PET images show the metabolic degeneration of the brain of a patient with Alzheimers Disease,so I would believe that the differance would be known as I have not heard of depression showing degeneration of the brain.
It's my understanding the only way an Alzheimer's diagnoses can be confirmed is through an autopsy when the brain can physically examined. I know it sounds horrible (it did to me when I was first told), but unfortunately that's all we have right now.
Yes. I agree with Margypops. My moms petscan showed degeneration.