MRI-DTI Imaging Reveals Specific Neuro-degeneration Signature in Precuneus Node of Awareness Processing in Brain under Alzheimer’s Disease

Abstract

Introduction:Alzheimer's disease(AD) displays progressive neurodegenerative atrophy, causing neuronal lossaffecting cognitive skills and memory. As precuneus is associated with episodic memory and is the reflexive self-awareness hub node, we consider precuneus as region-of-interest(ROI) for analysing AD.Objective:The main objective is find AD-caused alteration in nerve fibres, using diffusion tensor imaging(DTI) parameters like Mean Diffusivity(MD), Fractional Anisotropy(FA), and Nerve-tract Parameters, as number, length, volume, density, and thus, analyse the effect on precuneus by AD [when compared to normal subjects(CN)].Materials/Methods:Normals and Alzheimer’s subjects (n=50 each) were scanned with Siemens 3-tesla MRI-scanner. DTI parameters were estimated by DSI-FSL procedure, with statistical analysis usingt-test/ANOVA.Results:While ageing-process occurs in both AD and CN subjects, there is no change in “macro-structural” nerve fibre characteristics (e.g. Tract Indices: Number, density, volume, length). Contrastingly, there is significant alteration in “micro-structural” fibre characteristics, as increase in Mean Diffusivity(p=0.0006) and decrease in Fractional Anisotropy(p=0.0009) in Alzheimer's disease, when compared with normal subjects. Furthermore, comparing left-versus-right brain, Alzheimer’s patients (but not Normal subjects) show diminution in macro-structural nerve characteristics in left precuneus (compared to right precuneus): namely Tract’s number(p=0.0010), length(p=0.0107), volume(p=0.0225), density(p=0.0340).Conclusion:Under neurodegeneration, change in “micro-structural” nerve-fibre characteristics (Tract Indices), as opposed to “macro structural” fibre indices, can be hallmark for AD. Moreover, right precuneus is more protected in AD. Conversely, left precuneus has more neurodegeneration since its blood-flow is supplied by left common-carotid artery (unlike right common-carotid artery), this left artery arises directly from high-pressure aortic flow, transmitting turbulent hemodynamic stress to left precuneus.