Structured noise in computed tomography: effects of periodic error sources

Area of Science:

• Medical Imaging
• Computational Physics
• Image Processing

Background:

• Cyclic projection errors, such as x-ray intensity fluctuations, can introduce artifacts in computed tomography (CT) images.
• Understanding the nature and origin of these artifacts is crucial for accurate image reconstruction.

Purpose of the Study:

• To derive and verify the artifact generated by cyclic projection errors in CT images using computer simulations.
• To analyze the characteristics of these artifacts, including their dependence on Bessel functions, radial arguments, and angular modulation.

Main Methods:

• Computer simulations were employed to derive and verify the artifact caused by cyclic projection errors.
• The study analyzed the mathematical description of the artifact using Bessel functions and their properties.
• Simulations were performed for various CT scanner generations (first, third, and fourth) to assess the impact of sampling.

Main Results:

• The artifact is described by Bessel functions, appearing as a zero-value region up to a certain radius.
• In fourth-generation scanners, a fundamental artifact occurs at approximately 39 degrees detector fan angle, independent of error frequency.
• Sampling effects introduce multiple superimposed artifacts, with radii dependent on error frequency, but the fundamental artifact is independent.

Conclusions:

• The fundamental artifact in fourth-generation CT scanners is visible only with detector fan angles exceeding approximately 39 degrees.
• Sampling effects can lead to numerous artifacts, but judicious selection of sampling parameters can effectively eliminate them.
• The study provides insights into artifact reduction strategies in CT imaging by understanding the role of cyclic errors and sampling.