生物组织光热响应及其实验研究

基于激光与生物组织相互作用机理,概述了生物组织的光热响应过程。在此基础上对光热响应所建立的温度场的常用测量技术进行比较,并分别用热电偶和热成像设备进行实验测量。研究结果不仅具有重要的参考价值,对指导临床也有一定的意义。     

间质热疗法组织中温度分布与光纤加入端的关系

主要利用了有限元方法,模拟研究了在激光间质热疗法中,被加热区域组织中温度的分布情况。组织的温度对组织中细胞有着极其重要的影响,对温度的控制是间质热疗法成败的关键因素。到目前为止,在激光间质热疗法中,还没有一种很精确方法能够实时测量激光辐射后组织中温度分布。为了能为临床处理提供一些有用参考,利用Ansys对不同的光纤加入端所形成的温度场进行了模拟,不失为一种好的方法。     

有限元法分析人体皮肤热效应的空间分布

研究了He—Ne激光辐照下人体皮肤组织传热过程温度场空间分布的动态规律。利用有限元法实现皮肤组织非稳态传热方程的模拟计算,获得了人体皮肤组织光致热效应的径向和轴向分布行为及时间变化关系。研究结果对于激光外科临床应用中激光参数的合理确定有一定的指导意义。     

肿瘤微波热消融有效毁损区域温度场分布的仿真研究

本研究针对微波热消融肿瘤治疗过程中温度分布实时监测的核心问题,利用计算机模拟生物组织温度场分布,提出了基于有限元的微波消融温度场仿真方法。分别仿真了微波发射功率、作用时间及生物组织热物性参数对温度场分布的影响。研究结果表明:功率增大25%,毁损区温度平均升高20%;功率增大50%,温度升高40%;功率增大75%,温度升高60%。作用时间延长,温度场分布基本不变,但有效毁损体积增大,时间延长2倍可使毁损体积增大150%。导热系数对热疗远场区热能的扩散产生作用。经验证发现仿真结果与实验结果误差较小,证明了仿真方法的准确性。研究结果对于通过微波消融术前模拟来确定合适的发射功率和作用时间,以及制订合理的手术计划有重要的参考价值。     

激光与生物组织相互作用：光子迁移与生物传热理论

激光热疗中,激光与生物组织相互作用研究主要包含两方面：光子在生物组织中的迁移规律,以及光生扫热在生物组织在的传导。对前者的描述主要为,基于传输理论的解析法和Ｍｏｎｔｅ￣Ｃａｒｌｏ模拟,生物组织中光子迁移规律的研究能定量描述组织中的光分布,并进一步获得生物组织中的热分布;考虑到了生物组织特性,所建立了生物组织中温度场分布及变化规律。光子迁移与生物传热理论是研究激光热序不可分割的传热模型,全面描述了生     

高强度聚焦超声肿瘤治疗焦域的仿真研究

数值仿真是预测高强度聚焦超声(high intensity focused ultrasound,HIFU)治疗的温度分布、确定治疗剂量的有效方法之一。本研究采用Westervelt方程的近似式,并结合Pennes生物热传导方程,以猪肝肿瘤为例,在考虑肝组织声学特性对HIFU温度场影响的条件下,通过时域有限差分法仿真研究辐照时间和声强对肿瘤组织内可治疗焦域体积的影响。研究结果表明,一定声强条件下,肝组织声学特性对肿瘤内可治疗焦域的影响随着辐照时间的延长而凸显;可治疗焦域体积随时间增长或声强增大而非线性增加;相同辐照条件下,肿瘤组织内的可治疗焦域体积大于肝组织内的;当可治疗焦域体积一定时,辐照声强和辐照时间呈负相关;同时,等效热剂量判定的可治疗焦域大于温度阈值判定的可治疗焦域,且二者之差随声强而变化。     

基于有限元方法的角膜组织热分析研究

生物医学与虚拟现实技术、计算机仿真技术的结合是现代科学与技术的一个重要发展趋势。为了解决角膜热成形术中的预测性及可控制性问题,本文针对角膜的特性进行医学虚拟研究,分析其变形机理;利用有限元方法,模拟了激光作用于眼角膜时的温度场分布情况,给出了不同参数下的激光作用时角膜的温度场分布曲线和穿透深度的比较;仿真结果表明,激光能量对角膜组织穿透深度影响很大,为角膜热成形术的研究提供了定性的基础,在减少实验费用、提高手术的预测性方面有非常重要的价值。     

980 nm半导体激光照射对种植体表面结构和温度影响的实验研究

目的:980 nm半导体激光可用于种植体周围软组织处理和种植体周围炎治疗,但其对种植体的作用尚未完全被了解。本文研究980 nm半导体激光照射对种植体表面结构和温度变化的影响,以期为临床使用参数设置和操作方法提供依据。方法:980 nm半导体激光照射纯钛圆盘试件,扫描电镜观察钛盘表面结构变化,热电偶检测钛盘温度变化范围和到达骨组织损伤温度升高阈值(10℃)的照射时长。结果:实验全部参数设置下980 nm半导体激光照射,钛盘表面结构均无明显改变。脉冲模式输出功率1 W,移动照射20 s钛盘温度上升19.8℃;经过10.2 s钛盘温度升高可达10℃。连续输出模式或增加输出功率,钛盘温度显著上升,并可在数秒内超过10℃。结论:980 nm半导体激光照射对种植体表面结构无损伤,但存在种植体温度升高造成周围组织热损伤的风险。     

