交变磁场诱导冠状动脉支架的升温

背景:对于药物涂层支架的安全性问题目前尚存在争议。磁诱导热疗可以利用交变磁场诱导磁介质升温,对局部病灶进行热疗。由于心脏支架多以不锈钢、镍、铬等合金材料构成,因此具备在磁场下的升温条件,并且目前国内外尚无通过磁诱导心脏支架升温的相关报道。目的:观察不同冠状动脉支架在交变磁场下的升温情况。探讨磁场强度、磁场频率、磁场方向及支架的材质对冠状动脉支架升温的影响规律。方法:将不同材质冠状动脉支架(316L型、镍钛合金、钴铬合金)置于交变磁场中,调节磁场参数(场强、频率)和支架长轴与磁场方向的夹角,观察上述因素对交变磁场诱导冠状动脉支架升温的影响。结果与结论:支架材料对磁场诱导升温有显著影响,并以316L型支架升温效果最好;随着支架长轴与磁场方向所成角度的增大,升温效果明显降低;随着交变磁场频率及电流强度增加温度升高更明显。     

电容式射频热疗中加热机制分析及不同组织升温速率计算

拟就加热机制和人体不同组织的升温规律方面存在的一些认识上的偏差进行探讨。从电磁场的基本原理出发,分析电容式射频加热人体组织的理论机制。在忽略射频极板边缘效应且极板之间充有多层不同电介质的模式下,分别进行极板间任意两介质中单位体积耗散的功率比、比吸收率（SAR）比以及升温速率比的理论推导,然后针对人体不同组织（如人体肌肉、脂肪、皮质骨）的电参数和物理参数进行计算。结果表明,当采用27.12 MHz射频加热时,脂肪和皮质骨的升温速率比肌肉的升温速率分别高出18.9和20.2倍,而采用40.68 MHz射频时,则是高出19.8和19.1倍。电容式射频热疗时,电导率越大的人体组织升温速率越小,各组织的升温速率极不均匀。     

基于血管介入式加热的微创性全身热疗方法

全身热疗正逐渐被认为是对已扩散全身的恶性肿瘤实施有效治疗的一种可行途径.但因缺乏简便、微创的机体升温手段,使其尚不能广泛应用于临床.针对这一技术瓶颈,本文建立了崭新的加热探针介入式微创全身热疗方法,通过对大血管直接加热并借助其内血液的输运实现高效的全身加热.并研制了一套模拟血管内加热的全身热疗试验台,系统评估了该方法的加热能力及其对血流动力学参数的影响,而且从理论上分析了新方法的可行性.理论及模拟试验均表明了血管介入式全身热疗方法的优点.最后进一步讨论了新方法中亟待改进的一些问题,展望了其在肿瘤治疗中的应用前景.     

医学EIT复合电极结构参数优化设计

目的探索医学EIT复合电极结构参数变化对系统性能的影响。方法采用笔者建立的EIT电极结构及参数优化设计方法对复合电极进行了仿真研究，研究了位于成像区域不同位置的成像目标，复合电极各结构参数改变对成像质量和系统检测灵敏度影响的规律。结果和结论各结构参数的影响错综复杂，采用多参数仿真实验的方法是一种有效的方法。     

血液介电参数与血液学指标的相关性分析

利用4294A阻抗分析仪,在频率为0.01~100 MHz范围内测量了30例健康人血液样本的交流阻抗,同时测量了血沉(ESR)、红细胞比容(HCT)、血浆纤维蛋白原(FIB)及血糖(BG)等血液学指标,在获得完整数据的基础上,我们利用线性相关分析方法分析ESR与血液介电参数的相关性;并以多元回归统计学方法分析HCT、BG及FIB对全血细胞介电谱参数的影响。统计学结果显示ESR与部分血液介电参数呈线性相关;HCT和BG对部分血液介电参数有影响,其中HCT是影响血液介电参数最主要的血液学指标。     

细胞生长与增殖的生物力学实验研究进展

作者介绍了细胞力学领域中细胞分裂、细胞增殖方面的研究进展。着重介绍了基底加载各种参数对细胞增殖的影响 ,机械拉伸对细胞粘附及生长的影响 ,力学环境对血管内皮细胞分裂过程的影响     

