一般醫用超音波系統用於偵測血流速度之都卜勒技術(Doppler)會受到血流角度及最大量測速度的限制，因此本研究嘗試將高幀率(High Frame-Rate)的成像系統與斑點追蹤技術(Speckle Tracking)做結合，以期望能達到高準確度的血流向量估計。斑點追蹤技術需仰賴良好影像品質及高幀率影像系統來產生準確的血流估計，發射端不做聚焦的單一平面波成像(Single Plane Wave Excitation, SPWE)雖可大幅提升幀率，但其影像品質與訊雜比(Signal-to-Noise Ratio)均較差，因此我們藉由各個不同角度的平面波發射來進行同調性平面波複合成像(Coherent Plane Wave Compounding, CPWC)以改善上述的缺點，在取得各個不同角度的低解析度影像後再將這些影像做同調性的複合，並且利用遞迴技術(Recursive Technique)來減少擷取時間，產生多組具有不同特徵的高解析度影像以供斑點追蹤技術做流速偵測，將有利於血流影像及彈性影像中移動估計的準確度，此外遞迴技術在每次發射均能得到一組用於流速估計的資訊，所以該連續影像的產生將有助於濾波器(Wall Filter)之設計來分辨血流及管壁組織之訊號。
本研究之模擬結果顯示CPWC的橫向速度分量偵測於任何都卜勒角的STD及BIAS之效能都會優於SPWE，且其橫向速度分量偵測的STD會隨著軸向速度分量的上升而變差。然而在觀察軸向速度分量偵測，雖然CPWC於任何都卜勒角的STD效能仍同樣會優於SPWE，但是其BIAS效能卻會受到軸向移動的複合影像所帶來的點擴散函數偏移影響，使得CPWC的BIAS效能將會劣於SPWE。同時BIAS也會隨著複合影像間的軸向速度分量的增加而使其效能將變的更差。

Doppler technique is commonly used in medical ultrasound system. However, conventional Doppler is limited by the flow angle and the maximum detectable velocity. This research was designed to combine the high frame rate imaging system and the speckle tracking technique to provide accurate estimation of the vector velocity. The high accuracy of speckle tracking technique depends on high image quality and high frame rate. In this study, we investigate the coherent plane wave compounding imaging approach (CPWC) to improve the efficacy of blood velocity estimation in speckle tracking technique. In plane wave excitation, the ultrasound is not focused during the transmissions to increase the frame rate at the cost of degraded image quality. By compounding coherently the images obtained with several plane waves with different angles, both the image quality and SNR can be improved. It is also combined with the recursive technique to reduce the acquisition time by providing several high resolution images with different features for speckle tracking. This will benefit the estimation accuracy in flow imaging and elastography. Moreover, the continuous flow image data will also help the design of the wall filter to separate the blood flow from tissue.
The result in this study indicates that the STD and BIAS performance of the lateral velocity component tracking of CPWC in any Doppler angles is better than Single plane wave excitation approach (SPWE). The STD performance of the lateral velocity component tracking will decrease while the axial velocity component increases. Although the STD performance of the axial velocity component tracking of CPWC in any Doppler angles is still better than SPWE, the BIAS performance is inferior due to the point-spread-function shift by the axial movement of the imaged target. At the same time, the BIAS performance will decrease while the axial velocity component increases between the compounded images.

