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.     

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.     

Electrical Impedance of Isolated Amnion

The electrical impedance of the guinea pig amniotic membrane was measured, under standardized conditions, over the frequency range of 20 to 7000 cycles/second. This impedance can be represented analytically by a simple frequency-dependent function which is precisely of the form of the Debye relaxation equation. The observed data exhibit a broad dispersion centered at a frequency of 1050 cycles/second and a narrow distribution of time constants centered about 152 microseconds, both effects being due to the polydisperse nature of amniotic tissue. If the narrow time-constant distribution is approximated by a single time constant, amnion impedance can be simulated by a simple electrical circuit of frequency-independent elements. The Maxwell-Wagner interfacial treatment, although successfully adapted for cell suspensions, is shown to lose its quantitative significance in the case of the tightly structured amnion. In addition, determinations were made on the chemical composition of amniotic fluid, fetal blood and urine, and maternal blood and urine; the DC potential across the amniotic membrane was also measured.     

Microstructural Inhomogeneity of Electrical Conductivity in Subcutaneous Fat Tissue

Microscopic peculiarities stemming from a temperature increase in subcutaneous adipose tissue (sWAT) after applying a radio-frequency (RF) current, must be strongly dependent on the type of sWAT. This effect is connected with different electrical conductivities of pathways inside (triglycerides in adipocytes) and outside (extra-cellular matrix) the cells and to the different weighting of these pathways in hypertrophic and hyperplastic types of sWAT. The application of the RF current to hypertrophic sWAT, which normally has a strongly developed extracellular matrix with high concentrations of hyaluronan and collagen in a peri-cellular space of adipocytes, can produce, micro-structurally, a highly inhomogeneous temperature distribution, characterized by strong temperature gradients between the peri-cellular sheath of the extra-cellular matrix around the hypertrophic adipocytes and their volumes. In addition to normal temperature effects, which are generally considered in body contouring, these temperature gradients can produce thermo-mechanical stresses on the cells’ surfaces. Whereas these stresses are relatively small under normal conditions and cannot cause any direct fracturing or damage of the cell structure, these stresses can, under some supportive conditions, be theoretically increased by several orders of magnitude, causing the thermo-mechanical cell damage. This effect cannot be realized in sWAT of normal or hyperplastic types where the peri-cellular structures are under-developed. It is concluded that the results of RF application in body contouring procedures must be strongly dependent on the morphological structure of sWAT.     

Acupuncture Induces Divergent Alterations of Functional Connectivity within Conventional Frequency Bands: Evidence from MEG Recordings

As an ancient Chinese healing modality which has gained increasing popularity in modern society, acupuncture involves stimulation with fine needles inserted into acupoints. Both traditional literature and clinical data indicated that modulation effects largely depend on specific designated acupoints. However, scientific representations of acupoint specificity remain controversial. In the present study, considering the new findings on the sustained effects of acupuncture and its time-varied temporal characteristics, we employed an electrophysiological imaging modality namely magnetoencephalography with a temporal resolution on the order of milliseconds. Taken into account the differential band-limited signal modulations induced by acupuncture, we sought to explore whether or not stimulation at Stomach Meridian 36 (ST36) and a nearby non-meridian point (NAP) would evoke divergent functional connectivity alterations within delta, theta, alpha, beta and gamma bands. Whole-head scanning was performed on 28 healthy participants during an eyes-closed no-task condition both preceding and following acupuncture. Data analysis involved calculation of band-limited power (BLP) followed by pair-wise BLP correlations. Further averaging was conducted to obtain local and remote connectivity. Statistical analyses revealed the increased connection degree of the left temporal cortex within delta (0.5–4 Hz), beta (13–30 Hz) and gamma (30–48 Hz) bands following verum acupuncture. Moreover, we not only validated the closer linkage of the left temporal cortex with the prefrontal and frontal cortices, but further pinpointed that such patterns were more extensively distributed in the ST36 group in the delta and beta bands compared to the restriction only to the delta band for NAP. Psychophysical results for significant pain threshold elevation further confirmed the analgesic effect of acupuncture at ST36. In conclusion, our findings may provide a new perspective to lend support for the specificity of neural expression underlying acupuncture.     

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。     

测定植物抗寒性的电阻抗图谱法

电阻抗图谱(electrical impedance spectroscopy,EIS)分析作为测定植物抗寒性的一种方法,在农业、林业和园艺领域的应用正在不断扩大。该文从EIS的原理入手,讨论了影响电阻抗特性的生理和物理因子;介绍了测定EIS适用的模型;阐述了用EIS测定抗寒性的方法。在EIS分析中,胞外电阻率(re)是确定抗寒性最适用的一个参数,弛豫时间(τ1)是精确度最高的参数。     

Characterization of the Muscle Electrical Properties in Low Back Pain Patients by Electrical Impedance Myography

Objectives

This study aims to investigate the electrical properties of lumbar paraspinal muscles (LPM) of patients with acute lower back pain (LBP) and to study a new approach, namely Electrical Impedance Myography (EIM), for reliable, low-cost, non-invasive, and real-time assessment of muscle-strained acute LBP.

