1. PET scan < The patient lies in the PET scanning machine. First, the chest is scanned for a few minutes to determine how much radiation the tissues of the chest absorb. A radioactive sugar called fluorodeoxyglucose (FDG) is then injected through a catheter (thin plastic tube placed in a vein) and the heart is scanned for about 45 minutes to measure the amount of FDG in the blood inside the heart. The head is then scanned for about 20 minutes to measure FDG in the brain. This measurement tells how much sugar the brain uses for energy. The procedure requires insertion of two or three catheters. A special facemask may be molded to the patient's head to help hold the head still during the scanning.