超音波中無法察覺的位移往往在當今的臨床診斷中扮演著重要的角色。磁致動超音波成像(MMUS）基於超音波使用具有超順磁性氧化鐵奈米粒子（SPION）作為顯影劑的成像技術。在外部磁場的作用下，這些奈米粒子會振動並誘使周圍組織移動，再通過超音波檢測到微小的位移來找出磁奈米粒子於空間中的分布。其位移約為幾微米，在超音波B模式下難以察覺。另一種具有無法察覺位移的應用是剪力波彈性成像。使用聲輻射力推動組織，使其振動並發出剪力波。根據剪力波速度，可以進一步量化組織特性。在本研究中，我們透過探討空間軸和時間軸間的關係提出一放大位移幅度的方法並使放大後的位移在超音波B模式下可視化。我們藉由仿體實驗及活體實驗來驗證所提出的方法是否能夠放大位移並從B模式觀察到該位移。整體而言，透過我們所提出的放大位移幅度的方法，針對磁致動超音波在B模式影像上我們上建立新一新的成像模式，透過此模式能在B模式影像上觀察到原本無法察覺的位移。此外，此方法亦能用於改進剪切波彈性成像的視野。

The imperceptible displacement in ultrasound imaging plays an important role in clinical diagnosis nowadays. For the magneto-motive ultrasound imaging (MMUS), which is an ultrasound-based imaging technique with the superparamagnetic iron oxide nanoparticles (SPIONs) as the contrast agent, owing to the excitation by the external magnetic field, these magnetic nanoparticles would vibrate and cause displacement of the surrounding tissue. Then the tiny displacement can be detected by ultrasound to map the distribution of the magnetic nanoparticles. The displacement is around a few micrometers which is difficult to be visualized simply using B-mode ultrasound. Another application with imperceptible displacements is shear wave elastography where the acoustic radiation force is used to push the tissue and then generate the shear wave. By tracking the tiny displacements caused by the launched shear wave, the shear wave velocity can be estimated and then used to quantify the tissue elasticity property. In this study, by discovering the relationship between spatial and temporal axis, we propose a motion magnification method for the above two applications, which is able to magnify the displacements; thus making them visible in B-mode ultrasound. Phantom and in-vivo experiments are used to verify our proposed method. Generally, based on our proposed motion magnification method, for MMUS, we equivalently provide a new imaging mode visualizing the originally invisible magneto-motion simply using conventional B-mode ultrasound. In addition, the proposed method can be applied to broaden the field of view of the shear wave elastography.

摘要 I
Abstract II
Table of Contents IV
List of Figures & Table VI
Chapter 1. Introduction 1
1.1 Imperceptible motion magnification 1
1.2 Sub-wavelength displacement 2
1.3 Magneto-motive ultrasound imaging 2
1.4 Shear wave elastography 4
1.5 Motivation 6
1.6 Organization of the thesis 7
Chapter 2. Materials and Methods 9
2.1 Motion magnification 9
2.1.1 One-dimensional derivation 9
2.1.2 Narrowband condition 13
2.1.3 Intensity artifact 13
2.1.4 Applications to the ultrasound data 14
2.1.5 Signal processing flow 15
2.2 Ultrasound imaging 16
2.2.1 Plane wave imaging 17
2.2.2 Beamformation 18
2.2.3 Ultrasound engine 20
2.2.4 Displacement tracking 20
2.2.5 M mode display and PSNR 22
2.3 Magnified magneto-motive ultrasound 23
2.3.1 Setup 24
2.3.2 Signal processing flow with the proposed method 25
2.4 Magnified shear wave elastography 27
2.4.1 Setup 27
2.4.2 Signal processing flow with the proposed method 28
Chapter 3. Results and Discussions 31
3.1 Experiments of magneto-motive ultrasound 31
3.1.1 Phantom experiments 31
3.1.2 Phantom experiments (different concentration of SPIONs) 33
3.1.3 In-vivo experiments 36
3.1.4 Discussions for MMUS 38
3.2 Experiments of shear wave elastography 40
3.2.1 Phantom experiments 40
3.2.2 Ex-vivo experiments 43
3.2.3 Propagation through different tissues 45
3.2.3.1 From soft tissue to hard tissue 45
3.2.3.2 From hard tissue to soft tissue 48
3.2.4 Discussions for shear wave elastography 51
3.2.4.1 The corresponding elasticity 53
3.2.4.2 The corresponding elasticity 54
Chapter 4. Conclusions and Future Work 56
4.1 Conclusions 56
4.2 Future work 57
Reference 58

[1] Wu H-Y, Rubinstein M, Shih E, V. Guttag J, Durand F, T. Freeman W. Eulerian Video Magnification for Revealing Subtle Changes in the World. 2012.
[2] Ng A, Swanevelder J. Resolution in ultrasound imaging. Continuing Education in Anaesthesia Critical Care & Pain 2011;11(5):186-92.
[3] Evertsson M. Development of Magnetomotive Ultrasound Imaging. Department of Biomedical Engineering, Faculty of Engineering. Lund University; 2016.
[4] Mehrmohammadi M, Oh J, Mallidi S, Emelianov SY. Pulsed Magneto-motive Ultrasound Imaging Using Ultrasmall Magnetic Nanoprobes. Molecular imaging 2011;10(2):102-10.
[5] Evertsson M, Kjellman P, Cinthio M, Andersson R, Tran TA, in’t Zandt R, et al. Combined Magnetomotive ultrasound, PET/CT, and MR imaging of (68)Ga-labelled superparamagnetic iron oxide nanoparticles in rat sentinel lymph nodes in vivo. Scientific Reports 2017;7:4824.
[6] Chang Y-C. Ultrafast cyclic magnetomotive ultrasound imaging of sentinel lymph nodes: in vivo small animal study. Electrical Engineering. National Tsing Hua university, Hsinchu, Taiwan, R.O.C.; 2017.
[7] Houng J-Y. Development of a pulsed magnetomotive ultrasound imaging system. Electrical Engineering. National Tsing Hua university, Hsinchu, Taiwan, R.O.C.; 2016.
[8] Engel AJ, Bashford GR. A new method for shear wave speed estimation in shear wave elastography. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2015;62(12):2106-14.
[9] Bamber J, Cosgrove D, Dietrich C, Fromageau J, Bojunga J, Calliada F, et al. EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography. Part 1: Basic Principles and Technology. 2013.
[10] Nightingale K. Acoustic Radiation Force Impulse (ARFI) Imaging: a Review. Current medical imaging reviews 2011;7(4):328-39.
[11] Bercoff J, Tanter M, Fink M. Supersonic shear imaging: a new technique for soft tissue elasticity mapping. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2004;51(4):396-409.
[12] Administration FaD. Information for Manufacturers Seeking Marketing Clearance of Diagnostic Ultrasound Systems and Transducers. In: U.S. Department of Health and Human Services FaDA, Center for Devices and Radiological Health, ed.; 2008.
[13] Sarvazyan AP, Urban MW, Greenleaf JF. Acoustic Waves in Medical Imaging and Diagnostics. Ultrasound in Medicine & Biology 2013;39(7):1133-46.