Bittoun J, Jolivet O, Herment A, Itti E, Durand E, Mousseaux E, Tasu J P
Unité de Recherche en Résonance Magnétique Médicale, CNRS, Université Paris-Sud, Le Kremlin-Bicêtre, France.
Magn Reson Med. 2000 Nov;44(5):723-30. doi: 10.1002/1522-2594(200011)44:5<723::aid-mrm10>3.0.co;2-5.
Previous studies have shown that the multi-step approach of velocity or acceleration encoding is highly efficient in terms of the signal-to-noise ratio per unit time. This work describes a multidimensional extension of this method for simultaneously measuring multiple components of velocity and acceleration with a few encoding steps. N flow dimensions were encoded with an ND-matrix, obtained by combining the various flow-encoding gradients. The small matrix obtained with as few as two encoding steps can be extended by zero-filling in all N dimensions and using ND-Fourier transformation to obtain the maximum of the resulting peak in the ND-matrix, which gives simultaneously all the components of velocity and/or acceleration. The processing time was shortened by using a method of phase computation that gives the same precision as Fourier transformation, but is much faster. A rotating disk was used to show that the velocity-to-noise ratio increases with the number of dimensions acquired, demonstrating the efficiency of multidimensional flow measurements. The feasibility of the method is illustrated by 3D maps of the myocardium velocity, and 2D measurement of velocity and acceleration in the ascending aorta-both obtained by multidimensional phase encoding in volunteers.
先前的研究表明，速度或加速度编码的多步方法在单位时间的信噪比方面效率很高。这项工作描述了该方法的多维扩展，用于通过几个编码步骤同时测量速度和加速度的多个分量。N个流动维度用一个ND矩阵进行编码，该矩阵通过组合各种流动编码梯度获得。通过在所有N个维度上零填充并使用ND傅里叶变换来获得ND矩阵中所得峰值的最大值，从而可以扩展仅用两个编码步骤获得的小矩阵，这同时给出了速度和/或加速度的所有分量。通过使用一种相位计算方法缩短了处理时间，该方法具有与傅里叶变换相同的精度，但速度要快得多。使用旋转盘表明速度与噪声比随着获取的维度数量增加而增加，证明了多维流动测量的效率。通过志愿者的心肌速度3D图以及升主动脉中速度和加速度的2D测量（均通过多维相位编码获得）说明了该方法的可行性。