基于DTI的胶质瘤患者手术前后脑网络特性分析

目的利用弥散张量成像(diffusion tensor imaging,DTI)技术构建胶质瘤患者手术前后全脑结构网络和半脑结构网络,基于图论知识对脑网络参数进行定量研究及对比分析,探究胶质瘤及肿瘤切除手术对患者脑网络拓扑特性的影响。方法构建健康对照组、胶质瘤患者组手术前后全脑和半脑结构网络,定量分析两组大脑结构网络拓扑特性及网络参数,比较分析手术对患者全脑及半脑网络特性的影响。结果从全脑角度看,患者术后各全局网络参数较正常人均有所降低,但是小世界特性却有所增强,患者各全局参数在术前术后均无显著差异,患者术后的全脑局部参数明显低于术前;在半脑结构网络中,手术前后半脑全局参数无明显差异,而术后半脑全局参数明显低于术前。结论手术使得脑结构网络的局部脑区发生损伤,但并未对患者全脑及半脑全局参数造成显著影响,研究证实了人类大脑的代偿机制以及功能重组。该研究方法可对胶质瘤患者术后的疾病发展状况以及手术治疗效果评价提供帮助。     

封闭式“远红外”暖箱

一、前言我们研制的封闭式“远红外”暖箱,主要用于对新生儿硬肿症,早产及其他低温婴儿作“同步升温”,亦可作为普通恒温暖箱使用。工作时,由电路自动控制、婴儿的体温和暖箱的箱温分别由表头显示。作“同步升温”用时,可选择暖箱的箱温与待复温婴儿的体温之温差保持为某确定值(或1℃,或2℃,或3℃)自动的“同步升温”,直     

升温输液对烧伤休克兔肠系膜微循环的影响

目的探讨升温输液对烧伤休克兔肠系膜微循环的影响。方法将30只新西兰兔随机分成两组，建立烧伤休克模型，一组采用低温（18℃）输液，另一组采用升温（37℃）输液，分别观测肠系膜微循环的变化。结果升温输液组与低温输液组相比较，肠系膜微动脉管径（AD）、微静脉管径（VD）显著增大（P〈0．001），微动脉血流速度（AFV）和微静脉血流速度（VFV）明显增快（P〈0．（105），毛细血管血流流态由线粒流变为线流。低温输液组微血管周围有渗出与出血13例，血流中发现有微小血栓8例，而升温输液组微血管周围有渗出与出血4例，血流中发现有微小血栓2例，两组比较差异均有统计学意义（P〈0．01）。结论升温输液对改善烧伤休克肠系膜微循环，并对烧伤休克所致多器官损害具有一定防治作用。     

水、啤酒及药物对健康人胃电参数的影响

水、啤酒及药物对健康人胃电参数的影响     

柱面换能器声场在组织中的温度分布估计

本文分析了柱面聚焦换能器的声场特点,剖析了方向比（ratio）与声场的关系。结果表明：声场随方向比的降低而焦点强度减弱,声强最大值前移。在求解声场的基础上,对该类换能器的声场在组织中的温度分布进行估计,给出了组织内温度随时间变化的曲线,分析了方向比（ ratio）对焦区温度分布的影响,为该类换能器的参数选择和组织中的温度分布估计提供了参考。     

Comparison of modelled and observed in vivo temperature elevations induced by focused ultrasound: implications for treatment planning

Two numerical models for predicting the temperature elevations resulting from focused ultrasound heating of muscle tissue were tested against experimental data. Both models use the Rayleigh-Sommerfeld integral to calculate the pressure field from a source distribution. The first method assumes a source distribution derived from a uniformly radiating transducer whereas the second uses a source distribution obtained by numerically projecting pressure field measurements from an area near the focus backward toward the transducer surface. Both of these calculated ultrasound fields were used as heat sources in the bioheat equation to calculate the temperature elevation in vivo. Experimental results were obtained from in vivo rabbit experiments using eight-element sector-vortex transducers at 1.61 and 1.7 MHz and noninvasive temperature mapping with MRI. Results showed that the uniformly radiating transducer model over-predicted the peak temperature by a factor ranging from 1.4 to 2.8, depending on the operating mode. Simulations run using the back-projected sources were much closer to experimental values, ranging from 1.0 to 1.7 times the experimental results, again varying with mode. Thus, a significant improvement in the treatment planning can be obtained by using actual measured ultrasound field distributions in combination with backward projection.     

