磁致動超音波為一種在活體上觀察磁奈米粒子分布的的超音波影像技術，目前已證明它可以應用於磁奈米藥物監控、血管外超音波分子影像以及前哨淋巴結偵測的可能性。現今，磁致動超音波主要實現於前向模式，其中待掃描對象必須放置於超音波探頭與電磁鐵之間，這樣的模式並不適合臨床轉譯。為了加速磁致動超音波的臨床轉譯，我們提出了具手持式磁致動超音波探頭的逆向式脈衝磁致動超音波，該探頭結合了陣列探頭與電磁鐵，並帶有隔振能力。實驗驗證了所建立之逆向式脈衝磁致動超音波偵測埋於明膠仿體內超順磁奈米粒子分布的能力。從超快平面波成像(上至2500赫茲)並由相位差估計法得到的位移圖可以定位被外加磁場激發的超順磁奈米粒子。並使用匹配濾波搭配投影窗來增強影像對比度。我們提出的磁致動超音波成像系統基於量測得到的穿透深度、實際追蹤下限以及峰值訊號雜訊比，可知進行活體研究的可能性，以及此系統更利於臨床轉譯。

Magnetomotive ultrasound (MMUS) which enables the in vivo visualization of magnetic nanoparticle distribution using ulrasound, has shown its potential in monitoring of magnetic nano-drug delivery, extravascular ultrasound molecular imaging, and sentinel lymph node identification. To date, MMUS is mainly implemented in forward mode where the imaging object has to lie in between an ultrasound transducer and an electromagnet, which is not clinically translatable. To facilitate clinical translation of MMUS, we propose a backward mode pulsed MMUS system which features a handheld MMUS probe integrating an array transducer and an electromagnet and owning the ability to isolate vibration from the working electromagnet. The capability of the proposed backward mode pulsed MMUS system in identifying superparamagnetic iron oxide nanoparticles (SPIONs) embedded in gelatin phantoms was investigated. Displacement maps obtained from ultrafast plane-wave imaging (up to 2.5 kHz) and a phase-difference estimator are able to localize the SPIONs which were induced by a cyclic pulsed magnetic field. Matched filtering with projection window for enhancing image contrast was also performed. The penetration depth, the practical tracking lower bound and peak signal-to-noise ratio of the proposed MMUS imaging system have shown the potential in further study on in vivo testing. Overall, we demonstrated the capability of the proposed backward mode pulsed MMUS imaging system, which is more clinically translatable.

摘要 I
ABSTRACT II
Table of Contents III
List of Figures V
List of Tables VII
Chapter 1 Introduction 1
1.1 Conventional ultrasound 1
1.2 Magnetomotive ultrasound 2
1.3 Application of magnetomotive ultrasound 3
1.3.1 Magnetic nano-drug delivery monitoring 3
1.3.2 Sentinel lymph node identification 5
1.4 Magnetic force on superparamagnetic iron oxide nanoparticles 6
1.5 Motivation 8
Chapter 2 Materials and Methods 8
2.1 Experimental setup 9
2.1.1 PC with a DAQ card 10
2.1.2 Ultrasound engine with a linear array transducer 10
2.1.3 Programmable magnetic pulser 10
2.1.4 Electromagnet 12
2.1.5 Phantom preparation 13
2.2 Probe design 15
2.3 Cyclic pulsed magnetic field 17
2.4 Ultrafast plane-wave imaging 19
2.5 Signal processing 21
2.5.1 Beamforming 22
2.5.2 Magneto-motion tracking 23
2.5.3 Matched filtering with projection window 25
2.6 Practical tracking lower bound 27
Chapter 3 Experimental Results and Discussion 28
3.1 Vibration isolation 28
3.2 Field of View 31
3.3 Penetration depth and practical tracking lower bound 35
Chapter 4 Conclusion and Future Work 39
4.1 Conclusion 39
4.2 Future work 40
References 42

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