Prior to being scanned, patients are injected with a tiny amount of a safe, short-lived radioactive isotope: fluorine-18 fluorodeoxyglucose. This enables the scan to identify points of abnormally high concentration or absorption of glucose, which are likely locations of cancerous cells.
正子掃描就是利用此一特點，在受測者身上注入微量且尚無安全疑慮的放射性元素與「氟 - 18 去氧葡萄糖」結合的混和藥劑後，可以定位出人體內葡萄糖攝取異常、過度集中的部位，藉此找出癌細胞的可能所在。