IEEE Trans Ultrason Ferroelectr Freq Control. 2017 Jul;64(7):1050-1062. doi: 10.1109/TUFFC.2017.2693403. Epub 2017 Apr 12.
Several techniques can estimate the 2-D velocity vector in ultrasound. Directional beamforming (DB) estimates blood flow velocities with a higher precision and accuracy than transverse oscillation (TO), but at the cost of a high beamforming load when estimating the flow angle. In this paper, it is proposed to use TO to estimate an initial flow angle, which is then refined in a DB step. Velocity magnitude is estimated along the flow direction using cross correlation. It is shown that the suggested TO-DB method can improve the performance of velocity estimates compared with TO, and with a beamforming load, which is 4.6 times larger than for TO and seven times smaller than for conventional DB. Steered plane wave transmissions are employed for high frame rate imaging, and parabolic flow with a peak velocity of 0.5 m/s is simulated in straight vessels at beam-to-flow angles from 45° to 90°. The TO-DB method estimates the angle with a bias and standard deviation (SD) less than 2°, and the SD of the velocity magnitude is less than 2%. When using only TO, the SD of the angle ranges from 2° to 17° and for the velocity magnitude up to 7%. Bias of the velocity magnitude is within 2% for TO and slightly larger but within 4% for TO-DB. The same trends are observed in measurements although with a slightly larger bias. Simulations of realistic flow in a carotid bifurcation model provide visualization of complex flow, and the spread of velocity magnitude estimates is 7.1 cm/s for TO-DB, while it is 11.8 cm/s using only TO. However, velocities for TO-DB are underestimated at peak systole as indicated by a regression value of 0.97 for TO and 0.85 for TO-DB. An in vivo scanning of the carotid bifurcation is used for vector velocity estimations using TO and TO-DB. The SD of the velocity profile over a cardiac cycle is 4.2% for TO and 3.2% for TO-DB.
几种技术可以估计超声中的 2-D 速度向量。与横向振荡（TO）相比，定向波束形成（DB）可以更精确和准确地估计血流速度，但在估计血流角度时需要更高的波束形成负载。在本文中，提出使用 TO 来估计初始血流角度，然后在 DB 步骤中对其进行细化。使用互相关沿流方向估计速度幅度。结果表明，与 TO 相比，所提出的 TO-DB 方法可以改善速度估计的性能，并且波束形成负载比 TO 大 4.6 倍，比传统的 DB 小 7 倍。采用定向平面波传输实现高帧率成像，并在直血管中模拟峰值速度为 0.5 m/s 的抛物线流，在 45°至 90°的波束与流角度。TO-DB 方法估计角度的偏差和标准偏差（SD）小于 2°，速度幅度的 SD 小于 2%。仅使用 TO 时，角度的 SD 范围为 2°至 17°，而速度幅度的 SD 高达 7%。TO 的速度幅度偏差在 2%以内，而 TO-DB 略大但在 4%以内。尽管存在略微较大的偏差，但在测量中也观察到了相同的趋势。在颈动脉分叉模型中进行的现实流动模拟提供了复杂流动的可视化，TO-DB 的速度幅度估计值分布为 7.1 cm/s，而仅使用 TO 时为 11.8 cm/s。然而，TO-DB 的峰值收缩期速度被低估，TO 的回归值为 0.97，TO-DB 为 0.85。使用 TO 和 TO-DB 对颈动脉分叉进行体内扫描以进行向量速度估计。心脏周期内速度分布的 SD 为 TO 为 4.2%，TO-DB 为 3.2%。
