Application Of Quantitative Susceptibility Mapping On The Studies Of Brain Iron Deposition

Magnetic susceptibility is an intrinsic physical property of tissues and has been proved to correlate linearly with the tissue iron levels in the grey matter.Cerebral iron deposition may predispose individuals to high risk of a decrease in motor and cognitive function,and it occurs in a series of neurodegenerative diseases.Therefore,magnetic susceptibility may serve as an imaging biomarker to provide the valuable insight for disease pathological progression,cognitive decline process and studies of environmental factors which may influence brain iron concentration.Quantitative susceptibility mapping(QSM)has been developed to map the spatial distribution of magnetic susceptibility based on reconstruction of phase images.In this dissertation,we focus on the applications of QSM on the studies of brain iron deposition:(1)Effects of high-altitude hypoxia on brain iron levels were investigated using QSM.Twenty-nine healthy sea-level subjects were examined shortly before and after approximately one-month adaptation to the high-altitude environment at 4200 m Qinghai-Tibet Plateau.The hemisphere-and gender-related differences in iron deposition in deep grey matter regions were analyzed.Further studies based on diffusion tensor imaging(DTI)suggest changes of water diffusion after hypoxia and the correlation between water diffusion and iron levels.The results indicated that iron levels increased in grey matter in spite of acclimatization to high altitude,right brain structure and female are found to be more sensitive to the hypoxia,and iron deposition in putamen may affect the water diffusion.(2)Brain iron levels in premanifest and early stage in Huntington’s Disease(HD),the correlation between brain atrophy,disease progression,cognition and iron levels,the iron deposition rate through a longitudinal one-year follow-up test were investigated using QSM.The results indicated that high iron content and iron deposition rate were observed in closer-to-onset premanifest HD and early HD.Increased iron levels directly correlated with disease progression and brain atrophy,but not with cognitive scores.(3)Brain iron levels in cortical and deep grey matter and how iron affects global and domains-specific cognition in cognitively normal older adults were investigated using QSM.Positron emission tomography(PET)were used to detect the relationship between iron levels and β-amyloid,and their possible synergistic effect on cognition.The results indicated increased iron load may impair cognition independent of βamyloid during normal aging.