Parametric analysis of effective tissue thermal conductivity, thermal wave characteristic, and pulsatile blood flow on temperature distribution during thermal therapy

Abstract

This study examines the coupled effects of pulsatile blood flow in a thermally significant blood vessel, the effective thermal conductivity of tumor tissue, and the thermal relaxation time in solid tissues on the temperature distributions during thermal treatments. Due to the cyclic nature of blood flow as a result of the heartbeat, the blood pressure gradient along a blood vessel was modeled as a sinusoidal change to imitate a pulsatile blood flow. Considering the enhancement in the thermal conductivity of living tissues due to blood perfusion, the effective tissue thermal conductivity was investigated. Based on the finite propagation speed of heat transfer in solid tissues, a modified wave bio-heat transfer transport equation in cylindrical coordinates was used. The numerical results show that a larger relaxation time results in a higher peak temperature. In the rapid heating case I (i.e., heating power density of 100Wcm−3 and heating duration of 1s) and a heartbeat frequency of 1Hz, the maximum temperatures were 62.587 and 63.107°C for thermal relaxation times of 0.464 and 6.825s, respectively. In contrast, the same total heated energy density of 100Jcm−3 in a slow heating case (i.e., heating power density of 5Wcm−3 and heating duration of 20s) revealed maximum temperatures of 57.724 and 61.233°C for thermal relaxation times of 0.464 and 6.825s, respectively. In rapid heating cases, the occurrence of the peak temperature exhibits a time lag due to the influence of the thermal relaxation time. In contrast, in slow heating cases, the peak temperature may occur prior to the end of the heating period. Moreover, the frequency of the pulsatile blood flow does not appear to affect the maximum temperature in solid tumor tissues.