Reverse cupping–like appearance on CT: A beam hardening–related phenomenon with phantom correlation

The interaction of polychromatic X-ray beam with highly attenuating material leads to beam hardening which may manifest as “cupping” artifact, where the central part of the image appears relatively hypodense as compared to the periphery, a phenomenon arising out of the monochromatic beam assumption of the reconstruction algorithms. The presence of a central hyperattenuating structure with a surrounding homogeneous medium and a sufficient peripheral-to-central distance may result in a “reverse cupping-like” variant of the beam-hardening artifact, in which the central part of the image appears relatively hyperdense compared to the peripheral part. In this report, we describe a “reverse cupping-like” artifact observed in CT scans of the abdomens of 2 patients and reproduce the findings in a phantom experiment. We attempt to unearth the physical underpinnings of this phenomenon.