电阻抗断层成像技术研究进展

电阻抗断层成像(EIT)是一种重要的医学成像方法,通过对物体表面的分布电测量来获知物体内部的电特性图像,有着良好的应用前景.本文对EIT的硬件系统和成像算法的研究进展作了全面的描述.首先对硬件部分的信号源和驱动模式进行了介绍,并对目前使用的EIT系统作了简要的分析;然后介绍了成像算法,从二维和三维成像两个方面对目前EIT的重建算法进行阐述.最后,对EIT进行了讨论和总结.     

一种新的医学成像技术——电阻抗体层成像

目前,许多技术都可应用于人体组织的图像产生。其中X线放射成像是应用最古老且最广泛的技术,它根据人体吸收的X线的分布情况产生图像。测量X线吸收系数的X线计算机体层成像术(CT扫描)是一项可产生更多信息量的较新技术。其它技术有测量人体组织声阻抗变化的超声显像技术、放射性同位素显像技术、磁共振显像技术(MRI)和自动热摄影成像技术。电阻抗显像利用了电阻率作为测量参数,它通常称作电阻抗体层成像术(EIT)。 EIT(Electrical Impedance Imaging)是将组织的电阻作为测量参数,通过测量外     

基于径向基函数神经网络的肺部加权频差电阻抗成像方法

目的 对肺通气过程进行床旁实时连续图像监控，是机械通气患者和临床医生的迫切需求。肺部电阻抗成像（EIT）可反映呼吸引起的胸腔电特性变化分布，在肺通气监测方面具有天然的优势。本文目的在于建立基于径向基函数神经网络（RBFNN）的肺部加权频差电阻抗成像（wfd-EIT）方法，实现对肺通气的高空间分辨率成像。方法 利用肺部wfd-EIT成像方法实时描绘胸腔电导率分布状况，再通过RBFNN将目标区域可视化并精准识别其边界信息。首先通过数值分析模拟，在各个激励频率利用COMSOL与MATLAB软件建立2 028个仿真样本，分为训练样本集和测试样本集，验证所提出成像方法的可行性和有效性。其次，为了验证仿真结果，建立肺部物理模型，选用具有低电导特性的生物组织模拟肺部通气区域，对其进行成像实验，并采用图像相关系数（ICC）和肺区域比（LRR）定量数据衡量成像方法的准确性。结果 wfd-EIT方法可以在任意时刻进行图像重建，并能够准确反映出目标区域的电特性分布；利用基于RBFNN的算法能够增强目标区域的成像精度，ICC可达0.94以上，更好地凸显其边界轮廓信息。结论 通过wfd-EIT成像方法，利用多频阻抗谱同步测量实现目标区域的快速可视化，并结合RBFNN网络逼近任意非线性函数的优点，实现对目标区域电特性变化的精准识别，为下一步进行临床肺通气的EIT图像监测奠定了理论和技术基础。     

光学相干断层成像在临床医学中的应用

光学相干断层成像(OCT)是一种基于弱相干光学断层成像技术,可以对生物组织活体断层成像,是继计算机X射线摄影(CR)和数字X射线摄影(DR)、超声、电子计算机断层扫描(CT)、磁共振成像(MRI)之后又一新的生物组织成像方法。OCT在眼科、皮肤科、心血管科、肿瘤科、骨科、口腔科、妇科等对组织病变的早期光学诊断和实时动态监测方面具有广泛的应用及重要的临床价值。本文就OCT的基本原理、研究现状、主要的临床应用和应用过程中存在的问题进行综述并展望未来相关的发展趋势。     

神经肌肉电刺激下小腿肌肉的电学特性研究

目的 采用电阻抗成像（electrical impedance tomography,EIT）方法研究神经肌肉电刺激（neuromuscular electrical stimulation,NMES）下小腿肌肉的电学特性,旨在将EIT作为一种长期监测方法,从而可视化NMES训练对人类小腿肌肉的训练效果。方法 16名实验对象被随机分配到对照组（control group,CG,n=8）和最佳电压强度的NMES训练组（optimal voltage intensity training group,OG,n=8）。对照组保持正常生活方式并不进行NMES和其他的肌肉训练;NMES训练组中使用商业NMES设备对实验对象右小腿进行23 min的NMES训练,每周3次,为期5周。应用EIT测量在每周一训练开始前的电导率分布。并且采用生物电阻抗分析（bioelectrical impedance analysis,BIA）方法测量右腿细胞外含水量与身体总含水量的比率（ECW/TBW） βrl,及身体总含水量（TBW）τ。为了量化NMES在肌肉训练过程中的作用,使用配对样本t检验分析EIT重建图像的...     