森林火旋风研究进展

火旋风是林火蔓延过程中的特殊火行为现象,与树冠火和飞火关系密切.火旋风的发生机理在于旋转涡的生成和发展.构建室内火旋风模拟发生装置是当前火旋风研究的常用方法.在室内模拟试验中,红外热像和热电偶可用于测量火焰温度,高速摄影、三维激光多普勒和皮托管用于测量火旋风的转速.基于室内实验数据,可构建模拟火旋风发生发展的三维模型.     

森林火旋风研究进展

火旋风是林火蔓延过程中的特殊火行为现象,与树冠火和飞火关系密切.火旋风的发生机理在于旋转涡的生成和发展.构建室内火旋风模拟发生装置是当前火旋风研究的常用方法.在室内模拟试验中,红外热像和热电偶可用于测量火焰温度,高速摄影、三维激光多普勒和皮托管用于测量火旋风的转速.基于室内实验数据,可构建模拟火旋风发生发展的三维模型.     

Modeling of laser coagulation of tissue with MRI temperature monitoring

Light energy from a laser source that is delivered into body tissue via a fiber-optic probe with minimal invasiveness has been used to ablate solid tumors. This thermal coagulation process can be guided and monitored accurately by continuous magnetic resonance imaging (MRI) since the laser energy delivery system does not interfere with MRI. This report deals with mathematical modeling and analysis of laser coagulation of tissue. This model is intended for "real-time" analysis of magnetic resonance images obtained during the coagulation process to guide clinical treatment. A mathematical model is developed to simulate the thermal response of tissue to a laser light heating source. For fast simulation, an approximate solution of the thermal model is used to predict the dynamics of temperature distribution and tissue damage induced by a laser energy line source. The validity of these simulations is tested by comparison with MRI-based temperature data acquired from in vivo experiments in rabbits. The model-simulated temperature distribution and predicted lesion dynamics correspond closely with MRI-based data. These results demonstrate the potential for using this combination of fast modeling and MRI technologies during laser heating of tissue for online prediction of tumor lesion size during laser heating.     

Modelling and simulation of porcine liver tissue indentation using finite element method and uniaxial stress–strain data

We hypothesize that both compression and elongation stress–strain data should be considered for modeling and simulation of soft tissue indentation. Uniaxial stress–strain data were obtained from in vitro loading experiments of porcine liver tissue. An axisymmetric finite element model was used to simulate liver tissue indentation with tissue material represented by hyperelastic models. The material parameters were derived from uniaxial stress–strain data of compressions, elongations, and combined compression and elongation of porcine liver samples. in vitro indentation tests were used to validate the finite element simulation. Stress–strain data from the simulation with material parameters derived from the combined compression and elongation data match the experimental data best. This is due to its better ability in modeling 3D deformation since the behavior of biological soft tissue under indentation is affected by both its compressive and tensile characteristics. The combined logarithmic and polynomial model is somewhat better than the 5-constant Mooney–Rivlin model as the constitutive model for this indentation simulation.     

Laser-induced heating of dextran-coated mesocapsules containing indocyanine green

Indocyanine green (ICG) is a photosensitive reagent with clinically relevant diagnostic and therapeutic applications. Recently, ICG has been investigated for its utility as an exogenous chromophore during laser-induced heating. However, ICG's effectiveness remains hindered by its molecular instability, rapid circulation kinetics, and nonspecific systemic distribution. To overcome these limitations, we have encapsulated ICG within dextran-coated mesocapsules (MCs). Our objective in this study was to explore the ability of MCs to induce thermal damage in response to laser irradiation. To simulate tumorous tissue targeted with MCs, cylindrical phantoms were prepared consisting of gelatin, intralipid emulsion, and various concentrations of MCs. The phantoms were embedded within fresh chicken breast tissue representing surrounding normal tissue. The tissue models were irradiated at lambda = 808 nm for 10 min at constant power (P = 4.2 W). Five hypodermic thermocouples were used to record the temperature at various depths below the tissue surface and transverse distances from the laser beam central axis during irradiation. Temperature profiles were processed to remove the baseline temperature and influence of light absorption by the thermocouple and subsequently used to calculate a damage index based on the Arrhenius damage integral. Tissue models containing MCs experienced a maximum temperature change of 18.5 degrees C. Damage index calculations showed that the heat generation from MCs at these parameters is sufficient to induce thermal damage, while no damage was predicted in the absence of MCs. ICG maintains its heat-generating capabilities in response to NIR laser irradiation when encapsulated within MCs. Such encapsulation provides a potentially useful methodology for laser-induced therapeutic strategies.     

