Beam-hardening artifacts are caused by what phenomenon?

Beam-hardening artifacts occur due to the preferential absorption of low-energy x-ray photons as the x-ray beam passes through denser tissues or materials. In computed tomography, the x-ray beam consists of a spectrum of photon energies. As it moves through a medium, lower-energy photons are absorbed more readily than higher-energy photons. This means that the remaining x-ray photons, which are primarily of higher energy, create a beam that is "harder," or more penetrative.

As a result of this process, the images produced can exhibit areas that appear darker or cause inaccuracies in tissue characterization, leading to streaking or banding artifacts within the CT images. Understanding this phenomenon is crucial for technicians, as it highlights the importance of optimizing parameters and being aware of the potential for such artifacts in areas with high-density materials or structures.

Other options, while related to imaging, do not directly cause beam-hardening artifacts. Random photon detection pertains to statistical variations in photon counts, increased exposure time relates to radiation dose considerations, and movement during imaging typically results in motion artifacts—not beam hardening.