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Theoretical analysis of the heat convection coefficient in large vessels and the significance for thermal ablative therapies.

Ablative therapies such as radio-frequency (RF) ablation are increasingly used for treatment of tumours in liver and other organs. Often large vessels limit the extent of the thermal lesion, and cancer cells close to the vessel survive resulting in local tumour recurrence. Accurate estimates of the heat convection coefficient h for large vessels will help improve ablation techniques, and are required for estimation of thermal lesion dimensions in simulations. Previous estimates of h did not consider that only part of the vessel is heated, and assumed uniform temperature distribution at the vessel wall. An analytical relationship between the heat convection coefficient, blood velocity and temperature is formulated. The heat convection coefficient evaluated will assist both simulations and design of proper protocols for in vivo measurements. The mathematical model developed in this work describes the exchange of heat between a solid surface and a moving fluid and it is based on energy and motion equations for Navier-Stokes fluids. A particular case of a laminar blood flow in the portal vein is studied when a portion of its surface is heated. The results show that heating a larger portion of the vessels reduces convective heat loss, which may result in more effective ablation strategies.