HSS 532467
This is a good example of “scaling”, signal measurements on MR are not based on a physical standard (like HU are for CT) The lowest signal air is black and the highest is white and everything inbetween is diveded accordingly. When gado is given, the contrast become the highest signal, so the cyst may look artificially lower in attenuation.
http://www.ajnr.org/content/12/5/875.abstract?sid=45ddc144-9f59-4935-9b02-40779cd52a55
The Commentary that follows pp 881-883 gives an explanation of “scaling”.
Q: How can one eliminate this effect?
A: Add something to both the pre and post contrast studies so that the scanner scales to the same bright standard (e.g. a phantom composed of copper sulfate solution in a plastic tube)