Alzheimer's disease (AD) is a progressive neurodegenerative disease. Epidemiological studies suggest that type 2 diabetes (T2DM) patients are 2 times more likely to develop AD than healthy people. But it is unclear yet why more decreased saturation of blood oxygen and secondary more severe cognitive impairment are present in AD patients with diabetes. Susceptibility weighted imaging (SWI) is widely used in the diagnosis of central nervous system diseases and venous oxygen content is the basis of SWI angiography. As such, this study used SWI mapping to measure the changes of magnetic susceptibility as well as the change of blood oxygen.