Gach H M, Lowe I J
Department of Physics and Astronomy, University of Pittsburgh, Pennsylvania, USA.
Magn Reson Med. 1998 Oct;40(4):559-70. doi: 10.1002/mrm.1910400409.
MRI ultra-fast imaging techniques are used to characterize flow emerging from streamlined and abrupt stenoses inside cylindrical channels. Reattachment lengths of the shear boundary to the channel wall are measured using rotating ultra-fast imaging sequence (RUFIS) in-flow imaging. Velocity profiles of flow are created using velocity (sine and cosine)-encoded RUFIS sequences. The sine-encoded images permit one to identify reverse flow (i.e., eddies) that arise within the region of flow reattachment. The ratios of peak velocities (downstream/upstream of the stenosis) derived from the cosine-encoded images are used to identify the transition from the laminar to the turbulent regimen. Based on these experiments, the transition from the laminar to turbulent regimen occurs at a stenotic Reynolds Number of 350, whereas fully developed turbulence occurs at a stenotic Reynolds Number of 2600. These results are compared with the results from invasive studies.
磁共振成像（MRI）超快速成像技术用于描述圆柱形通道内流线型和突然变窄处流出的血流特征。使用旋转超快速成像序列（RUFIS）进行血流成像，测量剪切边界与通道壁的重新附着长度。使用速度（正弦和余弦）编码的RUFIS序列创建血流速度剖面。正弦编码图像允许识别在血流重新附着区域内出现的逆流（即涡流）。从余弦编码图像得出的峰值速度比（狭窄下游/上游）用于识别从层流到湍流状态的转变。基于这些实验，从层流到湍流状态的转变发生在狭窄雷诺数为350时，而完全发展的湍流发生在狭窄雷诺数为2600时。将这些结果与侵入性研究的结果进行比较。
