適用於稀疏同調平面波複合成像之超音波波束最佳化

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研究生：	謝雅玲 Hsieh, Ya-Ling.
論文名稱：	適用於稀疏同調平面波複合成像之超音波波束最佳化 Ultrasound Beam Optimization for Sparse Coherent Plane Wave Compounding
指導教授：	李夢麟 Li, Meng-Lin
口試委員:	沈哲州葉秩光 Yeh, Chih-Kuang 王昱欣 Wang, Yu-Hsin
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 電機工程學系 Department of Electrical Engineering
論文出版年：	2018
畢業學年度：	106
語文別：	英文
論文頁數：	43
中文關鍵詞：	假影、柵瓣、平面波、超音波影像
外文關鍵詞：	Grating-lobe, Ghost artifact
相關次數：	點閱：1 下載：0
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同調平面波複合成像在超音波成像中漸漸扮演重要的腳色，藉由發射多角度的平面波，同調平面波複合成像可以提供超快超音波成像與彈性影像。在本研究中，我們針對同調平面波複合成像提出了一個角度挑選策略，在發射較少平面波的情況下，我們提出的方法與常用的角度序列 – 等角度間距間隔抽取 (EAS-CPWC) 相比，可以達到較少的柵瓣與假影。在我們的策略中，首先找出傳統的合成孔徑成像與同調平面波複合成像的關係。透過我們的角度挑選策略，在給定發射的平面波最大角度後，同調平面波複合成像的等效合成孔徑會近似期望的雙向等效孔徑，並且具備適當的等效孔徑寬度、探頭間距與等效孔徑形狀，因此可以抑制柵瓣與假影。我們藉由超音波模擬(Field II)線仿體、消聲囊腫仿體與離體豬動脈來驗證我們的角度挑選策略。模擬與實驗結果顯示柵瓣與假影可分別抑制5 dB 與15 dB，而對比雜訊比可達到25± 5 % 的改進。整體上來說，我們證明了本篇論文所提出的角度挑選策略可以有效地抑制柵瓣與假影。

Recently, ultrasound imaging with coherent plane wave compounding has played an important role in high-quality ultrafast imaging and shear wave elastography, leveraging multiple angled plane-wave emissions. In this study, we propose an angle selection strategy for ultrasound imaging with coherent plane wave compounding (CPWC), featuring lower grating-lobe and ghost artifacts while fewer angled plane-wave emissions are required compared to commonly used equal-angular-spacing decimation in the angle sequence (EAS-CPWC). In our strategy, the relation between conventional synthetic transmit aperture imaging and CPWC is discovered. Given the number of the total tilted plane-wave excitations, with our angle selection strategy, the synthesized effective aperture by the CPWC approximates to the desired two-way effective aperture with an appropriate width, element spacing, and shape; thus enabling grating-lobe and ghost artifacts suppression. Field II simulations and experiments on wire, anechoic cyst phantoms and the ex vivo porcine artery were performed to verify our angle-selection strategy. Simulation and experimental results showed that with our proposed angle sequence, the grating-lobe and ghost artifacts were suppressed by 5 dB and 15 dB respectively, and 25 ± 5 % contrast-to noise ratio (CNR) improvement was achieved. Overall, we demonstrated the efficacy of our proposed angle sequence for grating-lobe and ghost artifacts suppression.

中文摘要    I
Abstract    II
Contents    III
List of Figures    V
List of Tables    IX
Chapter 1    Introduction    1
1.1    Coherent Plane Wave Based Ultrasound Imaging Using Linear Array    1
1.2    Artifacts of Sparse Coherent Plane Wave Compounding    3
1.2.1    Beam Pattern of a Linear Array    3
1.2.2    Ghost Artifact    5
1.2.3    Grating-Lobe Artifact    7
1.3    Artifacts Suppression    9
1.4    Motivation    11
1.5    Organization of the Thesis    12
Chapter 2    Materials and Methods    13
2.1    Relationship Between Transmit Elements and Plane-Wave Steering Angles under Continuous Wave Assumption    13
2.2    Strategy for Sparse Angle Selection    16
Chapter 3    Results and Discussion    21
3.1    Simulations    22
3.1.1    Single Point Target    22
3.1.2    Fully Developed Speckle Background    25
3.1.3    Multiple Point Targets    27
3.1.4    Cyst Phantom    29
3.2    Experiments    31
3.2.1    Single Point Target    31
3.2.2    Multiple Point Targets    33
3.2.3    Cyst Phantom    35
3.2.4    Ex Vivo Porcine Aorta    37
Chapter 4    Conclusions and Future Work    40
4.1    Conclusions    40
4.2    Future Work    41
References    42

                                

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