Short-lived radioactive isotopes are used in PET to minimize exposure to nuclear radiation and provide information with acceptable exposure levels.
The slides of my talk on PET are published here. They attempt to introduce the complex subject of nuclear radiation and its detection in an accessible way. The efficacy of PET in detection of various ailments is demonstrated by looking at some case studies. (unfortunately some of the information about the websites is lost but I implicitly acknowledge the pictures that I have used)