臺灣博碩士論文加值系統

相較於傳統成像技術需隨著掃描線位置與聚焦深度不同而進行多次發射聚焦成像，平面波成像技術只需發射一次平面波，即可對平面波所涵蓋範圍進行平行成像，故近年來已廣泛應用於超音波超快速成像，但因其波束旁瓣與柵瓣等成像假影的影響下，大幅降低影像品質。
平面波成像技術可以利用發射不同角度之平面波影像經同調複合以提升影像空間解析度，但當複合角度數目有限時，對影像對比度提升效果也有限。因此可利用通道信號的同調因子計算方式，估計影像上每一個像素點的通道信號的同調性，對應於原始影像的同調因子權重，通過這些同調因子的波束形成，可以抑制影像旁瓣和柵瓣，並獲得對比度的改善，但在背景區域會造成影像平滑程度的下降。本研究利用基於平面波超音波超快速成像，經過通道同調因子權重與角度複合技術，以提升平面波影像對比度，並且比較不同方式下結合角度複合技術與同調因子權重的影像優化效果。
結果顯示，平面波發射角度與接收端之加權函數同角度影像，經過同調因子權重計算及角度複合後，乘上平面波同調複合對影像優化效果最佳，模擬部分CNR可提升73％，實驗部分CNR可提升110％。由此結果顯示，經由同調因子權重與角度複合技術結合，能夠讓平面波影像保有一定之平滑程度，並且有效提升影像的對比度。

In recent years, inspired by ultrasound ultrafast imaging, plane wave emission technique has been widely utilized in ultrasound images. The traditional emission focus image is focused on the region of interest, with the different location and depth. The plane wave emission technique emits a plane wave and spread to the range of interest, a wide range of imaging is quickly obtained. The images obtained by plane wave are fast, but the effects of side lobes, grating lobes and speckle noise are sacrificed the image contrast.
The plane wave emission technique can be used to coherent sum with different angles to achieve to improve the image spatial resolution. Although coherent sum can effectively improve the image resolution by suppressing the artifacts, the corresponding image contrast-to-noise (CNR) is still limited. Therefore, in this study uses the plane wave based ultrasound ultrafast angle compounding combined with coherent factor weighting to enhance the image contrast.
Results indicate that, plane wave emission angle and receiver weighting function of the same angle, the CNR has the peak value. In simulation, the CNR can be increased by 73%, the experimental part of the CNR can be improved by 110%.
Through the coherent factor weighting and angle compounding technology, can make the plane wave image to maintain the image smoothness while improving the image contrast.

目錄
摘要 I
Abstract III
致謝 V
目錄 VI
圖目錄 IX
表目錄 XIII
第一章 緒論 1
1-1 醫用超音波基本原理 1
1-2 超音波影像品質 3
1-2-1 空間解析度 3
1-2-2 斑點雜訊 6
1-3 研究動機與目的 16
第二章 平面波超快速成像技術 18
2-1 平面波超快速成像 18
2-1-1 旁瓣假影 18
2-1-2 柵瓣假影 20
2-2 平面波同調複合成像 24
2-3 抑制影像假影 29
2-3-1 最小方差權重計算(MV) 30
2-3-2 同調因子權重計算(GCF) 31
第三章 研究方法 35
3-1 平面波角度複合成像技術 35
3-1-1加權孔徑函數(Apodization) 35
3-1-2延遲相加法(Delay-and-Sum) 40
3-2 平面波角度影像與同調因子權重角度複合 42
3-2-1 單一平面波發射與同調因子結合 44
3-2-2 多平面波發射角度複合與同調因子結合 45
第四章 研究結果 46
4-1 研究架構及參數 46
4-1-1 模擬設定 46
4-1-2 實驗設定 47
4-2 模擬結果分析 51
4-2-1 單一平面波發射 51
4-2-2 多平面波發射 54
4-3 實驗結果分析 60
4-3-1 單一平面波發射 60
4-3-2 多平面波發射 64
第五章 討論、結論與未來工作 70
參考文獻 75

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