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研究生： 黃振寧
Chen-Ning Huang
論文名稱： 旋轉式電阻抗斷層攝影術之研究
Study of Rotational Electrical Impedance Tomography
指導教授： 鍾鴻源
Hung-Yuan Chung
口試委員:
學位類別： 博士
Doctor
系所名稱： 資訊電機學院 - 電機工程學系
Department of Electrical Engineering
畢業學年度： 96
語文別： 英文
論文頁數： 97
中文關鍵詞： 旋轉式 、阻抗影像 、電阻抗斷層攝影術
外文關鍵詞： rotational, electrical impedance tomography, impedance image
相關次數： 點閱：12  下載：0 
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    • 電阻抗斷層攝影術 (Electrical impedance tomography, EIT) 是一用於探測物體內部電特性分佈相當有效的方法,與其他常用的成像技術相比，電阻抗斷層攝影術具有許多的優點，然而其空間解析度不足(poor spatial resolution) 與不適定的問題 (ill-posed problem)限制了電阻抗斷層攝影術應用上的發展，為了改善阻抗影像的品質，本研究提出一旋轉式電阻抗斷層攝影系統來轉動量測電極，藉由轉動電極所增加的量測位置可以當成新增的虛擬電極，利用相鄰法收集資料並且持續轉動電極，使得旋轉式的資料收集方法可以有效的增加獨立量測資料量。
    旋轉式電阻抗斷層攝影系統的硬體設計可以分為三個部分，(1)轉動機構設計，(2)訊號切換網路，以及(3)阻抗量測系統，量測過程首先由定電流源產生交流電流並透過訊號切換網路注入待測物，阻抗量測系統利用電極來擷取待測表面所產生的電位,當資料收集完成後，轉動機構驅動16個複合電極同時轉動到新的量測位置，量測過程所收集到的阻抗資料都利用EIDORS計劃所開發的程式來完成影像重建。
    旋轉式電阻抗斷層攝影系統的性能評估測試包含了數值模擬以及鹽水槽的假體實驗，首先以數值模擬的結果驗證了旋轉式資料收集方法的可行性，在鹽水槽的假體實驗中，根據實際量測資料所計算出的Jacobin矩陣奇異值顯示了非適定問題的改善，重建影像的剖面圖也顯示了空間解析度上的提升，與傳統電阻抗斷層攝影比較旋轉式電阻抗斷層攝影的成像品質在整體上均有所提升
    本研究所提出的旋轉式電阻抗斷層攝影術在實際應用上仍須考慮ㄧ些問題，例如電極圍繞所造成的金屬屏蔽效應、即時影像重建的可行性以及未來可能的應用領域，對於這些問題作者也提出相關建議與解決方法，並且希望旋轉式電阻抗斷層攝影的研究能夠為將來阻抗影像的應用發展帶來幫助。

    Electrical impedance tomography (EIT) is a powerful tool for mapping the electrical properties of the measured objects. The EIT technique has several potential advantages over the current imaging methods. However, the poor spatial resolution and ill-posed problem restrict the development of an EIT application. In order to improve the image quality, a rotational electrical impedance tomography (REIT) system is proposed to expand the measurement sites by shifting the electrodes. The expanded measurement sites could be regarded as pseudo electrodes. Thus, by successively acquiring the data with adjacent method and rotating the electrodes pair, the independent measurements substantially could be increased.
    The REIT system is composed of three subsystems, rotary scheme, switches network and measurement system. By injecting the alternating current into the object, a potential will be established on the boundary electrodes of object. The moving scheme is the most important part in the REIT system. 16 compound electrodes are driven by micro-stepping motor to collect additional measurements. A developed Matlab package for the EIDORS project is applied to reconstruct the impedance distribution from boundary measurement.
    The performance of REIT is explored by using the numerical simulation and trial of a saline-filled phantom. The numerical simulation is provided to verify the feasibility of scanning strategy. A plot of singular values shows the ill-posed degree between the EIT and the REIT. The improvement of spatial resolution is estimated by the edge response and position dependence of the reconstructed image. The impedance images reconstructed from both conventional EIT and REIT are also demonstrated to show the image quality improvement of REIT.
    REIT also has some practical issues which include metal-wall effect, real-time image reconstruction and the application fields. Some comments and suggestions are given for future work. It is expected to provide more experience and reference material to those who are interested in the field of rotational EIT.

    ABSTRACT III FIGURE CAPTION V TABLE CAPTION VIII CHAPTER 1 INTRODUCTION 1 1.1 Background of Electrical Impedance Tomography 1 1.2 Problems of the Conventional EIT 3 1.3 Motivations 5 1.4 Contributions 6 1.5 Organization 6 CHAPTER 2 THEORETICAL BACKGROUND 8 2.1 Introduction 8 2.2 Forward Problems 9 2.2.1 Governing equations 9 2.2.2 Finite element methods 11 2.3 Image Reconstruction Methods 12 2.3.1 Probabilistic approaches 13 2.3.2 Back-projection method 15 2.3.3 Sensitivity coefficient methods 17 2.3.5 One step Newton–Raphson algorithm 21 2.4 Regularization Techniques 23 2.4.1 Tikhonov regularization method 24 2.4.2 Truncated SVD (TSVD) Regularization 25 2.4.3 Choosing a regularization parameter 27 2.5 Electrical Impedance and Diffuse Optical Reconstruction Software (EIDORS) 30 CHAPTER 3 SYSTEM DESIGN 33 3.1 Introduction 33 3.2 Design of Electrodes 34 3.2.1 Design of electrodes material 34 3.2.2 Design the shape and size of electrodes 36 3.3 Rotary Scheme and Phantom Tank 37 3.4 Switching Networks and Measurement Systems 40 3.4.1 Constant current source 41 3.4.2 Switching networks 42 3.4.3 Lock-in amplifier 43 3.5 Experimental Setup 45 3.5.1 8-electrode REIT system 46 3.5.2 16-electrode REIT system 46 CHAPTER 4 THE DATA COLLECTION STRATEGY 48 4.1 Introduction 48 4.2 Data Collection Method 49 4.2.1 Adjacent data collection 49 4.2.2 Cross data collection 50 4.2.3 Opposite data collection 51 4.2.4 Modified adjacent data collection 53 4.3 Scanning Data Collection Method 54 CHAPTER 5 MAIN RESULTS 60 5.1 Numerical Simulation 60 5.2 Degree of Ill-condition 61 5.3 Spatial Resolution 63 5.4 Noise Distributions Measurements 65 5.5 Reconstructed Impedance Image 68 CHAPTER 6 SOME ISSUES AND APPLICATIONS 76 6.1 Introduction 76 6.2 Metal-wall Effect 76 6.3 Real-time Image Reconstruction 80 6.3.1 Data acquisition of scanning strategy 80 6.3.2 Numerical computation 81 6.4 Practical Applications 82 CHAPTER 7 CONCLUSIONS AND SUGGESTIONS 84 REFERENCES 87 Appendix Reciprocity Principle 95

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