Microwave ablation: results with double 915 MHz antennae in ex vivo bovine livers

Real-time Monitoring of Contrast-enhanced Ultrasound for Radio Frequency Ablation

Background

This study compared the realtime monitoring effects of conventional ultrasound and contrast-enhanced ultrasound (CEUS) on evaluating radio frequency ablation (RFA) in a living swine liver model.

Methodology

Liver RFA was performed on 10 young swine. Conventional ultrasound and CEUS were performed immediately. After the animals were sacrificed, ablation lesions were removed to histopathologically examine the range of the lesions. Ablation completeness based on three methods were compared using histopathology as the gold standard.

Results

Forty-three ablation lesions were produced in the animals. The horizontal diameter, vertical diameter and ablation lesion area based on conventional ultrasound were all significantly smaller than those based on the gross sample, but no significant differences existed between the results of the CEUS and the gross sample. Histopathology showed that 30 lesions were incompletely ablated and 13 were completely ablated, while CEUS showed that 28 lesions were incompletely ablated and 15 were completely ablated. Compared with histopathology, CEUS had an accuracy of 81.4%, a sensitivity of 83.3%, and a specificity of 76.9%. No significant difference in ablation completeness judgment between CEUS and histopathology was observed.

Conclusion

CEUS provides a real-time radiological foundation for evaluating RFA lesion ranges and completeness in a living swine liver model.

In vivo percutaneous microwave ablation in kidneys: Correlation with ex vivo data and ablation work

PURPOSE

To compare diameters of in vivo microwave ablation (MWA) performed in swine kidneys with ex vivo diameters, and to correlate with ablation work (AW), a new metric reflecting total energy delivered.

MATERIAL AND METHODS

Eighteen in vivo MWA were performed in 6 swine kidneys successively using one or two antennas (MicroThermX^®). Ablation consisted in delivering power (45-120W) for 5-15minutes. Ex vivo diameters were provided by the vendors and obtained on bovine liver tissue. AW was defined as the sum of (power)*(time)*(number of antennas) for all phases of an ablation (in kJoules). Kidneys were removed laparoscopically immediately after ablation. After sacrifice, ablations zones were evaluated macroscopically, and maximum diameters of the zones were recorded. Wilcoxon sum rank test and Pearson's correlation were used for comparisons.

RESULTS

For a single antenna (n=12), the in vivo diameters ranged from 12 to 35mm, and 15-49mm for 2 antennas (n=6). The in vivo diameters remained shorter than ex vivo diameters by 8.6%±30.1 on 1 antenna and 11.7%±26.5 on 2 antennas (P=0.31 and 0.44, respectively). AW ranged from 13.5 to 108kJ. Diameters increased linearly with AW both with 1 and 2 antennas, but only moderate correlations were observed (r=0.43 [95% confidence interval: -0.19; 0.81], P=0.16; and 0.57 [-0.44; 0.95], P=0.24, respectively).

CONCLUSION

Although diameters after in vivo renal MWA increased linearly with AW, the moderate correlation and wide standard deviations observed may justify a careful imaging monitoring during treatment delivery and settings adaptation, if needed, for optimal ablation.

Use of Percutaneous Sonographically Guided Microwave Ablation Therapy to Treat Inoperable Malignant Liver Tumours

AIMS

Microwave ablation (MWA) is a technique which is used to destroy tumours and soft tissues by using microwave energy to create coagulation and localized tissue necrosis. It is used to treat the tumours which are considered to be inoperable and used to treat those patients who are ineligible for surgery due to some factors. The main objective of this study was to evaluate the use of MWA in the treatment of liver cancer.

METHODS

The data were collected from Department of Ultrasound, Harbin Medical University Cancer Hospital. From July 2010 to August 2011, a total of 123 patients with liver tumours was referred to Harbin Medical University Cancer Hospital. One hundred patients were selected for this study and treated with MWA. The study group contained 64 (64%) males and 36 (36%) females with an average age (± SD) of 52 (± 5.1) years.

RESULTS

One month after therapy, complete ablation was obtained in nodules. The complete ablation rate in tumors ≤ 3 cm and those > 3 cm was 98% and 94%, respectively. Microwave ablation success was higher with nodules ≤ 3 cm (57/58; 98.3%) in comparison to nodules > 3 cm.

CONCLUSION

Sonographically guided percutaneous microwave ablation proved to be safe, fast and effective for treatment of hepatocellular carcinoma.

Microwave ablation: state-of-the-art review

This paper reviews state-of-the-art microwave ablation (MWA) of tumors. MWA is a novel method for treating inoperable tumors, ie, tumors that cannot be treated surgically. However, patients generally choose removal of the tumor by conventional techniques. A literature review of MWA for breast, liver, lung, and kidney tumors is reported here, with tabulation of our findings according to the type of technique used, with a detailed description of the time, type of microwave generator used, and number of patients treated with MWA. In some cases, the subjects were not human patients, but pig or bovine liver specimens. MWA is a technique that has proved to be promising and likely to be used increasingly in the ablation of cancerous tumors. However, MWA needs to be used more widely to establish itself as a common tool in the treatment of inoperable tumors.

