PET stands for Positron Emission Tomography. In a PET Scan, a physician injects a patient with a liquid called a contrast agent with a very low level of radioactive content. After a waiting period and a series of chemical events in body tissues, the contrast agent turns into a photon or light particle that can be seen and translated into an image by the scanner.
The advantages of doing a PET are
High sensitivity: PET scans can pick up cancer sites that other imaging tests like CT or MRI sometimes cannot. Differentiating tumor from fibrosis: Some cancer treatments, especially radiation therapy, can cause tumor areas to fibrose. Conventional imaging techniques cannot differentiate tumor from fibrosis, whereas PET can.