Positively Radiant

My sister and I were talking about flying and airports and I expressed concern about the amount of radiation that you get when you go through the body scans at the security checkpoints. I know you're only in that box for three seconds, but how much radiation is passing through your body during that time? As my sister noted, at least when you get zapped at the dentist's office when you have x-rays taken you get a lead apron to put on. At the airport you don't get anything. I know you can opt out of going through the airport's toxic box, but then you have to get felt up by the TSA. I don't know which option is worse.