<human>:  How does a Positron emission tomography (PET) scan work?
<bot>: A PET scan is a nuclear medicine imaging technique. It uses radioactive tracers to image the body. The tracers are injected into the body, and the PET scanner then measures the amount of radiation emitted from the tracer. The PET scanner can also measure the amount of radiation emitted from the tracer in different parts of the body. This information can be used to produce a 3D image of the body.