1. A method for detecting Alzheimer's Disease (AD) using positron emission tomography (PET), comprising the steps of: determining preselected regions of a patient's brain for analysis, prior to any imaging of said patient's brain to obtain image data for said analysis; obtaining PET image data of said patient's brain using a PET imaging apparatus; comparing, using a processor, PET image mean intensity data of said preselected regions of said patient's brain with a standard distribution of PET image mean intensity data of corresponding regions from a database of non-AD population to determine the distance of each mean from the mean of said standard distribution; determining, using a processor, the variation of said distance over said preselected regions; determining, using a processor, the probability of AD in said patient as a function of said variation; and displaying on a display device the probability of AD as a result of said determining step.