The BBC has an interesting story about the use intense x-rays at the ESRF in France to image the hidden second leg of a fossil Eupodophis descouensi:
In a process known as computed laminography, many hundreds of 2D images are produced which can be woven, with the aid of a smart algorithm, into a detailed 3D picture.
The finished product, which can be spun around on a computer screen, reveals details that will be measured in just millionths of a metre.
Here are the results:
The top part of the picture shows the visible leg and the bottom shows the hidden leg.
A video of the fossil can be found here