Final answer:
The cupping artifact in x-ray imaging is caused by the attenuation of low energy photons by the tissues of the body. This differential attenuation creates an artifact where the edges look brighter than the center. It's most likely due to uneven penetration of the x-ray beam through various tissue densities.
Step-by-step explanation:
The cause of the cupping artifact is related to the attenuation characteristics of x-rays as they pass through different tissues in the body. As x-ray energy increases, the Compton effect becomes more important in the attenuation of x-rays, which involves the scattering of x-rays from outer electron shells of atoms, imparting kinetic energy to ejected electrons while the x-rays lose energy themselves. Cupping artifacts occur when there is uneven attenuation of the x-ray beam, often due to the shape of the body part being imaged or variations in tissue density. The central tissues may not be fully penetrated by the x-ray beam, and the tissues also attenuate low energy photons. This differential attenuation can create a characteristic artifact on the radiograph where the edges appear brighter than the center, resembling a cup or bowl shape. The correct answer to the question is: 'b. the tissues of the body attenuate low energy photons', which is supported by the principles of x-ray attenuation. Furthermore, the depth of penetration by x-rays is related to the density of the material as well as the energy of the photon. High-energy photons are able to penetrate denser materials, and as such, are more likely to pass through and not be absorbed as heavily, which may contribute to the cupping effect if there is a discrepancy in energy absorption across different tissue densities. However, chemical composition, characterized by atomic number Z, is not as important in this context.