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Terry Hopping wrote: > > Can anyone tell me what can be detected on a PET scan and of what value it > is ? PET is the acronym for Positron-Emission Tomography. "Tomography" is the technique of forming a 3-dimensional picture of something without having to destroy it, so it's especially useful to visualize the inside of something that is both complex and valuable, such as a living brain. The "3-dimensional" picture is usually presented as a series of slices or cross-sections, just as one would see if the object (say, a brain) were actually sliced up like salami. Numerous tomography techniques, such as CAT scan, MRI, MRS, SPECT, and PET, all use the same mechanical principle and differ only in the kind of signal that is recorded. In the CAT scan, for example, the signal is just an x-ray like in your dentist's office. The mechanical principle requires that the recording device rotates around each point of the object so it "sees" that point from all directions, and the process is repeated for every point in the object. "Positron-Emission" means that a radioactive chemical, injected beforehand, emits penetrating particles called positrons, that are detected by the recording device mentioned above. The injected chemical used for research in Parkinson's Disease is one that acts on brain cells just like dopamine, except that the positrons tell how much there is at any one point. In this way, positron-emission tomography (PET) can show in 3 dimensions just how well the dopamine-related parts of the brain are working, either in a PD patient or a healthy person. Furthermore, PET can do this while the subject is performing a task, such as tapping a finger or walking on a treadmill, so the researchers can see just which part of the brain is doing what, and the effects of PD. There are tons of scientific reports about PET used for PD research, many of which are reviewed in the PIE archives; happy hunting! Cheers, Joe -- J. R. Bruman (818) 789-3694 3527 Cody Road Sherman Oaks, CA 91403-5013