Peeters F, Luypaert R, Eisendrath H, Osteaux M
Department of Physics, Faculty of Sciences, Vrije Universiteit Brussel, Belgium.
Magn Reson Med. 1995 Mar;33(3):337-54. doi: 10.1002/mrm.1910330308.
Phase-related unsteady (pulsatile) flow effects in MRI have been studied by means of linear response theory. These flow effects can be described in the frequency domain: the influence of the gradients on the phase shift is described by a transfer function, the spectrum of the gradient being the determining factor. An analysis of this transfer function is shown to provide information about the process of flow encoding: instant of encoding, induced distortions and how they are related to the gradient waveform. The connection with the traditional description in terms of the gradient moment expansion has also been investigated and clarified. This approach was applied to study the response of two time-resolved flow quantification techniques (Fourier flow method and phase mapping) by analyzing their amplitude and phase transfer functions. By simulation it is shown that a better interpretation of the measured velocity waveform is obtained and that Fourier analysis in combination with a correction by the inverse transfer function results in an accurate reconstruction of the velocity waveform studied.
通过线性响应理论研究了磁共振成像（MRI）中与相位相关的非稳态（脉动）流效应。这些流效应可以在频域中进行描述：梯度对相移的影响由传递函数描述，梯度谱是决定因素。对该传递函数的分析表明，它能提供有关流编码过程的信息：编码时刻、诱导失真以及它们与梯度波形的关系。还研究并阐明了与基于梯度矩展开的传统描述之间的联系。通过分析两种时间分辨流定量技术（傅里叶流方法和相位映射）的幅度和相位传递函数，将该方法应用于研究它们的响应。通过模拟表明，对测量的速度波形能有更好的解释，并且傅里叶分析与逆传递函数校正相结合可准确重建所研究的速度波形。
