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Finite element analysis of hepatic radiofrequency ablation probes using temperature-dependent electrical conductivity.

Chang I - Biomed Eng Online (2003)

Bottom Line: While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed.The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures.Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100 degrees C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Office of Science and Technology, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Rockville, MD, USA. iac@cdrh.fda.gov

ABSTRACT

Background: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed.

Methods: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion.

Results: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion.

Conclusion: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100 degrees C.

Show MeSH
Electric Field Strength as a Function of Source Voltage. For constant electrical conductivity simulations with (green) and without (red) tissue perfusion the maximum electric field is a linear function of the source voltage. Models that use temperature-dependent conductivity are slightly nonlinear.
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Figure 4: Electric Field Strength as a Function of Source Voltage. For constant electrical conductivity simulations with (green) and without (red) tissue perfusion the maximum electric field is a linear function of the source voltage. Models that use temperature-dependent conductivity are slightly nonlinear.

Mentions: Figure 3 shows a comparison of the maximum electric field strengths computed for the four models when a source voltage of 20.0 volts is applied. In each case, the electric field is shown to be non-uniform, favoring the proximal edge and the distal tip of the ablation probe. The maximum electric field occurs at the proximal edge. In the results from the two models that assume constant electrical conductivity, the maximum electric field is the same. The models that assume a temperature-dependent electrical conductivity have an electric field strength that is approximately 3% less. Figure 4 shows a plot of the maximum electric field strength plotted as a function of source voltage. For the cases that use constant conductivity, the electric field is directly proportional to the magnitude of the source. As the source voltage increases, the differences between the model results of the constant conductivity and temperature-dependent conductivity models increase. The nonlinearity in the results for temperature-dependent conductivity arise from solving Laplace's equation using the more general expression ∇·[σ(T)∇V] = 0. Tables 4 and 5 demonstrate that the changes in the electric field are not related to tissue perfusion. A plot of the electric field strength along the surface of the ablation probe (Figure 5) shows that in all four models, the resulting distribution of the electric field is nearly the same.


Finite element analysis of hepatic radiofrequency ablation probes using temperature-dependent electrical conductivity.

Chang I - Biomed Eng Online (2003)

Electric Field Strength as a Function of Source Voltage. For constant electrical conductivity simulations with (green) and without (red) tissue perfusion the maximum electric field is a linear function of the source voltage. Models that use temperature-dependent conductivity are slightly nonlinear.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC156890&req=5

Figure 4: Electric Field Strength as a Function of Source Voltage. For constant electrical conductivity simulations with (green) and without (red) tissue perfusion the maximum electric field is a linear function of the source voltage. Models that use temperature-dependent conductivity are slightly nonlinear.
Mentions: Figure 3 shows a comparison of the maximum electric field strengths computed for the four models when a source voltage of 20.0 volts is applied. In each case, the electric field is shown to be non-uniform, favoring the proximal edge and the distal tip of the ablation probe. The maximum electric field occurs at the proximal edge. In the results from the two models that assume constant electrical conductivity, the maximum electric field is the same. The models that assume a temperature-dependent electrical conductivity have an electric field strength that is approximately 3% less. Figure 4 shows a plot of the maximum electric field strength plotted as a function of source voltage. For the cases that use constant conductivity, the electric field is directly proportional to the magnitude of the source. As the source voltage increases, the differences between the model results of the constant conductivity and temperature-dependent conductivity models increase. The nonlinearity in the results for temperature-dependent conductivity arise from solving Laplace's equation using the more general expression ∇·[σ(T)∇V] = 0. Tables 4 and 5 demonstrate that the changes in the electric field are not related to tissue perfusion. A plot of the electric field strength along the surface of the ablation probe (Figure 5) shows that in all four models, the resulting distribution of the electric field is nearly the same.

Bottom Line: While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed.The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures.Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100 degrees C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Office of Science and Technology, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Rockville, MD, USA. iac@cdrh.fda.gov

ABSTRACT

Background: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed.

Methods: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion.

Results: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion.

Conclusion: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100 degrees C.

Show MeSH