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Research Papers

Effect of Input Waveform Pattern and Large Blood Vessel Existence on Destruction of Liver Tumor Using Radiofrequency Ablation: Finite Element Analysis

[+] Author and Article Information
Dohyung Lim1

Gerontechnology Center, Korea Institute of Industrial Technology, Cheonan, Chungnam 330-825, Korea

Bumseok Namgung1

Division of Bioengineering, and Department of Surgery, National University of Singapore, Singapore 117574, Singapore; Department of Biomedical Engineering, and Research Institute for Medical Instruments and Rehabilitation Engineering, Yonsei University, Wonju, Gangwon 220-710, Korea

Dae Gon Woo, Han Sung Kim

Department of Biomedical Engineering, and Research Institute for Medical Instruments and Rehabilitation Engineering, Yonsei University, Wonju, Gangwon 220-710, Korea

Jin Seung Choi

Department of Biomedical Engineering, Konkuk University, Chungju, Chungbuk 380-701, Korea

Gye Rae Tack2

Department of Biomedical Engineering, Konkuk University, Chungju, Chungbuk 380-701, Koreadli349@gmail.com

1

Both authors contributed equally to this work as first author.

2

Corresponding author.

J Biomech Eng 132(6), 061003 (Apr 21, 2010) (8 pages) doi:10.1115/1.4001029 History: Received October 06, 2009; Revised January 12, 2010; Posted January 18, 2010; Published April 21, 2010; Online April 21, 2010

Much research has been directed at improving the effectiveness of the radiofrequency (RF) ablation of hepatocellular carcinomas. In that point of view, this study was performed to provide comprehensive information of the relation between RF waveforms and thermodynamic response of the tissue with the consideration of four different types of RF waveforms (half-sine, half-square, half-exponential, and damped-sine) to maximize the amount of tumor tissue removed while maintaining the advantages of RF ablation. For the aim of this study, finite element models incorporating results from previous numerical models were used and validated with ex vivo experiments. From analyses of the entire results, we concluded that this study may prove valuable as a first step in providing comprehensive information of the relation between various RF waveforms and thermodynamic responses within the tissue during the RF ablation process. This study may also contribute toward studies to determine an optimum RF waveform capable of maximizing the amount of tumor tissue removed while maintaining the advantages of RF ablation.

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Figures

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Figure 1

FE models: (a) without a blood vessel and (b) with a blood vessel. The liver tissue is cylindrical with a radius of 6 cm and a height of 12 cm. The electrode is cylindrical with a radius of 0.75 cm and a height of 2 cm, with the last 4.5 mm modeled in the shape of a probe. The body, except for the insulated electrode, is a cylinder 4 cm high. The distance between the blood vessel and electrode is 0.5 cm and the blood vessel diameter is 1 cm.

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Figure 2

Four types of input waveforms considered in the current study. (a) half-sine waveform, (b) half-square waveform, (c) half-exponential waveform, and (d) damped-sine waveform. The functions of the waveform are shown in Eqs. 6,7,8,9.

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Figure 3

Considered parameters to estimate the temperature variation and gradient during a period. M1 and M2 indicate the temperature increase and decrease during a period, respectively. T1 and T2 indicate the time change corresponding with the M1 and M2, respectively.

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Figure 4

Procedure for measuring the ablation in ex vivo experiments. (a) Experimental setup, (b) a digital image of liver tissue ablation, (c) conversion to a grayscale image based on intensity-level histogram analysis, and (d) image segmentation based on the image profile data.

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Figure 5

Example of computing the extent of ablation predicted by FE analysis. This is determined quantitatively based on the result of temperature distribution in the liver tissue using the criteria of 47°C IT and 64°C TT.

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Figure 6

Volume of liver tissue with a temperature greater than 47°C IT (a) without and (b) with the blood vessel in the liver tissue. Arrows and ellipses indicate the ablations predicted by FE analyses. The ablations generally appeared along the length of the electrode.

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Figure 7

Volume of liver tissue with a temperature greater than 64°C TT (a) without and (b) with the blood vessel in the liver tissue. Arrows and ellipses indicate the ablations predicted by FE analyses. The ablations generally appeared along the length of the electrode or at both ends.

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