电阻抗断层成像电极系统性能与评价方法研究
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摘要
电阻抗断层成像技术(Electrical Impedance Tomography,EIT)是当今生物医学工程学重大研究课题之一,具有功能成像,无损伤和医学图像监护三大突出优势,是一种理想的、具有诱人应用前景的无损伤医学成像技术。
EIT电极系统直接与人接触,位于系统的最前端,是整个系统的关键部分之一。目前电阻抗断层成像技术现正处于一个从实验室研究阶段向临床应用过渡的时期,临床EIT直接与人体接触,电极系统面临一系列的问题需要研究和改进。而电极系统上发生的事件,包括有用信息、噪声、伪差、接触阻抗、极化电压等,都会进入后续电路被放大、传输,参与信号处理,影响图像重建结果,无用信息有时甚至会淹没有用信息,对系统检测灵敏度和图像重建质量的影响都非常大。场域边界移动形变造成的电极系统不确定性和电极排布方式也是影响成像结果的因素。根据实验室研究和临床研究的不同需求,研究电极特性,优化电极系统性能,具有十分重要的意义。
论文回顾了EIT研究历史,分析了EIT电极系统目前亟待解决的问题。在介绍EIT成像基本原理、硬件系统、成像算法的基础上,提出EIT图像重建质量的评价方法,建立了EIT成像软硬件平台和测试系统,比较了几种重建算法的成像效果及其局限。
基于强制等势点有限元模型,研究了电极类型、电极结构参数、电极数和激励测量模式对成像结果的影响,提出了电极系统优化设计方案。设计了一种用于EIT实验、参数可变的盐水槽电极系统,电极片拆卸方便,结构简单。
进行了EIT电极阻抗特性研究。提出了EIT电极阻抗特性的意义和重要性。对目前EIT人体实验通常采用的一次性心电电极进行了交直流阻抗特性测试和研究,提出了使用注意事项。
针对肺功能EIT检测时,由于电极运动和形变导致的图像伪差问题,采用改进的正则化算法和基于椭圆模型成像方法,改善图像质量。
设计了手持式平面电极系统,研究了平面电极阵列EIT成像方法。建立了3D有限元模型,应用基于等势面反投影法的改进的加权重建算法,仿真重建出了多深度层的断层图像,为EIT乳腺测量新方法奠定了基础。
Electrical impedance tomography (EIT) is one of the most important research topics in today's biomedical engineering. It has the following outstanding advantages: noninvasive, harmless, functional imaging and medical image monitoring. EIT is an attractive medical imaging technology with potential clinical application.
Electrode system lies in the front of the whole EIT system and contacts with human body directly. It is one of the most pivotal parts of EIT system. There are a lot of problems should be studied and improved in the electrode system of EIT. The useless information from electrode system, such as noise, contact impedance and polarization voltage etc, goes into the following circuits as useful signals. They are amplified, transferred and participate in signal processing process, and therefore influence the result of reconstruction finally. The uncertainty made by the change of boundary shape and electrode movement, as well as the arrange function of electrode system, are also affect the quality of reconstruction image greatly. These problems are even serious, as EIT is stepping from experimental study into clinical study currently. The study of both the property of electrode system and optimizing the electrode system is very important.
In this paper, firstly, the research history of EIT has been reviewed. Then the problems of current electrode systems have been presented. The principle of EIT, hardware system and image reconstruction method have been introduced. Several criteria functions used to evaluate the quality of reconstructed image have been proposed. The software, hardware and test platform have developed. Saveral reconstruction algorithms have been compared.
We studied the influence of electrode type, electrode structure parameter, electrode count and the exitation function on the quality of image reconstruction, based on the coercive equipotential node finite element model. Some optimizing design suggestion has been proposed. A new electrode install method with simple structure has been designed, which is convenient to remove and install the electrode slices. And the electrode parameter can be changed freely.
The impedance characteristic of EIT electrode, especially the amplitude and the stability of the alternating current impedance, is very important. Since the one-off ECG electrode has been widely used in clinical EIT measurement, we studied and compared more than ten ECG electrodes. Some suggestions need attention have been proposed.
To minish the image error made by electrode movement and boundary deform in EIT pulmonary function measurement, we used a modified regularization algorithm and an elliptical model based algorithm to improve the image quality.
An EIT method with planar electrode array has been proposed and a hand-held planar electrode system has been designed. Based on a 3-dimentional finite element model, a modified weighted backprojection algorithm, which is back-projected along equipotential surfaces of the 3D electric filed, is used to reconstruct slice images of 3D conductivity distribution, which is parallel to the electrode array. The method using planar electrode array establishs the foundation for EIT breast mesurement.
