In many ways, Alzheimer’s disease is the biological version of a slow-motion train wreck. The disease process begins years before symptoms are evident.

There is no cure, and current treatments alleviate symptoms temporarily at best.

As they evaluate new drug therapies, researchers are using various brain imaging techniques to better identify the patients who are most likely to benefit from treatment -- those at the earliest stages of the Alzheimer’s disease process. In this slide show, we show what these brain scans look like and what challenges remain.