Both varieties, backscatter and MMW, take their views from the front and back plane of the subject. Even on the MMW with its fancy swing around arms, only goes to approximately 45-degrees past the subject. Watch any of these machines in motion. The sides are not captured, and therefore cannot be analyzed.
I don't "think" it to be true, I work with imaging every day. I know it to be scientific fact.
Again, Mike, you may understand tech, you clearly do NOT understand imaging.
Imaging does not work in the way you suggest.
Jon is correct. I work with imaging. An object on the side of the subject will not bounce the x-rays back to the reader in the way human flesh will. Any item on the side of a body is invisible to these machines.