18 Questions
What is the main cause of partial-volume streak artifacts in CT images?
Detector measurements inconsistency
Why do small structures like bone pieces sometimes cause image streaks in CT scans?
They attenuate the beam traveling in one direction but are missed by the opposing beam
What is a common type of shading artifact in CT imaging that often appears near high-density objects?
Beam-hardening effects
Which factor contributes to the appearance of shading artifacts near high-density objects in CT scans?
Imperfect beam-hardening correction
How do opposing x-ray beams contribute to partial-volume streak artifacts in CT imaging?
They sample slightly different cone-shaped tissue volumes due to beam divergence
What effect do small structures, like bone pieces, have on detector measurements during CT scans?
Result in inconsistent measurements and image streaks
What is the primary cause of streak artifacts in CT scans?
Improper sampling of the data
Which of the following factors can lead to inconsistent or bad detector measurements, causing streak artifacts?
All of the above
What is the phenomenon illustrated in Figure (2) regarding partial-volume effects?
The same ray is sampled twice during a 360° axial scan, but with x-rays traveling in opposite directions
What is the effect of beam divergence in CT scans, as mentioned in the text?
It causes the cone-shaped x-ray beam to sample slightly different volumes in opposite directions
Which of the following artifacts is NOT mentioned in the text as one of the three main categories of CT artifacts?
Beam hardening artifacts
What is the appearance of shading artifacts, according to the text?
Gradual shading or variation in intensity across the image
Which type of artifact is caused by the projection readings of a single channel or a group of channels consistently deviating from the truth?
Ring or partial ring (arc) artifacts
What is the primary cause of ring or partial ring (arc) artifacts?
Defective detector cells or DAS channels
Which type of CT scanner is most prone to ring or partial ring (arc) artifacts?
Third-generation CT scanners
What is the primary cause of shading artifacts in CT scans?
Scatter from the patient
What is the primary cause of streak artifacts in CT scans?
Beam hardening effects
Which type of artifact is caused by the averaging of different tissue types within a single voxel?
Partial-volume effects
Study Notes
Streak Artifacts
- Caused by inconsistent measurements of the same ray path due to partial-volume effects, beam divergence, and other factors
- Can appear as intense straight lines across an image
- Factors contributing to inconsistencies include motion, insufficient x-ray intensity, and malfunctions
Partial-Volume Streaks
- Occur when a small structure, such as a bone edge, partially extends into the volume and is detected by one beam direction but missed by the opposing beam
- Results in inconsistent measurements and streak artifacts
Shading Artifacts
- Often appear near objects of high densities
- Caused by beam hardening, partial volume averaging, spiral/helical scanning, scatter radiation, off-focal radiation, and incomplete projections
- Most common type is beam-hardening effects, which appear as non-uniformities in CT numbers of a uniform material
- Can be caused by scatter radiation, although this is uncommon in modern scanners
Beam-Hardening Artifacts
- Present to some extent on all CT images
- Due to imperfect beam-hardening correction
- Appear as non-uniformities in CT numbers, with lower CT numbers at the center of a uniform phantom than at the periphery
Ring Artifacts
- Produced when projection readings of a single channel or group of channels consistently deviate from the truth
- Can be caused by defective detector cells or DAS channels, deficiencies in system calibration, or a sub-optimal image-generation process
- Predominantly a third-generation CT scanner phenomenon
Explore the different types of CT artifacts, focusing on streak artifacts caused by improper sampling of data, motion, metal, beam hardening, and more. Learn how these discrepancies are enhanced by the convolution process and manifested into lines during back-projection.
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