Wideband frequency-dependent dielectric properties of rat tissues exposed to low-intensity focused ultrasound in the microwave frequency range

Tissue dielectric properties can vary upon the incident of an acoustic wave.The goal of this study is to quantify this change due to the acoustoelectric effect(AE),and to obtain the frequency-dependent dielectric properties of tissues exposed to low-intensity focused ultrasound(LIFU).The dielectric properties of the blood,brain,chest muscle,heart,kidney,leg muscle,liver,lung,pancreas,and spleen of rats were measured by an open-ended coaxial probe method.The acoustic intensity of LIFU focus was 2.97 MPa(67.6 W/cm^(2)),3.95 MPa(120 W/cm^(2)),and 5.17 MPa(204 W/cm^(2)),respectively,and the measurement frequency band was 0.1–7.08 GHz.The measurement results show that with the LIFU modulation,the conductivity and dielectric constant decreased in the high-frequency band,and on the contrary,they increased in the lowfrequency band,and the larger the acoustic intensity was,the more obvious the phenomenon was.This work contributes to a better understanding of the mechanisms by which ultrasound acts on the dielectric properties of biological tissues.It is expected that the findings from this study will provide a basis that the response of tissue to LIFU modulation can be monitored by noninvasive techniques such as microwave-induced thermoacoustic imaging(MTI)and microwave imaging,present a new idea for improving the endogenous contrast between different biological tissues in MTI and acoustoelectric imaging,and possibly lead to the development of a new imaging method based on the relaxation time of tissue after LIFU modulation.

MEASUREMENT OF THE DIELECTRIC PROPERTIES OF BIOLOGICAL TISSUE

An open-ended coaxial line reflection method especially suitable for meas-uring the dielectric properties of biological tissue in vivo is described.This method offersthe advantage of not requiring any special preparation of the samples to be measured but aclose contact with the open end of a coaxial line.It is,therefore,very convenient to acquirea large number of measurement data in broad band rapidly.The method may also be usedto measure the properties of other substances.The measuring system consists of a networkanalyzer controlled by a microcomputer and calibrated by using ANA procedure to elimi-hate the influnce of error network introduced by the adapter,some connectors,etc.In or-der to reach higher accuracy,the iterative method is used to determine the parameters ofthe equivalent circuit.Measurements of permeativities of some living tissues have been per-formed in the frequency band of 0.5-2GHz.Compared with the results known in somepapers,the validity of this method has been confirmed.The difference in dielectric proper-ties between living and dead tissues,and the tissue permeativites(ε)versus frequency andduration of measurement after death have also been measured.

Comparative Study on the Dielectric Properties Between Living and Non-living from Human and Animal Livers

The data of dielectric properties of human tissues mainly come from animal tissues or human corpse at present. Up to now, there has not been a report of dielectric properties of human living liver. Our objective is to study the dielectric properties of human living liver and compare the results with those of animal living liver as well as the human non-living liver. In vitro measurements of living and non-living livers from human and rabbits are shown in the 10 Hz to 100 MHz range. Analysis of the conductivity, permittivity and characteristic parameters from the data were made. The conductivity of three kinds of liver were markedly different at low frequency of 0.06 s/m (living rabbit liver), 0.13 s/m (living human liver) and 0.24 s/m (non-living human liver). The Cole parameters that best characterize the liver of human and rabbit are R0 , fc1 , R1 , and R∞ The Cole parameters that best characterize the living and nonliving liver of human are R0 , fc1 , ΔR1 , ΔR2 and R ∞ . In conclusion, we can't substitute the dielectric properties of animal or human corpse liver for the living human liver. The results suggest that the dielectric properties of living human tissues has great significance on studying.

Additive manufacturing of biodegradable magnesium-based materials:Design strategies,properties,and biomedical applications

Magnesium(Mg)-based materials are a new generation of alloys with the exclusive ability to be biodegradable within the human/animal body.In addition to biodegradability,their inherent biocompatibility and similar-to-bone density make Mg-based alloys good candidates for fabricating surgical bioimplants for use in orthopedic and traumatology treatments.To this end,nowadays additive manufacturing(AM)along with three-dimensional(3D)printing represents a promising manufacturing technique as it allows for the integration of bioimplant design and manufacturing processes specific to given applications.Meanwhile,this technique also faces many new challenges associated with the properties of Mg-based alloys,including high chemical reactivity,potential for combustion,and low vaporization temperature.In this review article,various AM processes to fabricate biomedical implants from Mg-based alloys,along with their metallic microstructure,mechanical properties,biodegradability,biocompatibility,and antibacterial properties,as well as various post-AM treatments were critically reviewed.Also,the challenges and issues involved in AM processes from the perspectives of bioimplant design,properties,and applications were identified;the possibilities and potential scope of the Mg-based scaffolds/implants are discussed and highlighted.

