Velocity is one of the most important parameters to study in complex fluid flow systems. Magnetic resonance imaging (MRI) is a non-invasive tool for quantitative visualization of fast fluid flows. Many of the flow studies by MRI measure the velocity of a fluid media using either phase encoding or time of flight (TOF) measurements. Until now, motion-sensitized SPRITE is the best method for the velocity assessment of very fast flows when the structure is large enough compared to flow displacement during the encoding time ( $$t_{{\text{p}}}$$ t p ). However, when displacement during the encoding time becomes greater than the pixel size, velocity misregistration takes place. To detect the velocity with accuracy, we need to reduce the encoding time. There is a restriction on the encoding time reduction in motion-sensitized SPRITE: both the velocity encoding, and spatial encoding times take place simultaneously, causing longer encoding time. If these two steps are separated, it is possible to reduce the encoding time. In this paper, we demonstrate how this can be achieved by applying a TOF approach where the fluid is labeled by a spatially periodic modulation of the magnetization. The modulation part is performed when the liquid is still moving slowly, and the imaging part does not require the bipolar gradient to be switched on and off. This leads to a reduction of the encoding time and greater accuracy in the detection of the fast flow velocity.

中文翻译：

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带有标记 MRI 的小结构内快速流动的速度测量

速度是在复杂流体流动系统中研究的最重要参数之一。磁共振成像 (MRI) 是一种用于快速流体流动的定量可视化的非侵入性工具。MRI 的许多流动研究使用相位编码或飞行时间 (TOF) 测量来测量流体介质的速度。到目前为止，当结构与编码时间期间的流动位移相比足够大时，运动敏感的 SPRITE 是对非常快的流动进行速度评估的最佳方法 ( $$t_{{\text{p}}}$$ tp ) . 然而，当编码时间内的位移变得大于像素大小时，就会发生速度失准。为了准确检测速度，我们需要减少编码时间。运动敏感 SPRITE 的编码时间减少有限制：速度编码和空间编码时间同时发生，导致更长的编码时间。如果将这两个步骤分开，则可以减少编码时间。在本文中，我们展示了如何通过应用 TOF 方法来实现这一点，其中流体由磁化的空间周期性调制标记。调制部分在液体仍在缓慢移动时进行，成像部分不需要打开和关闭双极梯度。这导致编码时间的减少和快速流速检测中更高的准确度。我们演示了如何通过应用 TOF 方法来实现这一点，其中流体由磁化的空间周期性调制标记。调制部分在液体仍在缓慢移动时进行，成像部分不需要打开和关闭双极梯度。这导致编码时间的减少和快速流速检测中更高的准确度。我们演示了如何通过应用 TOF 方法来实现这一点，其中流体由磁化的空间周期性调制标记。调制部分在液体仍在缓慢移动时进行，成像部分不需要打开和关闭双极梯度。这导致编码时间的减少和快速流速检测中更高的准确度。