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Research Papers

Thermal-Electric Finite Element Analysis and Experimental Validation of Bipolar Electrosurgical Cautery

[+] Author and Article Information
Robert E. Dodde

Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109

Scott F. Miller

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109

James D. Geiger

Department of Surgery, Medical School, University of Michigan, Ann Arbor, MI 48109

Albert J. Shih

Department of Mechanical Engineering, Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109

J. Manuf. Sci. Eng 130(2), 021015 (Apr 09, 2008) (8 pages) doi:10.1115/1.2902858 History: Received August 24, 2007; Revised January 13, 2008; Published April 09, 2008

Cautery is a process to coagulate tissues and seal blood vessels using heat. In this study, finite element modeling (FEM) was performed to analyze temperature distribution in biological tissue subject to a bipolar electrosurgical technique. FEM can provide detailed insight into the tissue heat transfer to reduce the collateral thermal damage and improve the safety of cautery surgical procedures. A coupled thermal-electric FEM module was applied with temperature-dependent electrical and thermal properties for the tissue. Tissue temperature was measured using microthermistors at different locations during the electrosurgical experiments and compared to FEM results with good agreement. The temperature- and compression-dependent electrical conductivity has a significant effect on temperature profiles. In comparison, the temperature-dependent thermal conductivity does not impact heat transfer as much as the temperature-dependent electrical conductivity. Detailed results of temperature distribution were obtained from the model. The FEM results show that the temperature distribution can be changed with different electrode geometries. A flat electrode was modeled that focuses the current density at the midline of the instrument profile resulting in higher peak temperature than that of the grooved electrode (105 versus 96°C).

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

The Gyrus ACMI 5mm bipolar cutting forceps. Note the end of the device is magnified to show electrode detail.

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Figure 2

Experimental setup showing positioning of tissue, electrode, and thermistors

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Figure 3

Voltage input for FEM (a) measured ac voltage signal and close-up view of the 350kHz wave form and (b) resultant dc approximation of the wave form equivalent to rms value of the rf signal

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Figure 4

Schematic of the 3D FEM model showing (a) the tissue, electrodes, and symmetry plane defined by points EACG; (b) a representative mesh case; (c) top view of tissue regions identified for the compression-dependent regions (I, II, and III) and thermistors distance from electrode for temperature measurements; (d) cross-section view of the compression-dependent regions. Letters A–H mark planes for boundary conditions described in Table 2.

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Figure 5

Two electrodes: (a) FE; (b) GE in Gyrus ACMI bipolar instrument used in the experiment; (c) dimensions of the cross-section for GE

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Figure 6

Comparison of thermal profiles for in vivo experiments and FEM using a GE under a constant thermal conductivity, temperature-dependent electrical conductivity, and (a) compression-independent and (b) compression-dependent simulation

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Figure 7

FEM of the effect of temperature-dependent σ and k on tissue temperature. kTref and k(T) are constant and temperature-dependent thermal conductivity, respectively. σTref and σ(T) are constant and temperature-dependent electrical conductivity, respectively.

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Figure 8

Cross-sectional view of temperature profiles on a plane offset from Plane ABDC by 6mm at different times for a constant thermal conductivity, temperature-dependent electrical conductivity, and compression-independent simulation using a GE. Times (a)–(e) correlate to the end of each pulse and (f) correlates to the end of the simulation after sufficient cooling.

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Figure 9

Cross-sectional view of temperature profiles at 3.22s on different planes offset from Plane ABFE for a constant thermal conductivity, temperature-dependent electrical conductivity, and compression-independent simulation using a GE (distances indicating the offset from Plane ABFE) (same temperature scale as in Fig. 8).

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Figure 10

Cross-sectional view of temperature profiles for a constant thermal conductivity, temperature- and compression-dependent electrical conductivity simulation using a GE on a plane offset from Plane ABDC by 6mm at various times. Times (a)–(e) correlate to the end of each pulse and (f) correlates to the end of the simulation after sufficient cooling (same temperature scale as in Fig. 8).

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Figure 12

Effect of GE and FE on temperature profiles

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Figure 11

Cross-sectional view of temperature profiles at 3.22s for a constant thermal conductivity, temperature- and compression-dependent electrical simulation using a GE on different planes offset from Plane ABFE (distances indicating the offset from Plane ABFE) (same temperature scale as in Fig. 8).

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