What type of half-lives fo isotopes used in PET scans have?

Hi :) a PET scanner works by "seeing" radiation. A patient is injected with a contrast agent that contains a radioactive component that will continually give out gamma radiation (not high enough doses to hurt you), the PET scanner detects this gamma radiation and builds up an image of where it has pooled in your body. Because this contrast agent isn't designed to treat tumours, it is beneficial for the agent to leave the body quickly so that the person isn't irradiated longer than they need to be. Therefore, the contrast agent needs to have a half-life long enough to spread around the body and then be imaged, and short enough to leave the body sooner rather than later. A good half-life for this type of isotope would therefore be only a few hours long. (For exmaple, FDG-PET is a radioactive contrast agent used in PET scans and it has a half life of only 110 minutes)