磁致動超音波成像系統是以超音波成像技術配合磁奈米藥物及磁場進行成像的系統，它被認為是具有早期診斷的潛力。目前常見的系統以電磁鐵產生連續波的磁場為主，然而部份的能量在過程中轉換成熱並累積在線圈上，這樣的系統容易過熱而不適合產生更高強度的磁場。在此問題下系統的穿透深度及磁場分布範圍有限 。為了解決此問題，在本研究中我們提出並建立了一基於超快成像技術之脈衝式磁致動超音波成像系統 。我們客製了一可程式化之磁脈衝產生器。該裝置具有相對於一般電流放大器可提供較大的輸出電壓及峰值輸出電流，能產生僅5-10毫秒長度的磁脈衝。其可程式化的設計配合電腦上的類比輸出卡可以產生經設計的磁脈衝序列。透過高頻磁脈衝序列可使磁奈米粒子以產生相同頻率位移變化，搭配基於超快成像技術的斑點追蹤技術找出組織位移隨時間的變化，之後再匹配濾波器找出組織中位移變化與磁場變化有較高相關係數以及對應時間延遲的區域，便可壓低組織背景的移動雜訊而定位出磁奈米粒子累積的區域。我們亦測試了系統所能產生的磁脈衝長度及不同磁場配置下的磁場分布並對不同長度的單一脈衝作比較並選出最適合系統的高頻磁脈衝序列。此外，我們亦整合了超音波探頭及電磁鐵建立了適合臨床應用之反向式磁致動超音波探頭，並實驗驗證搭配此探頭之脈衝式磁致動超音波系統磁致動超音波穿透深度可達探頭以下1.5公分。

Magnetomotive ultrasound (MMUS) imaging system is an ultrasound based imaging system which accompanies with magnetic nanoparticles and magnetic field, and it has the feasibility for early diagnosis. The most common MMUS uses continuous wave magnetic field to induce the magnetomotion of the magnetic nanoparticles. However, a part of energy translates into heat and causes thermal problems in the system. Such a system suffers the thermal constraints and is not suitable to generate stronger magnetic field. Under this situation, the system has a limited penetration depth or small magnetic field area (i.e., imaging field of view). To solve this problem, in this study, we propose and develop a ultrafast imaging based pulsed MMUS imaging system. We build a custom-made programmable magnetic pulser. This module can generate higher voltage and current output than general current amplifiers and it can generate 5 to10-ms magnetic pulse. With the programmable capability, this module is able to generate a coded magnetic pulse sequence. The coded high frequency magnetic pulse sequence will induce a distinct displacement profile of magnetic nanoparticles from the background tissues. After matched filtering the displacement profile at each imaging point with the designed coded magnetic pulse sequence, the background tissue motion artifacts can be significantly suppressed and thus the distribution of magnetic nanoparticles can be found via thresholding of the derived correlation coefficient and corresponding lag time at each imaging point. We experimentally test the maximum and minimum achievable magnetic pulse length of the system and magnetic field intensity, and the corresponding magnetic field distribution. We also compares the imaging results with different magnetic pulse lengths and thus optimize the most suitable magnetic pulse sequence of the system. In addition, a clinically translatable backward mode MMUS probe integrating the ultrasound transducer and the electromagnet is build and the penetration depth of the system equipped with this probe is at least 1.5 cm.

摘要 i
Abstract ii
List of Figures v
Chapter 1. Introduction 1
1.1. Application of MMUS 2
1.1.1. Molecular imaging 2
1.1.2. Sentinel Lymph Node Locating 2
1.1.3. Elastography 3
1.2. Continuous wave MMUS 4
1.3. Pulsed MMUS 5
1.4. Motivation 5
Chapter 2. Materials and Methods 8
2.1. Principle of MMUS system 8
2.1.1. Time-Varying Magnetic Field 8
2.1.2. Ultrafast Ultrasound Plane Wave Imaging 13
2.1.3. Image Tracking 14
2.1.4. Matched Filter 16
2.2. Hardware Setup 18
2.2.1. Custom-made Programmable Magnetic Pulser 18
2.2.2. Forward Mode Electromagnet 19
2.2.3. Backward Mode Electromagnet 21
2.2.4. System Setup and Time Sequence 24
2.2.5. Phantom Preparation 27
Chapter 3. Results and Discussion 30
3.1. Magnetic Pulser Testing 30
3.2. Comparison of Different Signals 34
3.3. Penetrating Depth of Forward Mode 38
3.4. Penetrating Depth of Backward Mode 41
3.5. Discussion 45
3.6. Summary 47
Chapter 4. Conclusions and Future Work 48
4.1. Conclusion 48
4.2. Future Work 49
Reference 50

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