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.     

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〈12h，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&;#215;10^6Hz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&;#215;10^6Hz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1200Ω&;#183;cm，在100-1&;#215;10^6Hz频率范围内随着频率的增高而减小至650Ω&;#183;cm。人脑组织复电阻抗实部在0．1-100Hz频率范围内比较稳定，在100～1&;#215;10^6Hz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。     

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.     

基于梯度误差电阻抗断层成像技术的图像评价

国内目前的电阻抗断层成像技术工作重点是针对确定应用目标的实用化应用基础研究,电阻抗断层成像技术系统评价方法是从方法学基础向应用基础和临床应用研究过渡必须解决的关键问题之一。文章通过引入结构偏离度,提出了一种基于梯度误差的电阻抗断层成像技术图像重建评价函数。评价实验基于直径10cm的16电极盐水槽装置,采用相邻激励、相邻测量模式,由等位线反投影算法重建图像,在实验室建立的电阻抗断层成像仿真实验系统研究平台上进行。采用传统评价参数图像清晰度和交叉熵,与结构偏离度的对比仿真评价结果表明,结构偏离度参数比传统的图像评价参数更具优势。文章提出的基于Sobel算子的梯度误差评价方法,能很好地反映图像的边缘变化和组织纹理结构信息,具有很好的电阻抗断层成像技术图像质量评价性能,可以更有效地反映电阻抗断层成像图像重建效果。     

电阻抗断层临床应用研究进展

电阻抗断层临床应用研究进展包玉生，王秋涓，杨子彬目前有许多技术可用于组织成像，电阻抗成像（ｅｌｅｃｔｒｉｃａｌｉｍｒｅｄａｎｃｅｉｍａｇｉｎｇ，Ｅｌｆ）是将组织的电阻（ｔｉｓｓｕｅｒｅｓｉｓｔｉｖｉｔ歹）作为测ｔ＃数，迈过测量外加电场形成的电位来重建...     

椎动脉型颈椎病脑电地形图的变化

椎动脉型颈椎病脑电地形图的变化山东省泰安市中医院（泰安２７１０００）李秀香椎动脉型颈椎病是因颈椎病变引起椎动脉供血不足，其基本病理改变是由于局部脑组织缺血、缺氧造成水肿、软化、甚至坏死等，使脑细胞的正常生理功能受到抑制或破坏，出现脑电活动的异常。现将...     

电阻抗断层成像技术在呼吸系统肺功能成像中的应用

电阻抗断层成像技术（EIT）作为一项新兴的功能性成像技术，具有无损伤、便携、图像监护等突出特点。其中肺功能成像为目前EIT最主要的应用领域，可以实现肺通气及血流灌注的实时动态监测。本文介绍肺EIT在呼吸系统常见疾病如急性呼吸窘迫综合征、慢性阻塞性肺疾病、肺栓塞等疾病中的基础及临床研究进展，为未来EIT技术的进步及临床应用提供帮助。     

醒脑开窍针法对脑缺血及再灌注家兔脑自由基病理学超微结构的影响

利用皮瓣包埋方法阻断家兔左、右颈总动脉和椎底动脉造成急性不完全性脑缺血及再灌注模型，并采用醒脑开窍针法予以治疗，观察针刺手法对上述模型家兔脑组织含水量、自由基，脑组织和血中超氧化物歧化酶（ＳＯＤ）、过氧化脂质（ＬＰＯ）含量以及脑组织超微结构变化的影响。结果：脑缺血及再灌注家兔脑存在着明显的自由基病理学和超微结构改变，而以缺血后再灌注动物最为严重；醒脑开窍针法对上述改变具有明显的改善作用，以缺血后再灌注针刺组动物改善更为显著。作者认为：醒脑开窍针法对缺血性中风可适时地改善脑灌注，不失为治疗缺血性中风的方法。     

