Doctors take two approaches to diagnosing Alzheimer’s disease. First, they ask patients questions and fill out one of several standardized questionnaires to assess memory and other aspects of thinking. Second, doctors order various tests to rule out other conditions that can affect mental function. There is no direct test for Alzheimer’s disease, or for the risk of developing it. This article will clarify the value of PET, PET/CT, CT, and MRI in diagnosing Alzheimer’s disease.