White matter changes with age utilizing quantitative diffusion MRI

Abstract

Objective: To investigate the relationship between older age and mean cerebral white matter fiber bundle lengths (FBLs) in specific white matter tracts in the brain using quantified diffusion MRI.Methods: Sixty-three healthy adults older than 50 years underwent diffusion tensor imaging.Tractography tracings of cerebral white matter fiber bundles were derived from the diffusion tensor imaging data.Results: Results revealed significantly shorter FBLs in the anterior thalamic radiation for every 1-year increase over the age of 50 years. Conclusions:We investigated the effects of age on FBL in specific white matter tracts in the brains of healthy older individuals utilizing quantified diffusion MRI. The results revealed a significant inverse relationship between age and FBL. Longitudinal studies of FBL across a lifespan are needed to examine the specific changes to the integrity of white matter. Diffusion tensor imaging (DTI) is a noninvasive imaging technique frequently used to visualize age-related changes in white matter integrity. DTI measures water movement within a voxel and captures abnormalities in the underlying microstructural anatomy that change the direction and speed of diffusion in specific brain regions.1 Age effects demonstrated with DTI are regionally diverse and typically show an anterior-to-posterior pattern of age-related decline.2-4 In quantifying age-related decline, most DTI studies have examined white matter integrity in focal brain regions, utilizing region of interest (ROI) and voxel-based morphometry approaches.Quantitative tractography based on DTI (qtDTI) combines traditional tractography methods 4 with scalar metrics to detect region-specific microstructural changes in white matter fiber bundles.5 Specifically, the approach computes fiber bundle length (FBL) using fractional anisotropy (FA) to produce tract lines representing coherent bundles of nerve fibers. FBL constructed utilizing qtDTI provides additional detail about the direction and curvature of white matter pathways coursing throughout the brain. 6 This method is sensitive to white matter changes within entire tracts and thus may be more beneficial than methods that involve placing ROIs on 2-dimensional scalar DTI parameter maps. 6 In the present study, we utilized qtDTI tractography methods to examine the impact of aging on the white matter integrity in the brains among healthy older adults. All selected tracts have been previously associated with various factors related to age. We hypothesized that advanced age would negatively affect the microstructural integrity of white matter, resulting in shorter mean FBL in white matter tracts.

Fiber bundle length and cognition: a length-based tractography MRI study

“…A track with endpoints in the right temporal lobe and right parietal lobe was assigned to be both “temporal” and “parietal”. The logic of assigning tracks to lobes is further described in (Baker et al, 2014; Bolzenius et al, 2013; Salminen et al, 2013). For each subject, the mean track length was computed from the arc lengths and was normalized to intracranial volume.…”

“…As a sensitive noninvasive measure, tractography can help determine the location of FBL changes, whether these changes are a function of normal aging, and whether these changes are capable of impacting cognitive performance. We have recently reported significant alterations in FBL among older individuals compared to younger individuals (Baker et al, 2014), but no study has examined these imaging metrics in combination with cognitive performance.…”

Vulnerability of white matter tracts and cognition to the SOD2 polymorphism: A preliminary study of antioxidant defense genes in brain aging

“…Structural alterations in the ATR and cingulum have been reported in previous studies of brain aging [44,45,55,56], Alzheimer's disease [57–59], Parkinson's disease [60,61], and schizophrenia [62,63], among others. Oxidative stress is implicated in the pathogenesis of these conditions, which is consistent with studies reporting an increase risk for Alzheimer's disease, Parkinson's disease, and schizophrenia among CC genotypes of SOD2 /rs4880 [30–33].…”

“…Tracts of interest included white matter association tracts such as the superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF), inferior fronto-occipital fasciculus (IFOF), uncinate fasciculus (UF), and cingulum bundle [43]. Although not classically defined as an association tract, we also examined the anterior thalamic radiation (ATR), as this tract innervates association areas and has been previously associated with brain aging and decline in executive function, processing speed, and memory [44–46]. Each tract was modeled separately by hemisphere for a total of 12 distinct tracts.…”

Application of a Novel Quantitative Tractography-based Analysis of Diffusion Tensor Imaging to Examine Fiber Bundle Length In Human Cerebral White Matter

“…Our group recently reported a significant negative relationship between FBL and age, specific to the anterior thalamic radiation (3) and uncinate fasciculus (44). The anterior thalamic radiation is formed by fibers interconnecting the anterior and medial thalamic nuclei and the frontal lobe via the anterior limb of the internal capsule.…”