24 X-ray images aren\'t only used with human subjects but also, for example, on

Question

24 X-ray images aren't only used with human subjects but also, for example, on insects and flowers. In 2003, a team of researchers at Argonne National Laboratory used x-ray imagery to find for the first time that insects, although they do not have lungs, do not necessarily breathe completely passively, as had been believed pre- viously; many insects rapidly compress and expand their trachea, head, and thorax in order to force air in and out of their bodies. One difference between x-raying a human and an insect is that if a medical x-ray machine was used on an insect, virtually 100% of the x-rays would pass through its body, and there would be no contrast in the image produced. Less penetrating x-rays of lower energies have to be used. For comparison, a typical human body mass is about 70 kg, whereas a typical ant is about 10 mg. Estimate the ratio of the thicknesses of tissue that must be penetrated by x-rays in one case compared to the other

Explanation / Answer

The ratio of the organ-to-exit surface exposure is determined by the penetration of the tissue.

   The penetration of the tissue between the point of interest and the exit surface is determined by the distance between the two points, the type of tissue (lung, soft tissue, bone, etc. ), and the effective energy of the x-ray beam. For a given patient, the only factor that can be varied to alter penetration is the effective energy. This, in turn, depends on waveform, KV, and filtration. Generally speaking, three-phase, or constant potential, waveforms produce more penetrating radiation, which reduces patient exposure. It was shown earlier that adding filters to an x-ray beam selectively removes the low-energy, low-penetrating photons. This produces an x-ray beam with a greater penetrating ability. Filtration of an x-ray beam is especially significant in reducing the exposure to points near the entrance surface. Patient exposure is generally reduced by increasing KV. The problem is that the higher KV values give lower image contrast because of object penetration and more scattered radiation.

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