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Research Papers

An Experimental and Numerical Investigation of Phase Change Electrodes for Therapeutic Irreversible Electroporation

[+] Author and Article Information
Christopher B. Arena

Bioelectromechanical Systems Lab,
Virginia Tech-Wake Forest School of Biomedical
Engineering and Sciences,
Virginia Tech, 330 Kelly Hall (MC0298),
Stanger Street,
Blacksburg, VA 24061
e-mail: carena@vt.edu

Roop L. Mahajan

Institute for Critical Technology and
Applied Science (ICTAS),
Virginia Tech Department of
Mechanical Engineering,
Virginia Tech Department of Engineering
Science and Mechanics,
Virginia Tech, 410 H Kelly Hall (MC0298),
Stanger Street,
Blacksburg, VA 24061

Marissa Nichole Rylander

Tissue Engineering Nanotechnology and
Cancer Research Lab,
Virginia Tech-Wake Forest
School of Biomedical Engineering and Sciences,
Virginia Tech Department of
Mechanical Engineering,
Virginia Tech, 335 Kelly Hall (MC0298),
Stanger Street,
Blacksburg, VA 24061

Rafael V. Davalos

Bioelectromechanical Systems Lab,
Virginia Tech-Wake Forest School of
Biomedical Engineering and Sciences,
Virginia Tech, 329 Kelly Hall (MC0298),
Stanger Street,
Blacksburg, VA 24061

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received April 10, 2013; final manuscript received July 30, 2013; accepted manuscript posted September 6, 2013; published online October 3, 2013. Assoc. Editor: Ram Devireddy.

J Biomech Eng 135(11), 111009 (Oct 03, 2013) (9 pages) Paper No: BIO-13-1182; doi: 10.1115/1.4025334 History: Received April 10, 2013; Revised July 30, 2013; Accepted September 06, 2013

Irreversible electroporation (IRE) is a new technology for ablating aberrant tissue that utilizes pulsed electric fields (PEFs) to kill cells by destabilizing their plasma membrane. When treatments are planned correctly, the pulse parameters and location of the electrodes for delivering the pulses are selected to permit destruction of the target tissue without causing thermal damage to the surrounding structures. This allows for the treatment of surgically inoperable masses that are located near major blood vessels and nerves. In select cases of high-dose IRE, where a large ablation volume is desired without increasing the number of electrode insertions, it can become challenging to design a pulse protocol that is inherently nonthermal. To solve this problem we have developed a new electrosurgical device that requires no external equipment or protocol modifications. The design incorporates a phase change material (PCM) into the electrode core that melts during treatment and absorbs heat out of the surrounding tissue. Here, this idea is reduced to practice by testing hollow electrodes filled with gallium on tissue phantoms and monitoring temperature in real time. Additionally, the experimental data generated are used to validate a numerical model of the heat transfer problem, which is then applied to investigate the cooling performance of other classes of PCMs. The results indicate that metallic PCMs, such as gallium, are better suited than organics or salt hydrates for thermal management, because their comparatively higher thermal conductivity aids in heat dissipation. However, the melting point of the metallic PCM must be properly adjusted to ensure that the phase transition is not completed before the end of treatment. When translated clinically, phase change electrodes have the potential to continue to allow IRE to be performed safely near critical structures, even in high-dose cases.

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References

Figures

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Fig. 1

(a) Image of the experimental setup used to monitor temperature during electroporation with phase change electrodes. The electrodes and fiber optic temperature probe are spaced using a printed circuit board, inserted into the tissue phantom, and placed inside an incubator (white arrow). The insert displays the hollow brass electrodes with the inclusion of a gallium core (black arrow). (b) Representative mesh of the finite element model used to simulate the electroporation protocol with 79,198 elements.

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Fig. 7

(a) Melting profile for different PCM cores (gallium, keq/10, and keq/100) with a melting point 1 °C above baseline housed within a 1 mm radius electrode. The data is taken at the center of the core at a depth of 1.80 cm from the surface of the ultrasound gel. (b) Cross section of the volume fraction solid material through the center of the electrodes at the end of treatment.

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Fig. 2

Comparison of the measured temperatures (dotted lines) with those predicted by the numerical model (solid lines) for solid electrodes (black) and phase change electrodes (gray). The insert displays the volume fraction of solid material predicted by the numerical model at the end of the 99 s pulse protocol. Due to symmetry, only a single electrode is shown with the medial portion on the left.

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Fig. 3

Surface contour plots from the numerical model showing the (a) electric field distribution and temperature distribution for the (b) solid electrodes and (c) phase change electrodes. All plots are shown at the end of the 99 s pulse protocol. In the x-y plane, the cross section is taken at a depth of 1.80 cm from the surface of the ultrasound gel. In the x-z plane the cross section is taken through the center of the electrodes (y = 0).

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Fig. 4

Temperature profiles resulting from the parametric study on electrode radius (0.5, 0.75, 1.0, and 1.25 mm) and PCM melting point above the baseline temperature (1, 4, 7, and 10 °C) for gallium. Temperatures are plotted at the medial electrode–tissue interface at a depth of 1.80 cm from the surface of the ultrasound gel. Dotted lines represent solid electrodes for comparison. In (c) the vertical arrow indicates the end of melting and the horizontal arrow highlights the temperature at the end of treatment.

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Fig. 5

Temperature profiles resulting from the parametric study on electrode radius (0.5, 0.75, 1.0, and 1.25 mm) and PCM melting point above the baseline temperature (1, 4, 7, and 10 °C) when keq/100. Temperatures are plotted at the medial electrode–tissue interface at a depth of 1.80 cm from the surface of the ultrasound gel. Dotted lines represent solid electrodes for comparison. In (c) the vertical arrow indicates the end of melting and the horizontal arrow highlights the temperature at the end of treatment.

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Fig. 6

Comparison of the temperature change during treatment for (a) gallium core electrodes and (b) when keq/100 (b). (c) The difference between (b) and (a) to emphasize the most effective PCM for each parameter combination. White bars represent solid electrodes for comparison.

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