It just occured to me that Brian Redmond, ( of recent fame on Passfire for beating 9 felony counts in Oregon ) is a radiography technician, does X-rays for a living. I will ask him if he has ever tried to view PVC on standard X-rays. Maybe he can take a piece in and do a test shot or something. I would like to put the myth to rest, one way or the other.
Yeah, stick a piece of pipe through a piece of pork or something...
I am pretty confident all the fillers in common PVC water pipe would make it fairly radiopaque. Soft plasticised PVC flex tubing would probably be quite radiolucent, but the difference in radiopacity to the surrounding tissue should be visible if there is sufficient contrast.
I'd imagine a CT would resolve even objects of very near radiopacity because it would more easily visalise the disruption to the surrounding tissue, shrapnel doesn't just magically teleport into your body, there will be a path of damage and things pushed around where it stopped. An MRI would definately have no problems seeing the difference between artifical polymers and human tissue.