基于轮廓形状的肺部电阻抗成像三维插值方法

肺部三维信息利于医生做出更快更准确的诊断,但肺部三维重建的图像都是源自二维断层图像的叠加.二维图像的数量制约三维成像的效果,增加电极层数可获取更多层的二维图像,但同时也会增加计算量,减缓成像速度.虽然采取层间插值的方法可以解决这个问题,但是由于人体几何结构的特异性,肺部电阻抗图像(electrical impedance tomography,EIT)边界不规则,传统的规则图像插值方法不适合直接应用于肺部EIT三维插值.为此,提出适用于肺部电阻抗的插值算法,先获得插值图像轮廓,再用对应点插值像素值.通过仿真和实验验证新插值算法成像的相对误差比线性插值、样条插值成像的相对误差分别降低5.69％、3.3％.基于轮廓形状的肺部电阻抗三维插值方法,能在测量数据量有限的条件下,进一步提高三维电阻抗成像质量,更好地反映肺部的真实形态.     

基于小波多分辨分析和LSQR的快速EIT图像重建算法

针对LSQR(least square QR-factorization)算法在求解电阻抗层析成像(electrical impedance tomography,EIT)逆问题时,由于矩阵维数高、计算量大而导致重建速度较慢的问题,提出基于小波多分辨分析的LSQR算法(wavelet multi-resolution based least square QR-factorization,WALSQR)。该方法将EIT的图像重建过程投影到低维的尺度空间进行,通过提取有效信息减少数据计算量,明显提高了图像重建速度。同时由于去除了噪声和冗余信息,保证了成像质量。本文将SALSQR方法分别应用于二维、三维EIT成像实验,证明其有效性,并为三维动态EIT图像重建算法的研究奠定了基础。     

Noninvasive Imaging of Head-Brain Conductivity Profiles

Magnetic resonance electrical impedance tomography (MREIT) is a recently introduced noninvasive conductivity imaging modality, which combines the magnetic resonance current density imaging (MRCDI) and the traditional electrical impedance tomography (EIT) techniques.MREIT is aimed at providing high-spatial-resolution images of electrical conductivity because it avoids solving the well-known ill-posed problem in the traditional EIT. In this article, we review our research activities in MREIT imaging of head?brain tissue conductivity profiles. We have developed several imaging algorithms and conducted a series of computer simulations for MREIT imaging of the head?brain tissues. Our work suggests that MREIT brain imaging may become a useful tool in imaging conductivity distributions of the brain and head.     

肺部电阻抗成像电极阵列优化方法研究

肺部电阻抗层析成像(EIT)电极阵列的设计是影响系统性能与成像效果的关键因素之一,目前多在规则形状物场、等 间距分布的前提条件下对电极阵列进行优化,却并不适用于肺部不规则边界的情况。 本文提出基于深度学习的肺部电阻抗层 析成像电极阵列优化方法,以电极位置为优化目标,以重建图像相对误差、图像相关系数、敏感场分布的均匀性以及敏感场 Hessian 矩阵的条件数为网络输入,以阵列电极位置为网络输出,基于 DNN 网络构建优化模型。 实验结果表明,在呼气末和吸 气末两种状态下,与传统的电极阵列均匀分布方法相比,基于深度学习的肺部 EIT 电极阵列优化方法将重建图像相关系数 (image correlation coefficient,ICC) 分别提高了 33. 17%、33. 86%,结构相似度( structural similarity,SSIM) 分别提高了 14. 5%、 14. 39%,峰值信噪比(peak signal-to-noise ratio,PSNR)分别提高了 26. 3%、28. 27%。 因此可以得出结论,与传统方法相比基于深 度学习的 EIT 电极阵列优化方法更适用于肺部 EIT 成像。     

Code-Division-Multiplexed Electrical Impedance Tomography Spectroscopy

Electrical impedance tomography uses multiple impedance measurements to image the internal conductivity of an object, such as the human body. Code-division multiplexing is proposed as a new method that can provide simultaneous impedance measurements of the multiple channels. Code division provides clear advantages of a wide frequency range at reduced cost and reduced complexity of sources. A potential drawback is the lack of perfectly orthogonal code sets. This caused an increase of 0.62% in root-mean-square spectral error when two codes were used to record two impedance channels simultaneously on a low-pass filter network. The method described provides images and spectra which are equivalent to the conventional time-multiplexed method, with increases in frequency resolution and measurement speed which may be of benefit in some applications of electrical impedance tomography spectroscopy.     

