Equivalence of double and single wave vector diffusion contrast at low diffusion weighting
Equivalence of double and single wave vector diffusion contrast at low diffusion weighting
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DOI：
10.1002/nbm.1808
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发表时间：
2012-06-01
影响因子：
2.9
通讯作者：
Jespersen, Sune Norhoj
中科院分区：
文献类型：
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作者：
Jespersen, Sune Norhoj
近年来，多个脉冲场梯度扩散序列作为一种潜在的新型 MRI 造影剂再次受到人们的关注。这种关注很大程度上是由于能够使用低幅度扩散梯度测量孔径，以及区分各向异性孔隙的宏观各向同性系统和各向同性孔隙系统。本文表明，在许多情况下，可以通过组合在不同扩散时间获得的两个或多个标准单脉冲扩散加权实验来获得相同类型的信息。类似地，来自多个脉冲场梯度扩散的信息可以从多个单脉冲扩散实验中重建。这种可能性植根于扩散张量的时间依赖性中包含的信息，它提供了低梯度幅度下扩散加权 MR 信号的完整描述。讨论了累积展开式第四阶产生的新信息。发现长混合时间下波矢量的耦合是由单孔隙平均位移张量的方差控制的。特别地，讨论了四阶项对孔隙形状各向异性的敏感性是如何通过孔隙取向各向异性调制的，并在相干取向的均匀系综中消失。对于宏观各向同性系统，提出了一种新的孔隙形状各向异性指标。版权所有 (C) 2011 John Wiley & Sons, Ltd.
Multiple pulsed field gradient diffusion sequences have received renewed interest in recent years as a potentially new type of MRI contrast. This attention is largely a result of the ability to measure pore sizes using low-amplitude diffusion gradients, and to distinguish between macroscopically isotropic systems of anisotropic pores and systems of isotropic pores. In this article, it is shown that, under many circumstances, the same type of information can be obtained by combining two or more standard single pulse diffusion-weighted experiments acquired at different diffusion times. Similarly, information from multiple pulsed field gradient diffusion can be reconstructed from several single pulsed diffusion experiments. This possibility is rooted in the information contained in the time dependence of the diffusion tensor, which provides a complete description of the diffusion-weighted MR signal at low gradient amplitudes. The new information arising at the fourth order in the cumulant expansion is discussed. The coupling of the wave vectors at long mixing times is found to be controlled by the variance of the single pore mean displacement tensor. In particular, a discussion is given concerning the way in which the sensitivity of the fourth-order term to the pore shape anisotropy is modulated by pore orientation anisotropy and vanishes in coherently oriented homogeneous ensembles. For macroscopically isotropic systems, a new index of pore shape anisotropy is proposed. Copyright (C) 2011 John Wiley & Sons, Ltd.