Comparison of two types of microscopic diffusion anisotropy in mouse brain. (11th September 2022)

• Record Type: Journal Article
• Authors: Jensen, Jens H.; Voltin, Josh; Nie, Xingju; Dhiman, Siddhartha; McKinnon, Emile T.; Falangola, Maria F.
• Is Part Of: NMR in biomedicine. Volume 36:Number 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-11
• Subjects: 3xTg‐AD -- Alzheimer's disease -- double diffusion encoding MRI -- fractional anisotropy -- microscopic anisotropy -- mouse brain; Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.4816
• Languages: English
• ISSNs: 0952-3480

Abstract

Abstract : 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. Abstract : Two different types of microscopic diffusion anisotropy may be defined and quantified with double diffusion encoding MRI. These are investigated in brain for both normal mice and transgenic mice that develop Alzheimer's disease pathology. The metrics for the two types of anisotropy (μFA and μFA′) are characterized by distinct symmetry properties that are reflected in the metrics' experimental values, particularly in white matter regions.