超音波影像可以利用複合技術(Compounding)來降低斑點雜訊現象(Speckle noise)。複合技術是對同一受測物體改變散射子與成像孔徑(Aperture)的相對位置再取得影像後，將所取得的一系列影像做平均以降低斑點效應的過程，其中改變視角達成之角度複合成像技術是目前多數影像系統搭配線性陣列探頭(Linear array)的複合實施方式。本論文研究目的為探討角度複合技術在傳統逐條掃描成像(Beam-by-beam)與合成孔徑(Synthetic aperture)成像方式下的效能差異。
相較於發射聚焦於不同角度掃描線之傳統角度複合成像方式，合成孔徑角度複合成像技術針對原始影像點(image pixel)設計隨角度改變之發射端與接收端孔徑加權函數，並施加於波束延遲加總(delay/sum beamforming)過程中的各通道信號上而達到由不同角度觀測之影像，因此在複合過程無須座標轉換(Scan conversion)即可以平均的方式抑制斑點雜訊現象。
我們採用C_r，CNR，SNR，N_eff以及ρ_SID等量化參數比較兩種角度複合方法之影像品質，結果顯示複合實施前兩者接收f-number增加時皆因孔徑重疊減少而斑點相關性下降，複合實施後合成孔徑方式其斑點平滑度隨影像深度遞增但仍略低於傳統掃描方式，但綜合考慮影像解析度與斑點平滑度的取捨下以最大複合角度θ_max=10°之合成孔徑角度複合效果最佳，代表在適當合成孔徑成像參數下之角度複合技術可以達到抑制斑點雜訊與保持影像解析度之最佳效能。

Compounding is applied to reduce speckle noise in ultrasound imaging. Speckle noise is reduced by incoherently averaging several images of the same image object with changing the relative position from scatterers and aperture. Angle compounded ultrasound imaging which changing angle of view is currently the most of compounding implementation in image system. The purpose of this study is to explore the difference of performance from angle compounding between conventional beam by beam and synthetic aperture image system. Compared to conventional angle compounded imaging which transmit focus with different angle scanlines, Synthetic aperture angle compounded imaging is to design the aperture apodization at transmitter and receiver for the image pixel, and we can get several images with different angle observation when applying the aperture apodization to the channel data durning delay and sum beamforming. Speckle noise is reduced by incoherently averaging these images without scan conversion.
We use the quantitative parameter that is C_r,CNR,SNR,N_eff and ρ_SID to compare the image quality between two methods. The result showed that both methods before angle compounding, the speckle correlation decreased when f-number at receiver increased that reduced overlapping aperture. After angle compounding, the speckle smoothness of synthetic aperture angle compounded imaging is still lower than conventional angle compounded imaging. Considering the trade-off between image resolution and speckle smoothness, the compounded performance of synthetic aperture angle compounded imaging with the maximum angle 10° is the best, it shows that synthetic aperture angle compounded imaging with appropriate imaging parameters is the best performance that can suppress speckle noise and remain image resolution.

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