基于改进L1/2正则化的电阻抗层析成像

碳纤维复合材料的结构安全健康检测至关重要。电阻抗层析成像技术利用碳纤维复合材料的导电特性,可实现对其结构损伤检测。此技术具有成本低、非侵入和操作简便等优点,近年来成为广大学者的研究热点。在EIT的图像重构过程中存在着严重的病态性问题,本文提出了一种改进L1/2正则化算子的电阻抗层析成像算法。该方法采用L1/2范数构建稀疏正则化罚函数,通过布雷格曼交替方向乘子法的迭代算法对新目标函数进行求解,提高算法的性能。为验证算法有效性,使用COMSOL软件设计四种典型CFRP层合板损伤类型并搭建16电极EIT测试系统验证。仿真与实际实验结果表明,与其它算法相比,采用BADMM迭代算法求解L1/2正则化方法提高了图像相关系数,降低了图像误差,有效改善了重建图像的精度,且该方法对噪声具有较强的鲁棒性。     

Principles of the impedance technique

A simplified treatment of the electrical impedance of biological tissues is presented, examining the sources of impedance changes and the requirements for recording these changes. The author covers small electrodes, simple models, resistivity of blood, the reactive component in bioimpedance, the use of bioadmittance, the use of the finite-element technique and impedance matching.     

抑制共模干扰新方法及在阻抗成象数据采集中应用

本文介绍一种利用精密模拟开关组的共模干扰抑制方法。应用这种技术,阻抗成象数据采集系统在差分增益为1000时,对50kHz的同频共模干扰的共模抑制比CMRR为118dB。     

Intracardiac measurements with the impedance technique

The author describes how intracardiac volume can be assessed by means of the impedance presented to the passage of an electric current by the blood contained in that volume. It begins with an overview of impedance measurement, and then describes the measurement of cardiac impedance using transventricular electrodes. The calibration of intraventricular blood conductance in absolute volume terms, a major problem that is not as yet fully solved, is discussed. Three applications are examined: intraventricular pressure-volume diagrams: measurements of cardiac efficiency; and detection of regional myocardial ischemia.     

Impedance tomography and its application in deep venous thrombosisdetection

The authors have developed an impedance imaging prototype system and tested its functionality. They describe some enhancements made to their previous system and three algorithms for reconstructing impedance images. The system is capable of reconstructing cross-sectional impedance distributions from surface measured data. They discuss some experimental results with the saline tank and a preclinical study of applying the electrical imaging technique to detect deep venous thrombosis (DVT). Other potential applications include monitoring pulmonary edema, imaging the lungs, and noninvasive temperature monitoring during hyperthermia treatment.     

接地材料对杆塔接地装置冲击接地阻抗的影响

雷电流通过接地装置散流时,接地装置本身和土壤电阻率的大小都会影响散流过程,从而影响接地装置的冲击接地阻抗。基于电磁场和电路相结合的计算方法,使用自主开发的软件,计算了接地本体材料、不同接地体长度、直径和不同土壤电阻率对冲击接地阻抗的影响,并通过时域电压波形对这几个参数影响冲击接地阻抗的机理进行分析。由计算结果可知,接地体的磁导率对冲击接地阻抗影响很大。在接地体成本固定的情况下,铜接地装置的接地体长度越长,冲击接地阻抗越小。钢接地装置的接地体长度即使增长,但由于有效长度有限,其冲击接地阻抗降低幅度并不明显。随着土壤电阻率的增大,铜接地装置的冲击接地阻抗线性增加,而钢接地装置的冲击接地阻抗增加趋于平缓。     

