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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.

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Current Density Results of FEM Models. Comparison of current density distribution for four finite element models when a source voltage of 20.0 volts is applied. Numbers represent the maximum current density in units of Amps/meter.
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Figure 6: Current Density Results of FEM Models. Comparison of current density distribution for four finite element models when a source voltage of 20.0 volts is applied. Numbers represent the maximum current density in units of Amps/meter.

Mentions: Figure 6 shows a comparison of the maximum current density computed for the four models when 20.0 volts is applied. In the cases where the electrical conductivity is constant, the current density is a linear scaling of the electric field and is the same with and without tissue perfusion. For the case where temperature-dependent conductivity is applied in the absence of tissue perfusion, the current density increases 120%. When perfusion is added to the temperature-dependent conductivity model, the current density increases approximately 53%. These data indicate that current density is explicitly related to temperature-dependent phenomena and implicitly related to tissue perfusion. Therefore, any changes in the current density due to perfusion are only observable if temperature-dependent electrical conductivity is accounted for in computational models. Figures 7 and 8 demonstrate that in both of the cases with (green) and without (red) tissue perfusion which utilize constant electrical conductivity, the current density distribution is the same. The figures also indicate that adding temperature-dependent and perfusion phenomena produce substantially different results.


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

Chang I - Biomed Eng Online (2003)

Current Density Results of FEM Models. Comparison of current density distribution for four finite element models when a source voltage of 20.0 volts is applied. Numbers represent the maximum current density in units of Amps/meter.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: Current Density Results of FEM Models. Comparison of current density distribution for four finite element models when a source voltage of 20.0 volts is applied. Numbers represent the maximum current density in units of Amps/meter.
Mentions: Figure 6 shows a comparison of the maximum current density computed for the four models when 20.0 volts is applied. In the cases where the electrical conductivity is constant, the current density is a linear scaling of the electric field and is the same with and without tissue perfusion. For the case where temperature-dependent conductivity is applied in the absence of tissue perfusion, the current density increases 120%. When perfusion is added to the temperature-dependent conductivity model, the current density increases approximately 53%. These data indicate that current density is explicitly related to temperature-dependent phenomena and implicitly related to tissue perfusion. Therefore, any changes in the current density due to perfusion are only observable if temperature-dependent electrical conductivity is accounted for in computational models. Figures 7 and 8 demonstrate that in both of the cases with (green) and without (red) tissue perfusion which utilize constant electrical conductivity, the current density distribution is the same. The figures also indicate that adding temperature-dependent and perfusion phenomena produce substantially different results.

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