基于声换能器特性的磁感应磁声成像正问题分析

目的在考虑声换能器特性的基础上,对磁感应磁声成像的正问题进行研究,并探讨其声源的产生、传播及接收机制。方法参考CT的三维Phantom仿真模型建立磁感应磁声成像正问题的模型,并结合电磁场理论利用有限元软件comsol仿真分析模型内部电导率分布与磁场和磁感应电场的关系,得到模型内部的磁感应电流分布。然后再深入研究声偶极子模型,并检测分析声换能器的特性后,给出相应的仿真声信号检测结果。结果磁感应电流密度在中心位置处为0,在电导率边界处变化较大,声换能器的检测声场分布和声偶极子传播的指向性会极大的影响声换能器接收到的磁声信号的值。结论为磁感应磁声成像实验研究及由声信号重建物体内部的电导率分布提供理论基础。     

HIFU在牛肝组织中的传播衰减研究

运用辐射压力法研究高强度聚焦超声在牛肝组织中的传播衰减。在室温 2 0℃下 ,利用 4种治疗超声换能器 ,在不同的换能器表面输出声功率下 ,分别测量 2 0、4 0、6 0、80 m m不同厚度新鲜离体牛肝在放入脱气水前后的声辐射力 F、F′,然后计算出声衰减。使用治疗超声换能器 4 ,对于不同辐照深度 ,以声强 ISATA=2 2 .0× 10 3W/cm2、辐照时间 5 s的超声剂量定点辐照新鲜离体牛肝 ,以断层方式剖开后测量凝固性坏死组织体积。研究结果表明 ,对于一个具体的治疗超声换能器 ,在牛肝厚度一定时 ,辐射力穿透率 F′/F法与换能器表面声强及样品近治疗超声换能器表面声窗面积无关。采用最小 F′/F法拟合得出辐射力穿透率随牛肝厚度增加呈指数规律递减 ,且与凝固性坏死组织体积随牛肝厚度 (辐照深度 )增加呈指数规律递减趋势一致。采用最小二乘法拟合得出高度聚集超声在牛肝组织中传播的声衰随频率近似线性增加且呈幂函数关系。这为进一步研究高强度聚焦超声治疗剂量学提供了实验依据     

Design and construction of an esophageal phased array probe

The clinical urge for echocardiographic data from patients with inadequate image quality at the precordial examination has initiated the development of transesophageal scanning techniques. The orientation of heart structures with respect to the transducer position in the esophagus, the absence of interfering structures in the soundbeam and the constraints imposed by the anatomy of the esophagus result in a different set of parameters for the optimization of the transducer and its assembly. In this article, the design and construction of a miniaturized 5 MHz phased array transducer optimized for transesophageal scanning is described. Relevant parameters and their influence on the design will be discussed, such as: bandwidth, sensitivity, resolution (in three dimensions), focal depth and the production method.     

Photoplethysmography

Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) were compared and evaluated. The comparison was accomplished considering differences in physical principles and geometrical and optical conditions. Changes in human skin perfusion were induced by cold and hot water provocation on limited areas of the finger and the forearm. The results showed that LDF and PPG, using red light at 630-660 nm and a commercial PPG probe, were in general equally sensitive in detecting a blood perfusion increase following a skin temperature elevation. However, we also found that PPG occasionally showed an inverse response to a skin temperature elevation, especially in finger skin. Furthermore, the study indicated that laser light is unsuitable as a light source in PPG using optical fibres of small diameter and with no fibre separation. It was also found that the physical dimensions of the probe (including the light source and photodetector) play an important role in determining the measuring volume and the quality of the signal.     

Optimization of power deposition and a heating strategy for external ultrasound thermal therapy.

The purpose of this paper is to examine the thermal dose distribution, to configure the optimal absorbed power deposition, and to design an appropriate heating strategy for ultrasound thermal therapy. This work employs simulation programs, which are based on the transient bio-heat transfer equation and an ideal absorbed power deposition or an ideal temperature elevation within a cube of tissue, to study the optimal absorbed power deposition. Meanwhile, a simplified model of a scanned ultrasound transducer power deposition (a cone with convergent/divergent shape) is used to investigate the heating strategy for a large tumor with a sequence of heating pulses. The distribution of thermal dose equivalence defined by Sapareto and Dewey is used to evaluate the heating result for a set of given parameters. The parameters considered are the absorbed power density, heating duration, temperature elevation, blood perfusion, and the size of heating cube. The results demonstrate that the peak temperature is the key factor determining the thermal dose for this short-duration heating. Heat conduction has a very strong influence on the responses of temperature and thermal dose for a small heating cube and the boundary portion of a large heating cube. Hence, for obtaining the same therapeutic result, a higher power density is required for these two conditions to compensate the great temperature difference between the heating cube and the surrounding tissue. The influence of blood perfusion on the thermal dose is negligible on the boundary portion of the heating cube, while in the central portion it may become a crucial factor as a lower power density is used in this portion to save the delivered energy. When using external ultrasound heating method to treat a large tumor, the size of heating unit, the sequence of heating pulses, and the cooling-time interval between the consecutive heating pulses are the important factors to be determined to have an appropriate treatment within a reasonable overall treatment time.     

