For a PET diagnostic imaging is used 18F with an activity of 5,2 mCi and a T1/2 of 110 min.. How much fluorine 18 is there at the beginning of the exam?

Question

Those are the information that i know, it's a problem that i try to resolve, but i arrived to a very low quantity of 18F (like 10^-9 g i don't remember the exact number), i don't know why, but it's impossible (i found 5,2 mCi and T1/2 on the web)