人大脑组织复电阻抗频率特性及其等效电路模型

背景电阻抗断层成像技术是对人体施加无伤害的电信号,通过体表测量其响应信号,用一定的重构算法得到人体内部的电阻抗或其变化的分布.在电阻抗断层成像中,各种组织的电阻抗频率特性对于利用电阻抗断层成像技术对病灶进行成像、定位或监测至关重要.目的测量出人脑组织的电阻抗频率特性,并与已知的人体其他生物组织已知谱线和家兔脑组织曲线相比较.设计观察性实验.单位解放军第四军医大学生物医学工程系医学电子工程教研室.对象实验于2000-04/06在解放军第四军医大学生物医学工程系医学电子工程教研室电阻抗断层成像实验室完成.两例人脑组织来自解剖教学用新鲜尸体,死亡时间＜12 h,成年男性.干预分割2个人脑组织共得到15个样本,利用英国Solartron公司频率响应分析仪(1255B),阻抗接口(1294)以及自制的测量盒,采用4电极分别测量出0.1～1×106Hz频率范围内离体脑组织的复电阻抗频率特性.主要观察指标在0.1～1×106Hz频率范围内电阻率频率特性曲线,复电阻抗实部、虚部频率特性曲线,复电阻抗等效电路模型.结果人脑组织电阻率在0.1～100Hz频率范围内约为1 200Ω·cm,在100～1×106Hz频率范围内随着频率的增高而减小至650 Ω·cm.人脑组织复电阻抗实部在0.1～100 Hz频率范围内比较稳定,在100～1×106 H2频率范围内随着频率的增高而减小.人脑组织复电阻抗虚部绝对值的频率特性曲线呈单调上升趋势.结论人脑组织电阻率、复电阻抗实部频率特性曲线与其他生物组织(如肌肉、肝、肾、肺等)的谱线一致.人脑组织复电阻抗虚部绝对值的频率特性曲线同已知的其他动物组织(肌肉、肝、肾等)的复电阻抗虚部频率特性相比不同,但与离体家兔脑组织的曲线一致.脑组织的复电阻抗等效电路模型比已知的生物组织等效电路模型要复杂.     

在体兔脑组织电阻抗频率特性测量及电阻抗断层成像

背景电阻抗断层成像技术是对人体表施加无害电信号,体表测量其响应,用重构算法得到人体内部的电阻抗或其变化的分布图像.与现有的CT,MRI等技术相比,电阻抗断层成像技术具有实时性强、费用低廉、便于连续监测和功能成像等优势.目的在体测量兔脑组织在缺血前后的电阻抗频率特性,并对缺血脑组织进行电阻抗断层成像技术,验证电阻抗断层成像技术对脑功能变化成像的可能性.设计单一样本实验.单位解放军第四军医大生物医学工程系医学电子工程教研室.材料实验于2001-08/09在解放军第四军医大学生物医学工程系医学电子工程教研室电阻抗断层成像实验室完成.选择成年健康家兔10只用于实验.方法采用颈总动脉结扎法制造脑缺血动物模型,对缺血前后的脑组织电阻抗特性进行在体测量.利用电阻抗断层成像系统对单侧脑组织供血变化进行成像.主要观察指标①缺血前后的脑组织在0.1 Hz～1 MHz频率范围内电阻抗频率特性曲线.②单侧脑组织供血变化电阻抗断层成像结果.结果1只家兔钻透硬脑膜,9只家兔结果进入分析.①在缺血脑损伤发生后,脑阻抗明显增大,在10 Hz以下脑阻抗变化率可达75%,在1 kHz～1 MHz频率范围脑阻抗变化率约为15%且比较稳定.②初步的动态成像结果显示,脑组织供血变化一侧与其电阻率变化位置相一致.结论缺血前后脑组织阻抗变化率满足成像要求,可以将其作为一个成像变量.     

