Tractography reconstruction to assess the effects of age on arcuate fasciculus, corticospinal tract and cingulum bundle

Magnetic Resonance (MR) diffusion tractography is a non-invasive, in-vivo method for identifying anatomical connections in the brain by characterizing water motion within the brain tissue, that is sensitive to the orientation of white matter (WM) fibers. This work considers a probabilistic tractography reconstruction of cingulum bundle (CB) tract, that is a complex tract whose structure and functions are not fully identified. Being involved in the process associated with behavioral impairment in dementia, we aimed at characterizing the effects of age on it, by comparing the results of the CB analysis with those obtained after reconstruction of the corticospinal tract and arcuate fasciculus, for which effects of age are known from the literature. Each tract was divided into 3 branches, while data were provided by the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) by considering brain images of 150 healthy subjects (20 per decade from 18 to 90 y.o.). Statistical analysis was based on ANOVA and GLMs to find interaction effects between tracts and age for each DTI biomarker. We observed an overall axonal integrity reduction with ageing, more significant for AF and CB: CST is involved in (primary) movement functioning, which is not neurologically correlated so much with ageing, while AF and CB are involved in language and memory (higher-order functions) and a reduction in respective tasks with ageing is observed in healthy subjects. As far as we know, this is the first work about effects of age on CB with a detailed analysis of the other two tracts, showing that tractography can be employed to reconstruct even major WM tracts with a modest number of gradient directions. Future developments are the use of this automatic protocol, applicable in clinical practice, which will allow to regress out the physiological effects due to ageing, bringing out microstructural impairments related to the pathology rather than to ageing in patients with cognitive impairments.