Department of Radiology, University Hospital of Copenhagen, Denmark.
Ultraschall Med. 2009 Oct;30(5):471-7. doi: 10.1055/s-0028-1109572. Epub 2009 Sep 17.
Conventional ultrasound methods for acquiring color flow images of the blood motion are limited by a relatively low frame rate and are restricted to only giving velocity estimates along the ultrasound beam direction. To circumvent these limitations, the Plane Wave Excitation (PWE) method has been proposed.
The PWE method can estimate the 2D vector velocity of the blood with a high frame rate. Vector velocity estimates are acquired by using the following approach: The ultrasound is not focused during the ultrasound transmission, and a full speckle image of the blood can be acquired for each pulse emission. The pulse is a 13 bit Barker code transmitted simultaneously from each transducer element. The 2D vector velocity of the blood is found using 2D speckle tracking between segments in consecutive speckle images. Implemented on the experimental scanner RASMUS and using a 100 CPU linux cluster for post processing, PWE can achieve a frame of 100 Hz where one vector velocity sequence of approximately 3 sec, takes 10 h to store and 48 h to process. In this paper a case study is presented of in-vivo vector velocity estimates in different complex vessel geometries.
The flow patterns of six bifurcations and two veins were investigated. It was shown: 1. that a stable vortex in the carotid bulb was present opposed to other examined bifurcations, 2. that retrograde flow was present in the superficial branch of the femoral artery during diastole, 3. that retrograde flow was present in the subclavian artery and antegrade in the common carotid artery during diastole, 4. that vortices were formed in the sinus pockets behind the venous valves in both antegrade and retrograde flow, and 5. that secondary flow was present in various vessels.
Using a fast vector velocity ultrasound method, in-vivo scans have been recorded where complex flow patterns were visualized in greater detail than previously visualized by conventional color flow imaging techniques.
传统的超声方法获取血流的彩色流动图像受到相对较低帧率的限制，并且只能沿超声束方向给出速度估计。为了规避这些限制，提出了平面波激励（PWE）方法。
PWE 方法可以以高帧率估计血流的 2D 矢量速度。通过以下方法获取矢量速度估计：在超声发射期间不聚焦超声，并且可以为每个脉冲发射获取全斑点血流图像。脉冲是同时从每个换能器元件发送的 13 位 Barker 码。通过在连续斑点图像之间的段之间进行 2D 斑点跟踪来找到血流的 2D 矢量速度。在实验扫描仪 RASMUS 上实现并使用 100 个 CPU 内核的 Linux 集群进行后处理，PWE 可以实现 100Hz 的帧率，其中大约 3 秒的一个矢量速度序列需要 10 小时存储和 48 小时处理。本文介绍了在不同复杂血管几何形状中进行体内矢量速度估计的案例研究。
研究了六个分叉和两条静脉的流动模式。结果表明：1. 在颈动脉窦中存在稳定的涡流，与其他检查的分叉相反；2. 在股动脉的浅表分支中存在舒张期逆行血流；3. 在锁骨下动脉中存在舒张期逆行血流，而在颈总动脉中存在前向血流；4. 在静脉瓣后面的窦袋中形成了涡流，在顺行和逆行血流中都存在；5. 在各种血管中存在二次流。
使用快速矢量速度超声方法，记录了体内扫描，其中复杂的流动模式比以前使用常规彩色血流成像技术更详细地可视化。
