title: Multiple DTI index analysis in normal aging, amnestic MCI and AD. Relationship with neuropsychological performance.
abstract: White matter (WM) damage has been reported in Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI) in diffusion tensor imaging (DTI) studies. It is, however, unknown how the investigation of multiple tensor indexes in the same patients, can differentiate them from normal aging or relate to patients cognition. Forty-six individuals (15 healthy, 16 a-MCI and 15 AD) were included. Voxel-based tract based spatial-statistics (TBSS) was used to obtain whole-brain maps of main WM bundles for fractional anisotropy (FA), radial diffusivity (DR), axial diffusivity (DA) and mean diffusivity (MD). FA reductions were evidenced among AD patients with posterior predominance. A-MCI patients displayed reduced mean FA in these critical regions, compared to healthy elders. MD increases were widespread in both groups of patients. Interestingly, a-MCI patients exhibited DR increases in overlapping areas of FA shrinkages in AD, whereas DA increases were only observed in AD. Gray matter atrophy explained most DTI differences, except those regarding MD in both groups as well as DR increases in posterior associative pathways among a-MCI cases. FA values were the only DTI measure significantly related to memory performance among patients. Present findings suggest that most DTI-derived changes in AD and a-MCI are largely secondary to gray matter atrophy. Notably however, specific DR signal increases in posterior parts of the inferior fronto-occipital and longitudinal fasciculi may reflect early WM compromise in preclinical dementia, which is independent of atrophy. Finally, global measures of integrity, particularly orientation coherence (FA) of diffusion, appear to be more closely related to the cognitive profile of our patients than indexes reflecting water movement parallel (DA) and perpendicular (DR) to the primary diffusion direction.
authors.affiliation: Alzheimer's disease and other Cognitive Disorders Unit, Neurology Service, Hospital Clínic de Barcelona, Catalonia, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Bosch
authors.forename: Eider M
authors.initials: EM
authors.lastname: Arenaza-Urquijo
authors.forename: Lorena
authors.initials: L
authors.lastname: Rami
authors.forename: Roser
authors.initials: R
authors.lastname: Sala-Llonch
authors.forename: Carme
authors.initials: C
authors.lastname: Junqué
authors.forename: Cristina
authors.initials: C
authors.lastname: Solé-Padullés
authors.forename: Cleofé
authors.initials: C
authors.lastname: Peña-Gómez
authors.forename: Núria
authors.initials: N
authors.lastname: Bargalló
authors.forename: José Luis
authors.initials: JL
authors.lastname: Molinuevo
authors.forename: David
authors.initials: D
authors.lastname: Bartrés-Faz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D000544:Alzheimer Disease / Q000473:pathology* / Q000503:physiopathology / Q000523:psychology; D016880:Anisotropy; D001284:Atrophy; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000473:pathology*; D003071:Cognition; D060825:Cognitive Dysfunction / Q000473:pathology* / Q000503:physiopathology / Q000523:psychology; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory; D009483:Neuropsychological Tests; D011446:Prospective Studies