A survey of more than 100 studies involving PIB-PET, a diagnostic tool that involves injecting a radiotracer called Pittsburgh compound B into the brain via the bloodstream, and imaging the brain with positron emission tomography (PET), has confirmed its sensitivity in detecting amyloid-beta protein plaques. The tool is not yet commercially available. The study also provides strong evidence supporting the theory that accumulation of amyloid-beta protein plaques in the brain is central to the development of Alzheimer’s. The findings, that amyloid deposits appear to reach a plateau early in the disease course, may explain why Alzheimer's patients have not responded to promising experimental drugs that target amyloid. It may be that they are being administered too late.