第十一届电生物阻抗国际会议在挪威奥斯陆召开

２００１年６月１７日在挪威奥斯陆大学举行电生物阻抗专题演讲。６月１８日上午举行第十一届电生物阻抗国际会议开幕式，大会主席奥斯陆大学生物工程系主任Grimnes教授致欢迎词。会议共进行５日，于６月２１日晚举行闭幕式。２３个国家的２０６名代表出席会议、交流论文１５１篇，其中专题演讲６篇、组织与器官阻抗３６篇、细胞阻抗２０篇、身体成分阻抗检测１３篇、阻抗CT２４篇、心阻抗２３篇、脑阻抗５篇、阻抗仪器研究１４篇。中国有１１名代表出席，刊登论文１２篇，在会议论文集刊登的２３篇心阻抗论文中，中国有５篇，是数量最多…     

应用非线性动力学指标分析大鼠癫痫模型脑电信息变化

背景：脑电活动的动力学特征，是在癫痫发作前数分钟至数十分钟脑电活动的混沌分维数、相关维数、Lyapunov指数、混沌复杂度和自由度等指标显著减少，脑电趋于同步和周期化，预示癫痫发作。研究表明非线性动力学指标寻找表征脑电混沌状态的特征参数具有可行性。目的：探索应用非线性动力学指标近似熵和相关维，分析大鼠癫痫发作过程的整个脑电信号特征。设计：以动物为研究对象，观察、验证性研究。单位：解放军第二炮兵总医院医学工程科和消化内科及解放军第四军医大学生物医学工程系物理教研室。材料：实验于2001-09／2002-01在解放军第四军医大学生物医学工程系复杂性实验室完成。选择雄性SD大鼠6只，体质量150～200g。干预：雄性SD大鼠，腹腔注射水合氯醛0．5mL，处于深度麻醉状态．脑电平稳后，将贝美格注射液稀释一倍，腹腔注射0．5mL。一段时间后大鼠开始身体抽搐，并伴有低沉叫声的癫痫发作，连续记录整个过程。根据实验记录大鼠脑电波形与试验过程中的发作症状，分别抽取未发作、发作前、发作中和发作后四个阶段大鼠脑电波进行非线性分析。计算近似熵与相关维的变化。主要观察指标：未发作、发作前、发作中和发作后四个阶段近似熵与相关维的变化。结果：6只大鼠进入实验分析。癫痫发作中时，脑电信号的近似熵和相关维(0．447&;#177;0．126，2．166&;#177;0．377)明显低于发作前(0．807&;#177;0．182，4．773&;#177;0．319)和发作后(1．241&;#177;0．125，6．042&;#177;0．373)(t=-3．984～17．902．P&;lt;0．01)。其中发作前，发作中与未发作时脑电信号近似熵和相关维(1．313&;#177;0．090，6．405&;#177;0．694)的差异比较，t=-5．228～12．740．P&;lt;0．01。结论：非线性动力学方法近似熵和相关维数据变化，揭示了大鼠癫痫发作期和发作前后脑电信息活动特征性及其差异，表明了癫痫发作过程脑电信号复杂度的变化规律。     

Computation of intraluminal impedance

The measurement of the electrical impedance inside the esophagus provides information about its status, and is being explored in the study of the gastroesophageal reflux. This paper presents theoretical computation of impedance inside the esophagus. The results of the numerical solution for a simple geometry are compared against the solution formulated from the Green's function approach. The effect of the electrode configuration on the resulting impedance is studied as an application of the methodology developed in this paper. The results of this paper will be useful in the design of an intraluminal impedance catheter as well as in the interpretation of the resulting impedance signals.     

Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography

Introduction  

Electrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship.     

Clinical evaluation of impedance cardiography

Summary. We tested the validity of thoracic impedance cardiography for measuring cardiac output in man by comparing absolute values obtained using the non-invasive impedance method with values obtained using the invasive thermodilution method. We also compared per cent changes in cardiac output using impedance cardiography and thermodilution in response to environmental manipulations including cardiac pacing and intravenous administration of ergonovine, dipyridamole, or isoproterenol. Among 19 patients, absolute values for cardiac output, using the impedance and the thermodilution techniques, agreed well (r=0·85, P<0·001). The per cent change in cardiac output by impedance cardiography was positively correlated with the per cent change by thermodilution for the several manipulations (overall r=0·87, P<0·001). Impedance cardiography does appear, in general, to measure cardiac output and stroke volume validly in man, even in situations where heart rate and stroke volume change in opposite directions.     

