumor ablation, there are several modalities used worldwide: radiofrequency, microwave, laser, high-intensity focused ultrasound, cryoablation, and irreversible electroporation. Each technique, although similar in purpose, has specific and optimal indications. This review serves to discuss general principles and technique, reviews each modality, and discusses modality selection.

Microwave ablation of hepatic malignancy

Microwave ablation is an extremely promising heat-based thermal ablation modality that has particular applicability in treating hepatic malignancies. Microwaves can generate very high temperatures in very short time periods, potentially leading to improved treatment efficiency and larger ablation zones. As the available technology continues to improve, microwave ablation is emerging as a valuable alternative to radiofrequency ablation in the treatment of hepatic malignancies. This article reviews the current state of microwave ablation including technical and clinical considerations.

Mean scatterer spacing estimation in normal and thermally coagulated ex vivo bovine liver

The liver has been hypothesized to have a unique arrangement of microvasculature that presents as an arrangement of quasiperiodic scatterers to an interrogating ultrasound pulse. The mean scatterer spacing (MSS) of these quasiperiodic scatterers has been proposed as a useful quantitative ultrasound biomarker for characterizing liver tissue. Thermal ablation is an increasingly popular method for treating hepatic tumors, and ultrasonic imaging approaches for delineating the extent of thermal ablation are in high demand. In this work, we examine the distribution of estimated MSS in thermally coagulated bovine liver and normal untreated bovine liver ex vivo. We estimate MSS by detecting local maxima in the spectral coherence function of radio frequency echoes from a clinical transducer, the Siemens VFX 9L4 transducer operating on an S2000 scanner. We find that normal untreated bovine liver was characterized by an MSS of approximately 1.3 mm. We examined regions of interest 12 mm wide laterally, and ranging from 12 mm to 18 mm axially, in 2 mm increments. Over these parameters, the mode of the MSS estimates was between 1.25 and 1.37 mm. On the other hand, estimation of MSS in thermally coagulated liver tissue yields a distribution of MSS estimates whose mode varied between 0.45 and 1.0 mm when examining regions of interest over the same sizes. We demonstrate that the estimated MSS in thermally coagulated liver favors small spacings because the randomly positioned scatterers in this tissue are better modeled as aperiodic scatterers. The submillimeter spacings result from the fact that this was the most probable spacing to be estimated if the discretely sampled spectral coherence function was a uniformly random two-dimensional function.

High-powered gas-cooled microwave ablation: shaft cooling creates an effective stick function without altering the ablation zone

OBJECTIVE

The purpose of our study was to validate the ability of a new gas-cooled microwave device to secure antennas into tissue before ablation via shaft cooling and to verify that such cooling does not compromise the intended ablation.

MATERIALS AND METHODS

The force required to extract several types of applicators from ex vivo bovine liver before and after ablation was measured. Six groups were compared: cooled needle and multitined radiofrequency electrodes, secured and unsecured cryoprobes, and gas-cooled microwave antennas (n = 6 each). Ablations were next created in in vivo porcine livers for 2 and 10 minutes (n = 6 each) using the gas-cooled microwave system at 140 W. Extraction force was again measured before and after ablation and compared between groups using analysis of variance with post hoc Student t tests. Histologic analysis of the ablation zone was performed to evaluate cellular necrosis along the antenna shaft.

RESULTS

Ex vivo, the secured cryoprobe and microwave antenna required significantly more force to remove than unsecured radiofrequency, cryoprobe, and microwave applicators (p < 0.05, all comparisons). The multitined radiofrequency electrode and cooled radiofrequency electrode required significantly more force to remove after ablation than before ablation (p = 0.006 and 0.02, respectively). In vivo, the secured antenna required significantly more force to remove before ablation than after ablation at both 2 (p < 0.0001) and 10 minutes (p < 0.0001). There was no histologic evidence of cell preservation along the antenna shaft.

CONCLUSION

The gas cooling used in this microwave device can effectively secure antennas into tissue without altering ablation shape or reducing the intended thermal damage.

High-powered microwave ablation with a small-gauge, gas-cooled antenna: initial ex vivo and in vivo results

PURPOSE

To evaluate the performance of a gas-cooled, high-powered microwave system.

MATERIALS AND METHODS

Investigators performed 54 ablations in ex vivo bovine livers using three devices-a single 17-gauge cooled radiofrequency(RF) electrode; a cluster RF electrode; and a single 17-gauge, gas-cooled microwave (MW) antenna-at three time points (n = 6 at 4 minutes, 12 minutes, and 16 minutes). RF power was applied using impedance-based pulsing with maximum 200 W generator output. MW power of 135 W at 2.45 GHz was delivered continuously. An approved in vivo study was performed using 13 domestic pigs. Hepatic ablations were performed using single applicators and the above-mentioned MW and RF generator systems at treatment times of 2 minutes (n = 7 MW, n = 6 RF), 5 minutes (n = 23 MW, n = 8 RF), 7 minutes (n = 11 MW, n = 6 RF), and 10 minutes (n = 7 MW, n = 9 RF). Mean transverse diameter and length of the ablation zones were compared using analysis of variance (ANOVA) with post-hoc t tests and Wilcoxon rank-sum tests.

