Moutal Nicolas, Grebenkov Denis S
Laboratoire de Physique de la Matière Condensée (UMR 7643), CNRS - Ecole Polytechnique IP Paris, 91128 Palaiseau, France.
Laboratoire de Physique de la Matière Condensée (UMR 7643), CNRS - Ecole Polytechnique IP Paris, 91128 Palaiseau, France; Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany.
J Magn Reson. 2020 Nov;320:106836. doi: 10.1016/j.jmr.2020.106836. Epub 2020 Sep 26.
High diffusion-sensitizing magnetic field gradients have been more and more often applied nowadays to achieve a better characterization of the microstructure. As the resulting spin-echo signal significantly deviates from the conventional Gaussian form, various models have been employed to interpret these deviations and to relate them with the microstructural properties of a sample. In this paper, we argue that the non-Gaussian behavior of the signal is a generic universal feature of the Bloch-Torrey equation. We provide a simple yet rigorous description of the localization regime emerging at high extended gradients and identify its origin as a symmetry breaking at the reflecting boundary. We compare the consequent non-Gaussian signal decay to other diffusion NMR regimes such as slow-diffusion, motional-narrowing and diffusion-diffraction regimes. We emphasize limitations of conventional perturbative techniques and advocate for non-perturbative approaches which may pave a way to new imaging modalities in this field.
如今，高扩散敏感磁场梯度已越来越频繁地被应用，以更好地表征微观结构。由于产生的自旋回波信号显著偏离传统的高斯形式，人们采用了各种模型来解释这些偏差，并将它们与样品的微观结构特性联系起来。在本文中，我们认为信号的非高斯行为是布洛赫 - 托里方程的一个普遍特征。我们对在高扩展梯度下出现的局域化区域提供了一个简单而严格的描述，并确定其起源为反射边界处的对称性破缺。我们将由此产生的非高斯信号衰减与其他扩散核磁共振区域进行比较，如慢扩散、运动窄化和扩散衍射区域。我们强调传统微扰技术的局限性，并提倡采用非微扰方法，这可能为该领域的新成像模式铺平道路。
