Image Artifact
Image reconstruction error in computed tomography presents as a non-uniformity where the center of a uniform object appears darker than the edges. A cupping artifact typically arises from beam hardening when lower energy photons are absorbed more readily by the material than higher energy ones. This phenomenon results in an artificially low attenuation measurement in the middle of a dense PCB assembly.
Causal Mechanism
Differential absorption across a polychromatic X-ray spectrum produces an inconsistent effective energy for the beam as it traverses the target. Because the center of a cylindrical or thick component filters the radiation more heavily, the detector receives a hardened spectrum that registers lower absorption than expected. Softening of the beam at the periphery remains less pronounced, which creates a concave profile in the reconstructed cross-section.
Mathematical models often struggle to compensate for this non-linear energy shift without prior knowledge of the material composition. The result is a density gradient that does not exist in the physical part.
Error Correction
Pre-filtration using thin sheets of copper or aluminum removes low energy photons before they reach the circuit board. Numerical algorithms also apply correction curves to the raw projection data. These algorithms minimize the visual impact of cupping artifact in the final dataset.