RESULTS

Single ex vivo MW ablations were larger than single RF ablations at all time points (MW mean diameter range 3.5-4.8 cm 4-16 minutes; RF mean diameter range 2.6-3.1 cm 4-16 minutes) (P < .05). There was no difference in mean diameter between cluster RF and MW ablations (RF 3.3-4.4 cm 4-16 minutes; P = .4-.9). In vivo lesion diameters for MW (and RF) were as follows: 2.6 cm ± 0.72 (RF 1.5 cm ± 0.14), 3.6 cm ± 0.89 (RF 2.0 cm ± 0.4), 3.4 cm ± 0.87 (RF 1.8 cm ± 0.23), and 3.8 cm ± 0.74 (RF 2.1 cm ± 0.3) at 2 minutes, 5 minutes, 7 minutes, and 10 minutes (P < .05 all time points).

CONCLUSIONS

Gas-cooled, high-powered MW ablation allows the generation of large ablation zones in short times.

Microwave thermal ablation for hepatocarcinoma: six liver transplantation cases

Surgical resection for malignant hepatic tumors, especially hepatocarcinoma (HCC), has been demonstrated to increase overall survival; however, the majority of patients are not suitable for resection. Radiofrequency ablation (RFA) is the most widely used modality for radical treatment of small HCC (<3 cm). It improves 5-year survival compared with standard chemotherapy and chemical ablation, allowing down-staging of unresectable hepatic masses. Microwave ablation (MWA) has been extensively applied in Asia and was recently introduced in the United States of America and Europe with excellent results, especially with regard to large unresectable HCC. Our single-center experience between May 2009 and October 2010 included application of MWA to 154 patients of median age ± standard deviation of 63.5 ± 8.5 years, 6 males, and 1 female, of mean Model for End-Stage Liver Disease (MELD) score (10.1 ± 3.8). The HCC included, hepatitis C virus (HCV)-related (n=70; 45.5%); alcool (ETOH)-related (n=42; 27%), hepatitis B virus (HBV)-related (n=16; 10.5%); and cryptogenic cases (n=26; 17%). The cases were performed for radical treatment down-staging for multifocal pathology or bridging liver transplantation to orthotopic (OLT) in selected patients with single nodules. A computed tomography (CT) scan was performed at 1 month after the surgical procedure to evalue responses to treatment. Among 6 selected patients who underwent OLT; 5 (83.3%) showed disease-free survival at one-year follow-up. The radical treatment achieved no intraoperative evidence of tumor spread or of pathological signs of active HCC among the explanted liver specimens. In conclusion, a MWA seemed to be a safe novel approach to treat HCC and could serve as a "bridge" to OLT and down-staging for patients with HCC.

Principles of and advances in percutaneous ablation

Image-guided tumor ablation with both thermal and nonthermal sources has received substantial attention for the treatment of many focal malignancies. Increasing interest has been accompanied by continual advances in energy delivery, application technique, and therapeutic combinations with the intent to improve the efficacy and/or specificity of ablative therapies. This review outlines clinical percutaneous tumor ablation technology, detailing the science, devices, techniques, technical obstacles, current trends, and future goals in percutaneous tumor ablation. Methods such as chemical ablation, cryoablation, high-temperature ablation (radiofrequency, microwave, laser, and ultrasound), and irreversible electroporation will be discussed. Advances in technique will also be covered, including combination therapies, tissue property modulation, and the role of computer modeling for treatment optimization.

Microwave tumor ablation: mechanism of action, clinical results, and devices

Microwave ablation uses dielectric hysteresis to produce direct volume heating of tissue. Microwaves are capable of propagating through many tissue types, even those with high impedance such as lung or bone, with less susceptibility to "heat-sink" effects along vessels. Microwaves are highly conducive to the use of multiple applicators, showing the synergy seen with other energies, but also the potential capability for phasing of the electromagnetic field. As a result, larger, more customizable ablation zones may be created in less time. Although multiple microwave ablation systems are currently available, further study and continued development are needed.

Comparison of percutaneous 915 MHz microwave ablation and 2450 MHz microwave ablation in large hepatocellular carcinoma

PURPOSE

To compare the effectiveness of ultrasound (US)-guided percutaneous 915 MHz microwave (MW) ablation with the 2450 MHz MW ablation for large hepatocellular carcinoma (HCC) (>4 cm in diameter).