在体兔脑组织电阻抗频率特性测量及电阻抗断层成像

背景：电阻抗断层成像技术是对人体表施加尤害电信号，体表测量其响应，用重构算法得到人体内部的电阻抗或其变化的分布图像。与现有的CT，MRI等技术相比，电阻抗断层成像技术具有实时性强、费用低廉、便于连续监测和功能成像等优势。目的：在体测量兔脑组织在缺血前后的电阻抗频率特性，并对缺血脑组织进行电阻抗断层成像技术，验证电阻抗断层成像技术对脑功能变化成像的可能性。设计：单一样本实验。单位：解放军第四军医大生物医学工程系医学电子工程教研窜。材料：实验于2001-08／09在解放军第四军医大学生物医学工程系医学电子工程教研室电阻抗断层成像实验室完成。选择成年健康家兔10只用于实验。方法：采用颈总动脉结扎法制造脑缺血动物模型，对缺血前后的脑组织电阻抗特性进行在体测量。利用电阻抗断层成像系统对单侧脑组织供血变化进行成像。主要观察指标：①缺血前后的脑组织在0．1Hz～1MHz频率范围内电阻抗频率特性曲线。②单侧脑组织供血变化电阻抗断层成像结果。结果：1只家兔钻透硬脑膜，9只家兔结果进入分析。①在缺血脑损伤发生后，脑阻抗明显增大，在10Hz以下脑阻抗变化率可达75％，在1kHz～1MHz频率范围脑阻抗变化率约为15％且比较稳定。②初步的动态成像结果显示，脑组织供血变化一侧与其电阻率变化位置相一致。结论：缺血前后脑组织阻抗变化率满足成像要求，可以将其作为一个成像变量。     

生物电阻抗技术建立运动人体特征性参数相关模型的价值

生物电阻抗技术是利用生物组织与器官的电特性及其变化提取人体生物医学信息的一种无损伤检测技术。文章介绍了生物电阻抗技术的基本原理和研究方法,综述该技术的应用进展,分析其应用于运动人体科学的可行性。生物电阻抗技术在人体成分的测量、血液及血流动力学研究领域中的应用,可作为运动人体科学研究的借鉴;电阻抗断层图像技术为无创、实时、动态地监测运动人体器官与组织的结构和功能提供了可行性。可采取的研究策略是建立运动人体的特征性参数与生物电阻抗之间稳定可靠的相关模型或回归方程,运用统计学规律进行推断性研究。     

兔闭合性颅脑外伤功能影像学模型的建立

目的建立兔闭合性颅脑外伤影像学模型,观察是否适合常规设备影像学功能成像研究。方法实验组30只新西兰大白兔,切除少许顶骨,自由落体装置撞击硬脑膜造成局限性脑挫裂伤。对照组10只,仅开骨窗,保持硬脑膜完整。术后3～72h行CT灌注(CTP)成像、MR常规及扩散加权、扩散张量成像。观察手术侧额顶叶的血流灌注、MR信号是否异常,病理学上是否有外伤性病变。结果实验组25只(83.33%)模型制作成功,手术侧额顶叶CT灌注异常、MR各序列异常信号,镜下可见急性脑出血、坏死及水肿。对照组功能影像学及病理学均无异常。两组CT灌注参数差异有统计学意义。结论兔闭合性颅脑外伤的影像学模型制作简便,成功率较高,常规影像学设备能显示其功能影像学异常。     

分子影像学用于早期诊断乳腺癌及其分子分型进展

乳腺癌治疗方案主要取决于其分子分型,目前临床主要通过组织活检进行分型。分子影像学和多模态影像技术现已可于分子和细胞水平显示乳腺癌疾病进程。本文就分子影像学用于早期诊断乳腺癌及其分子分型进展进行综述。     

