臺灣博碩士論文加值系統

醫用超音波系統用於流速影像上之都卜勒向量(Vector Doppler)估計會受到血管角度的影響及最大流速的限制，因此本文使用較高幀率的平面波成像系統，並嘗試將Crossed-Beam Vector Doppler (VD)與斑點追蹤技術(Speckle Tracking, ST)做結合，來改善血管角度對流速估計的影響。VD為將不同發射旋轉角收到的回音信號，運用自相關(Autocorrelation)與最小方差法(Least-Squares)計算出流速向量。並利用VD所計算出的軸向流速(Vz-VD)與一維斑點追蹤技術(1-D ST)做結合，計算出更準確的橫向流速(Vx-ST)。由於不做聚焦的單一平面波成像(Single Plane Wave, SPW)能提高幀率，但影像品質與訊雜比均較差，因此藉由不同角度的平面波進行同調性平面波複合成像(Coherent Plane Wave Compound, CPWC)以改善上述缺點，達到準確的斑點追蹤效果。
本研究模擬及血流仿體實驗結果顯示，本文所使用的方法(VD+1-D ST)與VD相比，能夠在血管角度45度以下，對流速估計的標準差STD及誤差BIAS皆能有所改善，能夠得到較為穩定以及準確的流速估計，且在血管角度0度的橫向流速估計獲得大幅度改善。

Use vector Doppler to estimate flow velocity is limited by vessel angle and maximum flow velocity in medical ultrasound system. In this study, we tried to overcome the influence of vessel angle by combining crossed-beam vector Doppler (VD) with speckle tracking (ST) in high frame rate plane wave imaging. In VD, we used radio frequency signals from different steered transmission angles to estimate autocorrelation separately, and used least-squares to obtain flow vector. Then we combined the axial velocity from VD (Vz-VD) with one-dimension speckle tracking (1-D ST) to get more accurate lateral velocity (Vx-ST). Although single plane wave excitation (SPW) could get high frame rate, its image quality and signal-to-noise ratio became worse. In order to improve estimation, we used coherent plane wave compound imaging instead of single plane wave imaging to do speckle tracking.
The results of both simulation and experiment indicate that STD and BIAS performance of VD+ST is much better than VD below 45-degree vessel. Therefore, VD+ST has more stable and accurate flow velocity estimation, especially in lateral vessel.

口試委員會審定書 #
摘要 i
ABSTRACT ii
誌謝 iii
目錄 iv
圖目錄 vii
表目錄 ix
第一章 緒論 1
1-1 淺談超音波 1
1-2 平面波發射 2
1-3 同調性平面波複合影像 4
1-4 二維流速估計 9
1-4-1 都卜勒效應 9
1-4-2 Crossed-Beam Vector Doppler 12
1-4-3 斑點追蹤技術(Speckle Tracking, ST) 14
1-4-4 其他二維流速估計 16
1-5 平面波流速估計 19
1-6 研究動機與目的 21
1-7 論文架構 22
第二章 研究方法 23
2-1 Least-Squares Vector Doppler 23
2-2 一維斑點追蹤技術(1-D Speckle Tracking, 1-D ST) 26
2-3 模擬方法 31
2-3-1 流速設定 31
2-3-2 探頭設定 33
2-3-3 斑點追蹤設定 34
2-4 實驗設計 35
第三章 研究結果-模擬 38
3-1 Vector Doppler (VD) 模擬結果 38
3-1-1 發射角之跨度角影響 (Effect of TX span angle) 40
3-1-2 發射角之數目影響 (Effect of number of TX angle) 42
3-1-3 接收角之旋轉角影響 (Effect of RX steer angle) 44
3-1-4 觀察數目之影響 (Effect of number of ensemble) 46
3-2 1-D Speckle Tracking 模擬結果 (1-D ST) 47
3-2-1 點擴散函數比較 47
3-2-2 SPW與CPWC的追蹤比較 51
3-2-3 掃描線密度對一維斑點追蹤(1-D ST)的影響 53
3-2-4 VD加上1-D ST與VD的比較 54
3-3 血管角度0度橫向流速(Vx)之比較 56
第四章 研究結果-實驗 57
4-1 VD之發射角數目比較 57
4-2 VD之觀察數目比較 59
4-3 VD與1-D ST之比較 60
4-4 驗證血管0度橫向流速(Vx)比較 62
第五章 討論與結論 63
5-1 討論 63
5-1-1 流速梯度效應對一維斑點追蹤的影響 63
5-1-2 接收角旋轉在非零度血管角度下的影響 66
5-1-3 平面波流速成像上的限制 69
5-2 結論 72
參考文獻 74

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