What is a pet scan, and when would a doctor use it instead of a CT or an mri?

PET SCAN. Pet scan is diagnostic test used most of the time to help in the cases of seizures. Pet: positron emission test, depends on the function of the neurons in utilizing glucose, the actve neurons which are active and firing elecrical discharges and causing seizures, pet scan can help to localize the epileptic focus as preparation of epilepsy surgery.
Anatomy vs Physiolog. Mri and ct look at the structure of the body, the anatomy, and the way diseases change or distort it. Pet looks at the physiology, or how the body uses, or metabolizes something. For pet, the most common metabolism pathway looked at is how glucose is used. A low dose ct is often acquired at the same time as the pet (as in pet/ct scan), to correlate the pet findings with the ct anatomy.
Cancer Diagnosis. A pet scan is most commonly done to look for evidence for cancer. Cancer cells are more rapidly growing cells than non-cancer cells and take up the pet tracer chemical showing up as dark spots on the scan.