穿刺法兔VX2肺移植瘤模型的建立及其影像学评价

目的 尝试建立适于影像学评价的兔VX2肺移植瘤模型.方法 新西兰大白兔30只,随机分为两组,实验组采用CT引导下穿刺VX2肿瘤组织块注入法建立兔肺移植瘤模型,以常用的VX2肿瘤组织悬液注射法作为对照组,以病理结果作为金标准.结果 实验组肺内成瘤率86.67%(13/15),胸膜种植率40.00%(6/15),平均生存时间(57.84±6.00)天.对照组成瘤率100%(15/15),胸膜种植率86.67%(13/15),平均生存时间(29.00±7.01)天.生存时间采用Kaplan-Meier曲线分析,两组差异有统计学意义(P<0.01);实验组胸膜及胸壁种植率低于对照组(P<0.05),两组肿瘤种植成功率差异无统计学意义(P>0.05).结论 CT引导下穿刺VX2肿瘤组织块注入法建立兔肺移植瘤模型在肺内形成孤立结节,较常用的肿瘤组织悬液注射法明显降低了胸膜及胸壁种植率,延长了实验动物生存时间,适合于影像学研究.     

急性脑静脉闭塞动物模型的改进

目的对急性脑静脉闭塞动物模型加以改进,拟建立一个稳定的类似临床疾病的动物模型.方法家猫28只,随机分为3组(栓塞组18只,结扎组6只,假手术组4只),栓塞组和结扎组分别采用开颅上矢状窦穿刺注射醋酸纤维素聚合物(CAP)和上矢状窦(SSS)后份结扎制备急性脑静脉闭塞模型,术后1、3、6、12、24、48 h对各组模型行MRI、CT检查,观察脑实质损害的动态变化,并和病理作对照研究.结果栓塞组16只猫造模成功.MR发现13只猫,CT发现12只猫脑实质内异常灌注区.大体病理学16只猫上矢状窦、桥静脉及皮层静脉内见CAP凝固呈铸型改变.显微病理学见病灶以血管源性水肿为主,12 h后出现静脉性脑梗死、脑出血.结扎组和假手术组脑实质未见异常改变.结论上矢状窦穿刺注射CAP制备急性脑静脉闭塞模型方法可行,该模型适合于病理生理及影像学研究.     

重视脑血流和代谢检查在缺血性脑血管病诊断治疗中的价值

缺血性脑血管病严重危害人民生命健康,是我国临床防治的关键问题。利用影像学技术无创、精准评估脑血流及代谢异常、监测其动态演变与临床预后的相关性,对临床早诊断、早评估、早治疗缺血性脑血管病具有重要价值。CT、MRI、SPECT和PET等影像学检查手段对于评估脑血流及代谢各具优势和特色,一体化PET/MR为精准定量血流和代谢带来了新的机遇。     

实验兔胡桃夹综合征模型的建立及其MSCTA评价

目的 制作适于影像学研究的胡桃夹综合征(NCS)的动物模型,并应用MSCTA评价左肾静脉(LRV)的形态学变化.方法 30只新西兰大白兔.随机分为LRV 50%结扎组(A组)、LRV 75%结扎组(B组)和对照组(C组),每组10只.采用探针腔外与LRV并行结扎的方法建立动物模型,A、B两组分别结扎LRV近下腔静脉(IVC)侧断面的50%和75%,并于结扎前后分别行MSCTA检查,测量并评价LRV的狭窄面积.通过C组与A、B组间LRV-IVC压差的测定,评估模型的可靠性.结果 A与B组LRV实际和理论结扎狭窄面积差异均无统计学意义(P>0.05),A、B两组结扎后与C组比较LRV-IVC压差明显增大,其绝对值≥5 cmH2O,差异有统计学意义(P<0.05).结论 通过腔外结扎LRV制作的动物模型可真实地模拟NCS时LRV的形态和压力改变,MSCTA可对其进行客观评价.     

