Fujita N, Harada K, Murakami T, Akai Y, Kozuka T
Department of Radiology, Osaka University Medical School, Japan.
Magn Reson Med. 1990 Aug;15(2):275-86. doi: 10.1002/mrm.1910150210.
The effects of to-and-fro pulsatile flow, i.e., an oscillatory fluid motion with no net flow, on signal intensity in gated spin-echo magnetic resonance imaging are considered both theoretically and experimentally. On the basis of hydrodynamic principles, to-and-fro pulsatile flow at large Womersley numbers consists of uniform inner flow and boundary-layer-type flow adjacent to a tube wall. Therefore, the velocity profile is "trapezoidal" rather than parabolic at all times during the pulsation period. Contrary to the absence of phase dispersion and loss of signal within the inner flow where no velocity gradient exists, large velocity differences cause phase dispersion and, hence, loss of signal within the boundary layer, whose thickness is inversely proportional to the Womersley number. An understanding of these features of to-and-fro pulsatile flow provides the theoretical basis of cerebrospinal fluid flow phenomena in magnetic resonance imaging, since this type of flow exists in cerebrospinal fluid pathways.
在门控自旋回波磁共振成像中，对往复脉动流（即无净流的振荡流体运动）对信号强度的影响进行了理论和实验研究。基于流体动力学原理，在大沃默斯利数下的往复脉动流由均匀的内部流和与管壁相邻的边界层型流组成。因此，在脉动周期的所有时刻，速度剖面都是“梯形”而非抛物线形。与内部流中不存在速度梯度因而不存在相位色散和信号损失相反，大速度差异会导致相位色散，进而导致边界层内的信号损失，边界层厚度与沃默斯利数成反比。对往复脉动流这些特征的理解为磁共振成像中脑脊液流动现象提供了理论基础，因为这种类型的流动存在于脑脊液通路中。
