@neverendingjourney is right.
I get stopped every time and finally got the guts to ask a nice security guard, and he said the scanner checks for discrepancies in density. I travel fairly often and never had an issue, but a while back I had hernia surgery. Not only did I have that mesh put in, but since the muscles were cut, there is now obvious scar tissue which is a lot thicker.
Without fail EVERY time I go through the scanners a red blob appears on the screen exactly where my surgery was.
I\'m no expert, but it would make sense, as
PMMA is a foreign and dense body that it would show up on the scan just as my scar tissue/mesh implant does. Obviously they aren\'t the same, but I don\'t think a robotic scanner is smart enough to tell the difference. If it\'s checking for density, it would make sense that some of the
PMMA (or collagen) triggers the scanner.