考虑血液灌注温度依赖特性的相变生物传热分析

目的 基于温度依赖型血液灌注率,分析生物组织在体表冷刀作用下的降温冻结及相应的复温过程。方法 依据经典Pennes生物传热方程。用变时间步长的隐式有限差分法,通过循环迭代逼近来求解。结果 数值计算得到体表冷刀温度固定（-196℃及-30℃）和体表冷刀降温速度恒定（8.95℃/min)两种情况下不同血液灌注率（血液灌注率为常数,零、随温度变化及平均血液灌注率）对生物组织降温及相变过程的温度影响,瞬态降温速度分布及复温的温度响应。结论 血液灌注率的温度依赖模型较传统平均血液灌注率模型更接近活体组织的实际血液灌注率,而基于两者的相变分析差别显著。因此低温外科手术中精确温度预示应采用前者,本文结果对其有积极的参考价值。     

冷冻手术时生物组织相变传热过程的数值模拟

目的 通过模拟一个完整的组织冻融过程来了解手术过程中的热传递过程.方法 考虑到肿瘤组织和正常组织的不同热物性,建立了一个生物组织的相变传热模型.假设生物组织为多孔介质,并且考虑组织中骨架和流体(如组织液)的不同性质.采用显热容法解决相变问题.结果 研究结果表明在冻结过程中,冷刀初始温度越低,冷刀降温速度越快,组织温度下降得越快;在融化过程中,冷刀升温速度越快,组织温度上升得越快.同时研究表明生物组织的孔隙率以及血液灌注率和新陈代谢都对组织温度变化有着重要的影响.结论 研究生物组织在冷冻手术中的热传递过程,对于冷冻手术今后的开发利用有着重要的启发作用.     

低温液体灌注产生亚低温的进展

低温对脑损伤的保护作用已被众多动物实验所证实,在临床方面,尤其是发现轻度和中度低温的保护作用之后,应用逐渐增多.近年来,亚低温被用于治疗新生儿缺氧性脑病、心肺复苏后脑保护、脑外伤及脑卒中等领域.目前临床及实验中所应用的低温方式主要为全身亚低温,如降温毯、冰袋等,这些方式降温效率低,不易迅速实现亚低温,而且全身低温可伴有多种并发症,如心律紊乱、凝血功能障碍等.低温液体或自体血液灌注是目前最有效的降温方式,而且局部动脉内灌注低温液体更可以快速实现局部亚低温.介入技术的进步使得快速局部动脉内低温液体灌注成为可能.我们详细回顾相关动物实验及临床应用文献,介绍低温液体灌注产生亚低温的研究进展.     

激光汽化活体生物组织的传热过程分析

目的研究激光汽化生物活体组织的传热过程及其影响因素.方法基于血液灌注率温度依赖型Pennes 生物传热方程,建立激光与生物活体组织热相互作用的一般模型,研究组织表面发生汽化相变、中间组织出现热凝结、内层组织发生温升的过程.由此探讨组织中的激光传输特性, 以及血液灌注率和边界冷却等因素的影响情况.结果通过数值计算,得出活体组织表面汽化速度及内部温度分布.研究表明,活体组织对不同激光的吸收能力、血液灌注率与边界冷却条件对组织汽化速度、组织凝结过程及温度分布有显著影响.结论该模型可用于预测激光汽化蚀除组织的过程,分析结果对激光临床应用具有理论指导意义.     

激光汽化活体生物组织的传热过程分析

目的：研究激光汽化生物活体组织的传热过程及其影响因素，方法：基于血液灌注率温度依赖型Pennes生物传热方程，建立激光与生物活体组织热相互作用的一般模型，研究组织表面发生汽化相变，中间组织出现热凝结，内层组织发生温升的过程，由此探讨组织中的激光传输特性，以及血液灌注率和边界冷却等因素的影响情况。结果：通过数值计算，得出活体组织表面汽化速度及内部温度分布，研究表明，活体组织对不同激光的吸收能力，血液灌注率与边界冷却放松择组织汽化速度，组织凝结过程及温度分布有显著影响。结论：该模型可用于预测激光汽化蚀除组织的过程，分析结果对激光临床应用具有理论指导意义。     