Percutaneous microwave ablation vs radiofrequency ablation in the treatment of hepatocellular carcinoma

Hepatocellular cancer ranks fifth among cancers and is related to chronic viral hepatitis, alcohol abuse, steatohepatitis and liver autoimmunity. Surgical resection and orthotopic liver transplantation have curative potential, but fewer than 20% of patients are suitable candidates. Interventional treatments are offered to the vast majority of patients. Radiofrequency (RFA) and microwave ablation (MWA) are among the therapeutic modalities, with similar indications which include the presence of up to three lesions, smaller than 3 cm in size, and the absence of extrahepatic disease. The therapeutic effect of both methods relies on thermal injury, but MWA uses an electromagnetic field as opposed to electrical current used in RFA. Unlike MWA, the effect of RFA is partially limited by the heat-sink effect and increased impedance of the ablated tissue. Compared with RFA, MWA attains a more predictable ablation zone, permits simultaneous treatment of multiple lesions, and achieves larger coagulation volumes in a shorter procedural time. Major complications of both methods are comparable and infrequent (approximately 2%-3%), and they include haemorrhage, infection/abscess, visceral organ injury, liver failure, and pneumothorax. RFA may incur the additional complication of skin burns. Nevertheless, there is no compelling evidence for differences in clinical outcomes, including local recurrence rates and survival.

Practice guidelines for ultrasound-guided percutaneous microwave ablation for hepatic malignancy

Primary liver cancer and liver metastases are among the most frequent malignancies worldwide, with an increasing number of new cases and deaths every year. Traditional surgery is only suitable for a limited proportion of patients and imaging-guided percutaneous thermal ablation has achieved optimistic results for management of hepatic malignancy. This synopsis outlines the first clinical practice guidelines for ultrasound-guided percutaneous microwave ablation therapy for hepatic malignancy, which was created by a joint task force of the Society of Chinese Interventional Ultrasound. The guidelines aim at standardizing the microwave ablation procedure and therapeutic efficacy assessment, as well as proposing the criteria for the treatment candidates.

Comparison of ablation zones among different tissues using 2450-MHz cooled-shaft microwave antenna: results in ex vivo porcine models

Background

For complete tumor ablation in different tissues, it is necessary to investigate the exact coagulation zone of microwave ablation in different tissues. The aim of this study was to compare the extent of microwave ablation zone in muscle, liver and adipose tissue in ex vivo porcine models and assess the shape of microwave coagulation zone among these tissues.

Materials and Methods

Microwave ablations were performed in ex vivo porcine muscle, liver and adipose tissue using 2450-MHz cooled-shaft microwave antenna. The content of water, fat and protein in these three tissues was determined. Two power increments (40 and 80 W) and five time increments (1, 3, 5, 7, and 10 minutes) were used in this study. Diameters and shapes of the ablation zones were assessed on gross specimens.

Results

The average percentages of water, fat and protein in these three tissues were significantly different (P < 0.001), respectively. The long-axis and short-axis diameters among these three tissues at each time-power combination were not significantly different (P > 0.05). The coagulation zones were all elliptical in muscle, liver and adipose tissue. When microwave ablation was performed in the tissue containing both muscle and adipose tissue, the coagulation zone was also elliptical. Regardless of the output power, the ellipticity index (EI) value of 1 minute treatment duration was higher than that of 10 minutes treatment duration (P < 0.05). Furthermore, the EI value did not decrease significantly when the treatment duration was more than 5 minutes (P > 0.05).

Conclusion

The extent of microwave ablation zones was not significantly different among completely different tissues. Microwave ablations with ≥ 5 minutes time duration can induce coagulation zones with clinical desirable shape. Future clinical studies are still required to determine the role of microwave ablation in different tissues.

Preinjected fluids do not benefit microwave ablation as those in radiofrequency ablation

RATIONALE AND OBJECTIVES

To detect whether the efficacy of microwave ablation (MWA) could be improved by preinjected fluids in an ex vivo porcine liver model.

MATERIALS AND METHODS

Ablations were performed for 12 minutes using energy output of impedance-based (power output gradually rose to 200W, maintained until increases in tissue impedance of 20 Ω, reduced to 10W, and switched on again 15 seconds later) in radiofrequency ablation (RFA) or 80 W in MWA. Before ablation, 5 mL of ethanol, distilled water, 0.9% NaCl solution, or 10% NaCl solution (n = 6 each) was injected into the targeted liver tissue. Ablations without fluid injection served as control. The ablation diameter, volume, shape index, and temperature were recorded and compared.

RESULTS

Preinjection of 0.9% or 10% NaCl solution resulted in larger coagulation volumes than that of the control group in RFA experiments (28.1 ± 2.9 cm(3), 45.3 ± 6.3 cm(3), 20.0 ± 2.5 cm(3), respectively; P < .05). Ethanol and distilled water had no impact on coagulation volumes in RFA. Preinjection of ethanol or 10% NaCl solution created smaller coagulation volumes than that of the control group in MWA experiments (34.3 ± 2.0 cm(3), 33.9 ± 4.1 cm(3), 58.0 ± 6.6 cm(3), respectively; P < .001). 0.9% NaCl solution and distilled water had no impact on coagulation volumes in MWA.

CONCLUSION

In an ex vivo porcine liver, preinjected fluids do not benefit microwave ablation as those in radiofrequency ablation.