Hogan,

This is actually a refinement on an older well used principle. For a number of years, certain ports in the US have had the ability to scan incoming small craft, containers etc.
The DEA in particular has made use of it.

The chief difference here is, rather than having a receptor screen on the back side of the object, the device picks up the back scattering photons, and magnetically focuses them and electronically refines the same into a coherent image. Picture the scanner at the airport, it will be a little rougher image than that, but the same principle.

The principles of Compton scattering and photoelectric scattering are the root of it, and physically have been plausible for a long time just waiting on processing speed to catch up to the physics.

Least anyone get any bright ideas, it's a long long long way from being sensitive enough to perform quality inspections. Laser assisted ultrasonics will beat it to the punch for real time flaw formation monitoring.

Regards,
Gerald