“How is Alzheimer's diagnosed with a PET scan?”

It is mostly experimental as there is no good test for this diagnosis.

It looks for areas of decreased uptake of the radiotracer in certain parts of the brain.

Dr Cox

There is a PET agent that binds to amyloid which is increased in the brain of Alzheimer’s patients. FDG is also used but not as accurate.

With FDG-PET, hypometabolic activity (decreased glucose utilization) in certain parts of the brain namely temporal and occipital lobe is characteristic of Alzheimer’s disease and can distinguish this from Lewey Body dementia and vascular dementia as well as Parkinson’s dementia. Florbetaben is an FDA approved imaging agent that directly bonds to beta amyloid in the brain showing diffuse increased cortical uptake of the radiotracer in Alzheimer’s disease. Hope this helps understand this kind of PET imaging a little better.

The word PET means positron emission tomography and uses F-18 labeled agents typically glucose. The presence of the F-18 replacing one of the hydroxyl groups in the glucose allows it to be treated by the body as glucose which becomes trapped in the cells as the phosphorylated form. The presence of the fluorine atom blocks further metabolism of the molecule which remains in the cell and allows it to be imaged as positrons are emitted from decay of the F18 into Oxygen. The half life of the F-18 is 110 minutes.

Brian