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Abstract
Normal ageing is accompanied by a progressive decline in cognitive function but the
mechanisms for this are not fully understood. Nevertheless, the importance of white
matter degeneration is supported by diffusion tensor imaging (DTI) studies, although
several important questions remain about the pattern and nature of age-related white
matter degeneration. Firstly, there is a lack of longitudinal data determining the
rate of change in DTI parameters with age, and whether this can be detected over short
time periods. Secondly, it is unclear whether observed changes are uniform across
the brain or whether accelerated white matter degeneration is localised to particular
brain regions, as would support the frontal-ageing hypothesis. This study uses DTI
techniques to quantify structural integrity change to determine whether regional differences
are apparent in the rate of degeneration during longitudinal follow-up in a sample
of healthy middle aged and older adults aged between 50 and 90years. Longitudinal
differences in fractional anisotropy, axial and radial diffusivity are investigated
using 1D coronal slice profiles, and 2D column maps in standard space, as well as
using 3D tract-based spatial statistics (TBSS) to investigate local age-related structural
changes on a voxel-by-voxel basis at baseline and two-year follow-up. Results indicate
that DTI can detect age-related change in white matter structure over a relatively
short follow-up period and that longitudinal analyses reveal significant changes in
white matter integrity throughout the brain with no evidence of accelerated decline
in the frontal lobe regions during a 2year period. Common changes across different
diffusion characteristics are discussed.
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