Design

Patients with muscle-strained acute LBP (n = 30) are compared to a healthy reference group (n = 30). Electrical properties of LPM are studied.

Background

EIM is a novel technique under development for the assessment of neuromuscular disease. Therefore, it is speculated that EIM can be employed for the assessment of muscle-strained acute LBP.

Methods

Surface electrodes, in 2-electrode configurations, was used to measure the electrical properties of patient''s and healthy subject''s LPM at six different frequencies (0.02, 25.02, 50.02, 1000.02, 3000.02, and 5000.02 kHz), with the amplitude of the applied voltage limited to 200 mV. Parameters of impedance (Z), extracellular resistance (R_e), intracellular resistance (R_i), and the ratio of extracellular resistance to intracellular resistance (R_e/R_i) of LBP patient''s and healthy subject''s LPM were assessed to see if significant difference in values obtained in muscle-strained acute LBP patients existed.

Results

Intraclass correlation coefficient (ICC) showed that all measurements (ICC>0.96 for all studying parameters: Z, R_e, R_i, and R_e/R_i) had good reliability and validity. Significant differences were found on Z between LBP patient''s and healthy subject''s LPM at all studying frequencies, with p<0.05 for all frequencies. It was also found that R_e (p<0.05) and R_e/R_i (p<0.05) of LBP patient''s LPM was significant smaller than that of healthy subjects while R_i (p<0.05) of LBP patient''s LPM was significant greater than that of healthy subjects. No statistical significant difference was found between the left and right LPM of LBP patients and healthy subjects on the four studying parameters.

Conclusion

EIM is a promising technique for assessing muscle-strained acute LBP.     

Dynamic Impedance Model of the Skin-Electrode Interface for Transcutaneous Electrical Stimulation

Transcutaneous electrical stimulation can depolarize nerve or muscle cells applying impulses through electrodes attached on the skin. For these applications, the electrode-skin impedance is an important factor which influences effectiveness. Various models describe the interface using constant or current-depending resistive-capacitive equivalent circuit. Here, we develop a dynamic impedance model valid for a wide range stimulation intensities. The model considers electroporation and charge-dependent effects to describe the impedance variation, which allows to describe high-charge pulses. The parameters were adjusted based on rectangular, biphasic stimulation pulses generated by a stimulator, providing optionally current or voltage-controlled impulses, and applied through electrodes of different sizes. Both control methods deliver a different electrical field to the tissue, which is constant throughout the impulse duration for current-controlled mode or have a very current peak for voltage-controlled. The results show a predominant dependence in the current intensity in the case of both stimulation techniques that allows to keep a simple model. A verification simulation using the proposed dynamic model shows coefficient of determination of around 0.99 in both stimulation types. The presented method for fitting electrode-skin impedance can be simple extended to other stimulation waveforms and electrode configuration. Therefore, it can be embedded in optimization algorithms for designing electrical stimulation applications even for pulses with high charges and high current spikes.     

干旱胁迫下小麦叶片的电阻抗图谱参数与生理参数的关系

通过盆栽实验,在适宜水分、中度干旱和严重干旱水分条件下,分别测定了3个不同抗旱类型的7个小麦品种叶片的电阻和电抗以及保护酶活性、MDA含量、细胞膜相对透性、脯氨酸和含水量等生理参数,并拟合了胞外电阻、胞内电阻、驰豫时间以及驰豫时间的分布系数等电阻抗图谱参数,分析了叶片的电阻抗图谱参数与生理参数之间的相关性。结果表明,在受到水分胁迫后,小麦叶片的CAT、POD活性较适宜水分条件下降低,MDA含量、细胞膜相对透性和脯氨酸含量增加,含水量减小;胞外电阻、胞内电阻、驰豫时间以及驰豫时间的分布系数在品种间差异均极显著(P<0.01),而仅胞内电阻在水分处理间差异显著(P<0.05);在适宜水分条件下,胞外电阻与细胞膜透性有显著负相关,驰豫时间与丙二醛、含水量之间有显著正相关,而在严重干旱条件下,驰豫时间分布系数与丙二醛含量之间有显著正相关,胞内电阻与含水量之间有显著负相关。可见,胞内电阻和驰豫时间分布系数在一定程度上反映了小麦叶片受水分胁迫的程度。     

