Surface electrode switching of a 16-electrode wireless EIT system using RF-based digital data transmission scheme with 8 channel encoder/decoder ICs

A Radio Frequency (RF) based digital data transmission scheme with 8 channel encoder/decoder ICs is proposed for surface electrode switching of a 16-electrode wireless Electrical Impedance Tomography (EIT) system. A RF based wireless digital data transmission module (WDDTM) is developed and the electrode switching of a EIT system is studied by analyzing the boundary data collected and the resistivity images of practical phantoms. An analog multiplexers based electrode switching module (ESM) is developed with analog multiplexers and switched with parallel digital data transmitted by a wireless transmitter/receiver (T_x/R_x) module working with radio frequency technology. Parallel digital bits are generated using NI USB 6251 card working in LabVIEW platform and sent to transmission module to transmit the digital data to the receiver end. The transmitter/receiver module developed is properly interfaced with the personal computer (PC) and practical phantoms through the ESM and USB based DAQ system respectively. It is observed that the digital bits required for multiplexer operation are sequentially generated by the digital output (D/O) ports of the DAQ card. Parallel to serial and serial to parallel conversion of digital data are suitably done by encoder and decoder ICs. Wireless digital data transmission module successfully transmitted and received the parallel data required for switching the current and voltage electrodes wirelessly. 1 mA, 50 kHz sinusoidal constant current is injected at the phantom boundary using common ground current injection protocol and the boundary potentials developed at the voltage electrodes are measured. Resistivity images of the practical phantoms are reconstructed from boundary data using EIDORS. Boundary data and the resistivity images reconstructed from the surface potentials are studied to assess the wireless digital data transmission system. Boundary data profiles of the practical phantom with different configurations show that the multiplexers are operating in the required sequence for common ground current injection protocol. The voltage peaks obtained at the proper positions in the boundary data profiles proved the sequential operation of multiplexers and successful wireless transmission of digital bits. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn again indicates a sequential and proper operation of multiplexers as well as the successful wireless transmission of digital bits. Hence the developed RF based wireless digital data transmission module (WDDTM) is found suitable for transmitting digital bits required for electrode switching in wireless EIT data acquisition system.     

A Chicken Tissue Phantom for Studying an Electrical Impedance Tomography (EIT) System Suitable for Clinical Imaging

The study of practical phantoms is essential for assessing the reconstruction algorithms and instrumentation used in Electrical Impedance Tomography (EIT). Responses of saline phantoms with insulator inhomogeneities differ from the real tissue phantoms in several aspects. Also, it is difficult to reconstruct the actual resistivity of the insulator inhomogeneity in a saline background because of their large resistivity difference. A practical biological phantom consisting of two different materials with low resistivity difference is more suitable for impedance imaging studies. In order to demonstrate this, a chicken tissue phantom was developed to study the resistivity imaging in EIT. A 16-electrode array was placed inside the phantom tank filled with chicken muscle tissue paste and chicken tissue. A 1 mA, 50 kHz sinusoidal current was injected at the phantom boundary and the boundary potentials are measured using opposite current injection protocol. Resistivity images were reconstructed from the boundary data using Electrical Impedance and Diffuse Optical Reconstruction Software (EIDORS) and the reconstruction was evaluated by calculating the contrast parameters of the images. Results show that the resistivity of the chicken fat is successfully reconstructed with a proper background resistivity. Impedance spectroscopic studies show that the chicken tissue phantom can be suitably used to evaluate a multifrequency EIT system.     

Studying the resistivity imaging of chicken tissue phantoms with different current patterns in Electrical Impedance Tomography (EIT)

A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IR_Mean and IR_Max neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom.     

