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Effect of variable heat transfer coefficient on tissue temperature next to a large vessel during radiofrequency tumor ablation.

dos Santos I, Haemmerich D, Pinheiro Cda S, da Rocha AF - Biomed Eng Online (2008)

Bottom Line: The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter).For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity.However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, University of Brasilia, Brasilia, DF 70910-900, Brazil. icaro@ieee.org

ABSTRACT

Background: One of the current shortcomings of radiofrequency (RF) tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (h) have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable.

Methods: This paper presents a realistic time-varying model in which h is a function of the temperature distribution at the vessel wall. The finite-element method (FEM) was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter).

Results: When the ablation procedure takes longer than 1-2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5-10 s) and when the electrode is 1 mm away from the vessel, the use of constant h can lead to errors as high as 20% in the estimation of the coagulation zone.

Conclusion: For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

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(a) Convective heat transfer coefficient during 120 s simulation for the electrode 1 mm away from the vessel. (b) Close up view for the first 8 s of simulation. The dotted line indicates the steady state value of h.
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Figure 3: (a) Convective heat transfer coefficient during 120 s simulation for the electrode 1 mm away from the vessel. (b) Close up view for the first 8 s of simulation. The dotted line indicates the steady state value of h.

Mentions: Figure 3(a) shows the evolution of the convective heat transfer coefficient at the vessel wall when the electrode is placed 1 mm away from the vessel. One can see in Figure 3(b) that h increases sharply at the beginning of the ablation procedure, followed by a sharp decrease within a second. The final value of h is indicated with a dotted line in Figure 3.


Effect of variable heat transfer coefficient on tissue temperature next to a large vessel during radiofrequency tumor ablation.

dos Santos I, Haemmerich D, Pinheiro Cda S, da Rocha AF - Biomed Eng Online (2008)

(a) Convective heat transfer coefficient during 120 s simulation for the electrode 1 mm away from the vessel. (b) Close up view for the first 8 s of simulation. The dotted line indicates the steady state value of h.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2500024&req=5

Figure 3: (a) Convective heat transfer coefficient during 120 s simulation for the electrode 1 mm away from the vessel. (b) Close up view for the first 8 s of simulation. The dotted line indicates the steady state value of h.
Mentions: Figure 3(a) shows the evolution of the convective heat transfer coefficient at the vessel wall when the electrode is placed 1 mm away from the vessel. One can see in Figure 3(b) that h increases sharply at the beginning of the ablation procedure, followed by a sharp decrease within a second. The final value of h is indicated with a dotted line in Figure 3.

Bottom Line: The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter).For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity.However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, University of Brasilia, Brasilia, DF 70910-900, Brazil. icaro@ieee.org

ABSTRACT

Background: One of the current shortcomings of radiofrequency (RF) tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (h) have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable.

Methods: This paper presents a realistic time-varying model in which h is a function of the temperature distribution at the vessel wall. The finite-element method (FEM) was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter).

Results: When the ablation procedure takes longer than 1-2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5-10 s) and when the electrode is 1 mm away from the vessel, the use of constant h can lead to errors as high as 20% in the estimation of the coagulation zone.

Conclusion: For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

Show MeSH
Related in: MedlinePlus