MATERIALS AND METHODS

Patients with HCC >4 cm in diameter who underwent US-guided percutaneous MW ablation with curative intention between March 2007 and December 2008 (39) were randomly divided into two groups, 915 MHz MW group and 2450 MHz MW group. We compared the results of ablation between the two groups.

RESULTS

Fewer antenna insertions for each tumour were required in the 915 MHz MW group (3.69 +/- 0.6) than in the 2450 MHz MW group (4.71 +/- 1.61) (p = 0.01). According to the follow-up contrast-enhanced imagings, technique effectiveness rate was 85.7% (18/21) and 73.7% (14/19) in the 915 MHz MW group and 2450 MHz MW group, respectively (p = 0.44). The rate of local tumour progression (LTP) was 14.3% (3/21) and 26.3% (5/19) in the 915 MHz MW group and 2450 MHz MW group, respectively (p = 0.44). There were no deaths and no thrombosis of major vessels in any patient.

CONCLUSIONS

Compared with 2450 MHz MW ablation, our initial experience showed that percutaneous 915 MHz MW ablation with cooled-shaft antennae was safe and could achieve a high technique effectiveness rate with fewer insertion numbers in the treatment of large HCC. Therefore, percutaneous 915 MHz MW ablation may provide a new method for the treatment of large HCC.

Microwaves create larger ablations than radiofrequency when controlled for power in ex vivo tissue

PURPOSE

To compare ablation zones created with equal amounts of 2.45 GHz microwave and 480 kHz radiofrequency (RF) energy in ex vivo liver and lung.

METHODS

A total of 38 ablations were performed in ex vivo liver and lung for 10 min each. Nineteen RF ablations (nine liver, ten lung) were performed with a 480 kHz system (200 W max, impedance-based pulsing) and cooled electrode while measuring the average RF power applied. Nineteen microwave ablations (nine liver, ten lung) were then created using a cooled triaxial antenna to deliver 2.45 GHz at the same power level as in RF experiments. Ablation zones were then sectioned and measured for minimum, maximum and mean diameters, and circularity. Measurements were compared using t-tests, with P < 0.05 indicating statistical significance.

RESULTS

Mean diameters of microwave ablations were greater than RF ablations in both liver and lung (4.4 +/- 0.3 vs 3.3 +/- 0.2 cm in liver; 2.45 +/- 0.3 vs 1.6 +/- 0.5 cm in lungs; P < 0.0005 all comparisons). There was no significant difference in the mean power applied during microwave or RF ablations in either organ (54.44 +/- 1.71 W vs 56.4 +/- 6.7 W in liver, P > 0.05; 40 +/- 0.95 W vs 44.9 +/- 7.1 W in lung, P > 0.05).

CONCLUSIONS

Using a single cooled applicator, microwave energy at 2.45 GHz produces larger ablations than an equivalent amount of 480 kHz RF energy in normal liver and lung. This was more apparent in lung, likely due to the high baseline impedance which limits RF, but not microwave power delivery.

Microwave ablation: An experimental comparative study on internally cooled antenna versus non-internally cooled antenna in liver models

RATIONAL AND OBJECTIVES

Microwave ablation is an alternative therapy with high cost-effectiveness for liver malignancy. The authors designed this experiment to compare the effect of microwave ablation using a non-internally cooled (NIC) antenna with that using an internally cooled (IC) antenna in both an ex vivo and an in vivo liver models.

MATERIALS AND METHODS

Sixty-two microwave ablations were performed in ex vivo porcine and in vivo canine liver models (NIC antenna, 28 coagulations; IC antenna, 34 coagulations). Pair comparisons were executed in terms of the coagulation parameters, including short-axis diameter (SD), long-axis diameter (LD), and spherical ratio (SR, SD/LD). The distributions of tissue temperatures were compared in ex vivo ablation. During in vivo ablation, the temperatures of antenna shaft were measured and unintended tissue coagulation were observed and compared.

RESULTS

In both ex vivo and in vivo ablations, less charring areas were found around the IC antenna shaft. With a longer SD (P < .01) and a shorter LD (P < .01), the coagulations of IC antenna appeared to be more spherical than those of NIC antenna (P < .01). During ablations in vivo, the temperatures of NIC antennas shaft were up to 90 degrees C or even higher, which resulted in some unintended tissue coagulation, whereas the temperatures of IC antennas shaft were lower than 20 degrees C in all ablation processes without any unintended tissue coagulation (P < .01).

CONCLUSION

The IC antenna performed better than NIC antenna in microwave ablation for liver models and might be more suitable for therapy for liver malignancy in clinical practice.