让冻伤冻疮远离冬训场

<正>冻伤和冻疮是部队官兵在冬季经常会遇到的两种病,两者不是一会回事:前者为全身或局部组织的损伤,后者的炎症较为局限,但有时两者同时存在。致病原因三九严冬,大雪纷飞,如果人体长时间受到寒冷的侵袭,外露的皮肤受到冷冻的刺激,皮下的小血管(动脉)发生痉挛而收缩,静脉瘀血,导致血液循环发生障碍而流通不畅,体内产热不足,发生全身或局部的血液瘀滞、组织缺氧、体温降低,从而造成局部皮肤或肌肉损伤。     

氩氦刀冷冻手术中冻结与复温问题的数值模拟

目的 通过对Endocare型氩氦冷刀的工作性能进行数值模拟,考察其优缺点,为肿瘤冷冻治疗提供参考。方法 针对组织的冷冻及复温,用等效比热法及等热流边界条件预测刀头外周组织的温度变化及组织内冰球的生长演化过程,并分析活体组织内的传热行为。结果 氩氦刀冷冻时,刀头附近组织能在短时间内下降到很低的温度;冰球在冷冻初期增长很快,此后增长速率明显下降,当工质由氩切换为氦后,冰球很快熔化;相同冷冻条件下,氩氦刀在不同组织中产生的冰球的增长速度差别较大。结论 氩氦刀具有较好的快速冷冻和复温性能,但其有效杀灭范围十分有限,对大块肿瘤,需采用多刀联用。     

实验性降温延长止血带时间致骨骼肌损伤的光镜和超微结构观察

临床上，使用降温延长止血带一次使用时间有利于手术的进行。笔者在家兔后肢作了低温下延长止血带时间和再灌注的实验，在光镜和电镜下观察局部肌肉组织的病理改变。结果显示，低温下缺血４小时再灌注１～２小时对肌肉的损伤较轻，肌膜多无明显损伤。提示在此条件下手术较为安全。     

脑出血灶周损伤的功能性磁共振成像

尽管脑出血产物会影响局部磁场均匀性,但利用扩散加权成像、灌注加权成像以及波谱等功能性磁共振成像技术对脑血肿周围组织进行研究,可从血肿周围水肿的性质和形成机制、血流动力学改变以及组织代谢等方面观察脑出血对其周围组织的影响,有助于深入理解和认识血肿周围损伤机制,指导临床制定合理的治疗方案和预后评估.     

快速冰冻切片组织的固定冻切与新鲜冻切的比较

<正> 手术中快速病理诊断以往在没有冷刀设备,尤其是没有恒冷低温切片机的条件下,都采用先将送检组织固定而后冷冻切片方法。近年来我们采用德国Leica冰冻切片机对50例送检标本分别进行加温煮沸固定冻切与新鲜冻切     

Positron emission tomography in oncology--the Massachusetts General Hospital experience

Positron tomography has been used to measure blood flow, oxygen utilization, and glucose metabolism in soft-tissue tumors in rabbits and in human tumors in extremities. Both blood flow and oxygen utilization were increased in tumor in contrast to normal muscle tissue. Oxygen extraction fraction was, however, decreased in tumor. The most sensitive indicator of tumor growth was the glucose metabolic rate. The effect of irradiation was observed by blood flow measurements in human tumors and by blood flow and oxygen utilization in tumors in rabbits. Blood flow increased both in tumor and normal muscle tissue during irradiation and decreased afterwards. Oxygen utilization decreased in tumor and increased in normal tissue during irradiation.     