超声弹性成像技术及其应用

超声弹性成像作为一种新的超声成像方法,它通过获取有关组织弹性信息进行成像,弥补了X射线、超声成像(US)、磁共振成像(MRI)、计算机断层扫描(CT)等传统医学成像模态不能直接提供组织弹性的不足,具有无创、简单、便宜、容易应用等优点,被广泛应用于临床,成为目前医学弹性成像的一个研究热点。本文介绍了弹性成像基本的原理,详细阐述了血管内超声弹性成像、超声振动声成像、超声剪切波弹性成像、瞬时弹性成像、心肌弹性成像等不同激励方式下的几种超声弹性成像的基本原理、成像方法、国内外目前的研究现状、成像优缺点等,叙述了超声弹性成像在乳腺检测、前列腺癌的检测、射频消融监测和检测、冠状动脉粥样硬化的治疗等临床应用,并总结了超声弹性成像的发展趋势。     

超声弹性成像技术在乳腺肿块诊断中的研究进展及应用

超声弹性成像技术(UE)是一种新的超声成像技术,能够根据组织硬度进行成像,估计出组织内部的弹性信息,从而反映它的结构特点,该技术较传统触诊检查更加客观,在乳腺肿块的鉴别诊断中有较高的价值,其临床应用广泛并且得到了快速的发展。现就国内外文献对UE技术的原理、图像分析方法、技术研究进展及其在乳腺肿块鉴别诊断中的应用进行综述。     

头部组织三维核磁共振电阻抗成像算法的仿真研究

文章给出了一种基于核磁共振技术的三维阻抗成像（电导率分布）重构算法,并将该方法应用于人体头部组织电导率分布重构上。该代数重构方法是利用高分辨率的核磁共振成像系统对成像物体进行三维构建和不同组织的边界区分,根据核磁共振系统中测量得到的磁感应强度Bx和By分量并结合有限元数值计算得到的电流密度分布J组成非线性矩阵,通过迭代求解此非线性矩阵,来解决三维电导率分布的重构问题。在三层球头模型（包括头皮、颅骨和大脑）上分别进行的仿真实验结果表明,该算法具有较强的抗噪声能力和较好的收敛性,重构的头部电导率分布图像具有较高的精确性。     

体外循环血栓非侵入在线电阻抗成像方法

目的 在体外循环系统中,血栓的在线检测和可视化具有重要意义。本文提出了基于电阻抗成像（EIT）的体外循环血栓非侵入在线检测方法。方法 首先通过联合仿真研究了传感器尺寸对成像效果的影响。其次,根据仿真结果设计了直径为20 mm的16铜质电极EIT传感器,搭建了循环流动实验平台,并设计了静态和循环流动实验。使用尺寸为3～6 mm的猪血块代替血栓,将血块置于新鲜猪血样本中,采用Tikhonov正则化算法进行成像。将3 mm和5 mm的血块分别置于循环系统中,重建血块在传感器截面的大小和位置图像,并与高速相机拍摄结果进行对比。结果 仿真结果显示当目标物与传感器面积比（AR）不小于0.01时,传感器直径为20 mm和30 mm对应的图像相关系数（IC）均大于0.06,成像效果较好。静态成像结果显示,相对尺寸覆盖率误差（RCR）小于等于0.1。循环流动实验显示,血块经过传感器时,检测到归一化后的相对电导率变化值分别为80和200,结果显示该方法能够检测到循环系统中的血块。结论 该方法具有实时性和非侵入的优点,有望应用于体外血栓的检测。     

