Investigation of microscopic diffusion anisotropy reveals
microstructural changes in normal aging of the human brain
-
1
University Medical Center Hamburg-Eppendorf, Department of Systems Neuroscience, Germany
Introduction
Many investigations on white matter (WM) microstructure rely on DTI. Its FA also depends on the macroscopic fiber orientation distribution. Recently introduced microscopic diffusion anisotropy measures derived from double diffusion encoding (DDE) experiments for the long mixing time regime (e.g. MA index, [1]) overcome this limitation being independent of the orientation distributions of axons and fibers. Even in a WM region-of-interest (ROI) that appeared isotropic in a DTI experiment, anisotropic diffusion could be detected [2]. Recent studies showed that MA measurements are feasible in human brain in vivo [3].
Results
Mean values of MA and FA and their variation in groups of young (< 33 y) and old
(> 60 y), healthy volunteers have been determined. Mean values in selected ROIs show differences in both measures between groups. Statistical analysis of MA and FA maps revealed large regions with significant age-related changes. FA changes were found to be in line with the literature. FA exhibited reduced values in deep WM but increased in several GM ROIs such as the putamen and the thalamus. In contrast, MA decreased globally with only few exceptions. MA revealed age-related changes also in regions with insignificant FA in particular in regions known to contain fiber crossings (Fig 1). Being more consistent between different white matter ROIs and less dependent on the fiber orientation distribution than FA, MA may provide a more direct and more sensitive access to changes of tissue microstructure.
The determination of the MA in cortical gray matter regions (Fig. 2) is more challenging since the modulation is typically smaller than in WM. To circumvent confounding partial volume effects with WM, a gray matter DDE variant has been used involving an adiabatic inversion recovery pulse that aims to null the WM signal in order to minimize the partial volume effect [4].
[1] Lawrenz M et al., J. Magn. Reson. 202, 43, (2010) [2] Lawrenz M et al., Magn. Reson. Med. 69, 1072 (2013)
[3] Lawrenz M et al., Magn. Reson. Med. 73, 773 (2015) [4] Lawrenz M et al., Proc. ISMRM 2014, p. 2638
Fig. 1: t-maps (p<0.001) for age-related changes of the MA and FA. Most regions with significant FA change also reveal significant MA change, but MA changes can also be seen in regions without FA changes.
Fig. 2: MA map of cortical gray matter.
Keywords:
Diffusion,
MRI,
dMRI,
multidimensional,
diffusion encoding
Conference:
New dimensions in diffusion encoding, Fjälkinge, Sweden, 11 Jan - 14 Jan, 2016.
Presentation Type:
Oral presentation
Topic:
New Dimensions in Diffusion Encoding
Citation:
Lawrenz
M and
Finsterbusch
J
(2016). Investigation of microscopic diffusion anisotropy reveals
microstructural changes in normal aging of the human brain.
Front. Phys.
Conference Abstract:
New dimensions in diffusion encoding.
doi: 10.3389/conf.FPHY.2016.01.00024
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Received:
07 Jul 2016;
Published Online:
07 Jul 2016.
*
Correspondence:
Dr. Jürgen Finsterbusch, University Medical Center Hamburg-Eppendorf, Department of Systems Neuroscience, Hamburg, 20246, Germany, j.finsterbusch@uke.uni-hamburg.de