Dual Reciprocity Boundary Element Method for Solving Thermal Wave Model of Bioheat Transfer

将新近发展出的双倒易边界元方法拓展应用于生物传热热波模型的求解。在一定边界条件和微波空间加热条件下对二维生物组织中的温度场演化进行了模拟，初步得出一些有益结论。该方法的有效性通过与常规有限差分法在一维情况下进行比较后得到了证明。双倒易边界元方法因其不受生物体的复杂形状所限、无需空间离散因而具有可节省大量计算时间及容易处理不同的生物传热模型等优点，可能成为今后高低温医疗技术中用于生物体温度场预示和控制的重要方法     

求解生物传热热波模型的双倒易边界元方法

将新近发展出的双倒易边界元方法拓展应用于生物传热热流模型的求解。在一定边界条件和微波空间加热条件下对二维生物组织中的温度场演化进行了模拟，初步得出一些有益结论。该方法的有效性通过与常规有限差分法在一维情况下进行比较后得到了证明。双倒易边界元方法因其不受生物体的复杂形状所限、无需空间离散因而具有可节省大量计算时间及容易处理不同的生物传热模型等优点，可能成为今后高低温医疗技术中用于生物体温度场预示和控     

Simultaneous temperature and regional blood volume measurements in human muscle using an MRI fast diffusion technique

The thermal dependence of the translational diffusion coefficient and of the regional blood volume was investigated in vivo by using a special MR pulsed gradient technique with reduced sensitivity to bulk tissue motion. Measurements were done at 0.5 T, using a small gradient insert. The diffusion coefficient of muscle water was calibrated against thermocouple-measured temperature in vitro, both with the muscle fibers parallel and perpendicular to the diffusion gradient. The maximum muscle temperature variation obtained by percutaneous conduction was ?8.8 ± 1.6°C under cooling and +3.7 ± 1.6°C under heating, from basal state. Simultaneously the fractional regional blood volume decreased by a factor of 3.5 under cooling and increased by a factor of 2.7 under heating. Due to the interdependence of microcirculation and tissue temperature, this technique may be used to follow heat production or deposition in living tissue (muscle exercise, electromagnetic irradiation, etc.).     

葛胺酮对在体和离体动物脑动脉舒张作用的研究

目的研究葛胺酮对在体和离体动物脑动脉的舒张作用。方法在体实验采用激光多普勒血流仪,连续动态观察葛胺酮对正常大鼠脑血流灌注压、血压(收缩压、舒张压、平均动脉压)、心率、心电图指标的的影响。体外实验采用分离犬基底动脉条,分别以重酒石酸去甲肾上腺素(5 mg·L-1),KCl(3 mol·L-1),5-羟色胺(3.3 mg·L-1)收缩效应的百分率作为评价抑制强度的指标,研究葛胺酮对基底动脉的舒张作用强度及特点。结果在体实验观察到葛胺酮25、50、100 mg·kg-1对大鼠脑血流量灌注压均有增加作用,100 mg·kg-1组比给药前脑血流增加了2～3倍。葛胺酮在增加脑血流量的同时对收缩压、舒张压均有短暂的降压作用,舒张压下降幅度大于收缩压,平均血压下降了10～40 mmHg。体外实验发现葛胺酮0.01、0.1 mg·ml-1对重酒石酸去甲肾上腺素、KCl、5-羟色胺诱导的犬基底动脉收缩均有明显的抑制作用,其舒张率达21%～99%。结论葛胺酮具有增加脑血流量同时降低血压的作用,优于葛根素。其增加脑血流量的作用与其舒张动脉的作用有关。葛胺酮可能是一个多靶点的血管紧张抑制剂,对脑缺血可能具有一定的保护作用,值得进一步研究。     

Electromagnetic and thermal modeling of SAR and temperature fields in tissue due to an RF decoupling coil.

The finite difference time domain method is used to calculate the specific absorption rate (SAR) due to a butterfly surface coil in a realistic tissue model of the leg. The resulting temperature distribution and temperature changes are found using a finite difference solution to the bioheat transfer equation. Reasonable agreement is found between predicted temperature changes and those measured in vivo provided that the resulting hyperthermia does not induce noticeable changes in perfusion. The method is applicable to radiofrequency dosimetry problems associated with high Bo field magnetic resonance systems and where knowledge of spatial variation in SAR is important in assessing the safety of new magnetic resonance procedures.     