人类小腿肌肉对运动训练生理响应的电学特性研究

目的 运动训练已被证明能够改善许多慢性肌肉功能疾病,被用于治疗衰老型肌萎缩。本文采用电阻抗成像(electrical impedance tomography,EIT)研究人类小腿肌肉对运动训练生理响应的电学特性,旨在使用EIT方法可视化运动训练对人类小腿响应肌肉隔室内肌肉纤维体积增加的效果。方法 实验对象被要求在连续5个实验日进行左、右腿单侧提踵训练,应用EIT检测每日运动训练前和运动训练后小腿肌肉的电导率分布。为了定量分析运动训练对响应肌肉隔室的作用,使用配对样本t检验分析EIT重建图像的空间平均电导率<σ>。结果 运动训练后,由小腿腓肠肌组成的M₁肌肉隔室空间平均电导率<σ>_M1显著增加。此外,连续5个实验日的EIT测量结果显示,运动训练前的空间平均电导率<σ^pre>_M1呈上升趋势。所有实验对象在实验日1早晨进行实验前的腿部瘦体重与<σ>_M1呈线性关系,即<σ>_M1随腿部瘦体重增加而增加;运...     

Analysis of parametric estimation of head tissue conductivities using Electrical Impedance Tomography

We study the theoretical performance of using Electrical Impedance Tomography (EIT) to measure the conductivity of the main tissues of the head. The governing equations are solved using the Finite Element Method for realistically shaped head models with isotropic and anisotropic electrical conductivities. We focus on the Electroencephalography (EEG) signal frequency range since EEG source localization is the assumed application. We obtain the Cramér-Rao Lower Bound (CRLB) to find the minimum conductivity estimation error expected with EIT measurements. The more convenient electrode pairs selected for current injection from a typical EEG array are determined from the CRLB. Moreover, using simulated data, the Maximum Likelihood Estimator of the conductivity parameters is shown to be close to the CRLB for a relatively low number of measurements. The results support the idea of using EIT as a low-cost and practical tool for individually measure the conductivity of the head tissues, and to use them when solving the EEG source localization. Even when the conductivity of the soft tissues of the head is available from Diffusion Tensor Imaging, EIT can complement the electrical model with the estimation of the skull and scalp conductivities.     

Precise two-dimensional D-bar reconstructions of human chest and phantom tank via sinc-convolution algorithm

ABSTRACT: BACKGROUND: Electrical Impedance Tomography (EIT) is used as a fast clinical imaging technique formonitoring the health of the human organs such as lungs, heart, brain and breast. Eachpractical EIT reconstruction algorithm should be efficient enough in terms of convergencerate, and accuracy. The main objective of this study is to investigate the feasibility of preciseempirical conductivity imaging using a sinc-convolution algorithm in D-bar framework. METHODS: At the first step, synthetic and experimental data were used to compute an intermediate objectnamed scattering transform. Next, this object was used in a 2-day integral equation whichwas precisely and rapidly solved via sinc-convolution algorithm to find the square root of theconductivity for each pixel of image. For the purpose of comparison, multigrid and NOSERalgorithms were implemented under a similar setting. Quality of reconstructions of syntheticmodels was tested against GREIT approved quality measures. To validate the simulationresults, reconstructions of a phantom chest and a human lung were used. RESULTS: Evaluation of synthetic reconstructions shows that the quality of sinc-convolutionreconstructions is considerably better than that of each of its competitors in terms ofamplitude response, position error, ringing, resolution and shape-deformation. In addition, theresults confirm near-exponential and linear convergence rates for sinc-convolution andmultigrid, respectively. Moreover, the least degree of relative errors and the most degree oftruth were found in sinc-convolution reconstructions from experimental phantom data.Reconstructions of clinical lung data show that the related physiological effect is wellrecovered by sinc-convolution algorithm. CONCLUSIONS: Parametric evaluation demonstrates the efficiency of sinc-convolution to reconstruct accurateconductivity images from experimental data. Excellent results in phantom and clinicalreconstructions using sinc-convolution support parametric assessment results and suggest thesinc-convolution to be used for precise clinical EIT applications.     

