Which artifact is commonly associated with missing projections in a CT scan?

Which artifact is commonly associated with missing projections in a CT scan?

• A. Beam hardening artifact
• B. Motion artifact
• C. Alias artifact
• D. Out-of-field artifact

Answer: (C)

The alias artifact is commonly associated with missing projections in a CT scan because it occurs when incomplete data is used in image reconstruction. This typically happens when certain projections are absent, leading to extrapolation errors. The reconstruction algorithm attempts to create an image from limited information, resulting in visible distortions or repetitive patterns that do not accurately represent the object being scanned. In contrast, beam hardening artifacts stem from the differential attenuation of X-rays as they pass through various tissues, which can create darker bands or streaks in areas of high-density materials. Motion artifacts are caused by patient movement during the acquisition of the scan, leading to blurring or doubling of structures. Out-of-field artifacts occur when part of the anatomy lies outside the scanned area, which can create light or dark areas on the image but is not directly linked to missing projection data. The alias artifact’s specific tie to the absence of data directly clarifies why it is the correct answer, as it highlights a failure during the data collection phase that affects the resulting image quality.

The alias artifact is commonly associated with missing projections in a CT scan because it occurs when incomplete data is used in image reconstruction. This typically happens when certain projections are absent, leading to extrapolation errors. The reconstruction algorithm attempts to create an image from limited information, resulting in visible distortions or repetitive patterns that do not accurately represent the object being scanned.

In contrast, beam hardening artifacts stem from the differential attenuation of X-rays as they pass through various tissues, which can create darker bands or streaks in areas of high-density materials. Motion artifacts are caused by patient movement during the acquisition of the scan, leading to blurring or doubling of structures. Out-of-field artifacts occur when part of the anatomy lies outside the scanned area, which can create light or dark areas on the image but is not directly linked to missing projection data.

The alias artifact’s specific tie to the absence of data directly clarifies why it is the correct answer, as it highlights a failure during the data collection phase that affects the resulting image quality.