Thermal property of biological tissues characterized by piezoelectric photoacoustic technique

A photoacoustic piezoelectric method based on a simplified thermoelastic theory is employed to determine thermal diffusivities of biological tissues. The thermal diffu-sivities of porcine tissues with different preparation condi-tions, including fresh, dry and specially prepared conditions, are characterized. Comparing the experimental evaluated diffusivities of the tissues in three conditions with each other, it can be seen that the diffusivities of the fresh tissues are the biggest and the diffusivities of the specially prepared tissues are bigger than that of the dry ones generally. The results show that the piezoelectric photoacoustic method is espe-cially effective for determining macro-effective (average) thermal diffusivities of biological materials with micro- inhomogeneity and easy to be performed, which can provide useful information for researching thermal characters of biological tissues.

基于Morris方法的微波消融肺组织温度场参数敏感度分析

为了获取微波消融肺组织温度场中组织特性敏感度,采用有限元方法建立微波消融肺组织计算模型,进行电磁场-温度场的耦合,基于Morris方法获取组织电导率(σ)、相对介电常数(ε)、导热率(k)、密度(ρ)、比热容(Cp)和血液灌注率(ωb)的敏感度,建立二维有限元模型.肺组织的σ、ε、k、ρ、Cp、ωb六个参数各设置4个水平,分别获取在50 W、300 s时的微波消融肺组织的消融面积和中心温度,并采用Morris方法,分析各参数对消融面积和消融形状的影响程度.结果表明,血液灌注率、相对介电常数、电导率是对微波消融肺组织的消融区域和消融形状影响较大的参数.

生物医学微波热声成像

微波热声成像是一种以生物组织电特性差异为原理基础的多物理场耦合成像方法.其采用脉冲微波作为激发源,通过热弹性效应产生的超声波呈递深层生物组织的结构与功能信息,融合了微波成像高对比度和超声成像高分辨率的优点.目前已在无损脑结构成像、乳腺肿瘤筛查、人体关节炎成像、肝脂肪含量检测等方面展现出了广阔的医学应用前景,有望成为新的物理医学影像方法.本文对微波热声成像技术的物理原理、系统装置以及近来的代表性研究进展进行了系统性的介绍,并分析探讨了微波热声成像技术值得关注的发展方向以及面临的挑战.

生物组织及其细胞溶液介电谱测量研究

为阐明生物组织中细胞及组织液等电介质介电谱之间的相互关系,本研究测量了肝组织、肝细胞悬液(BRL)、肝癌细胞悬液(RH-35)、细胞培养基(dulbecco′s modified eagle medium,DMEM)、磷酸缓冲盐溶液(phosphate buffered saline,PBS)、超纯水的介电谱。测量结果显示,肝组织和超纯水介电损耗谱ε″最大值分别为6.18×10^(6)和2.60×10^(4),测量精度为9.03%和9.52%,相对介电常数谱ε′最大值分别为1.96×10^(6)和1.80×10^(3),测量精度为16.85%和12.97%;BRL、RH-35、DMEM、PBS的ε″具有峰现象,最大值分别为5.00×10^(5)、4.40×10^(5)、3.70×10^(5)、5.90×10^(5),测量精度RH-35为5.44%,其他不超过2%;ε′最大值分别为1.90×10^(6)、1.80×10^(6)、1.40×10^(6)、2.00×10^(6),测量精度RH-35为2.34%,其他不超过2.00%。结果表明,生物组织介电损耗谱ε″和相对介电常数谱ε′随频率呈单调下降,测量精度较低;而生物溶液介电损耗谱ε″呈峰现象,具有弛豫性,相对介电常数谱ε′随频率呈单调下降,测量精度较高;生物组织中的有极细胞可消耗较多的电场能量,是产生电磁生物效应的重要因素。

Comparative Study on the Dielectric Properties Between Living and Non-living from Human and Animal Livers

The data of dielectric properties of human tissues mainly comes from animal tissues or human corpse at present.Up to now,there has not been a report of dielectric properties of human living liver.This paper aims to studying the dielectric properties of human living liver and comparing the results with those of animal living liver as well as the human non-living liver.In vitro measurements of living and non-living livers from human and rabbit are shown in the range of 10 Hz to 100 MHz.Analysis of the conductivity,permittivity and characteristic parameters from the data were made.The conductivity of three kinds of liver were markedly different at low frequency: 0.06 S/m(living rabbit liver),0.13 S/m(living human liver) and 0.24 S/m(non-living human liver); The Cole parameters that best characterize the liver of human and rabbit are R0,fc1,ΔR1 and R∞; The Cole parameters that best characterize the living and non-living liver of human are R0,fc1,ΔR1,ΔR2 and R∞.In conclusion,we can't substitute the dielectric properties of animal or human corpse liver for the living human liver.The results suggest that the study on the dielectric properties of living human tissues has great significance.

