We use the fresnel shader in all sorts of channels to get the x-ray look. You can really nail it down for a still but if its an animation, keep in mind that as the angle objects change so too will the density of the edge “fog” created by the fresnel shader. There are ways around this with expresso determining what things are pointing at and adjusting the grad used in the fresnel channel.
For the x-ray look, apply the fresnel (usually in the transparency channel) and reverse the nodes in the gradation. Then give the luminence channel the full colour of what you want the tint to be.