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities in 2D-electrical impedance tomography

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities is studied with a simple instrumentation and data acquisition system for Electrical Impedance Tomography. The reconfigurable phantom is developed with stainless steel electrodes and a sinusoidal current of constant amplitude is injected to the phantom boundary using opposite current injection protocol. Nylon and polypropylene cylinders with different cross sectional areas are kept inside the phantom and the boundary potential data are collected. The instrumentation and the data acquisition system with a DIP switch-based multiplexer board are used to inject a constant current of desired amplitude and frequency. Voltage data for the first eight current patterns (128 voltage data) are found to be sufficient to reconstruct the inhomogeneities and hence the acquisition time is reduced. Resistivity images are reconstructed from the boundary data for different inhomogeneity positions using EIDORS-2D. The results show that the shape and resistivity of the inhomogeneity as well as the background resistivity are successfully reconstructed from the potential data for single or double inhomogeneity phantoms. The resistivity images obtained from the single and double inhomogeneity phantom clearly indicate the inhomogeneity as the high resistive material. Contrast to noise ratio (CNR) and contrast recovery (CR) of the reconstructed images are found high for the inhomogeneities near all the electrodes arbitrarily chosen for the entire study.     

Coping with electrode polarization for development of DC-Driven electrical impedance tomography

An electrical impedance tomography (EIT) system design is proposed for imaging of phase distribution in gas-water two-phase flow from boundary measurement of electrical potentials in response to direct current (DC) injection. DC injection simplifies substantially the system design, but introduces problems due to polarization of injection electrodes. Electrode polarization means charge accumulation on the electrode-water interface causing a drift in the interfacial potential difference. The polarization problems are coped with by using dedicated electrodes for injection and potential measurement, and using a current source unaffected by the polarization of current-carrying electrodes (CCEs). Furthermore, the polarization of CCEs is controlled, to lessen the possible influence on the sensing electrodes (SEs), by using a short (milliseconds in width) pulse for injection with a charge balanced injection strategy. The impact of electrode polarization and the effectiveness of countermeasures introduced in the present design are discussed through comparisons of measured boundary potentials and of images reconstructed for a simple object simulating large bubbles in water.     

Projection Error Propagation-based Regularization (PEPR) method for resistivity reconstruction in Electrical Impedance Tomography (EIT)

A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP).     

An element-free Galerkin forward solver for the complete-electrode model in electrical impedance tomography

An element-free Galerkin method (EFGM) is used for solving forward problem based on the complete electrode model (CEM) in electrical impedance tomography (EIT). The EFGM requires only nodal data and has the ability of providing mesh-independent solutions because no element connectivity is needed to be used in this method. However, direct imposition of Dirichlet boundary conditions for the EFGM is difficult because the shape functions employed in this method do not have the property of Dirac delta function. Solving the EIT forward problem based on the CEM by the EFGM, the effects of electrodes and contact impedances are taken into account and the complete solution of equations is provided without imposing Dirichlet boundary conditions. The numerical results are validated with experimental results obtained from a 2D circular homogeneous phantom, and the performance of the EFGM compared with the finite element method is also illustrated. Moreover, results obtained from the EFGM are presented for an inhomogeneous numerical phantom.     

基于 Tikhonov 和 TV 混合正则化的接地 网电阻抗成像算法研究

电阻抗成像技术(EIT)是解决接地网腐蚀定位问题的方法之一,为了改善接地网 EIT 逆问题的病态性,提高求解稳定 性以及重建图像清晰度,提出了经典吉洪诺夫正则化(Tikhonov)和全变差正则化(TV)相结合的混合正则化(Tikhonov-TV)接地 网成像算法。 首先,在循环测量原理的基础上,创新地借助 COMSOL 与 MATLAB 联合仿真求取接地网 EIT 正问题模型电压数 据;其次,在理论分析基础上,通过 Tikhonov-TV 正则化的 EIT 算法分别求解基于先验拓扑信息和未知拓扑信息的两种接地网逆 问题模型的场域电阻率分布;最后仿真和实验对比了 Tikhonov、TV 以及 Tikhonov-TV 3 种正则化算法的接地网 EIT 重建图像,并 采用电阻率均方误差(Resistivity MSE)和截线电阻率曲线图来衡量图像质量,实验得出基于先验拓扑信息的 1 处和 2 处腐蚀情 况下 Resistivity MSE 分别达到 1. 27×10 -15 和 1. 59×10 -15 ,电阻率均方误差最小。 结果表明,提出的 Tikhonov-TV 正则化算法有效 地改善了 EIT 逆问题的病态性,收敛性能最优,重建图像效果优于 Tikhonov 和 TV 正则化算法。     

