Investigation of nonlinear temperature distribution in biological tissues by using bioheat transfer equation of Pennes’ type

In this paper, a two level finite difference scheme of Crank-Nicholson type is constructed and used to numerically investigate nonlinear temperature distribution in biological tissues described by bioheat transfer equation of Pennes’ type. For the equation under consideration, the thermal conductivity is either depth-dependent or tem-perature-dependent, while blood perfusion is temperature-dependent. In both cases of depth- dependent and temperature-dependent thermal conductivity, it is shown that blood perfusion decreases the temperature of the living tissue. Our numerical simulations show that neither the localization nor the magnitude of peak tempera-ture is affected by surface temperature;however, the width of peak temperature increases with surface temperature.

Nonoverlapping Dirichlet-Neumann method for transient bioheat transfer in the human eye

This paper presents a 2D simulation of transient heat transfer in the human eye using appropriate boundary conditions.The mathematical model governing bioheat transfer in the human eye is discussed and the existence and uniqueness of the solution are proven.Four methods based on finite element method and nonoverlapping domain decomposition method to obtain transient heat transfer in the human eye are presented and described in details.After conducting numerous simulations using realistic parameters obtained from the open literature and after comparison with measurements reported by previous experimental studies,all proposed methods gave an accurate representation of transient heat transfer in the human eye.The results obtained by the domain decomposition of the human eye into four subdomains are found to be the closest to reality.

An Analytic Solution of One-dimensional Steady-state Pennes' Bioheat Transfer Equation in Cylindrical Coordinates

Based on the Pennes’ bioheat transfer equation, a simplified one-dimensional bioheat transfer model of the cylindrical living tissues in the steady state has been set up for application in limb and whole body heat transfer studies, and by using the Bessel’s equation, its corresponding analytic solution has been derived in this paper. With the obtained analytic solution, the effects of the thermal conductivity, the blood perfusion, the metabolic heat generation, and the coefficient of heat transfer on the temperature distribution in living tissues are analyzed. The results show that the derived analytic solution is useful to easily and accurately study the thermal behavior of the biological system, and can be extended to such applications as parameter measurement, temperature field reconstruction and clinical treatment.

An analytical solution of non-Fourier Chen-Holmes bioheat transfer equation

An algebraically explicit analytical solution with heat wave effect is derived for the non-Fourier bioheat transfer Chen-Holmes model. Besides its important theoreti-cal meaning (for example, to expand the understanding of heat wave phenomena in living tissues), this analytical solu-tion is also valuable as the benchmark solution to check the numerical calculation and to develop various numerical computational approaches.

Analytical solution of unsteady one-dimensional bioheat transfer equation

A basic bioheat transfer equation based upon porous medium model was derived by Wang et al. in 1993 to improve the Pennes equation in common use previously. A steady one-dimensional general analytical solution of this new equation was given by Wang et al. later under the condition of constant coefficients and rectangular coordinates. This analytical solution compared well with experimental data. In order to expand the understanding of the new equation, an unsteady one-dimensional particular analytical solution

Numerical Simulation of Fluid and Heat Transfer in a Biological Tissue Using an Immersed Boundary Method Mimicking the Exact Structure of the Microvascular Network

The aim of this study is to develop a model of fluid and heat transfer in a biological tissue taking into account the exact structure of the related microvascular network,and to analyze the influence of structural changes of such a network induced by diabetes.A cubic region representing local skin tissue is selected as the computational domain,which in turn includes two intravascular and extravascular sub-domains.To save computational resources,the capillary network is reduced to a 1D pipeline model and embedded into the extravascular region.On the basis of the immersed boundary method(IBM)strategy,fluid and heat fluxes across a capillary wall are distributed to the surrounding tissue nodes by a delta function.We consider both steady and periodic blood pressure conditions at the entrances of the capillary network.Under steady blood pressure conditions,both the interstitial fluid pressure and tissue temperature around the capillary network are larger than those in other places.When the periodic blood pressure condition is considered,tissue temperature tends to fluctuate with the same frequency of the forcing,but the related waveform displays a smaller amplitude and a certain time(phase)delay.When the connectivity of capillary network is diminished,the capacity of blood redistribution through the capillary network becomes weaker and a subset of the vessel branches lose blood flow,which further aggravates the amplitude attenuation and time delay of the skin temperature fluctuation.