EIT电极系统直接与人接触,位于系统的最前端,是整个系统的关键部分之一。目前电阻抗断层成像技术现正处于一个从实验室研究阶段向临床应用过渡的时期,临床EIT直接与人体接触,电极系统面临一系列的问题需要研究和改进。而电极系统上发生的事件,包括有用信息、噪声、伪差、接触阻抗、极化电压等,都会进入后续电路被放大、传输,参与信号处理,影响图像重建结果,无用信息有时甚至会淹没有用信息,对系统检测灵敏度和图像重建质量的影响都非常大。场域边界移动形变造成的电极系统不确定性和电极排布方式也是影响成像结果的因素。根据实验室研究和临床研究的不同需求,研究电极特性,优化电极系统性能,具有十分重要的意义。
论文回顾了EIT研究历史,分析了EIT电极系统目前亟待解决的问题。在介绍EIT成像基本原理、硬件系统、成像算法的基础上,提出EIT图像重建质量的评价方法,建立了EIT成像软硬件平台和测试系统,比较了几种重建算法的成像效果及其局限。
基于强制等势点有限元模型,研究了电极类型、电极结构参数、电极数和激励测量模式对成像结果的影响,提出了电极系统优化设计方案。设计了一种用于EIT实验、参数可变的盐水槽电极系统,电极片拆卸方便,结构简单。
进行了EIT电极阻抗特性研究。提出了EIT电极阻抗特性的意义和重要性。对目前EIT人体实验通常采用的一次性心电电极进行了交直流阻抗特性测试和研究,提出了使用注意事项。
针对肺功能EIT检测时,由于电极运动和形变导致的图像伪差问题,采用改进的正则化算法和基于椭圆模型成像方法,改善图像质量。
设计了手持式平面电极系统,研究了平面电极阵列EIT成像方法。建立了3D有限元模型,应用基于等势面反投影法的改进的加权重建算法,仿真重建出了多深度层的断层图像,为EIT乳腺测量新方法奠定了基础。
Electrical impedance tomography (EIT) is one of the most important research topics in today's biomedical engineering. It has the following outstanding advantages: noninvasive, harmless, functional imaging and medical image monitoring. EIT is an attractive medical imaging technology with potential clinical application.
Electrode system lies in the front of the whole EIT system and contacts with human body directly. It is one of the most pivotal parts of EIT system. There are a lot of problems should be studied and improved in the electrode system of EIT. The useless information from electrode system, such as noise, contact impedance and polarization voltage etc, goes into the following circuits as useful signals. They are amplified, transferred and participate in signal processing process, and therefore influence the result of reconstruction finally. The uncertainty made by the change of boundary shape and electrode movement, as well as the arrange function of electrode system, are also affect the quality of reconstruction image greatly. These problems are even serious, as EIT is stepping from experimental study into clinical study currently. The study of both the property of electrode system and optimizing the electrode system is very important.
In this paper, firstly, the research history of EIT has been reviewed. Then the problems of current electrode systems have been presented. The principle of EIT, hardware system and image reconstruction method have been introduced. Several criteria functions used to evaluate the quality of reconstructed image have been proposed. The software, hardware and test platform have developed. Saveral reconstruction algorithms have been compared.
We studied the influence of electrode type, electrode structure parameter, electrode count and the exitation function on the quality of image reconstruction, based on the coercive equipotential node finite element model. Some optimizing design suggestion has been proposed. A new electrode install method with simple structure has been designed, which is convenient to remove and install the electrode slices. And the electrode parameter can be changed freely.
The impedance characteristic of EIT electrode, especially the amplitude and the stability of the alternating current impedance, is very important. Since the one-off ECG electrode has been widely used in clinical EIT measurement, we studied and compared more than ten ECG electrodes. Some suggestions need attention have been proposed.
To minish the image error made by electrode movement and boundary deform in EIT pulmonary function measurement, we used a modified regularization algorithm and an elliptical model based algorithm to improve the image quality.
An EIT method with planar electrode array has been proposed and a hand-held planar electrode system has been designed. Based on a 3-dimentional finite element model, a modified weighted backprojection algorithm, which is back-projected along equipotential surfaces of the 3D electric filed, is used to reconstruct slice images of 3D conductivity distribution, which is parallel to the electrode array. The method using planar electrode array establishs the foundation for EIT breast mesurement.
引文
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[10]http://www.rpi.edu.
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[2]任超世,生物电阻抗测量技术,中同医疗器械信息,2004,10(1):21-25。
[3]Henderson R P and Webster J G 1978 An impedance camera for spatially specific measurements of the thorax IEEE Trans.Biomd.Eng 25 250-254.
[4]A.M.Dijkstra,B.H.Brown,A.D.Leathard,et al,Review Clinical Application of Electrical Impedance Tomography,Journal of Medical Engineering & Technology,1993,17(3):89-98
[5]Kerner T E 2001 Electrical impedance tomography for breast imaging,Phd thesis,Dartmouth College.
[6]Frerichs I,Electrical impedance tomography(EIT) in applications related to lung and ventilation:a review of experimental and clinical activities,Physiol.Meas.200021:R1-21
[7]Yang W Q and York T,A new ac-based capacitance tomography system,Proc.IEE,1999,146:47-53.
[8]Jin Keun Seo,Ohin Kwon,et al,Megnetic resonance Electrical Impedance Tomography(MREIT),Ⅻ International Conference on Electrical Bio-lmpedance & Ⅴ Electrical Impedance Tomography.Gdansk,Poland,June 20-24,2004:19-22.
[9]David Holder.Electrical Impedance Tomography of Brain Function,Ⅻ International Conference on Electrical bio-lmpedance & Ⅴ Electrical Impedance Tomography,Gdansk,Poland,June 20-24 2004:7-12
[10]http://www.rpi.edu.
[11]史学涛 霍旭阳 尤富生 付峰 刘锐岗 徐灿华 董秀珍。颅内出血电阻抗成像系统及初步动物实验。航天医学与医学工程。2007,20(1):24-27
[12]廖琪梅,董秀珍,付峰,陈广生,阎艳,张聚良,凌瑞,漆家学,郭青霞。乳腺癌浸润部位对其电阻抗频谱特性影响的研究。航天医学与医学工程。2007,20(4):269-273
[13]王化祥 李璐 王春艳。用于肺功能监测的电阻抗成像系统。医疗卫生装备。2007(7):1-3
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