Design of wearable and wireless electrical impedance tomography system

Electrical impedance tomography (EIT) is a non-invasive approach to reconstruct the cross-section impedance image of the body. Many EIT systems and impedance image reconstruction algorithms have been proposed in previous studies. However, most of these EIT systems are bulky to cause the limitation of applications. In this study, a wearable and wireless EIT system is proposed to reconstruct impedance images non-invasively and wirelessly. By microminiaturizing the conventional EIT system, the proposed system can provide the advantages of small volume and wireless transmission to reduce the application limitation of conventional EIT systems. Finally, the phantom experiment is tested to validate the performance of the proposed EIT system. The experimental results show the average BR value of the reconstructed image obtained by the proposed system being 1.3 ± 0.2 and the averaged location error ratio being about 6.27 ± 3.14%. Therefore, the proposed wearable and wireless EIT system can be viewed as a good system prototype and may be applied to more clinical applications in the future.     

EIT系统复合电极结构性能分析及优化设计

本文研究了医学电阻抗成像（MEIT）系统复合电极结构对敏感场分布的影响，并提出了一个具有边界强制等势点的有限元模型，通过计算机仿真，分析了复合电极宽度对敏感场分布的影响，并对不同激励模式下敏感电极的结构尺寸进行了优化设计。     

阻抗断层成象系统的研究

描述了一阻抗断层成象系统。该系统用安装在有机玻璃筒壁上的３２只电极来注入电流和测量在边界是的电压分布。提出的一种快速成象算法利用所测到的一组电压值来重建筒内物体的断层阻抗分布图象。与其它成象方法相比，阻抗断层成象有着高速、简单、可靠的优点，适合于一些工业过程的动态监控与测量。     

A proposal of multi-imaging system of electrical and ultrasonic properties

In this paper, we propose a multi-imaging system which can simultaneously create both an ultrasound and electrical impedance images by using the data collected by piezoelectric ceramic transducers (PZTs) for the living body. In the proposed system, ultrasonic time of flight is not only measured by several combinations of PZTs arranged around the target and but also measured by those of front surface electrodes of PZTs. From these data, the electrical and ultrasonic properties at the same space are simultaneously reconstructed. This enables advancement of the detection ability in the target because two different images at the same space are simultaneously obtained. First of all, we established an ultrasound reflective and electrical impedance imaging system with 16 PZTs. As the experiments, we demonstrated both reconstructed images of electrical and ultrasonic properties from measurement data of electrical conductance and ultrasonic time of flight.     

Noise Reduction of Electrical Impedance Tomography via Movable Electrodes

Abstract

In this paper, a movable electrical impedance tomography (MEIT) system is introduced to reduce the noise of electrical impedance tomography. This moving scheme could yield more independent measurements and reconstruct improved impedance images. After averaging the entire reconstructed image, we could improve the image quality substantially. The experiment result shows a quality improvement compared with the measuring systems without moving scheme. This preliminary work provides a feasibility to reduce the noise of electrical impedance tomography by a moving electrode scheme.     

不接触电极探测方法研究

介绍不接触电极电法测量的基本原理，分析视电阻率测量与视阻抗探测方法，进行视电阻率模型试验；提出视阻抗测量的理论模型，并进行了金属和非金属异常体模型试验，验证了视阻抗测量方法的正确性，可以适用于不同环境探测，区分介质的导电性差异和介电性差异，为工程探测提供一种快速、方便、准确的多参数检测手段。     

An EKF based estimation scheme for sedimentation processes in vessels using EIT-type measurement data

Sedimentation is usually parameterized by settling curves, settling velocities and the concentration of the constituent layers. The estimation of sedimentation parameters leads to useful information in the fields of environmental and industrial engineering. This paper presents an extended Kalman filter (EKF) based dynamic estimation scheme to extract sedimentation parameters from electrical impedance tomography (EIT) measurements obtained across the electrodes attached to the walls of a process vessel. A state evolution model has been developed for three-layer sedimentation based on the solids flux theory for batch sedimentation. The performance of the proposed method has been verified by carrying out numerical experiments.     

