Question

Why radiologists do not take direct x-ray photographs of intestine?

Answer 1

The reason is one of physics, not radiation dose. Plain x-rays, as opposed to CT scans, will only differentiate 4 types of tissue; air, bone, fat and 'meat'. By meat I mean all tissues that are not fat or bone. Blood, muscle, brain, nerves, heart etc are all of the same intrinsic radiographic density. For some structure to be visible on a plain x-ray film it must be adjacent to a region of different radiographic density. The stomach is mostly smooth muscle (meat), surrounded by peritoneum (meat), so it will not be visible. The only exception is that most people have some air in their stomach and the air/fluid level will show if the person is standing, but not if they are lying down when the x-ray was taken. Those conditions that alter the amount of air in the bowel, such as mechanical obstruction, will show bloated bowel but usually only small pockets of bowel gas (air) will be visible.

So basically the amount of useful information yielded is minimal and the radiation dose, although tiny, is not justified.