What To Expect When You Have a PET Scan 

Before your PET scan, your doctor may recommend you fast for at least 4 to 6 hours and drink plenty of water. 

During your PET scan, a radiologist will inject your bloodstream with a small amount of dye charged with a radioactive tracer that travels throughout your body. Depending on what part of your body is being examined, you may also swallow or inhale the tracer. 

By watching how the dye interacts with certain parts of your body, your doctor can identify where a disease is located and whether or not it has spread.  

PET scans are commonly used to detect and trace dementia, cancer and epilepsy.