This is probably one of the toughest questions that I've seen,
I do believe I have an answer for you that you can accept. Mamograms require compression of the breasts, so it's not like a dental x-ray or a chest x-ray. Detection isn't necessarily looking for masses by also changes in structure. You can see some of those changes in this paper:
http://www.jatit.org/volumes/researc...6/7Vol5No6.pdf
Adding highly compressed fabric against the breasts is like putting a screen in front of the breast and fine features would disapear. Take a look at your lawn through a screen vs. a window. If yu put any fabric at all in front of a breast, it would still crease, even if it was 500 threads per inch.
Here is a technique that doesn;t require that requires less compression and can detect cancers as small as 1.5 to 2 mm.
Remember that these images will also be compared with one another at a later date and you may have a physical exam as well.
I can't really provide any direct references.