The only other obstacle to the wider use of PET-CT is the difficulty and cost of producing and transporting the radiopharmaceuticals used for PET imaging, which are usually extremely short-lived. For instance, the half-life of radioactive fluorine-18 (18F) used to trace glucose metabolism (using fluorodeoxyglucose, FDG) is only two hours.
https://en.wikipedia.org/wiki/PET-CT