Temperature evolution in tissues embedded with large blood vessels during photo-thermal heating

During laser-assisted photo-thermal therapy, the temperature of the heated tissue region must rise to the therapeutic value (e.g., 43 °C) for complete ablation of the target cells. Large blood vessels (larger than 500 micron in diameter) at or near the irradiated tissues have a considerable impact on the transient temperature distribution in the tissue. In this study, the cooling effects of large blood vessels on temperature distribution in tissues during laser irradiation are predicted using finite element based simulation. A uniform flow is assumed at the entrance and three-dimensional conjugate heat transfer equations in the tissue region and the blood region are simultaneously solved for different vascular models. A volumetric heat source term based on Beer–Lambert law is introduced into the energy equation to account for laser heating. The heating pattern is taken to depend on the absorption and scattering coefficients of the tissue medium. Experiments are also conducted on tissue mimics in the presence and absence of simulated blood vessels to validate the numerical model. The coupled heat transfer between thermally significant blood vessels and their surrounding tissue for three different tissue-vascular networks are analyzed keeping the laser irradiation constant. A surface temperature map is obtained for different vascular models and for the bare tissue (without blood vessels). The transient temperature distribution is seen to differ according to the nature of the vascular network, blood vessel size, flow rate, laser spot size, laser power and tissue blood perfusion rate. The simulations suggest that the blood flow through large blood vessels in the vicinity of the photothermally heated tissue can lead to inefficient heating of the target.     

Isopycnic density values for lysosomes and mitochondria in rat adrenal cortex

Adrenocortical tissues of male adult Wistar rats were fractionated by isopycnic density gradient centrifugation. Fractions were analyzed for density, protein and marker enzymes for lysosomes and mitochondria with rat liver being used as a reference tissue for subcellular enzyme distribution. Both lysosomes and mitochondria of adrenal cortex showed unimodal distribution profiles of marker enzymes with their modal isopycnic density values at 1.165. This value was significantly lower than the corresponding ones for lysosomes and mitochondria in rat liver but was very close to those in porcine adrenal cortex. Modal isopycnic density as well as distribution profiles of marker enzymes for lysosomes and mitochondria remained unchanged 24 hr after 0.1 or 10 units of ACTH (Cortrosyn Z) administration. As in porcine adrenal cortex, lysosomes in rat adrenal cortex were characterized by a higher content of cathepsin D than those in rat liver.     

Multiple freezing points as a test for viability of plant stems in the determination of frost hardiness

A technique is presented for a simple, rapid, and reliable means of determining the viability of plant tissue subjected to freezing temperatures. Freezing curves of excised stems of Cornus stolonifera Michx., and several other genera were studied. Tissue temperature was recorded during freezing of plant stem sections. The heat of crystallization deflected the resultant freezing curves at points where tissue froze. Living stem sections of all genera studied revealed 2 freezing points, while dead tissue exhibited only 1. The influence of variables such as moisture content, sample size, thermocouple placement, and cooling rate on freezing curves was analyzed. Stem samples wrapped in moisture-proof film with a thermocouple inserted into the pith were frozen to a predetermined test temperature, thawed, and subjected to a second freezing cycle. The presence or absence of 2 freezing points in the second freezing cycle was used as a criterion for establishing viability. The results were immediately available and identical to results from regrowth tests which took about 20 days.     

汞与硒在不同汞暴露水平地区猪肝脏和肾脏蛋白质中的分布

通过对贵州万山汞污染地区及北京地区猪肝脏和肾脏组织上清液进行凝胶过滤色谱分离(SephadexG 10 0 ) ,随后用原子荧光法测定它们蛋白质组分中汞和硒的含量 ,研究在汞暴露水平不同状态下微量元素汞和硒在动物体蛋白质分子水平上的分布 .发现这两个地区猪肝脏和肾脏组织上清液蛋白质组分中汞和硒的分布模式有明显差异 .贵州万山汞污染地区猪肝脏上清液中汞浓度比北京地区高 ,硒浓度也相应高 ,且前者与高分子量和低分子量蛋白结合的硒均明显高于后者 ;而北京地区猪肝脏上清液中的硒主要以与高分子量蛋白结合的形式存在 .贵州汞污染地区猪肝脏上清液中汞主要与高分子量蛋白结合 ,而北京地区猪肝脏上清液中汞则分布较为均匀 .贵州万山地区猪肾脏上清液中 ,含硒峰在高分子量蛋白区和低分子量区都有分布 ;而北京地区猪肾脏上清液中 ,硒则主要集中分布于高分子量蛋白范围 .这两个地区猪肾脏上清液中都有分子量约为 11kD的金属硫蛋白 (MT)存在 ,北京地区猪肾脏上清液中汞主要以与金属硫蛋白结合的形式出现 ,而贵州万山地区猪肾脏上清液中的汞除与金属硫蛋白结合外 ,尚有相当大部分是以与高分子量蛋白结合的形式存在 .研究结果表明 ,由于这两个地区汞暴露水平的差异 ,不仅使这两地区猪肝、肾上清液中的汞与硒含量