LARGE BLOOD-VESSEL COOLING IN HEATED TISSUES - A NUMERICAL STUDY

Large blood vessels can produce steep temperature gradients in heated tissues leading to inadequate tissue temperatures during hyperthermia. This paper utilizes a finite difference scheme to solve the basic equ ations of heat transfer and fluid flow to model blood vessel cooling. Unlike previous formulations, heat transfer coefficients were not used to calculate heat transfer to large blood vessels. Instead, the conse rvation form of the finite difference equations implicitly modelled th is process. Temperature profiles of heated tissues near thermally sign ificant vessels were calculated. Microvascular heat transfer was model led either as an effective conductivity or a heat sink. An increase in perfusion in both microvascular models results in a reduction of the cooling effects of large vessels. For equivalent perfusion values, the effective conductivity model predicted more effective heating of the blood and adjacent tissue. Furthermore, it was found that optimal vess el heating strategies depend on the microvascular heat transfer model adopted; localized deposition of heat near vessels could produce highe r temperature profiles when microvascular heat transfer was modelled a ccording to the bioheat transfer equation (BHTE) but not the effective thermal conductivity equation (ETCE). Reduction of the blood flow thr ough thermally significant vessels was found to be the most effective way of reducing localized cooling.