While I am not an expert in this field, I think we may be confusing two different technologies. One is an X-ray machine that images using backscatter of the X-rays. The other employs deep infrared (terahz), which is submillimeter wavelength radiation. The former uses ionizing radiation which has, indeed, the possibility to do damage to tissue. Deep infrared radiation is not dangerous in the same way. It is my guess that the X-ray machine is what the TSA is using in the majority of cases, and I don't like that. It is more properly described as the nude-o-scope. While I admit to being somewhat lazy in looking all of this stuff up, maybe someone with real expertise in the field could enlighten us as to what is being used and where, and how we can recognize which is which in our local airport...