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A Matter of Contrast!
First of all, notice the ribs. The lowest pair is the 12th. Observe the bodies of vertebrae. They are made of a thin shell of solid bone and spongy bone inside. The oval outlines (one shown by the blue arrow) are joints between the articular processes. The red arrow shows a spine. Remember that the spine of a vertebra is at a lower level than its body (check your knowledge of lumbar vertebrae!) Again, the lighter bands between the bodies of vertebrae are the intervertebral discs, which appear somewhat lighter because of the overlap of the neural arches.
And what are the dark blobs – three of them are shown by white arrows. These are bubbles of gas in the colon. Ordinarily, the colon is invisible because it blends with the other viscera in an X-ray image. Gas in the colon creates contrast. But then, we cannot depend on such ‘natural’ contrast to see hollow organs.
We have artificial means of introducing contrast for visualising certain organs. Let us see one more example of ‘natural’ contrast before we go to artificial contrast.
By the way, the white bands in the previous picture were psoas major muscles!
Key Point :
Contrast once more!