What is positron emission tomography (PET)

A sophisticated functional imaging study that uses radioactive “tags” in combination with computed tomography to create three-dimensional pictures of internal organs and structures. For a PET scan, the person receives an injection of a solution containing radioactive isotopes small particles that the tissues to be studied will “uptake” or absorb more than the surrounding tissues will. In most studies in people with Parkinson’s, a radioactively labeled form of dopamine, called fluorodopa, is used. They highlight the tissues that absorb them, making those tissues detectable by radiation detectors. An array of detectors provides data that a computer assembles into two- or three-dimensional pictures.

PET allows doctors to visualize structures deep inside the brain such as the basal ganglia and brainstem and provides as much information about what it does not show as about what it does. Problems such as lesions (tumors) or damage due to stroke show up on a PET scan. This capacity helps to diagnose conditions other than Parkinson’s. The absence of cells and tissue that should be present also becomes apparent with PET scanning. Doctors often can identify areas of atrophy (tissue loss) in the substantia nigra where dopaminErgic neurons have died, for example, in middle to late stages of Parkinson’s. Although this does not constitute a conclusive diagnosis of Parkinson’s, it can help doctors mark the progression of the disease and make some treatment choices. Atrophy is also apparent in other nEurodEgEnErativE conditions such as CREUTZFELDT-JAKOB DISEASE (CJD).

The equipment necessary to conduct PET scanning is very sophisticated and very expensive, including a device called a cyclotron to prepare the radioactive isotopes, which typically must be used within minutes of their creation. Typically only major research centers have the necessary equipment and personnel to do PET scans. Some large hospitals have the less costly single photon emission computed tomography (SPECT), which provides somewhat less precise but similar imaging.