Use of Electrical Impedance Tomography to Monitor Regional Cerebral Edema during Clinical Dehydration Treatment

Objective

Variations of conductive fluid content in brain tissue (e.g. cerebral edema) change tissue impedance and can potentially be measured by Electrical Impedance Tomography (EIT), an emerging medical imaging technique. The objective of this work is to establish the feasibility of using EIT as an imaging tool for monitoring brain fluid content.

Design

a prospective study.

Setting

In this study EIT was used, for the first time, to monitor variations in cerebral fluid content in a clinical model with patients undergoing clinical dehydration treatment. The EIT system was developed in house and its imaging sensitivity and spatial resolution were evaluated on a saline-filled tank.

Patients

23 patients with brain edema.

Interventions

The patients were continuously imaged by EIT for two hours after initiation of dehydration treatment using 0.5 g/kg intravenous infusion of mannitol for 20 minutes.

Measurement and Main Results

Overall impedance across the brain increased significantly before and after mannitol dehydration treatment (p = 0.0027). Of the all 23 patients, 14 showed high-level impedance increase and maintained this around 4 hours after the dehydration treatment whereas the other 9 also showed great impedance gain during the treatment but it gradually decreased after the treatment. Further analysis of the regions of interest in the EIT images revealed that diseased regions, identified on corresponding CT images, showed significantly less impedance changes than normal regions during the monitoring period, indicating variations in different patients'' responses to such treatment.

Conclusions

EIT shows potential promise as an imaging tool for real-time and non-invasive monitoring of brain edema patients.     

Breast imaging using 3D electrical impedence tomography

Aim: To determine the diagnostic efficiency of 3D Eletrical Impedance Tomography (EIT) compared to Mammography (MG) and Ultrasonography (USG) in imaging the breast. Materials and Methods: A group of 88 patients presenting with various breast complaints was examined using combined Mammography and Ultrasonography (MG & USG) or either of these modalities alone. The same patients were then examined using the 3D EIT imaging system "MEIK". The findings were then compared. The sensitivity of these modalities for this group of patients were later determined and statistically analysed. Results: Of the total of 88 patients, 59 findings were "suspicious" by any of the 3 modalities alone or by their combination. EIT had a sensitivity of 77.8 % compared to MG with a sensitivity of 83.3 % and USG with a sensitivity of 94.4 % regarding cases of fibrocystic mastitis. For cases involving cysts, EIT had 100 % sensitivity which was the same as that for USG compared to MG with a sensitivity of only 81 %. Among cases of fibroadenoma, EIT had a sensitivity of just 68.8 % compared to MG with a sensitivity of 87.5 % and USG with a sensitivity of 75 %. Finally among cases of carcinoma, EIT had a sensitivity of 75 % compared to the sensitivity of 100 % of MG and USG in our group of patients. The study revealed that there was no overall significant difference in sensitivity between MG-USG (p = 0.219) and MG-EIT (p = 0.779) and USG-EIT (p = 0.169). However, in regard to identifying cysts there was significant difference in the sensitivity of MG compared to USG & EIT suggesting that EIT has a role in these cases. Conclusion: Electrical impedance could be used as an adjunct to Mammography and Ultrasonography for breast cancer detection. However, the differentiation of malignant from benign lesions based on impedance measurements needs further investigation. Multifrequency electrical impedance imaging appears the most promising for detecting breast malignancies but methodological improvements need to be made to realise its potential.     

Electrical Impedance Tomography of Electrolysis

The primary goal of this study is to explore the hypothesis that changes in pH during electrolysis can be detected with Electrical Impedance Tomography (EIT). The study has relevance to real time control of minimally invasive surgery with electrolytic ablation. To investigate the hypothesis, we compare EIT reconstructed images to optical images acquired using pH-sensitive dyes embedded in a physiological saline agar gel phantom treated with electrolysis. We further demonstrate the biological relevance of our work using a bacterial E.Coli model, grown on the phantom. The results demonstrate the ability of EIT to image pH changes in a physiological saline phantom and show that these changes correlate with cell death in the E.coli model. The results are promising, and invite further experimental explorations.     