Three-dimensional electrical impedance tomography of human brain activity

Regional cerebral blood flow and blood volume changes that occur during human brain activity will change the local impedance of that cortical area, as blood has a lower impedance than that of brain. Theoretically, such impedance changes could be measured from scalp electrodes and reconstructed into images of the internal impedance of the head. Electrical Impedance Tomography (EIT) is a newly developed technique by which impedance measurements from the surface of an object are reconstructed into impedance images. It is fast, portable, inexpensive, and noninvasive, but has a relatively low spatial resolution. EIT images were recorded with scalp electrodes and an EIT system, specially optimized for recording brain function, in 39 adult human subjects during visual, somatosensory, or motor activity. Reproducible impedance changes of about 0.5% occurred in 51/52 recordings, which lasted from 6 s after the stimulus onset to 41 s after stimulus cessation. When these changes were reconstructed into impedance images, using a novel 3-D reconstruction algorithm, 19 data sets demonstrated significant impedance changes in the appropriate cortical region. This demonstrates, for the first time, that significant impedance changes, which could form the basis for a novel neuroimaging technology, may be recorded in human subjects with scalp electrodes. The final images contained spatial noise and strategies to reduce this in future work are presented.     

Multiple frequency bioelectrical impedance analysis: a cross-validation study of the inductor circuit and Cole models

It has been proposed that multiple frequency bioelectrical impedance models of the human body should include an inductive property for the circulatory system, the inductor circuit model (ICM), and that such a model, when coupled with a new method of data analysis, can improve the predictive power of multiple frequency bioelectrical impedance analysis (MFBIA). This hypothesis was tested using MFBIA measurements and gold standard measures of total body and extracellular water volumes in a cross-validation study in two subject groups (viz. controls and HIV). The MFBIA measurements were analysed using the current, widely accepted Cole model and the alternative ICM model which includes an inductive component. Correlations in the range 0.75 to 0.92 (for TBW) and 0.46 to 0.79 (for ECW) for impedance quotients versus gold standard measures within the subject groups were observed. These decreased, to as low as r = 0.50 for TBW and r = 0.29 for ECW, when the derived algorithms were applied to the alternative subject group. These results suggest that lack of portability of MFBIA algorithms between subject groups is not due to an inadequacy of the analogue circuit model per se but is possibly due more to fundamental flaws in the principles associated with its application. These include assuming a constant proportionality of body segment geometries and tissue fluid resistivities. This study has also demonstrated that this inadequacy cannot be overcome by simply introducing an inductive component into the analogue electrical circuit.     

Multi-frequency parameter mapping of electrical impedance scanning using two kinds of circuit model

Electrical impedance scanning (EIS) is a kind of potential bio-impedance measurement technology, especially aiding the diagnosis of breast cancer in women. By changing the frequency of the driving signal in turn while keeping the other conditions stable, multi-frequency measurement results on the object can be obtained. According to the least square method and circuit theory, the parameters in two models are deduced when measured with data at multiple driving frequencies. The arcs, in the real and imaginary parts of a trans-admittance coordinate, made by the evaluated parameters fit well the realistic data measured by our EIS device on female subjects. The Cole-Cole model in the form of admittance is closer to the measured data than the three-element model. Based on the evaluation of the multi-frequency parameters, we presented parameter mapping of EIS using two kinds of circuit model: one is the three-element model in the form of admittance and the other is the Cole-Cole model in the form of admittance. Comparing with classical admittance mapping at a single frequency, the multi-frequency parameter mapping will provide a novel vision to study EIS. The multi-frequency approach can provide the mappings of four parameters, which is helpful to identify different diseases with a similar characteristic in classical EIS mapping. From plots of the real and imaginary parts of the admittance, it is easy to make sure whether there exists abnormal tissue.     

Complex fMRI analysis with unrestricted phase is equivalent to a magnitude-only model

Due to phase imperfections, voxel time course measurements are complex valued. However, most fMRI studies measure activation using magnitude-only time courses. We show that magnitude-only analyses are equivalent to a complex fMRI activation model in which the phase is unrestricted, or allowed to dynamically change over time. This suggests that improvements to the magnitude-only model are possible by modeling the phase in each voxel over time.     

