An empirical method for lag correction in cone-beam CT.

Area of Science:

• Medical Imaging
• Radiotherapy Physics
• Image Processing

Background:

• Image lag is a known artifact in cone-beam CT (CBCT) systems.
• This artifact significantly degrades image quality, affecting CT number accuracy, uniformity, and contrast.
• Skin-line artifacts are a common manifestation of image lag in CBCT.

Purpose of the Study:

• To quantify the impact of image lag on CBCT image quality.
• To investigate the effectiveness of a lag correction method in mitigating these artifacts.
• To assess improvements in specific imaging parameters after lag correction.

Main Methods:

• Measurements were conducted on a radiotherapy CBCT system using a flat-panel imager.
• Image lag was analyzed in relation to signal magnitude, photon energy, and frame number.
• An empirical lag correction method involving subtraction of weighted previous frames was developed and applied.
• The CatPhan 500 phantom was used to evaluate artifact reduction and image quality improvements.

Main Results:

• CBCT images after lag correction showed significant improvements in skin-line reconstruction.
• CT number accuracy, image uniformity, and contrast-to-noise ratio were enhanced post-correction.
• The developed lag correction method effectively reduced lag artifacts in projection images.
• Correction was particularly beneficial for objects with contrast inserts, improving low contrast visibility near high contrast areas.

Conclusions:

• Algorithmic correction of projection images can effectively reduce image lag artifacts in CBCT.
• Lag correction is crucial for accurate imaging, especially in complex anatomical regions or with contrast agents.
• While lag correction improves overall image quality, its impact on skin-line artifacts varies with object shape.