傳統發射聚焦超音波透過逐條建構掃描線完成單張超音波影像，面臨了低畫面幀率的問題，而能被用來提高畫面幀率的單一平面波成像或是多角度平面波成像則會遇上影像品質較差的挑戰。多角度平面波複合成像使用延遲加總(DAS)於不同發射角度上的低解析度影像，複合出一張高解析度影像，以得到與發射聚焦差不多的影像品質，然而高幀率與可使用的平面波角度間存在權衡，發射平面波角度數量會影響影像品質。
延遲相乘加總(DMAS)成像能針對接收通道對或是發射事件信號間進行耦合相乘，利用信號的空間相關性提升影像解析度與對比度，並藉由p 值的設定來決定仰賴信號相關性的程度。本論文在不同發射角度上以DMAS 波束成形取代傳統DAS 波束成形，可以有效降低影像雜訊並達到可以使用的影像品質，此方法具體做法為保留時間延遲後的複數信號相位，並將其振幅開p 次方根，在不同發射角度將信號加總後進行p 次方計算以恢復原始信號維度，由此得到高解析度影像。因為使用的是不同發射角度的低解析度影像信號，因此與傳統其他應用於接收通道間的可適性波束成形方法相比，不須大量的儲存空間，可有效降低軟硬體負擔。
本論文中將 DMAS 波束成形應用於功率都卜勒血流偵測中，取代傳統多角度平面波複合成像中的DAS 波束成形，透過考量信號相關性，能得到較好的影像品質。並提出了新穎的互補發射事件(CST)技術，透過施加權重於多角度平面波發射事件間，進一步抑制雜訊對血流偵測的影響，在模擬及實驗都能觀測到其效果。
在血流模擬中單獨使用DMAS 波束成形技術並將p 值設定為2取代傳統DAS 波束成形時，比較功率都卜勒影像能夠得到都卜勒SNR 8.2 dB 的提升，並且透過進一步使用CST 技術，都卜勒SNR能得到另外6 dB 的提升。而CST 權重施加方法也能單獨使用於傳統DAS 波束成形中，功率都卜勒影像也能得到較小幅度的改善。另外，在實驗中，DMAS 波束成形以及CST 技術也都各自展現其效果，且因其不需額外儲存空間的緣故，此方法有望能直接取代DAS波束成形，對於臨床應用有著不小的潛力。

Conventional transmit focused ultrasound construct a single ultrasound image by line-by-line scanning, which faces the problem of low frame rate. However, single plane wave imaging or multi-angle plane wave imaging that can be used to increase the frame rate will encounter the challenge of poor image quality. Multi-angle plane wave composite imaging uses delay-and-sum (DAS) to combine low-resolution images at different transmit angles to compound a high-resolution image, which getting similar image quality to conventional techniques. There is a tradeoff between frame rate and usable transmit angles of the plane wave. The number of angles of the plane wave will affect the image quality.
Delay-Multiply-Sum (DMAS) imaging can couple and multiply the receiving channel pair or the transmitted event signal, use the spatial correlation of the signal to improve the image resolution and contrast, and determine the dependence of signal correlation by setting the p value. In this paper, DMAS beamforming is used to replace conventional DAS beamforming at different transmit angles, which can effectively reduce image clutter and achieve usable image quality. The specific method of this technique scales the magnitude of time-delayed signal by p -th root while maintaining the phase. After the summation between different transmit events the output signal is restored by p -th power. The method uses low-resolution image signals with different transmit events, so it is different from other traditional adaptive beamforming methods which apply between receiving channels. The aforementioned method does not
require a large amount of storage space, and can effectively reduce the burden on software and hardware.
In this paper, DMAS beamforming is applied to power Doppler blood flow detection, instead of DAS beamforming in conventional multi-angle plane wave composite imaging. By considering signal correlation, better image quality can be obtained. A novel complementary subset transmit(CST) technology is proposed, which further suppresses the influence of noise on blood flow detection by applying weights between multi-angle plane wave events.
Taking the blood flow simulation as an example, when DMAS beamforming is used alone and the p value is set to 2 to replace traditional DAS beamforming, the Doppler SNR can be improved by 8.2 dB compared with the power Doppler image, and through the further use of CST technology, Doppler SNR can get another 6 dB improvement. The
CST method can also be used in traditional DAS beamforming, and the power Doppler image can also perform a smaller improvement. In experiments, both DMAS beamforming and CST technology have shown their respective effects. It should be noted that the technique does not require additional storage space, and could directly replace DAS
beamforming. Making a great potential for clinical applications.

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