正常乳腺脂肪与腺体组织介电特性研究

目的:进一步深入研究乳腺主要组成成分脂肪和腺体的介电特性差异,为准确区分乳腺各组织成分奠定基础。方法:从手术刚刚切下的患者乳腺组织样本中分别分离出正常脂肪和腺体组织,于温控箱中控制温度在37℃。先用Solartron 1294和Solartron1260阻抗分析仪相结合,在10 Hz～1 MHz频段内采用四电极法进行阻抗测量。再用Agilent4294阻抗分析仪在40 Hz～10.475 5 MHz频段内,采用两电极法进行同样的测量,测量完成时间控制在组织离体后20 min之内。利用4～40 kHz内的拟合系数,将2台仪器的测量结果——阻抗值转换成电导率和介电常数后加权拟合,再对拟合的结果进行频谱分析。结果:在所测频率范围内,脂肪组织的电导率为0.05～0.07 S/m,腺体组织的电导率为0.6～0.8 S/m;在1～1.26 kHz范围内,两者的阻抗虚部值差异最显著,脂肪组织的阻抗虚部值约为腺体组织虚部值的18倍。结论:所测频率范围内,2种主要乳腺组织在电导率、介电常数等方面均有显著差异,其电阻抗虚部在1 kHz附近的差异较为显著。因而,有望利用这一特性实现对2种组织进行区分。

植入式医学装置电场耦合式电能传输新方法

提出一种人体植入式医学装置电能传输新方法,该方法以人体组织作为耦合介质,通过体内、外耦合极板构建耦合电容,以耦合电场实现电能的无线传输。分析了人体组织的电学特性,设计了电能传输系统,并通过实验验证了该方法的可行性。实验中,通过36 cm2的耦合面积,穿越2 cm厚度的生物组织,可传输100 m W的可用电能,传输效率为35%~40%。该电能传输方式具有无电涡流致热、电磁干扰小、易于与医学仪器集成的优点,是人体植入式医学装置无线电能供给的新思路。

电场对低温保存生物组织介电特性影响的研究

以SD大鼠的肾、皮肤、肝脏、大脑皮层、心脏和肌肉为研究对象,在对其进行慢速冻结的过程中施加外电场,研究了电场对生物组织低温保存介电特性的影响。结果表明:不同条件下6种离体生物组织的阻抗均随着频率的升高而减小,介质损耗因数随着频率的升高先增大后减小;在相同频率下,电冷冻保存的阻抗和介质损耗因数介于刚离体新鲜组织与直接冷冻保存的阻抗和介质损耗因数之间。阻抗越大,损耗越低,组织新鲜度和完整性越高,说明电冷冻保存离体组织的新鲜度和完整性比直接冷冻有不同程度的提高。

热凝固对生物组织热物性影响的实验研究

本文以蛋清为实验对象,研究了热凝固对生物组织热物性的影响,测量方法为阶跃温升法。实验结果表明,热 凝固后,蛋清的热导率平均上升了6.60％。因此,生物组织的热物性不但与其化学组成有关,还与其物理状态有关;采用 热凝固的方法治疗肿瘤时,应考虑热凝固对其热物性的影响,从而实现更加有效的治疗。

翅果油树的研究进展

本文就翅果油树的生物学特性 ,经济价值以及开发利用前景作一分析 ,并对组织培养的进展作一介绍。

人体肺部组织介电特性实验研究

研究人体肺癌组织与正常组织介电特性差异,建立人体肺部组织介电参数频率谱图,为基础医学和临床诊断提供理论依据和数据参考。以肺癌手术中切下的患者癌变组织和癌周正常组织为样本,控制测试舱的温度和湿度,采用Agilent公司的4294A阻抗分析仪,在100 Hz～100 MHz频率范围内测量样本组织的介电特性。基于Cole-Cole模型利用最小二乘曲线拟合方法,提取两种组织的特征参数。在所测频率范围内,肺癌组织的相对介电常数为正常组织的3～5倍,电导率为正常组织的1.6～3.3倍,肺癌组织的介电谱明显地向低阻抗方向移动。在提取的特征参数R0、R∞、α、τ和fc中,低频电阻R0的差异具有统计学意义(P<0.05)。人体肺癌组织与正常组织的相对介电常数、电导率及低频电阻R0存在明显差异,可为人体肺组织介电特性研究和EIT测量提供基础数据。