An image reconstruction algorithm of EIT based on pulmonary prior information

Using a CT scan of the pulmonary tissue, a human pulmonary model is established combined with the structure property of the human lung tissue using the software COMSOL. Combined with the conductivity contribution information of the human tissue and organ, an image reconstruction method of electrical impedance tomography based on pulmonary prior information is proposed using the conjugate gradient method. Simulation results show that the uniformity index of sensitivity distribution of the pulmonary model is 15.568, which is significantly reduced compared with 34.218 based on the round field. The proposed algorithm improves the uniformity of the sensing field, the image resolution of the conductivity distribution of pulmonary tissue and the quality of the reconstruction image based on pulmonary prior information. __________ Translated from Journal of Tianjin University, 2008, 41(4): 383–388 [译自: 天津大学学报]     

Converting far infrared image information to other physiologicaldata

Skin temperature is determined by blood-flow rate, structure of subcutaneous tissue, and activities of the sympathetic nervous system, which regulate heat dissipation from the body surface. Because of this, we can noninvasively detect distributions of many physiological functions from thermal images of the skin surface obtained by far infrared (FIR) imaging. If we can describe equations by which we calculate values of some functions from skin temperature, we might be able to analyze pathophysiological abnormalities by remote sensing. However, it is clear that we cannot convert a thermal image into other physiological function images unless we eliminate influences of many environmental conditions, structural variations, and other physiological parameters of skin-surface temperature. One solution is to introduce some physical, chemical, or neurohumoral stress to a patient and then take time-sequential thermal images. Dynamic fluctuation of such physiological functions might be revealed by sequential thermal images taken after stress is applied. We analyzed the theoretical backgrounds to determine regional skin temperature and thus developed application software to carry out the process. This article discusses algorithms we developed for detecting static abnormality or transient change of some physiological functions such as skin blood-flow rate, blood volume in cutaneous and subcutaneous vascular beds, and activities of the sympathetic nervous system     

Adaptive and self-evaluating registration method for myocardial perfusion assessment

With the advent of ultra-fast MR I, it is now possible to assess non-invasively regional myocardial perfusion with multislice coverage and sub-second temporal resolution. First-pass contrast enhanced studies are acquired with ECG-triggering and breath holding. Nevertheless, some respiratory induced movements still remain. Myocardial perfusion can be assessed locally byparametric imaging methods such as Factor Analysis of Medical Image Sequences (FAMIS), provided that residual motion can be corrected. An a posteriori registration method implemented in the image domain is proposed. It is based on an adaptive registration model of the heart combining three elementary shapes (left ventricle, right ventricle and pericardium). The registration procedure is performed on a potential map derived from the distance map. To evaluate the quality of the registration procedure a superimposition score between the registration model and the contour automatically extracted in the sequence is proposed. Rigid transformation hypotheses and registration analysis provide an efficient and automatic method which allows the rejection of outlier images, such as; outof synchronisation images, out of plane acquisitions. When compared to a manual registration method, this approach reduces processing time and requires a minimal intervention from the operator. The proposed method performs registration with a subpixel accuracy. It has been successfully applied to simulated images and clinical data. It should facilitate the use of MR first-pass perfusion studies in clinical practice.     

基于深度神经网络的电阻层析成像重建方法

电阻层析成像技术因其非侵入式测量特点、结果可视化的直观性和测量方法便捷性，被广泛用于医学造像，两相流工业检测和特殊材料检测。但其图像重建的逆过程由于固有的欠定性、病态特点，使得结果有一定偏差。针对该情况，设计了基于Resnet34改进的深度神经网络来求解电阻抗层析成像逆问题。通过设置场域内以像素点为中心，小范围内随机半径与电阻率分布变化强度，正向计算仿真32电极情况下各电极处边界电压，以此建立训练与测试数据集。经调参、训练后，该方法能较快收敛，并和高斯-牛顿法、全变差法以及Tikhonov正则化算法相比较，得到较好的判定性能。     

