基於自相關法之低複雜度可適性超音波波束成像技術｜國立臺灣科技大學博碩士論文系統

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研究生：	邢永騏 Yung-chi Xing
論文名稱：	基於自相關法之低複雜度可適性超音波波束成像技術 Adaptive Imaging Using the Generalized Coherence Factor Base On Autocorrelation
指導教授：	沈哲州 Che-Chou Shen
口試委員:	廖愛禾 Ai-Ho Liao 鄭耿璽 Geng-Shi Jeng
學位類別：	碩士 Master
系所名稱：	電資學院 - 電機工程系 Department of Electrical Engineering
論文出版年：	2015
畢業學年度：	103
語文別：	中文
論文頁數：	40
中文關鍵詞：	抑制旁瓣、對比度、彩色都普勒、自相關、廣義同調因子、傅立葉頻譜、可適性波束成像、低計算複雜度
外文關鍵詞：	Reduce side lobe, Contrast, Doppler, Autocorrelation, Adaptive beamforming, Generalized Coherence Factor, FFT, Low complexity of algorithms
相關次數：	點閱：279 下載：3
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在超音波亮度模式(B-mode)成像中最廣泛運用的波束形成技術為延遲加總法 (Delay And Sum) ，此方法藉由調整各通道間的延遲時間和權重而使聲波聚焦到指定聚焦點以調控波束位置與特性，波束加總前的各通道所接收的信號稱為通道信號（Channel data），然而延遲加總法其臨床上影像品質常受限於相位擾動(Phase aberration)現象而導致波束旁瓣上升而降低影像品質，因此發展可適性技術以增強B-mode 影像對比度(Contrast Noise Ratio)以及抑制旁瓣假影(Sidelobe artifacts)一直是醫用超音波影像的研究重點之一。
近年來廣泛使用的基於傅立葉轉換之廣義同調因子（Generalized Coherence Factor base on Fast Fourier Transform）是利用通道信號同調性來判別超音波聚焦品質優劣並據此優化影像，由於其同調性估計方式是依賴通道信號空間頻譜之低頻成份強度，因此實現上需完整計算通道信號的傅立葉轉換而導致較高計算複雜度。基於自相關法的廣義同調因子(GCF Autocorrelation)採用計算複雜度較低的自相關法估計通道信號之入射角正弦值平均((sinφ) ‾)和標準差（σ_sinφ）這兩項特性頻域參數，並利用該兩項參數形成通道信號之高斯虛擬空間頻譜後計算其優化影像權重。此研究除了使用Field II 模擬相位陣列(Phase array)對線仿體(Wire Phantom)及斑點仿體(Speckle)成像外，在實驗部分則使用相位陣列對線仿體及斑點仿體進行成像及改善，亦使用相位陣列對人體心臟進行照影和優化。
本研究實驗結果顯示,以80個通道的超音波陣列影像系統而言, GCFAR相較於GCFFFT能降低計算複雜度達78%且同樣具有改善影像對比度的效果,在空間角頻率閾值相等條件下最佳化之GCFAR設定可較最佳化之GCFFFT提昇影像對比度至少12%，相較於原始影像之對比度提昇則為102%。

In B-mode, Delay And Sum is a conventional way of Beamforming, Ultrasound is fired and received by probe, and echo that received by probe is called Channel Data. In clinical images, qualities of images usually decrease because of “Phase aberration effect” which would increase sidelobe artifacts and reduce contrast of images, thus how to use adaptive beamforming methods to raise contrast of images is an important topic in medical ultrasound imaging.
Recently, Generalized Coherence Factor base on Fast Fourier Transform has been mixed by many kinds of methods to enhance contrast of ultrasound images, it use the differences of Fourier spectrum transformed by channel data in mainlobe and sidelobe area, GCFFFT use these differences to judge the qualities of focusing, and reconstruct images. Because GCFFFT has to do Fourier transform in every single point, it’s complexity of algorithms is pretty high.
This research use autocorrelation which has low complexity of algorithms to calculate two eigenvalues: Average angle of incidence ((sinφ) ‾) and it’s Standard Deviation（σ_sinφ）, use them to generate Gaussian distribution spatial weighting spectrum and optimize images. This article use Field II to simulate images of wire and speckle phantom that imaged by phase array, beside we also use phase array to observe speckle and wire phantoms.
According to our experiments, in a 96 channels systems, GCFAR’s contrast is at least 112% times higher than GCFFFT and 202% times higher than original images, in the same time GCFAR can decrease complexity of algorithms to 22% compare to GCFFFT.

目錄
第一章 緒論................................................1
1-1 醫用超音波影像原理.....................................1
1-2 延遲相加波束成像技術...................................2
1-3 非理想狀況下的亮度模式影像..............................3
1-4 研究動機與目的.........................................6
第二章 可適性波束成像技術...................................7
2-1 可適性波束成像用於提高超音波影像對比度...................7
2-2 基於傅立葉轉換之廣義同調因子權重法 (GCFFFT).............8
  2-2.1 原理介紹...........................................8
  2-2.2  FFT 頻譜、權重與計算量 ...........................8
2-3 基於自相關法之廣義同調因子權重法 (GCFAR)...............10
  2-3.1 原理介紹..........................................10
  2-3.2 AR頻譜、權重與計算量..............................12
第三章 研究結果與討論.....................................15
3-1 模擬.................................................15
  3-1.1 模擬方法與參數....................................15
  3-1.2 模擬結果與討論....................................16
    3-1.2(I)單行點仿體....................................16
    3-1.2(II)斑點仿體.....................................19
3-2 實驗............. ...................................22
  3-2.1 實驗架構與參數....................................22
  3-2.2 實驗結果與討論....................................22
    3-2.2(I)線仿體.......................................23
    3-2.2(II)斑點仿體.....................................27
    3-2.2(III)人體心臟造影................................36
第四章 結論與未來工作.....................................38
4-1 結論.................................................38
4-2 未來工作..............................................38
參考文獻..................................................39

                                

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