电磁场曝露对生物组织电磁特性的影响

电磁辐射严重影响着人体的健康.电磁场生物效应的发生机制与电磁场本身的特性相关,同时也与生物组织在电磁场作用下电磁特性的改变密切相关.生物体内的信号分子、自由基以及磁颗粒等处于外加电磁场中时其电磁特性会发生变化,尤其是不同频率电磁场曝露作用下生物组织的导电、介电以及磁学等特性会有非常显著的区别.明确不同频率电磁场作用下生物组织电磁特性的变化规律是研究电磁场生物效应发生机制以及预防问题的关键.综述了近年来电磁场对于生物组织电磁特性影响的研究成果,并对未来的研究方向做了展望.

基于修正四阶Cole-Cole模型的太赫兹波段生物组织介电特性估算方法探索

为了获得生物组织在太赫兹波段的相对介电常数和电导率,在四阶Cole-Cole模型基础上进行修正,使修正后的模型不仅能描述生物组织在10 Hz^100 GHz频段的介电特性,还能描述生物组织在太赫兹波段的介电特性。在四阶Cole-Cole模型上新增了一项ωk/i,对正常皮肤组织在10 Hz^20 GHz和0.15~1.95 THz频段的介电特性的实验数据按照文献方法进行处理,提取四阶Cole-Cole修正模型的参数。在10 Hz^100 GHz频段内,原有模型和修正模型计算值的相对误差在5%以内,并且在太赫兹波段正常皮肤组织修正模型的相对介电常数和电导率的计算值与实验数据的相对误差基本在10%以内,结果验证了四阶Cole-Cole修正模型的正确性。将该修正模型应用在脑白质和脑灰质太赫兹波段的介电特性的计算中,得到脑白质和脑灰质在0.15~1.95 THz频段的相对介电常数和电导率。所提出的四阶Cole-Cole修正模型还可以对其他生物组织在太赫兹波段的介电特性进行预测。

有限宽光束在生物组织中传输的蒙特卡罗方法

基于光在生物组织中的传输理论,研究有限宽光束在生物组织中的传输特性.利用入射光强与格林函数进行卷积计算,推导了有限宽光束在圆柱坐标系下的光传输过程,给出了有限宽光束的光传输方程.以高斯光源和平圆光源为例,进一步给出了两种光源的有限宽光束在生物组织中的光传输方程.介绍了Monte Carlo方法原理及模拟光在多层生物组织中的传输过程.给出了典型三层生物组织的散射系数、吸收系数和折射率等光学参数.利用Monte Carlo方法模拟了有限宽光束在三层生物组织中的传输特性,对比研究了高斯光源和平圆光源有限宽光束在三层生物组织传输时光学参数漫透射率、漫反射率和光能流率的变化规律.这些参数的变化规律可为光在生物组织传输的实际应用提供理论指导.

生物组织的折射和折射率

光在生物组织中的传播与组织的光学性质有关。光通过组织时，光强和光的偏振状态会发生变化。而折射率是组织光学用来评价组织改变光线行进方向的基本参量。本文以菲涅耳公式为理论依据，用空气一组织界面的反射率、生物组织薄膜的反射率和生物组织反射光的倔振分量，推算生物组织的折射率。

以组织工程建构技术修复周围神经损伤的难点

背景:组织工程构建技术是近年来周围神经损伤修复的重要方法之一,在周围神经治疗领域有着良好的前景。目的:总结近年来利用组织工程学构建技术对周围神经损伤修复的研究进展。方法:应用计算机检索万方数据库、CNKI和PubMed数据库中1995年1月至2011年12月关于组织工程构建技术的文章,在标题和摘要中以"组织工程,神经导管支架,生物活性,周围神经损伤"或"Tissueengineering,Nervescaffold,Bioactivity,Peripheralnervedefect"为检索词进行检索,初检得到156篇文献,最终纳入56篇文献进行综述。结果与结论:周围神经损伤组织工程修复的两个要素是神经支架材料的选择和生物功能化。构建神经的支架材料包括可降解和非可降解两大类,通常需要具有三维多孔结构和相应的孔隙率及比表面积,其力学性能、表面活性、生物相容性和导电性等直接影响神经损伤修复的效果;生物功能化的主要生物活性因子包括支持细胞,种子蛋白和神经营养因子,将这些生物活性因子接种在神经导管支架材料上,促进受损神经的修复与功能替代。组织工程技术应用于周围神经损伤修复与再生的研究重点在于导管、细胞与生长因子的综合应用。组织工程技术与生物技术的联合应用将成为周围神经损伤修复的研究热点。