PET scans use a substance called 18-Fluorodeoxyglucose, which is an isotope of Fluorine bonded to glucose. This isotope undergoes a nuclear decay process called positron emission. A positron is the antimatter counterpart of an electron, so when the two meet they emit two gamma ray photons at 180 degrees to each other. Since the isotope produces the positron in the patient, there is no need for containment systems. However they would be useful for capturing the positrons produced by the substance before injection into the patient, simply because antimatter is so hard to produce.
The containment system is not useful for PET, but would be extremely useful for space exploration or for making complex collisions in particle accelerators.