Center for Biomedical Imaging, Medical University of South Carolina, Charleston, South Carolina, USA.
Department of Neuroscience, Medical University of South Carolina, Charleston, South Carolina, USA.
NMR Biomed. 2023 Jan;36(1):e4816. doi: 10.1002/nbm.4816. Epub 2022 Sep 11.
Two distinct types of microscopic diffusion anisotropy (MA) are compared in brain for both normal control and transgenic (3xTg-AD) mice, which develop Alzheimer's disease pathology. The first type of MA is the commonly used microscopic fractional anisotropy (μFA), and the second is a new MA measure referred to as μFA'. These two MA parameters have different symmetry properties that are central to their physical interpretations. Specifically, μFA is invariant with respect to local rotations of compartmental diffusion tensors while μFA' is invariant with respect to global diffusion tensor deformations. A key distinction between μFA and μFA' is that μFA is affected by the same type of orientationally coherent diffusion anisotropy as the conventional fractional anisotropy (FA) while μFA' is not. Furthermore, μFA can be viewed as having independent contributions from FA and μFA', as is quantified by an equation relating all three anisotropies. The normal control and transgenic mice are studied at ages ranging from 2 to 15 months, with double diffusion encoding MRI being used to estimate μFA and μFA'. μFA and μFA' are nearly identical in low FA brain regions, but they show notable differences when FA is large. In particular, μFA and FA are found to be strongly correlated in the fimbria, but μFA' and FA are not. In addition, both μFA and μFA' are seen to increase with age in the corpus callosum and external capsule, and modest differences between normal control and transgenic mice are observed for μFA and μFA' in the corpus callosum and for μFA in the fimbria. The triad of FA, μFA, and μFA' is proposed as a useful combination of parameters for assessing diffusion anisotropy in brain.
两种不同类型的微观扩散各向异性（MA）在正常对照和转基因（3xTg-AD）小鼠的大脑中进行了比较，这些转基因小鼠会发展出阿尔茨海默病病理。第一种 MA 是常用的微观分数各向异性（μFA），第二种 MA 称为μFA'。这两个 MA 参数具有不同的对称性质，这是它们物理解释的核心。具体来说，μFA 对隔室扩散张量的局部旋转不变，而μFA'对全局扩散张量变形不变。μFA 和μFA'之间的一个关键区别是，μFA 受与传统分数各向异性（FA）相同类型的各向同性扩散各向异性的影响，而μFA'不受影响。此外，μFA 可以看作是 FA 和μFA'的独立贡献，这可以通过一个与所有三个各向异性相关的方程来量化。正常对照和转基因小鼠在 2 至 15 个月的年龄范围内进行研究，使用双扩散编码 MRI 来估计μFA 和μFA'。μFA 和μFA'在低 FA 脑区几乎相同，但在 FA 较大时，它们表现出明显的差异。特别是，在穹窿中发现 μFA 和 FA 之间存在很强的相关性，但 μFA'和 FA 之间没有。此外，在胼胝体和外囊中，μFA 和μFA'均随年龄增长而增加，在胼胝体中观察到正常对照和转基因小鼠之间μFA 和μFA'的差异，在穹窿中观察到 μFA 的差异。FA、μFA 和μFA'的三联体被提出作为评估大脑扩散各向异性的有用参数组合。