Tissue contraction caused by radiofrequency and microwave ablation: a laboratory study in liver and lung

PURPOSE

To determine the amount of tissue contraction during radiofrequency (RF) and microwave ablation.

MATERIALS AND METHODS

Markers were inserted into explanted bovine liver and lung 10 mm (inner), 20 mm (middle; not used in lung), and 30 mm (peripheral) diametrically around an ablation applicator. Aside from unablated controls, RF and microwave ablations 25-30 mm in diameter were then created and sectioned to measure the distance between markers (n = 12, liver RF; n = 8, other). Total contraction was calculated by subtracting postablation measurements from controls at each position. Relative contraction was calculated by subtracting the nearest more central measurement. Sample water content was measured to determine the relationship between dehydration and relative contraction. A mixed-effects model tested for differences in diameters, total and relative contraction, and water content with energy, tissue, and marker position as independent variables.

RESULTS

Total contractions at the inner, middle, and peripheral positions in liver were 2.9 mm (31%), 4.8 mm (24%), and 4.5 mm (15%) for RF and 3.6 mm (38%), 6.6 mm (33%), and 9.0 mm (30%) for microwave, respectively. Significantly more contraction was noted in lung (P < .001): 5.1 mm (55%) and 14.2 mm (49%) for RF and 4.8 mm (52%) and 13.7 mm (47%) for microwave at the inner and peripheral positions, respectively. Microwaves produced more contraction than RF in liver (P < .05) but not in lung. A positive correlation between dehydration and relative contraction was observed in all cases.

CONCLUSIONS

Ablation-induced tissue contraction is substantial and influenced by dehydration. Contraction should be considered when testing devices and computer models or comparing pre- and postablation images.

Ultrasound-based relative elastic modulus imaging for visualizing thermal ablation zones in a porcine model

The feasibility of using ultrasound-based elastic modulus imaging to visualize thermal ablation zones in an in vivo porcine model is reported. Elastic modulus images of soft tissues are estimated as an inverse optimization problem. Ultrasonically measured displacement data are utilized as inputs to determine an elastic modulus distribution that provides the best match to this displacement field. A total of 14 in vivo thermal ablation zones were investigated in this study. To determine the accuracy of delineation of each thermal ablation zone using elastic modulus imaging, the dimensions (lengths of long and short axes) and the area of each thermal ablation zone obtained from an elastic modulus image were compared to the corresponding gross pathology photograph of the same ablation zone. Comparison of elastic modulus imaging measurements and gross pathology measurements showed high correlation with respect to the area of thermal ablation zones (Pearson coefficient = 0.950 and p < 0.0001). The radiological-pathological correlation was slightly lower (correlation = 0.853, p < 0.0001) for strain imaging among these 14 in vivo ablation zones. We also found that, on average, elastic modulus imaging can more accurately depict thermal ablation zones, when compared to strain imaging (14.7% versus 22.3% absolute percent error in area measurements, respectively). Furthermore, elastic modulus imaging also provides higher (more than a factor of 2) contrast-to-noise ratios for evaluating these thermal ablation zones than those on corresponding strain images, thereby reducing inter-observer variability. Our preliminary results suggest that elastic modulus imaging might potentially enhance the ability to visualize thermal ablation zones, thereby improving assessment of ablative therapies.

Theoretical Modeling for Hepatic Microwave Ablation

Thermal tissue ablation is an interventional procedure increasingly being used for treatment of diverse medical conditions. Microwave ablation is emerging as an attractive modality for thermal therapy of large soft tissue targets in short periods of time, making it particularly suitable for ablation of hepatic and other tumors. Theoretical models of the ablation process are a powerful tool for predicting the temperature profile in tissue and resultant tissue damage created by ablation devices. These models play an important role in the design and optimization of devices for microwave tissue ablation. Furthermore, they are a useful tool for exploring and planning treatment delivery strategies. This review describes the status of theoretical models developed for microwave tissue ablation. It also reviews current challenges, research trends and progress towards development of accurate models for high temperature microwave tissue ablation.

Theoretical modeling for hepatic microwave ablation

Thermal tissue ablation is an interventional procedure increasingly being used for treatment of diverse medical conditions. Microwave ablation is emerging as an attractive modality for thermal therapy of large soft tissue targets in short periods of time, making it particularly suitable for ablation of hepatic and other tumors. Theoretical models of the ablation process are a powerful tool for predicting the temperature profile in tissue and resultant tissue damage created by ablation devices. These models play an important role in the design and optimization of devices for microwave tissue ablation. Furthermore, they are a useful tool for exploring and planning treatment delivery strategies. This review describes the status of theoretical models developed for microwave tissue ablation. It also reviews current challenges, research trends and progress towards development of accurate models for high temperature microwave tissue ablation.