![]() If uncorrected during CT reconstruction, these differences in the expected attenuation profile lead to a perceived peripheral dense appearance. ![]() As the beam becomes harder and passes a higher mean beam energy, the lower attenuation coefficient means the CT number goes down for longer paths. Cupping artifactīeam hardening will cause the middle of the image to decrease in value, not increase edge value, as the lower energy photons preferentially get attenuated over longer path lengths. It is the result of the polychromatic x-ray being ‘hardened’ at different rates according to rotational position of the tube/detector. Streaking may also occur along the long axis of a single high attenuation object. Streaking artifact appears as multiple dark streaking bands positioned between two dense objects, for example at the posterior fossa. CT beam hardening artifact has two distinct manifestations, streaking (dark bands) and cupping artifacts. bone or iodinated contrast) may result in characteristic artifacts. In CT, beam hardening from a very dense target (e.g. This same phenomenon is exploited in radiography and CT, by use of metal filters in order to "pre-harden" the x-ray spectrum and minimize low energy photons (see filters) 2. The effect is conceptually similar to a high-pass filter, in that only higher energy photons are left to contribute to the beam and thus the mean beam energy is increased ("hardened") 1. Beam hardening is the phenomenon that occurs when an x-ray beam comprised of polychromatic energies passes through an object, resulting in selective attenuation of lower energy photons.
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