PET images of Alzheimer’s brain
PET (positron emission tomography; said like “pet”- the animals you have at home) is a type of imaging that relies on a radioactive ligand (injected into the patient) to give off a signal for a particular type of chemical. For instance, if you want to look at a specific receptor or neurotransmitter, you could put in a competitive radioactive ligand that would bind to that receptor and it would tell you where that receptor is and how much of the neurotransmitter is binding. It’s not completely straightforward (for instance, if the signal decreases, it could mean more neurotransmitter is taking up the receptors OR it could mean there are fewer receptors there in general).
This is a PET image of a healthy control and an early/late-stage AD patient’s brain. This type of PET is glucose-based, so it’s just tracking overall brain metabolism. You can see the early AD brain is already decreased in overall glucose metabolism (how much energy the brain is using), and by the late stage, it is severely decreased. This is likely due to the severe, progressive neurodegeneration that occurs in AD.