Alzheimer's disease (AD) is difficult to diagnose in its early stages, and even 
if detected early, there is no preventative treatment. Imaging modalities such 
as MRI, PET, and SPECT have the potential to contribute to both the diagnosis of 
Alzheimer's disease, as well as assist in the search for more effective 
treatments. A number of AD-related biomarkers have been proposed and evaluated. 
The use of PET imaging to detect alterations in regional brain metabolism using 
[(18)F]FDG has enabled more sensitive and accurate early diagnosis of AD, 
especially in conjunction with traditional medical evaluation. Additionally, 
magnetic resonance imaging and spectroscopy provide a wide range of biomarkers 
that have been shown to correlate with the progression of AD. Some of these 
markers have been pursued in clinical trials. Progress has been made toward the 
evaluation of other more AD-specific biomarkers. However, many questions remain 
concerning the validity and sensitivity of these imaging biomarkers to aid in 
the assessment of potential new treatments, especially those related to 
increased levels of amyloid peptides in the brain.