Meaning
Geometric errors arise when X-ray beams diverge from a point source and pass through an object at steep angles away from the central axis. This cone-beam distortion leads to a stretching or blurring of features in the reconstructed image, particularly at the top and bottom edges of the field of view. The effect becomes more pronounced as the cone angle increases or as the object moves further from the center of rotation.
Correcting these errors requires specialized algorithms or the use of a more restricted beam geometry.
Divergence Geometry
Mathematical models for reconstruction often assume that the X-rays travel in parallel paths, which is only an approximation for laboratory sources. When cone-beam distortion occurs, the path length through the material varies depending on the vertical position of the detector pixel. This variation creates a mismatch between the expected projection and the actual data collected.
Reconstruction Artifact
Distant features in the scanned volume may appear to have shadows or artificial streaks that do not exist in reality. These artifacts resulting from cone-beam distortion can hide small cracks or pores in a structural component. Designers must account for this when placing parts in the scanner.
Angular Variance
Reducing the height of the scan or increasing the distance between the source and the object can minimize the impact. A small tilt in the detector can also introduce similar errors that exacerbate cone-beam distortion if the system is not perfectly aligned. High-precision manufacturing demands that these geometric offsets be characterized during the initial system setup.
