Oxygen-18 is a stable isotope of Oxygen and is labelled an environmental isotope. This isotope is also used in PET scans. Oxygen-18 is used to produce fludeoxyglucose which is injected into a patient as a marker to be shown on PET IMAGING.

Oxygen-15 is a Radioisotope of Oxygen used most frequently in PET Imaging. It has 8 protons, 7 neutrons and 8 electrons.