My 3 month old needs chest x rays?

I have a almost 3 month old and I took him to the doctor and she told me that he has bronchitis. He's had this horrible horrible cough and he'll cough for minutes and sometimes it's like he's not breathing anymore, and he has been really wheezy. Well he's not getting any better and I talked to her again to today and now she wants him to go in for chest x rays. I am a little apprehensive about it and am wondering if it is safe. Could chest x rays be harmful to him?