Analysis of intraluminal impedance measurements

Intraluminal impedance is an emerging technique to monitor the esophagus so that the occurrence of gastroesophageal reflux episodes can be observed. The impedance traces of the esophagus have wide variations which correspond to the occurrence of activities such as swallow or reflux that cause the impedance to change. This paper presents a technique to detect and classify reflux episodes from intraluminal impedance. Evaluation of the technique based on 660 h of combined data from 30 patients showed that the proposed methodology can detect episodes in the esophagus to a sensitivity of 89% with positive predictivity of 83%.     

The effect of haematocrit on transthoracic electrical impedance and on the calculation of cardiac output by an impedance cardiograph

The Transthoracic electrical impedance (TEI) was measured using the Bomed NCCOM3 non-invasive cardiac output monitor in 27 patients with polycythemia rubra vera (PCRV) and in a control group of 27 patients with normal haematocrits. The mean haematocrit was 49.4% (SD2.61) in the patients with PCRV and 42.1% (SD 2.95) in the control group, a difference that was significant (p<0.001). The mean TEI was also significantly higher in patients with PCRV than in the control group (p<0.05), the respective values being 31.25 (5.48) Ohms and 27.5 (3.31) Ohms. The mean values for cardiac output (CO) and cardiac index (CI) were similar in both groups.     

Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation

BACKGROUND: Two mechanisms by which firm external paddle force decreases transthoracic impedance (TTI) have been proposed. Decreased impedance at the paddle-skin interface has been assumed to be the primary mechanism, but expulsion of air from the lungs, reducing lung volume is also likely to contribute. The relative contribution of each mechanism is unknown. METHODS AND RESULTS: Thirty five intubated patients undergoing general anaesthesia for cardiac surgery were studied. TTI across external defibrillation paddles was measured as paddle force was increased to 12kgf. Measurements were performed twice; once allowing the volume of the lungs to change and once with lung volume held at functional residual capacity. TTI with constant lung volume was significantly higher at (P< 0.001), confirming that a reduction in lung volume contributes to the decrease in TTI. At an optimal paddle force of 8kg, the reduction in lung volume contributed to 16.2% of the overall decrease in TTI. CONCLUSION: The decrease in TTI seen with increasing external paddle force is due primarily to improved electrical contact at the paddle-skin interface, with a decrease in thoracic volume accounting for no more than 16% of the overall decrease at forces used clinically.     

Electrical impedance spectroscopy and the diagnosis of bladder pathology

Bladder pathology is usually investigated visually by cystoscopy. At present, definitive diagnosis of the bladder can be made by biopsy only, usually under general anaesthesia. This is a relatively high-cost procedure in terms of both time and money and is associated with discomfort for the patient and morbidity. Thus, we used an electrical impedance spectroscopy technique for differentiating pathological changes in the urothelium and improving cystoscopic detection. For ex vivo study, a whole or part of the patient's urinary bladder was used to take the readings less than half an hour after excision at room temperature, about 27 degrees C, using the Mk3.5 Sheffield System (2-384 kHz in 24 frequencies). In this study, 145 points (from 16 freshly excised bladders from patients) were studied in terms of their biopsy reports matching to the electrical impedance measurements. For in vivo study, a total of 106 points from 38 patients were studied to take electrical impedance and biopsy samples. The impedance data were evaluated in both malignant and benign groups, and revealed a significant difference between these two groups. The impedivity of the malignant bladder tissue was significantly higher than the impedivity of the benign tissue, especially at lower frequencies (p < 0.001). In addition, the receiver operating characteristic (ROC) curve for impedance measurements indicated that this technique could provide diagnostic information (individual classification is possible). Thus, the authors have investigated the application of bio-impedance measurements to the bladder tissue as a novel and minimally invasive technique to characterize human bladder urothelium. Therefore, this technique, especially at lower frequencies, can be a complementary method for cystoscopy, biopsy and histopathological evaluation of the bladder abnormalities.