LIU BOYUANBIOMEDICAL ENGINEERING2017-08-162017-08-162017-01-10LIU BOYUAN (2017-01-10). ESTIMATION OF WATER DIFFUSIVITY IN TISSUE OF THE BRAIN AND ITS APPLICATION TO BRAIN AGING STUDY. ScholarBank@NUS Repository.https://scholarbank.nus.edu.sg/handle/10635/136359In this thesis, a novel method for estimating diffusivity in the context of diffusion MRI is proposed. This method computes the conditional variance in constant solid angle and uses it as a measure of diffusivity. This is an improvement on the existing Q-ball imaging method because it enables one to measure diffusivity beyond a probabilistic measure. The novel method is fast, robust and easy to implement. The illustration of the method has been shown and the testing of the method have been made. A statistical analysis on the estimated diffusivity and orientational distribution function is implemented to study the aging effect on the human brain white matter. It is shown that generalised fractional anisotropy decreases and mean diffusivity increases in most parts of brain in aging, which is consistent with the literatures relevant to brain aging.endiffusion MRI, Q-ball imaging, water molecule diffusion, brain aging, neural image,ThesisNOT_IN_WOS