I heard body scanners at airports emit high levels of radiation. is this true? if so can i choose not to go through it?

No and yes: they claimed that the amount of radiation is not more than a simple x ray. but if you are frequent flyer or a flight attendant and there is a possibility that you might get exposed to it on a daily basis, then i will think twice before i do that. and to answer your second question, the answer is yes every passenger has the right to refuse the exposure and go through a manual search.

Pat down: i personally am not sure I believe the claims about safety. Always ask for a pat down. This does take longer, so plan your schedule to allow for the extra 15 or so mins this will take.