What causes bright areas on the edges of a CT image?

Bright areas on the edges of a CT image, often referred to as beam hardening artifacts, are primarily caused by the differing energy levels of the X-ray photons as they pass through varying densities of tissue. In CT imaging, when X-rays penetrate denser materials (such as bone), lower-energy photons are more likely to be absorbed. This phenomenon results in a greater proportion of higher-energy photons contributing to the image. Consequently, the periphery of structures, which may contain high-density materials, can appear artificially bright, creating misleading images at the edges of these regions.

Understanding beam hardening is crucial for radiologists and technologists as it helps in evaluating image quality and understanding potential discrepancies in diagnoses. Managing this artifact might involve implementing calibration adjustments or using techniques that smooth the imaging data to minimize its impact.