Estimation of temperature elevation generated by ultrasonic irradiation in biological tissues using the thermal wave method

In most previous models,simulation of the temperature generation in tissue is based on the Pennes bio-heat transfer equation,which implies an instantaneous thermal energy deposition in the medium.Due to the long thermal relaxation time τ（20 s-30 s） in biological tissues,the actual temperature elevation during clinical treatments could be different from the value predicted by the Pennes bioheat equation.The thermal wave model of bio-heat transfer（TWMBT） defines a thermal relaxation time to describe the tissue heating from ultrasound exposure.In this paper,COMSOL Multiphysics 3.5a,a finite element method software package,is used to simulate the temperature response in tissues based on Pennes and TWMBT equations.We further discuss different factors in the bio-heat transfer model on the influence of the temperature rising and it is found that the temperature response in tissue under ultrasound exposure is a rising process with a declining rate.The thermal relaxation time inhibits the temperature elevation at the beginning of ultrasonic heating.Besides,thermal relaxation in TWMBT leads to lower temperature estimation than that based on Pennes equation during the same period of time.The blood flow carrying heat dominates most to the decline of temperature rising rate and the influence increases with temperature rising.On the contrary,heat diffusion,which can be described by thermal conductivity,has little effect on the temperature rising.

双倒易边界元拓展于模拟生物组织中热波传播问题

The Dual Reciprocity Boundary Element Method (DRBEM) is extended to simulatethe thermal wave propagation in biological tissues. The higher the thermal relaxation timeis, the stronger the thermal wave effect will be. Under changing heat source, bioheat trans-fer has distinct wave characters. The thermal wave propagation in biological tissues obeysthe superposition and resolution principle of ordinary wave. Reflected by a rigid wall’ (thefirst boundary condition), the thermal wave will show a phase jumping phenomenon. TheDRBEM is an efficiellt pure boundary iotegral method without domain integral for solvingthermal wave problems. Thermal wave and their refiection, phase jumping, superposition,resolution can be correctly located and sharply captured. There are no the oscillatory behav-ior in the wave front and wave peak region, which is presented in reported finite differencesolution with TVD high accuracy scheme.

生物组织中几类热波传播特性的研究

为探讨热波在不同边界条件下发生反射、衰减、相位突变、叠加与分解特性，考虑到热波的相位，以生物组织中的正弦波和方波为例，对不同热松弛时间下热波的传播过程进行了数值考察和分析，其结果可为将热波效应应用于活体热状态辨识及处理某些复杂的生物热问题打下一定的基础。本文还基于数值算例对一个从常规角度看来不易理解的生物热现象作出了合理解释，指出了该类效应在相关医学问题上的应用前景。

时间延迟型生物传热方程及其振荡特性的初步分析

生物传热学是一门新兴的不断发展着的科学,它正在根据一些新的发现和认识使其基本命题和定理不断趋于完善,并由此而提出新的概念,本文基于对活体组织温度振荡效应的最新认识,提出三个新观念下的时间延迟生物传热方程,它有可能刺激相应数学分析工作的开展,并将积极推进对蕴藏于生物组织中的各类热现象本质规律的认识。

Generalized time delay bioheat equation and preliminary analysis on its wave nature

As a new developing field, the science of bioheat transfer is making its fundamental propositions and theories much more complete and thus postulates new concepts based on the new discovery and knowledge. In this note, an important improvement on the previously developed thermal wave models of bioheat transfer (TWMBT) is given.

Qualitative Experimental Evidences for the Thermal Wave Mechanisms of Temperature Oscillations in Living Tissues

To make it possible for the thermal wave theory on temperature oscillation (TO) effects in living tissues to be founded on the substantial experimental basis, a series of typical decisive experiments in vivo as well as in artificially simulating constructions were carried out. Conclusions obtained including some other scholars' animal experimental results all greatly support the thermal wave viewpoint qualitatively.A few experimental facts used hot to be easily understood from the classical viewpoint are also well reinterpreted. The revealing on the thermal wave mechanisms of TO in living tissues is a brand new discovery and deep insight into this important thermophysiological phenomenon. It may possibly promote new investigations on the corresponding topics in the field of bioheat transfer science.

生物活体组织温度振荡效应的理论与实验

报道了在一类介于生理学与热物理学之间的生命热现象——活体组织温度振荡机理研究方面所取得的成果，阐述了新的温度振荡理论的建构思想，介绍了用以证实该理论而设计的仿真实验、活体动物实验的技术路线，报道了实验中所发现的一些新现象及其研究结论，解释了以往动物实验中观察到的生命热现象的物理实质。其结论可促使人们重新全面认识生物传热本身并继而修改以往的一些温度预示模型和模式，直至推向新的临床应用。

肿瘤热疗中探针加热下组织温度场演化规律的研究

研究了肿瘤热疗中实施组织温度场预示、优化加热及功率调节一体化的问题。基于新近建立的生物传热热波方程，采用双倒易边界元方法，对在一定加热方式下生物组织内的热量传递规律进行了考察。对传统Ｐｅｎｎｅｓ方程和生物传热热波方程的对比研究发现，在针对真实热疗过程中由于调节加热功率而导致的温度场演化进行模拟时，两类方程的预示结果存在明显差别，这提示了在预测和控制生物体内微小温度时所采用的精细模型应是理论基础更为严密的生物传热热波方程，且在瞬变加热作用下尤为关键。文章还研究了血液灌注率在组织温度场发生改变中的作用及其生理学意义。这些研究为建立实用的肿瘤热疗仪器打下了一定的基础。