磁致動超音波能夠成像出體內的磁奈米粒子分佈，且已經證明其於血管外超音波分子影像、磁奈米藥物監控和前哨淋巴結偵測的可行性。到目前為止，世界上大部分的團隊都是使用前向式磁致動超音波，此架構待掃描對象必須放置於超音波探頭與電磁鐵之間，此模式不適合臨床轉譯。為了促進磁致動超音波的臨床轉譯，我們依磁粒子影像原理提出新的策略藉著預磁化超順磁奈米粒子來改善逆向式磁致動超音波。新的磁致動超音波探頭包含一個用於磁激勵的電磁鐵及用於預磁化超順磁奈米粒子的靜磁鐵。預磁化是指事先用磁場磁化超順磁奈米粒子，根據超順磁奈米粒子磁化曲線的非線性特性，預磁化後超順磁奈米粒子擁有更高的磁化率，從而增加超順磁奈米粒子跟電磁鐵磁場間的磁致力。因此，可以增加由超順磁奈米粒子磁化引起的位移，而可以強化逆向式磁致動超音波的可檢測性。總體來說，本論文證明了我們提出的策略在改進逆向式磁致動超音波的有效性。我們的結果亦可用於包括靜磁鐵和相對低強度的電磁鐵的新型磁致動超音波探頭輕量化設計，使其更適合臨床應用。

Magnetomotive ultrasound (MMUS), capable of imaging in vivo magnetic nanoparticle distribution, has shown its potential in extravascular ultrasound molecular imaging, magnetic nano-drug delivery monitoring, and sentinel lymph node identification. To date, most of the research teams in the world mainly implemented forward mode Magnetomotive ultrasound where the imaging object has to lie in between an ultrasound probe and an electromagnet, which is not clinically translatable. To facilitate clinical translation of magnetomotive ultrasound, learning from the principle of magnetic particle imaging, we propose a new strategy to improve the backward-mode magnetomotive ultrasound via pre-magnetization of superparamagnetic iron oxide nanoparticle (SPIONs). The new magnetomotive ultrasound probe consists of an electromagnet for magnetic excitation and a permanent magnet for pre-magnetization of SPIONs. The pre-magnetization is to magnetize the SPIONs with a preset magnetic field in advance so that according to the nonlinear characteristics of the SPION magnetization curve, SPIONs can have higher magnetic susceptibility of SPIONs during magnetic excitation; thus increasing the magnetomotive force applied to SPIONs. Therefore, the displacement resulting from the magnetomotion of the SPIONs can be increased, which in turn improves the magnetomotive ultrasound detectability of the SPIONs in backward mode. Overall, it has been demonstrated that the effectiveness of the proposed strategy in the improvement of the backward mode magnetomotive ultrasound. The results also implicitly indicate a new lightweight design of the magnetomotive ultrasound probe consisting a permanent magnet and a relatively low strength electromagnet, which is more suitable for clinical applications.

Table of Contents
摘要 1
Abstract 2
Table of Contents 4
List of Figures 6
List of Tables 8
Chapter 1 Introduction 9
1.1 Problems of the conventional magnetomotive ultrasound 9
1.2 Backward-mode magnetomotive ultrasound 12
1.3 Magnetomotive force 13
1.3.1 Superparamagnetism of superparamagnetic nanoparticles 15
1.3.2 Cyclic pulsed magnetic field in magnetomotive force 16
1.4 Motivation 19
Chapter 2 Materials and Methods 21
2.1 Pre-magnetization principle 21
2.2 Pre-magnetization experimental setup 22
2.2.1 Steady magnet setup 22
2.2.2 Electromagnet setup 26
2.3 Closed magnetic line experimental setup 33
2.4 Backward-mode magnetomotive ultrasound setup 35
2.5 Signals processing 36
2.5.1 Magneto-motion tracking 37
2.5.2 Matched filtering 38
Chapter 3 Experimental Results and Discussion 40
3.1 Magnetomotive ultrasound with pre-magnetization only 40
3.2 Magnetomotive ultrasound via closed magnetic line 44
3.3 Closed loop design 46
Chapter 4 Conclusions and Future Work 50
4.1 Conclusions 50
4.2 Future Work 51
References 55
 

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