Consumer advocacy organization Public Citizen has submitted a letter to the editor to the Journal of the American Medical Association, criticizing the Clark et al study, published Jan. 19, which reported a strong quantitative correlation between the biomarker florbetapir F18's signal on PET scans and the presence of beta-amyloid in the brain at death, suggesting that imaging biomarkers may be applied for diagnosing and determining early risks for Alzheimer's disease.