Scientists in the United States have proposed a new way to define Alzheimer’s disease. They want the definition based on biological signs, such as changes in the brain, instead of memory loss and other customary signs of the disease. The Associated Press says the move is aimed at improving Alzheimer’s research by using more objective, factual measures, like brain imaging tests. The researchers want to choose patients for studies and get them tested sooner, when treatments may have more chance to help. But it is too soon to use these brain scans and other tests in patient care because U.S. health officials have yet to approve them for that purpose, experts say. For now, American doctors continue to depend on the tools they have long used to study thinking skills to identify most cases.