Here is what the TSA says about radiation strength on their blog (http://blog.tsa.gov/2009/11/response-to-oops-backscatter-x-ray.html):
The Transportation Security Administration (TSA) has assessed multiple types of AIT systems including X-ray backscatter and millimeter wave. Both offer safe and effective whole body screening for weapons and explosives concealed on a person’s body. Backscatter X-ray technology uses X-rays that penetrate clothing, but not skin, to create an image.
Here is a picture from their machine:
Can you tell me what's between that guy's knees and his ankles? Remember, TSA says the rays don't penetrate the skin, so what could those shadows be?
Okay, let's try another:
Hmm. What's this from knees to ankles? Sports brace? Shin guard? Good thing it's not X-rays penetrating the body and showing us bones. We can trust the TSA on that:
Backscatter X-ray technology uses X-rays that penetrate clothing, but not skin, to create an image.
And wow, what a scary scary man. He's definitely packing.