Positron Emission Tomography (PET) Brain Scans for Alzheimer's Disease

Christine Kennard Health Pro
  • Positron Emission Tomography (PET) scans, are a type of nuclear medicine imaging that can be used to map the brain. The scan uses very small amounts of radioactive material, usually injected, to diagnose and determine the severity of a disease and exclude others. Most PET scans are performed on instruments that are combined PET and Computed Tomography (CT) scanners. This allows the information from two different exams to be correlated and interpreted on one image.


    How is a PET scan used in Alzheimer's?

    This so-called functional test can be used in Alzheimer's to:

    • Show the physiology and chemistry of the brain that can help towards a diagnosis, and into research of the causes and disease process of Alzheimer's. It can measure important body functions, such as blood flow, oxygen use, and sugar (glucose) metabolism, to help doctors evaluate how well the brain is functioning.
    • PET scans are used to help make a diagnosis of Alzheimer's as well as exclude other causes with similar symptoms such as vascular dementia, seizures, and other nervous system disorders. It can also exclude cancer.
    • The scan can map the normal brain. This may be helpful at a later date to compare and contrast changes.
    • PET scans can help spot brain plaque that is believed to be a sign of Alzheimer's, although high levels of plaque is also seen in other neurological diseases and it also not necessarily present in all cases of Alzheimer's

    A PET scan can be used for many types of intricate tests which are now giving us huge insights into what is happening in the brain of someone with Alzheimer's. A recent example is a study into predicting who will suffer cognitive decline over time.

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    What Happens During the Test?

    A PET scanner is a large machine with a round shaped hole in the middle. Within this machine are multiple rings of detectors that record the emission of energy from the radiotracer that is in your body from the injection. All metal objects including jewelry, eyeglasses, dentures and hairpins that may affect the CT images are removed prior to your exam, as are hearing aids and removable dental work.


    The PET works by tracing the small amount of energy in the form of gamma rays that accumulates in the brain. A gamma camera, PET scanner, or probe detects this energy and with the help of a computer. This creates pictures of the structure and function of the organ. Nuclear medicine imaging shows areas of greater intensity, called "hot spots," that indicate where large amounts of the radiotracer have accumulated and where there is a high level of chemical or metabolic activity. Less intense areas, or "cold spots," indicate a smaller concentration of radiotracer and less chemical activity.


    Does a PET Scan Hurt?

    No a PET scan does not hurt. The radiotracer that can be swallowed or inhaled is most often injected into a vein in the arm for brain scans. You will feel a small prick and you may feel a slight coldness as it moves up your arm. Some people can feel claustrophobic as the table moves into the hole in the middle of the PET machine. If you inform the staff in advance a mild sedative can be given. For people with Alzheimer's who may be confused or more uncooperative a mild sedative can help minimize any feeling of discomfort and can help them relax.

  • The imaging process will not cause any pain itself but keeping still while lying on a hard surface may cause discomfort. 

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    How Long Does PET Scan Take?

    The PET scan itself takes about 30 minutes, if a CT scan is combined this only takes 2 minutes. Sometimes the scan may take longer depending on the number of additional tests and the tracer being used. It may take up to 3 hours. The radiotracer may take time to get through the so called blood brain barrier prior to the test.


    What Happens to the Scan Results

    The PET scans will be interpreted by a radiologist or physician specialised and trained in nuclear medicine. Their report of the results will be sent to your referring specialist.


    Is a PET Scan Safe?

    No long term adverse side effects from PET scans are known.

    • The radio tracer used contains radioactive material in very low doses and acceptable for diagnostic exams. The potential benefits are outweighed by the diagnostic and treatment potential offered by the technology.
    • Allergic reactions to radiopharmaceuticals are extremely rare and are usually mild. Redness at the source of the injection of the tracer may occur but disappear quickly.
    • Pregnancy or breastfeeding, not usually an issue in Alzheimer's investigations, should be reported to your referring doctor or specialist.
    • The resolution of structures of the body with nuclear medicine may not be as high as with other imaging techniques, such as CT or MRI. False reading can result if chemicals balances in the body are not normal.
    • A person who is very obese may not fit into the opening of a conventional PET/CT unit.
    • Because the radioactive substance decays quickly and is effective for only a short period of time, it is important for the patient to be on time for the appointment and to receive the radioactive material at the scheduled time


Published On: March 08, 2012