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What is a PET scan?
Positron emission tomography (PET) uses a small amount of a radioactive substance, called a tracer, to measure specific brain activity or to detect abnormal accumulations of certain proteins. Different types of PET scans use different tracers. PET is frequently used in dementia research but less frequently in clinical settings.

Where will the scan take place?
The UCSD Alzheimer's Disease Research Center currently sends participants to the Radiation Oncology PET/CT center on the UCSD medical campus and to the California Protons Cancer Therapy Center in Miramar for PET scans. The exact procedure site will depend on the study protocol.

What happens during the procedure?
The exact steps can vary depending on the protocol and type of scan. Typically, the person having a PET scan receives an injection of a radioactive tracer into a vein in the arm. The tracer looks and feels like cool water upon injection. The person then waits for 50 minutes to allow the tracer to circulate into the brain. When time is up, they are moved by a technician into the scanner, which consists of a cushioned table and a donut shaped machine. The PET scanner takes pictures of the brain for about 20 minutes, revealing regions of normal and abnormal chemical activity. The person having the PET must keep his or her head still for the duration of the scan. A PET scan is much quieter than MRI, and looks like a CT scanner. The entire process, including the injection, waiting time, and scan takes a little over an hour.

What if I need to cancel or reschedule my PET scan?
If you cannot make it to your scheduled PET scan, please inform the study coordinator at least 24 hours before your assigned check-in time. Each dose of radioactive tracer must be prepared for every participant visit ahead of time. Due to the short, radioactive half-life of the tracers, we cannot recycle or reuse doses at a future time. Please be sure to arrive at your PET scan appointment on time to ensure that the dose of tracer is not wasted.

Is the radiation exposure safe?
The amount of radiation exposure during a PET scan is relatively low. However, you may be discouraged from participating in a PET scan study if you have received many x-rays, imaging scans, or radiation therapy (e.g. for cancer treatment) in the past.

What does it show?
Fluorodeoxyglucose (FDG) PET scans measure glucose (energy) use in the brain. Studies show that people with dementia often have abnormal patterns of decreased glucose use in specific areas of the brain. An FDG PET scan can show a pattern that may support a diagnosis of a specific cause of dementia.
Amyloid PET scans measure abnormal deposits of a protein called beta-amyloid. Higher levels of beta-amyloid are consistent with the presence of amyloid plaques, a hallmark of Alzheimer's disease.
Tau PET scans detect abnormal accumulations of a protein, tau, which forms tangles in nerve cells in Alzheimer's disease and many other dementias.

Why are PET scans important for research?
Amyloid and tau PET scans are used to determine which individuals may be at greatest risk for developing Alzheimer's disease, to identify clinical trial participants, and to assess the impact of experimental drugs designed to affect amyloid or tau pathways.

Will I receive the results of my PET scan?
We currently do not disclose the results of PET scans performed for research, although this may change in the near future. Ask your study coordinator for more information regarding the disclosure guidelines for your specific protocol.