Tolerance to geometrical inaccuracies in CBCT systems: A comprehensive study

Area of Science:

• Medical Imaging
• Radiological Physics
• Image Reconstruction

Background:

• Cone-beam CT (CBCT) is vital in medical imaging, including dentistry and mammography.
• Mechanical strains and manufacturing tolerances can cause CBCT system geometry inaccuracies.
• Accurate geometrical calibration is crucial for high-quality CBCT image reconstruction.

Purpose of the Study:

• To systematically study the impact of detector misalignments on CBCT image quality.
• To quantify the tolerance of CBCT systems to geometrical calibration errors.
• To establish guidelines for CBCT system design and calibration processes.

Main Methods:

• Simulations of four phantoms with systematic and random detector misalignments.
• Comparison of reconstructed images with and without calibration errors.
• Visual assessment of artifacts to identify error sources and define tolerances.

Main Results:

• Systematic errors cause blurring, shape distortion, and reduced field of view.
• Random errors result in streaks and blurring, with a higher tolerance than systematic errors.
• Tighter tolerances exist for tangential detector shifts (skew, horizontal) than for longitudinal shifts or magnification errors.

Conclusions:

• Detector misalignments significantly affect CBCT image quality, introducing specific artifacts.
• Defined tolerances can guide the mechanical precision required for CBCT systems.
• Visual artifact analysis aids in identifying predominant geometrical calibration error sources.