Originally Posted by janetdoe

It only takes some basic physics knowledge to determine the penetration depth of X-rays into soft tissue and bone.


From a prior lengthy discussion: The x-rays are in the 20-30 keV range.

High-energy medical x-rays mostly pass through the body, and end up hitting the detector or film behind you. Backscatter works differently. The x-rays hit you and some percentage bounce backwards to hit the detector in front of you.

This means that the bones that you see on the pictures do NOT indicate the total depth of x-ray penetration. The things you see in the picture are things that the X-rays hit and still have at least 50% of their original energy to reflect back to the detector. As a rough rule of thumb, at least 50% of the initial x-rays penetrate to the deepest levels you see in the image. 25% of the x-rays make it to double that depth. 12.5% make it to triple that depth... and on and on.

The majority of the x-rays will penetrate the body, but they will not have enough energy to escape (backscatter). Instead, they are mostly dissipated within your tissues, generally through the photoelectric effect or Compton scattering. Both of these mechanisms involve knocking an electron out of an atom, i.e. they are ionizing.

There is general lack of knowledge on the biological impact of these low energy x-rays, but preliminary findings seem to indicate that a dose of low-energy x-rays can be 2x or 4x as damaging as the same dose of high-energy x-rays or gamma rays. (Discussed in previous threads.)