FDTD analysis of human body-core temperature elevation due to RF far-field energy prescribed in the ICNIRP guidelines

This study investigated the relationship between the specific absorption rate and temperature elevation in an anatomically-based model named NORMAN for exposure to radio-frequency far fields in the ICNIRP guidelines (1998 Health Phys. 74 494-522). The finite-difference time-domain method is used for analyzing the electromagnetic absorption and temperature elevation in NORMAN. In order to consider the variability of human thermoregulation, parameters for sweating are derived and incorporated into a conventional sweating formula. First, we investigated the effect of blood temperature variation modeling on body-core temperature. The computational results show that the modeling of blood temperature variation was the dominant factor influencing the body-core temperature. This is because the temperature in the inner tissues is elevated via the circulation of blood whose temperature was elevated due to EM absorption. Even at different frequencies, the body-core temperature elevation at an identical whole-body average specific absorption rate (SAR) was almost the same, suggesting the effectiveness of the whole-body average SAR as a measure in the ICNIRP guidelines. Next, we discussed the effect of sweating on the temperature elevation and thermal time constant of blood. The variability of temperature elevation caused by the sweating rate was found to be 30%. The blood temperature elevation at the basic restriction in the ICNIRP guidelines of 0.4 W kg(-1) is 0.25 degrees C even for a low sweating rate. The thermal time constant of blood temperature elevation was 23 min and 52 min for a man with a lower and a higher sweating rate, respectively, which is longer than the average time of the SAR in the ICNIRP guidelines. Thus, the whole-body average SAR required for blood temperature elevation of 1 degrees C was 4.5 W kg(-1) in the model of a human with the lower sweating coefficients for 60 min exposure. From a comparison of this value with the basic restriction in the ICNIRP guidelines of 0.4 W kg(-1), the safety factor was 11.     

The influence of model parameter values on the prediction of skin surface temperature: I. Resting and surface insulation

A model is presented of heat transfer and temperature distributions in the skin and superficial tissues. It is based on a finite difference numerical solution of the one-dimensional multilayer coupled bioheat equation. In this paper, the model is used to investigate the influence of the values of parameters chosen to represent the physiological and heat transfer processes on the temperature of the skin under resting conditions and after insulation of the skin surface. Equilibrium resting temperatures were strongly influenced by deep body temperature especially at lower heat transfer coefficients on the skin surface, but slightly affected by the values chosen for skin blood flow and metabolic heat generation; both the heat transfer coefficients and environmental temperature strongly influenced the surface temperature. After surface insulation the temperature elevation was strongly influenced by the thermal conductivities of tissues, skin blood flow and deep boundary temperature; metabolic heat generation was only significantly at unphysiologically high values.     

Endotoxin-induced prostaglandin (PGF2 alpha) biosynthesis, fever and miosis in dexamethasone-treated goats

Prostaglandin-releasing, adrenocortical, febrile and miotic responses to endotoxin (ET) (E. coli lipopolysaccharide; 0.25 microgram kg-1) were studied in goats with and without prolonged dexamethasone influence. The i.v. injection of ET induced a three-fold peak elevation in plasma 15-ketodihydro-PGF2 alpha at 1.5 h post-injection, that is, between the first and second phase of the temperature elevation. During the latter phase, the plasma concentration of this primary PGF 2 alpha metabolite gradually returned to basal level, which implies that the second phase of ET fever is not PG dependent. The PG response exhibited a similar pattern, but was less pronounced in the dexamethasone-ET experiments, where the duration of maximum temperature elevation and of the miosis became shortened by about 20 min, and the typical biphasic pattern of ET fever was no longer seen. The ET-induced rise in plasma aldosterone concentration was completely blocked by dexamethasone. The corresponding rise in plasma cortisol concentration was prevented for 2 h, but was later only partially inhibited in spite of the repeated dexamethasone treatment.