Exact analytical solution to three-dimensional phase change heat transfer problems in biological tissues subject to freezing

Analytically solving a three-dimensional （3-D） bioheat transfer problem with phase change during a freezing process is extremely difficult but theoretically important. The moving heat source model and the Green function method are introduced to deal with the cryopreservation process of in vitro biomaterials. Exact solutions for the 3-D temperature transients of tissues under various boundary conditions, such as totally convective cooling, totally fixed temperature cooling and a hybrid between them on tissue surfaces, are obtained. Furthermore, the cryosurgical process in living tissues subject to freezing by a single or multiple cryoprobes is also analytically solved. A closed-form analytical solution to the bioheat phase change process is derived by considering contributions from blood perfusion heat transfer, metabolic heat generation, and heat sink of a cryoprobe. The present method is expected to have significant value for analytically solving complex bioheat transfer problems with phase change.

基于微型风扇阵列系统的人体降温空调服

论证基于微型风扇阵列的人体降温空调服的概念,并从理论和实验方面对其可行性进行评估。通过数值求解各类典型热环境条件下的三维Pennes生物传热方程,揭示出在皮肤表面引入微型风扇阵列时,其强化散热作用可显著降低体表的温度水平。同时,还采用红外成像技术及热电偶测温方式,对模拟人体的发热块经受风扇阵列强化散热作用前后的降温情况进行实验测定,进一步证实微型风扇阵列的高效降温特性,期望引申出新一代可灵活调节的空调服。

人体足部传热数值模拟及加热实验

针对极低温条件下的人体足部防寒保暖问题,建立了基于经典Pennes生物传热方程的足部传热学模型,得到其一维解析解,并采用Fluent软件对足部的传热学过程进行三维数值模拟,得到常温(291 K)及极低温(233 K)情况、足底有无加热源条件下的4组计算结果。同时设计加热实验对数值模拟结果进行验证,引入红外成像技术及热电偶测温方法对实验过程及结果加以观测和记录,并对实验中所采用的锂电池供电性能进行测试。研究结果可为今后研制相关高性能可加热产品提供参考。

生物医学传热学的研究进展

概述了生物传热学在现代生物医学工程领域和相关领域内的研究现状及其自身的研究特点，指出了其中尚待解决的问题及应用前景，并对现有生物传热学模型的建立方法和生物热物性测试技术的优缺点进行了综述．

基于生物传热学的艾灸疗法物理学剂量研究

目的:利用艾灸设备进行保健灸,建立正常人体艾灸的物理学剂量,为进一步研究患者艾灸剂量范围提供依据。方法:利用自制高精度温度传感器测定手足部、胸腹部及腰背部等穴位灸前瞬时温度,最高耐受瞬时温度,并记录产生最高耐受瞬时温度所需要的时间,通过自定义公式:穴位艾灸的物理学剂量=(灸前瞬时温度+最高耐受温度)/2×产生最高耐受温度所需要的时间,拟建立不同部位穴位的艾灸物理学剂量范围,并分析艾灸不同部位的物理学剂量范围差异。结果:手阴经的穴位艾灸时所需要的物理学剂量低于足阴经、胸腹部的穴位,手阳经的穴位艾灸时所需的物理学剂量低于足阳经、背腰部穴位,提示艾灸时手部经穴所需的物理学剂量低于足部及躯干部的穴位,说明手部穴位较之足部、躯干部穴位对光热更敏感。结论:不同部位的穴位均有一定的剂量范围,进行灸疗时,只要达到穴位的剂量范围,即可取得相应的效果。

舌横纵剖面温度场的实验研究与计算

用红外热成象技术与动物实验等多种方法对舌体的生物传热特性进行了研究。结合中医舌诊机理,用有限元法计算了猪舌内部横、纵剖面的二维温度场。结果表明,舌体传热的特征是温度梯度由舌根到舌尖较大,沿舌厚度方向较小,舌体温度分布受血管分布和血管截面积的影响。得到的舌表面温度场与横纵剖面温度场之间的关系,为结合病症对人舌温度场进行分析计算提供了思路和依据。

相控阵聚焦超声消融肿瘤的建模与仿真

相控阵聚焦超声可以同时产生多焦点的声场分布,形成较大的治疗热场,能够很好地解决传统球面换能器焦斑体积小,治疗时间长的问题。提出一种基于Rayleigh-Sommerfeld积分和Pennes生物传热方程的三维声热模型,采用有限元分析方法,在ANSYS仿真环境中研究了相控阵聚焦超声治疗时血流灌注对温度场和焦斑的影响。仿真中所有声场和温度场计算均为三维。焦斑体积根据Sapareto-Dewey方程确定。仿真结果表明采用该模型可以较为准确地预测焦斑的生成情况,反映血流灌注对焦斑的影响,血流灌注对焦斑生成的影响将随着照射时间的变化而发生变化。

