Abstract: Mild cognitive impairment (MCI) represents a transitional state between healthy aging and very mild Alzheimer's disease. MCI patients have a substantially higher rate of progression to Alzheimer's disease compared with cognitively normal elderly people. Functional neuroimaging modalities, including PET、SPECT and functional MRI show that MCI patients have special abnormalities in brain metabolism and perfusion, so they can offer great value in the predicting cognitive decline and early diagnosis of dementia.