动态因果模型及其参数估计理论在脑功能成像中的应用

功能核磁共振成像技术能够对人脑进行无损伤探测,这使得人们又多了一种能实时研究大脑神经活动的有力工具。为了能更好地揭示功能核磁共振成像数据中所包含的丰富信息,特别是关于脑区间有效连接的信息,研究人员使用了多种方法和手段。其中新近出现的动态因果模型是专门为研究有效连接设计的方法,并已经在研究中取得了一些新的结果。文章着重描述动态因果模型的基本模型和参数估计理论;然后举例介绍动态因果模型的应用情况;最后对此方法的特点、局限、发展趋势等进行总结。     

Properties of creatine kinase-BB from canine and human brain tissues

Creatine kinase (EC 2.7.3.2) BB isoenzyme (CK-BB) was purified to homogeneity from canine and human brain tissues. The purified protein from both sources exhibits Mr of 84,700 daltons. The canine isoenzyme exhibits several properties similar to human isoenzyme with respect to reactive and total thiol groups, UV spectra, isoelectric points and reaction kinetics. While both canine and human CK-BB isoenzymes are unstable compared to other CK isoenzymes, canine CK-BB is even less stable than the human enzyme, losing most of its activity within 20 h at 4 degrees C at pH 5.0. Addition of 2-mercaptoethanol does not prevent rapid loss of the enzyme activity. Increasing the pH to 9.0, however, increases the stability of both CK-BB isoenzymes. Agarose electrophoresis demonstrated the presence of MM as well as BB isoenzyme in various parts of brain tissues. BB was present at an activity of 90.8-93.3 U/mg and MM at 6.7-9.2 U/mg.     

Body composition modeling in the calf using an equivalent circuit model of multi-frequency bioimpedance analysis

An equivalent electrical circuit model is used to describe the response of different tissue components in the calf to multi-frequency current. This model includes seven electrical components: skin resistance, contact capacitance, fat resistance, fat capacitance, extracellular resistance, intracellular resistance and cell membrane capacitance. Calf bioimpedance was measured on 30 pts using a multi-frequency bioimpedance device (Xitron 4200) with a range of frequency from 5 kHz to 1000 kHz. MRI was performed on each measured calf to provide body composition components: fat, muscle mass and bone. An equivalent circuit containing seven parameters (P1, P2, P3, P4, Q1, Q2, Q3) was constructed to represent the model. To identify the effect of different body compositions on their parameters, subjects were subgrouped according to (1) their range of fat mass: F1>0.4 kg, F2>0.4 & F2<0.25 kg and F3<0.25 kg; (2) their range of muscle mass: M1>1.2 kg, M2<1.2 & M2>1.0 kg and M3<0.25 kg. Curve fitting and simulation programs (Matlab Toolbox) were used to obtain the solution of the electrical equations. The results show a decrease in impedance with an increase in excitation frequency that differed among subjects with different fat contents. Simulation results show a high correlation (R2>0.98) between the bioimpedance measurements and the value calculated from the model. There are significant differences in parameters P1 (32.5+/-5.9 versus 26+/-4.4, p<0.05), P3 (-15,330+/-3352 versus -10,973+/-3448, p<0.05) and P4 (42,640 versus 24,191, p<0.05) between groups F1 and F3. P2 is significantly different (1045+/-442 versus 1407+/-349, p<0.05) between groups M1 and M2. The parameters that characterize the bioimpedance data depend upon many more tissue characteristics of electrical properties than those incorporated in current models and they are affected by aspects of body composition that are not considered in the fitting of bioimpedance data. This study shows a new model and methodology to analyze bioimpedance data and further work is likely to lead to much better understanding of electrical properties of body tissue.