基于 V-ResNet 的电阻抗层析成像方法

电阻抗层析成像技术(EIT)因其非侵入和可视化等特性为人体肺部空间特性的监测提供了一种有效的方法。但是EIT的逆问题具有严重的非线性、病态性和欠定性,使得图像重建结果含有严重的伪影。针对上述问题,提出了一种由预映射、特征提取、深度重建以及残差去噪四个模块构成的V-ResNet的深度网络成像算法,实现对场域空间位置和电导率参数分布的重建。该算法有效地增加了前馈信息的多重传递并解决了深度网络的梯度消失问题,同时残差去噪模块有效地平滑了图像边界。采用相对误差(RE)和结构相似度(SSIM)来衡量成像质量,实验得出RE的平均值为0.14,SSIM平均值为0.96。仿真与实验结果表明,基于V-ResNet的成像算法与传统的成像算法相比,图像重建结果边界清晰,空间分辨率高。     

一种单源电流激励方法的电阻抗成像仿真及实验

为电阻抗断层成像技术的实际应用选择一种较优的电流激励方法,本文研究了一种单电流源两电极对向激励方法。通过计算机仿真、物理模型实验和初步的动物实验,结合电阻抗成像的反投影算法,与传统的邻近电流激励的电阻抗成像进行比较研究,并分析图像质量、定位误差以及重构误差。结果表明,与邻近激励相比,基于对向激励方法的电阻抗成像的抗噪性能较好。因此在临床较强噪声环境下,对向激励方法更适合于电阻抗成像的实际应用。     

Nonlinear image reconstruction using a GA-ECT technique in electrical capacitance tomography

Electrical capacitance tomography (ECT) is a non-invasive measurement technique that estimates the dielectric permittivity distribution of an inhomogeneous object from the boundary potentials at floating electrodes or mutual capacitances. In this paper, a stochastic inverse technique based on genetic algorithm (GA-ECT) is developed, which is adapted to the two different methods, i.e. potential measurement and capacitance measurement. Numerical simulation results are presented to evaluate the inverse technique both for noise free and noisy data and the results show that quantitative image can be reconstructed not only with the low permittivity contrast but also with the high contrast. Furthermore, the influence of a priori knowledge to image reconstruction is discussed.     

An adaptive non-convex hybrid total variation regularization method for image reconstruction in electrical impedance tomography

The image reconstruction of conductivity distribution in electrical impedance tomography (EIT) is a seriously ill-posed inverse problem. To cope with the problem, it is recognized that the regularization method is an effective approach. In this paper, an adaptive non-convex hybrid total variation (ANHTV) regularization method is proposed to reconstruct the conductivity distribution in EIT. The iterative reweighted least squares algorithm and the iterative alternating direction method of multipliers algorithm are developed to solve the ANHTV-based inverse model in the image reconstruction. Besides, all the parameters utilized in the inverse model are adaptively selected. To validate the advantage of the proposed method, extensive numerical simulation and experimental work have been carried out. Also, qualitative and quantitative comparisons with two convex TV-based regularization methods are conducted. The results show that the proposed method is more advantageous in terms of staircase effect suppression, edge information preservation and noise resisting in the image reconstruction.     

三维柔性神经微电极阵列的制作

神经-电极接口是植入式微器件和生物电子器件中最关键的问题之一。但是目前常规的平面微电极阵列均为“三明治”结构,难以保证电极与靶神经细胞的良好接触,以致刺激或记录效果不理想。为了克服这一缺陷,本文提出了一种具有三维凸起结构的柔性神经微电极的制作工艺和方法。该方法采用光敏型聚酰亚胺（Durimide 7510）作为微电极的基质材料,通过硅各向异性腐蚀、光刻、腐蚀金属、电化学释放等工艺制成具有塔形凸起结构的微电极阵列。电极的塔形凸起结构可保证电极位点与靶细胞实现更紧密的接触。通过FEMLAB软件模拟和成品电极的阻抗谱测试,结果显示,相对于传统的平面微电极阵列,三维凸起微电极阵列具有更好的刺激效果。