Why do I have to fast before a PET scan?

Why do I have to fast before a PET scan?

Hossein Jadvar (Doctor) gives expert video advice on: How does a PET scan work?; How should I prepare for a PET scan?; Why do I have to fast before a PET scan? and more...

The reason that a patient needs to fast for a FDG PET (Positron Emission Tomography) scan is because FDG is a glucose analog. So, when the patient eats before a procedure, the glucose level in the blood is going to interfere with the uptake of the FDG, for example, tumor. So to make sure that the tumor receives the most amount of FDG so that we can see it well on our images, we ask the patient to fast so that there's no competition with glucose in the blood.