[1]沈哲州，”醫用超音波影像上課講義”，國立台灣科技大學電機所，民國98年。
[2]李維寧，”高效能斑點追蹤技術及其在乳房超音波影像之應用”，國立台灣大學，碩士論文，民國92年。
[3]陳韋廷，”基於明亮差異值之超音波影像斑點雜訊抑制”，國立台灣科技大學，碩士論文，民國97年。
[4]G. E. Trahey, S. W. Simith, and O. T. von Ramm, “Speckle pattern correlation with lateral aperture translation: Experimental results and implications for spatial compounding,” IEEE Trans. Ultrason., Ferroelect. Freq. Contr., vol. Uffc-33, no. 3, pp. 257-264, May 1986.
[5]G. E. Trahey, J. W. Allison, S. W. Simith, and O. T. von Ramm, “A quantitative approach to speckle reduction via frequency compounding,” Ultrason. Imag., vol. 8, no. 3, pp. 151-164, 1986.
[6]T. Loupas, W. N. McDicken, and P. L. Allan, “An adaptive weighted median filter for speckle suppression in medical ultrasonic images,” IEEE Trans. Circuits Syst., vol. 36, no. 1, pp. 129-135, Jan. 1989.
[7]E. J. Chen, W. K. Jenkins and W. D. O’Brien, “Performance of ultrasonic speckle tracking in various tissue,” J. Acoust. Soc. Am., vol. 98, pp. 1273-1278, 1995.
[8]L. N. Bohs, B. J. Geiman, M. E. Anderson, S. C. Gebhart and G. E. Trahey, “Speckle tracking for multi-dimensional flow estimation,” Ultrasonics, vol. 38, pp. 369- 375, 2000.
[9]周敬涵，”都卜勒頻寬橫向血流估計之分析與改進”，國立台灣科技大學，碩士論文，民國96年。
[10]B. Dunmire, K. W. Beach, K. Labs, M. Plett, and D. E. Strandness, “Cross-beam vector Doppler ultrasound for angle-independent velocity measurements,” Ultrasound Med. Biol., vol. 26, pp. 1213-1235, Oct. 2000.
[11]S. L. Wang, M. L. Li, P. C. Li, “Estimating the blood velocity vector using aperture domain data,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 54, no. 1, pp. 70-78, 2007.
[12]G. E. Trahey, J. W. Allison, and O. T. von Ramm, “Angle independent ultrasonic detection of blood flow,” IEEE Trans. Biomed. Eng., vol. 34, pp. 965-967, 1987.
[13]吳詩盈，”斑點追蹤在高速超音波成像之效能探討”，國立台灣大學，碩士論文，民國98年。
[14]T. G. Bjastad, “High frame rate ultrasound using parallel beamforming ,” Ph.D dissertation, Norwegian University of Science and Technology, 2009.
[15]M. H. Perdersen, K. L. Gammelmark, and J. A. Jensen, “In-vivo evaluation of convex Array synthetic aperture imaging,” Ultrasound in Med. & Biol., vol. 33 no. 1, pp. 37-47, 2007.
[16]R. Y. Chiao, L. J. Thomas, and S. D. Silverstein, “Sparse array imaging with spatially-encoded transmits,” in Proc. IEEE Ultrason. Symp., pp. 1679-1682, 1997.
[17]M. Karaman, P. C. Li, and M. O’Donnell, “Synthetic apertureimaging for small scale systems,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 42, pp. 429-442, 1995.
[18]J. Udesen, F. Gran, K. L. Hansen, J. A. Jensen, C. Thomsen, and M. B. Nielsen, “High frame-rate blood vector velocity imaging using plane wave: simulation and preliminary experiments,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 55, no. 8, pp. 1729- 1743, 2008.
[19]G. Montaldo, M. Tanter, J. Bercoff, N. Benech, and M. Fink, “Coherent plane wave compounding for very high frame rate ultrasonography and transient elastography ,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 56, no. 3, pp. 489-506, 2009.
[20]S. I. Nikolov, K. Gammelmark, and J. A. Jensen, “Recursive ultrasound imaging,” in Proc. IEEE Ultrason. Symp., pp. 1621–1625, 1999.
[21]L. N. Bohs and G. E. Trahey, “A novel method for angle independent ultrasonic imaging of blood flow and tissue motion,” IEEE Trans. Biomed. Eng., vol. 38, pp. 280-286, 1991.

[22]J. A. Jensen, “Field: A program for simulating ultrasound systems,” Med. Biol. Eng. Comp., vol. 4, Suppl. 1, pt. 1, pp. 351-353, 1996b.
[23]J. S. Jeong, J. S. Hwang, M.H. Bae, T. K. Song, “Effects and limitations of motion compensation in synthetic aperture techniques,” IEEE Ultrason. Symp., pp. 1759–1762, 2000.
[24]P. C. Li, M. L. Li, “Adaptive imaging using the generalized coherence factor,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 50, no. 2 pp. 128-141, 2003.