Warhol: high contrast

I found this painting in the Andy Warhol exhibition at the Whitworth Gallery in Manchester. I have been teaching about contrast media used in medical physics. X-rays are attenuated by high density materials, dependent on atomic number. Calcium is especially good at attenuating X-rays so bones block X-rays but soft tissue containing water, mainly hydrogen and oxygen, mostly let X-rays through. There is a big contrast between the two media and you get a clear image of the bones. X-rays of organ systems like the digestive system fare less well because the muscles attenuate as badly as the contents. So patients are given a barium meal which occupies the space inside the bowels which attenuates a lot so giving high contrast with the muscle walls, The barium meal is called  a contrast medium.