高温胁迫对菊花电阻抗图谱参数的影响

以菊花(Chrysanthemum morifolium)‘神马’扦插苗茎段和叶片为材料,测定其高温胁迫(25~50℃)下电阻抗图谱参数的变化,通过膜透性(相对电导率)与电阻抗图谱参数间的相关性,来证明电阻抗图谱法研究菊花耐热性的有效性。结果表明:随着温度升高,茎叶的胞外电阻、胞内电阻、弛豫时间呈现先增加,后急剧下降的趋势,而弛豫时间分布系数变化趋势为不规则下降。茎叶相对电导率是随着温度的升高先增加后降低再急剧增加。经过菊花茎叶电阻抗图谱参数拟合菊花的耐热性与相对电导率表示的耐热性温度极为接近。相关分析表明,高温胁迫下菊花茎叶相对电导率与胞外电阻(茎p<0.01,叶p<0.05)、弛豫时间(p<0.05)之间有显著的相关。由此可见,胞外电阻和弛豫时间是测定菊花耐热性的适合参数。     

Electrical Impedance Myography to Detect the Effects of Electrical Muscle Stimulation in Wild Type and Mdx Mice

Objective

Tools to better evaluate the impact of therapy on nerve and muscle disease are needed. Electrical impedance myography (EIM) is sensitive to neuromuscular disease progression as well as to therapeutic interventions including myostatin inhibition and antisense oligonucleotide-based treatments. Whether the technique identifies the impact of electrical muscle stimulation (EMS) is unknown.

Methods

Ten wild-type (wt) C57B6 mice and 10 dystrophin-deficient (mdx) mice underwent 2 weeks of 20 min/day EMS on left gastrocnemius and sham stimulation on the right gastrocnemius. Multifrequency EIM data and limb girth were obtained before and at the conclusion of the protocol. Muscle weight, in situ force measurements, and muscle fiber histology were also assessed at the conclusion of the study.

Results

At the time of sacrifice, muscle weight was greater on the EMS-treated side than on the sham-stimulated side (p = 0.018 for wt and p = 0.007 for mdx). Similarly, in wt animals, EIM parameters changed significantly compared to baseline (resistance (p = 0.009), reactance (p = 0.0003) and phase (p = 0.002); these changes were due in part to reductions in the EIM values on the EMS-treated side and elevations on the sham-simulated side. Mdx animals showed analogous but non-significant changes (p = 0.083, p = 0.064, and p = 0.57 for resistance, reactance and phase, respectively). Maximal isometric force trended higher on the stimulated side in wt animals only (p = 0.06). Myofiber sizes in wt animals were also larger on the stimulated side than on the sham-stimulated side (p = 0.034); no significant difference was found in the mdx mice (p = 0.79).

Conclusion

EIM is sensitive to stimulation-induced muscle alterations in wt animals; similar trends are also present in mdx mice. The mechanisms by which these EIM changes develop, however, remains uncertain. Possible explanations include longer-term trophic effects and shorter-term osmotic effects.     

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.     

Functional Regions of Interest in Electrical Impedance Tomography: A Secondary Analysis of Two Clinical Studies

Introduction

Patients with acute respiratory distress syndrome (ARDS) typically show a high degree of ventilation inhomogeneity, which is associated with morbidity and unfavorable outcomes. Electrical impedance tomography (EIT) is able to detect ventilation inhomogeneity, but it is unclear which method for defining the region of interest (ROI) should be used for this purpose. The aim of our study was to compare the functional region of interest (fROI) method to both the lung area estimation method (LAEM) and no ROI when analysing global parameters of ventilation inhomogeneity. We assumed that a good method for ROI determination would lead to a high discriminatory power for ventilation inhomogeneity, as defined by the area under the receiver operating characteristics curve (AUC), comparing patients suffering from ARDS and control patients without pulmonary pathologies.

Methods

We retrospectively analysed EIT data from 24 ARDS patients and 12 control patients without pulmonary pathology. In all patients, a standardized low-flow-pressure volume maneuver had been performed and was used for EIT image generation. We compared the AUC for global inhomogeneity (GI) index and coefficient of variation (CV) between ARDS and control patients using all EIT image pixels, the fROI method and the LAEM for ROI determination.

Results

When analysing all EIT image pixels, we found an acceptable AUC both for the GI index (AUC = 0.76; 95% confidence interval (CI) 0.58–0.94) and the CV (AUC = 0.74; 95% CI 0.55–0.92). With the fROI method, we found a deteriorating AUC with increasing threshold criteria. With the LAEM, we found the best AUC both for the GI index (AUC = 0.89; 95% CI 0.78–1.0) and the CV (AUC = 0.89; 95% CI 0.78–1.0) using a threshold criterion of 50% of the maximum tidal impedance change.

Conclusion

In the assessment of ventilation inhomogeneity with EIT, functional regions of interest obscure the difference between patients with ARDS and control patients without pulmonary pathologies. The LAEM is preferable to the fROI method when assessing ventilation inhomogeneity.     

Development of Medical Sensor Systems in Pulmonology Based on Electrical Impedance Measurement

Biophysics - In order to experimentally confirm the dependence of the bioelectrical impedance on the flow rate of charged aerosol particles and the composition of bronchial secretions in small...