纳秒脉冲电晕放电的衰减及电晕线电阻率对其的影响

在线-板电晕放电反应器模型上,分别采用电阻率较高的镍铬不锈钢线和电阻率较低的青铜线作为电晕线进行了脉冲电晕放电试验研究。结果表明,在其它条件相同的情况下,镍铬不锈钢线比青铜线上的纳秒脉冲衰减要大,两者的差别达15％。这表明,在纳秒脉冲电晕放电的实际应用中,电晕线的电阻率对纳秒脉冲电晕放电的衰减影响不容忽视。     

基于面部红外热图的恐惧情绪识别

恐惧情绪是人体应对外界刺激的一种反应,其产生会引起人体面部皮肤温度的变化。根据红外热图反映物体表面温度分布的原理,提出了一种基于面部红外热图对恐惧情绪进行识别的方法。首先采用指数函数拟合方法对现有的传热模型进行简化,将红外热像仪所采集的面部红外热图转化为血液灌注伪彩色图,寻找感兴趣区域(前额区域);然后,提取感兴趣区域的血液灌注变化曲线的相关特征(斜率、置信度、均值、标准偏差),并采用斯皮尔曼相关系数分析其与受试对象恐惧程度自评分之间的相关性;最后采用与恐惧程度自评分相关性最高的标准偏差对受试对象进行恐惧情绪的识别。实验结果表明,当受试对象产生恐惧情绪时,前额区域的血液灌注呈现出明显的下降趋势,这与现有的恐惧情绪研究结论一致;血液灌注值的标准偏差可以作为恐惧情绪识别的主要特征(阈值0.14)。采用本文所提出的方法,对28例样本进行测试,受试对象恐惧情绪的识别准确率达到85.7%,具有较高的可靠性。     

局部放电远程识别中的分形图像压缩方法

研究了局部放电图像分形压缩技术 ,分析了解码图像误差对识别结果的影响。大量的样本数据识别结果说明 :采用分形图像压缩技术能获得较高的局放图像压缩比 ,提高了系统对远程计算机存储局放图像的识别速度 ,使局放图像远程识别系统具有更强的实用性     

注入电流式磁声成像平面模型的逆问题研究

注入电流式磁声成像是电阻抗成像和超声成像相结合的一种新型成像技术,具有电阻抗成像的高对比度和超声成像高分辨率的优势,是一种有望获得高质量图像的生物电阻抗成像技术,在生物医学成像领域具有广阔的应用前景。作为一种新型成像技术,目前在电导率的重建方面还没有形成完整的体系。针对二维平面模型,提出一种由声场信号准确重建被测样品电流密度的方法。首先采用维纳滤波反卷积方法由超声换能器测量的声场信号重建被测样品原始声场p(r,t),接着利用时间反演法获取声源分布0??(J×B),然后考虑到二维平面模型只有电流密度的两个分量,结合电流连续性定理,从而重建电流密度的两个分量xJ、yJ,最后设计并搭建注入式磁声成像实验平台,利用生物组织进行实验,最终得到猪肉组织的电导率图像,重建结果证明了重建方法的可行性。     

基于椭圆几何模型的胸部电阻抗成像

电阻抗成像技术是通过测量生物体表面电压,计算生物体横截面的电阻抗分布。由于生物体的边界形状是各异的,尤其在胸部应用中,建立不同边界形状会影响成像的精度和清晰度,所以构建合适的边界形状是求解EIT问题的前提。根据实际视觉效果,椭圆几何比较符合胸部边界形状,由于圆形几何的构建和有限元划分相当成熟,本文通过保角变换方法将圆形转换为椭圆几何,并分别进行两种几何与原始胸部形状的分析比较,实验结果表明,在求解正问题时建立椭圆边界形状分析胸部结构精度高,在求解逆问题时重建误差小。