近年來受到合成孔徑雷達技術啟發，合成孔徑技術已廣泛應用於超音波影像。傳統合成孔徑影像(STA)是利用陣列探頭單一元素發射球面波，球面波所擴散範圍即為感興趣區域，並由陣列探頭全部元素接收回音信號，這些信號經時間延遲之補償後可形成低解析度的影像(LRI)。將每一次由單一元素發射所得的低解析度影像作同調性相加後即可得一張高解析度的影像(HRI)。由合成孔徑所形成的影像具有較好的橫向解析度，但依然容易受到斑點雜訊影響對影像的判讀。
合成孔徑影像複合技術可以利用隨角度改變發射端與接收端加權函數，以達到複合不同角度影像之抑制斑點雜訊效果，雖然角度複合應用在合成孔徑成像上能有效提升訊雜比(SNR)，但對不同影像強度間之對比度(CNR)提升效果卻有限。因此本研究利用基於通道域同調因子之旁瓣抑制法結合角度複合技術以提升合成孔徑影像對比度，並比較使用傅立葉轉換與自相關估算分別於LRI與HRI實施模式下計算像素同調性，且比較不同方式下結合角度複合技術與同調因子計算的影像優化效果。
實驗結果顯示，合成孔徑各角度之影像經過複合後乘上零角度同調因子權重對影像優化效果最佳，±15˚複合角度下相較於原合成孔徑複合影像，結合傅立葉轉換同調因子權重時CNR可上升68.4%但SNR下降11.2%，結合自相關同調因子權重時CNR進一步提升113.5%且SNR只下降7%。由此結果顯示，經由同調因子與角度複合技術結合，能夠讓合成孔徑影像保有一定之雜訊比，並且有效提升影像的對比度。

Synthetic aperture technique has been widely utilized in medical ultrasound imaging due to its success in radar applications. The synthetic aperture image has better lateral resolution than conventional B-mode image, but the images also suffer from speckle artifacts. Although angle compounding can effectively improve the image signal-to-noise (SNR) by suppressing the speckle noises, the corresponding image contrast-to-noise (CNR) is still limited.
In this study, angle compounding is combined with adaptive coherent weighting to enhance the image contrast. Efficacy of coherent weighting using either LRI or HRI data is examined. Various combinations of coherent weighting and angle compounding are also compared for optimization of synthetic aperture image.
Results indicate that, when the angle compounded B-mode image is processed by 0˚ GCF weighting, the CNR has its peak value. With ±15˚ angle compounding, the GCF-FFT improves CNR by 68 % with SNR decrease of 11 %. In contrast, the GCF-AR increases CNR by 114 % with SNR decrease of only 7 %. Combining the adaptive coherent weighting with angle compounding in synthetic aperture image could maintain the speckle smoothness while improving image contrast.

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