Effects of Thermal Relaxation on Temperature Elevation in Ex Vivo Tissues During High Intensity Focused Ultrasound

Abstract

The introduction of thermal relaxation makes non-Fourier heat transfer more effective than Pennes equation to reflect rapid bio-heat transferring during HIFU, however, the contribution of thermal relaxation in specific tissues needs to be further clarified. In this study, we first measured the thermal relaxation times of porcine muscle and porcine fat. Combining with experimental measurements, the effects of thermal relaxation on temperature elevation in the tissues were investigated by using Pennes equation, thermal wave model of bio-heat transfer (TWMBT) and dual phase-lag (DPL) bio-heat transfer. Results showed that: a) The thermal relaxation times of porcine muscle and porcine fat are experimentally determined as 5.71±0.11 s and 5.02±0.06 s, respectively. b) In the absence of cavitation, DPL bio-heat transfer is more accurate to predict the temperature elevation at the focus and 2 mm from the focus than Pennes equation and TWMBT. Particularly, comparing with the reported of bologna (16 s) used in most of the theoretical analysis, the utilization of the measured thermal relaxation time for a specific tissue in DPL bio-heat transfer is more effective in predicting the temperature elevation during HIFU. c) Acoustic cavitation and nonlinear propagation is easier to happen in fat, under which all bio-heat transfer models are failed to forecast the temperature elevation induced by HIFU. The results demonstrate that different tissues have different thermal relaxation, DPL bio-heat transfer with the measured thermal relaxation times of specific tissues can accurately predict the temperature elevation during HIFU without cavitation.

Comparative Evaluations on Real-Time Monitoring of Temperature Sensors during Endoscopic Laser Application

“…Upon laser irradiation, the initial tissue temperature measured by the TC increased rapidly as the incident laser energy was absorbed by the TC (Figure 3) or TC and tissue (Figure 4). Then, the temperature increase became steady due to thermal convection to the air or conduction to the surrounding tissue [36]. Therefore, the surrounding medium can determine the amount of light absorption and thus the extent of the temperature elevations for the two sensors.…”

Fluid–Structure Interaction and Non-Fourier Effects in Coupled Electro-Thermo-Mechanical Models for Cardiac Ablation

“…where τ q is the thermal relaxation time that represents the time delay between heat flux and the associated heat conduction through a medium (i.e., the delay arising from thermal inertia) [21,25], τ t is the phase lag in establishing temperature gradient across the medium (i.e., the delay arising from micro-structural interactions). While the models accounting for thermal relaxation in the context of hyperbolic thermo-elasticity have a longer history [26][27][28], a comprehensive analysis and applications of such models in the context of thermal ablation of biological tissues are fairly new [21].…”