热氧灌注法缓解肺部SARS病毒侵害的可行性研究 一项关于SARS物理治疗方法建立的初步探索

分析了SARS病毒攻击肺泡组织的耗氧模式,提出缓解SARS病毒侵害的热氧灌注疗法,建立支气管末端肺泡组织的传热模型,对肺泡组织在不同热氧灌注条件下的温度响应进行理论分析。结果表明,显著温升主要发生于肺泡壁即病毒聚集区。由于病毒复制需要通过其所攻击的宿主细胞的酶进行,因而通过热氧灌注造成的温度改变可望有效地削弱该处细胞酶的催化特性,继而抑制病毒的活性,同时又能将氧气通过肺泡壁供应到人体组织内。从临床实用性出发,进一步讨论了相应的热氧灌注措施,为SARS患者临床治疗提供了一种新的物理疗法治疗思路。

基于三点法的柱状生物组织热特性参数估计

针对柱状生物活体组织,提出了通过测量组织表面三个测量点的温度变化,同时确定多个热特性参数的新的非稳态无损测量方法。基于Pennes生物传热方程,建立了描述三点法测量系统传热过程的数学模型,进行了正问题的求解。根据数值计算以及参数灵敏度分析的结果,采用改进的高斯方法,对生物活体组织的热特性参数估计进行了模拟计算及分析。结果表明,采用三点测温同时确定活体生物组织的导热系数、血液灌注率、综合换热系数的测量方法是有效和可行的。

激光低损伤加热疗法的理论分析

激光低损伤加热疗法将激光照射与表面冷却相结合 ,能实现只让病变组织细胞凝固 ,而体表健康组织则不受损伤。它是治疗靠近体表肿瘤的一种很有希望的方法。为了进一步认识这种治疗方法 ,本文提出了一个适用于激光低损伤加热疗法的数值计算模型 ,模拟了热疗过程中的光传输和热传递 ,得到组织内部的瞬态温度分布。在此基础上 ,详细讨论了散射系数、吸收系数、各向异性系数等光学参数 ,激光加热功率、照射半径、表面对流换热系数等热学参数 ,以及血液灌注率和新陈代谢等生理参数对这种低损伤加热疗法的影响。结果发现 ,只要通过适当调节吸收系数、散射系数和照射功率等参数就可实现对加热区域位置和范围的控制。

考虑脑脊液层的局部脑冷却传热分析

基于对脑部生理结构的分析,将脑部分为白质、灰质、脑脊液、颅骨和头皮5层,建立了三维脑部传热模型.讨论了外部冷量,血液灌注率和代谢产热率对温度分布的影响,研究各关键参数对脑部温度的影响规律.并着重比较了考虑脑脊液层与未考虑脑脊液层时的温度分布.结果表明,外部施加的冷量值和血液灌注率对温度分布有较大影响;在未考虑脑脊液层和考虑脑脊液层两种情况下,头皮、颅骨、脑脊液和部分灰质层的温度有较大差异.当冷量值增大时,此温差也会增大.并且两种情况下温差的峰值出现在脑脊液层.

体表温度及其总体平均值的测量与统计分析

提供了青年组体表平均温度的实际测量值及其统计分析结果表现出很好的正态分布特性．将这些结果与国外发表的数据进行了对比．讨论了影响体表温度测量的因素．

活体组织血液灌注率无损测量方法的研究

活体组织血液灌注率的无损测量是生物医学工程领域中一个十分重要而困难的课题。本文基于新近报道的血液灌注率无损测量方法 ,提出了简化的一次加热测量措施以取代原方法中必须经两次加热的不足 ,从而大大缩短了小灌注率组织的测量时间。由此导出了体表在一次简谐加热作用下组织温度响应的解析解 ,解的形式及随后的计算结果表明了方法的可行性。针对空间非均匀或温度依赖型血液灌注率情形 ,本文采用双倒易边界元方法研究了加热能流密度、简谐热流振幅、加热频率、皮下血管、血液灌注率、加热片面积大小等对组织温度响应幅度、相位等的影响规律 ,由此提出了无损估测非均匀血液灌注率的措施。这些系统性结论为发展适合于临床应用的血液灌注率无损测量仪器建立了相对完整的理论基础。

激光辐照下皮肤组织中温度场的理论分析和数值模拟

基于 Pennes传热方程 ,采用更能反映活体组织真实情况的血液灌注率和代谢热产率 ,从理论上分析了激光作用在生物皮肤组织时所引起的组织温度场变化 ,给出了皮肤组织温度变化的分析解 ,数值模拟了激光辐照下组织的温度场分布 .并讨论了激光辐照时间、组织深度以及生物组织热物性对组织温升的影响 .