Estimation of time since death by heat-flow Finite-Element model. Part I: method, model, calibration and validation

The determination of the time since death which often represents the presumed time of an offence plays an important role in medico-legal practice. In the early postmortem phase analyses of postmortem cooling provide the most accurate estimates. Empirical models of postmortem cooling are methodically restricted to standard conditions while heat flow models can in principle be applied to any complex cooling situations. The main problem having so far prevented heat flow models from being used in practice was the difficulty of solving the heat transfer equation for complex geometrical, initial and boundary conditions. This problem is now overcome by using the Finite-Element-Method as a numerical procedure. The study presents a three-dimensional Finite-Element-Model of the human body containing various tissue compartments with different thermal tissue properties. The initial temperature field is modelled inhomogeneously with a temperature gradient between body core and shell. Heat loss by conduction, convection and radiation as well as heat gain by supravital activity or irradiation from external sources can be simulated. One model parameter, the decrease rate of the supravital energy production, was calibrated and the model successfully validated using the experimentally verified empirical model by Marshall and Hoare.     

Salivary IgA response to prolonged exercise in a cold environment in trained cyclists

PURPOSE: The purpose of the present study was to determine the effect of a prolonged bout of exercise in freezing cold conditions on saliva immunoglobulin A (s-IgA) responses in endurance-trained males. METHODS: Using a randomized cross-over design, 15 trained male cyclists cycled for 2 h on a stationary ergometer at 70% VO(2max) in an environmental chamber on one occasion at a temperature of -6.4 +/- 0.1 degrees C (cold) and on another occasion at a temperature of 19.8 +/- 0.2 degrees C (control). Trials began at 12:30 h to avoid the fall in s-IgA concentration that occurs during the morning hours. Unstimulated whole-saliva samples were collected over a 2-min period at preexercise, postexercise, and 2-h postexercise. The s-IgA concentration was determined using a sandwich-type ELISA method. RESULTS: Saliva flow rate decreased postexercise by 31%, returning to preexercise levels by the 2-h postexercise collection (main effect of time: < 0.01). The decrease in saliva flow rate postexercise in the control trial (39% compared with 22% on cold trial) approached significance (interaction: = 0.08) and may have accounted for the corresponding increase in s-IgA concentration postexercise in the control trial (s-IgA concentration: control preexercise; 91 +/- 12; postexercise; 110 +/- 13 mg x L(-1); < 0.05). Saliva IgA secretion rate decreased postexercise by 19.5% returning to preexercise levels by 2-h postexercise measure (main effect of time: < 0.05). CONCLUSIONS: These data show that performing a bout of prolonged exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in freezing cold conditions does not influence saliva flow rate or s-IgA secretion rate responses to prolonged exercise.     

Simultaneous temperature and magnetization transfer (MT) monitoring during high‐intensity focused ultrasound (HIFU) treatment: Preliminary investigation on ex vivo porcine muscle

Purpose

To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high‐intensity focused ultrasound (HIFU) treatment.

Materials and Methods

This study proposed an interleaved dual gradient‐echo technique to monitor the heat and tissue damage brought to the heated tissue. The technique was applied to tissue samples to test its efficacy.

Results

Ex vivo experiments on the porcine muscle demonstrated that both temperature changes and MTR exhibited high consistency in localizing the heated regions. As the heat dissipated after the treatment, the temperature of the heated regions decreased rapidly but MTR continued to be elevated. Moreover, thermal dose (TD) maps derived from the temperature curves demonstrated a sharp margin in the heated regions, but MTR maps may show a spatial gradient of tissue damage, suggesting complimentary information provided by these two measures.

Conclusion

In a protocol of spot‐by‐spot heating over a large volume of tissue, MTR provides additional values to mark the locations of previously heated regions. By continuously recording the locations of heated spots, MTR maps could help plan the next target spots appropriately, potentially improving the efficiency of HIFU treatment and reducing undesirable damage to the normal tissue. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.