Contributions and Letters Dement Geriatr Cogn Disord Extra 2012;2:649–651 How Much Is a Picture Worth? Putting Amyloid Imaging to the Test

Accurate clinical diagnosis of Alzheimer’s disease (AD) is vital but has remained chal-lenging because of the dichotomy between clinical diagnosis (made using cognitive tests) and definitive diagnosis (which requires pathological evidence of -amyloid plaques and tangles in the brain) [1–4]. A recent clinical-autopsy correlative study of more than 900 cases seen at the very best US memory centers found that nearly 40 % of patients clinically diagnosed with non-AD dementia had postmortem histopathology consistent with AD [2]. Likewise, studies suggest that up to 30 % of patients clinically diagnosed with possible or probable AD may not meet postmortem pathologic criteria for AD [1–4]. It is important to accurately differentiate the early stage of AD from other types of cognitive disorders, which may have different prog-nosis and different potential for treatment [1–4]. Efforts to bridge the gap between clinical and pathological diagnosis have led to the development of PET tracers with high affinity for -amyloid neuritic plaques, such as 11 C-PiB, 18 F-florbetaben and 18 F-florbetapir [1] as well as the recent US marketing of florbetapir for clinical use [1, 3–7]. Although these amyloid PET tracers correlate well with postmortem histopathology [1, 3] , less is known about their impact on clinical decision-making and patient outcomes