Limits...
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
Model Geometry. The center of the finite element geometry is the tip of the ablation probe. Source voltage is applied at the electrically conducting tip. External surfaces of the cubic model serve as the electrical ground and are at body temperatures (37°C). The entire ablation probe is assumed to be thermally insulating.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC156890&req=5

Figure 2: Model Geometry. The center of the finite element geometry is the tip of the ablation probe. Source voltage is applied at the electrically conducting tip. External surfaces of the cubic model serve as the electrical ground and are at body temperatures (37°C). The entire ablation probe is assumed to be thermally insulating.

Mentions: Figure 1 shows a diagram of a single needle ablation electrode that is typically used in clinical practice for hepatic tumor ablation. As seen from the figure, the probe is 6.0 cm long with a diameter of 0.15 cm. The distal 2.0 cm of this probe is an electrically conductive metal (i.e. stainless steel) and the proximal 4.0 cm of the probe is covered with an electrically insulating material. Figure 2 shows the three-dimensional geometry of the model. The active portion of the probe is embedded into a 12.0 cm × 12.0 cm × 12.0 cm cubic region that simulates tissue surrounding the probe tip, which is located at the center of the model. The electrical properties used in the model were acquired from Gabriel et al. [11] for the liver (Table 1). The perfusion properties and thermal properties were acquired from Tungjitkusolmun et al. [21] and Duck [20]. A source voltage is applied to the conducting tip of the ablation probe. All of the outer surfaces of the cube serve as a return ground electrode. The insulating shaft is both thermally and electrically non-conducting.


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

Chang I - Biomed Eng Online (2003)

Model Geometry. The center of the finite element geometry is the tip of the ablation probe. Source voltage is applied at the electrically conducting tip. External surfaces of the cubic model serve as the electrical ground and are at body temperatures (37°C). The entire ablation probe is assumed to be thermally insulating.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Model Geometry. The center of the finite element geometry is the tip of the ablation probe. Source voltage is applied at the electrically conducting tip. External surfaces of the cubic model serve as the electrical ground and are at body temperatures (37°C). The entire ablation probe is assumed to be thermally insulating.
Mentions: Figure 1 shows a diagram of a single needle ablation electrode that is typically used in clinical practice for hepatic tumor ablation. As seen from the figure, the probe is 6.0 cm long with a diameter of 0.15 cm. The distal 2.0 cm of this probe is an electrically conductive metal (i.e. stainless steel) and the proximal 4.0 cm of the probe is covered with an electrically insulating material. Figure 2 shows the three-dimensional geometry of the model. The active portion of the probe is embedded into a 12.0 cm × 12.0 cm × 12.0 cm cubic region that simulates tissue surrounding the probe tip, which is located at the center of the model. The electrical properties used in the model were acquired from Gabriel et al. [11] for the liver (Table 1). The perfusion properties and thermal properties were acquired from Tungjitkusolmun et al. [21] and Duck [20]. A source voltage is applied to the conducting tip of the ablation probe. All of the outer surfaces of the cube serve as a return ground electrode. The insulating shaft is both thermally and electrically non-conducting.

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