Ventilation distribution in rats: Part 2 -- A comparison of electrical impedance tomography and hyperpolarised helium magnetic resonance imaging

ABSTRACT: BACKGROUND: Hyperpolarised helium MRI (He3 MRI) is a new technique that enables imaging of the air distribution within the lungs. This allows accurate determination of the ventilation distribution in vivo. The technique has the disadvantages of requiring an expensive helium isotope, complex apparatus and moving the patient to a compatible MRI scanner. Electrical impedance tomography (EIT) a non-invasive bedside technique that allows constant monitoring of lung impedance, which is dependent on changes in air space capacity in the lung. We have used He3MRI measurements of ventilation distribution as the gold standard for assessment of EIT. METHODS: Seven rats were ventilated in supine, prone, left and right lateral position with 70% helium/30% oxygen for EIT measurements and pure helium for He3 MRI. The same ventilator and settings were used for both measurements. Image dimensions, geometric centre and global in homogeneity index were calculated. RESULTS: EIT images were smaller and of lower resolution and contained less anatomical detail than those from He3 MRI. However, both methods could measure positional induced changes in lung ventilation, as assessed by the geometric centre. The global in homogeneity index were comparable between the techniques. CONCLUSION: EIT is a suitable technique for monitoring ventilation distribution and inhomgeneity as assessed by comparison with He3 MRI.     

Mechanical strain promotes osteoblast ECM formation and improves its osteoinductive potential

Background

Hyperpolarised helium MRI (He3 MRI) is a new technique that enables imaging of the air distribution within the lungs. This allows accurate determination of the ventilation distribution in vivo. The technique has the disadvantages of requiring an expensive helium isotope, complex apparatus and moving the patient to a compatible MRI scanner. Electrical impedance tomography (EIT) a non-invasive bedside technique that allows constant monitoring of lung impedance, which is dependent on changes in air space capacity in the lung. We have used He3MRI measurements of ventilation distribution as the gold standard for assessment of EIT.

Methods

Seven rats were ventilated in supine, prone, left and right lateral position with 70% helium/30% oxygen for EIT measurements and pure helium for He3 MRI. The same ventilator and settings were used for both measurements. Image dimensions, geometric centre and global in homogeneity index were calculated.

Results

EIT images were smaller and of lower resolution and contained less anatomical detail than those from He3 MRI. However, both methods could measure positional induced changes in lung ventilation, as assessed by the geometric centre. The global in homogeneity index were comparable between the techniques.

Conclusion

EIT is a suitable technique for monitoring ventilation distribution and inhomgeneity as assessed by comparison with He3 MRI.     

无限制克隆技术研究进展及其应用

无限制克隆(restriction-free cloning,RFC)是近年来建立起来的一种简单通用的DNA克隆技术,它可以精确地将目的片段插入到质粒内任意位置,是一种不受酶切位点、连接酶效率、目的基因长度或载体序列等条件限制的新型DNA重组技术.与其他多种克隆方法相比,RFC技术拥有不可替代的优势.本文在总结国内外RFC技术研究的基础上,系统阐述了RFC技术的原理、特点和在克隆方面的研究进展,并探讨其在分子生物学和合成生物学等领域的应用价值.     

Review on Biomedical Techniques for Imaging Electrical Impedance

Electrical impedance of a medium helps to predict the behavior of electrical currents in a medium. Electrical impedance refers indeed to the “difficulty”, for an electrical current, to spread through the medium. While the first impedance measurements were focused on cardiovascular parameters, techniques are now being applied to the whole body, as electrical impedance present important variations through the human body and could then offer a new source of contrast.Combining electrical current, magnetic fields, and acoustics in various ways have led to interesting techniques to image this parameter: Electrical Impedance Tomography, Magnetic Resonance Electrical Impedance Tomography, Acousto-Electric Imaging, Lorentz Force Electrical Impedance Tomography and Magneto-Acoustic Tomography. These techniques are detailed in this review.