Peeters F, Luypaert R, Eisendrath H, Osteaux M
Biomedical MR Unit, Academic Hospital AZ-VUB, Brussels, Belgium.
Magn Reson Med. 1996 Nov;36(5):758-66. doi: 10.1002/mrm.1910360515.
The traditional approach to flow effects in MRI is based on the gradient moment expansion. Recently, we have presented an alternative description by using linear response theory: the distortions of the velocity waveform induced by the gradient waveforms were analyzed in the frequency domain on the basis of the transfer function. In the present paper, we perform an analysis of flow encoding and quantification in the time domain, on the basis of the impulse response. The analysis shows that flow encoding should be interpreted as a weighted averaging process. Instantaneous flow encoding is determined by the centroid of the impulse response, but care should be taken regarding the physical meaning of the instant of encoding. The relationship of this approach to the frequency domain and gradient moment expansion approaches is clarified. By way of example, some interesting applications are investigated: asymmetrical phase encoding gradients to minimize misregistration and oscillating read-out gradients for flow quantification. A variety of new applications are expected to derive from the combination of both the time and frequency domains.
磁共振成像（MRI）中传统的血流效应处理方法基于梯度矩展开。最近，我们提出了一种使用线性响应理论的替代描述：基于传递函数，在频域中分析梯度波形引起的速度波形失真。在本文中，我们基于脉冲响应在时域中对血流编码和量化进行分析。分析表明，血流编码应被解释为加权平均过程。瞬时血流编码由脉冲响应的质心确定，但应注意编码时刻的物理意义。阐明了该方法与频域方法和梯度矩展开方法的关系。通过举例，研究了一些有趣的应用：用于最小化配准误差的不对称相位编码梯度和用于血流量化的振荡读出梯度。预计时域和频域的结合将产生各种新的应用。
