Computed Tomography Test CT Image Quality and Reconstruction 2 — Questions and Answers
Question 1: What is the primary advantage of iterative reconstruction over filtered back projection (FBP) in CT?
- Significant noise reduction at equivalent or lower dose (Correct answer)
- Faster reconstruction time
- Better spatial resolution at high kVp
- Elimination of metal artifacts
Correct answer: Significant noise reduction at equivalent or lower dose
Iterative reconstruction repeatedly refines the image estimate against raw data, reducing noise substantially, which allows lower dose acquisition without sacrificing image quality.
Question 2: Which window level and window width settings are appropriate for evaluating brain parenchyma on CT?
- Level 35 HU, Width 80 HU (Correct answer)
- Level 400 HU, Width 2000 HU
- Level −600 HU, Width 1500 HU
- Level 60 HU, Width 350 HU
Correct answer: Level 35 HU, Width 80 HU
Brain window settings (level ~35 HU, width ~80 HU) optimize contrast between gray matter, white matter, and CSF within the narrow HU range of brain tissue.
Question 3: Ring artifacts in CT are most commonly caused by which problem?
- Defective or mis-calibrated detector elements (Correct answer)
- Patient motion
- High kVp settings
- Incorrect FOV selection
Correct answer: Defective or mis-calibrated detector elements
A single malfunctioning detector channel consistently produces incorrect readings at the same projection angle, creating a characteristic ring or arc artifact in the reconstructed image.
Question 4: What is the relationship between CT slice thickness and the partial volume artifact?
- Thinner slices reduce partial volume artifact (Correct answer)
- Thicker slices reduce partial volume artifact
- Slice thickness has no effect on partial volume
- Thinner slices increase partial volume artifact
Correct answer: Thinner slices reduce partial volume artifact
Thinner CT slices reduce the volume of each voxel, decreasing the chance that multiple tissue types are averaged together within a single voxel.
Question 5: What does multiplanar reformation (MPR) allow clinicians to do with CT data?
- View reconstructed images in coronal, sagittal, and oblique planes from axial data (Correct answer)
- Increase spatial resolution after acquisition
- Remove contrast enhancement from images
- Generate 3D models for printing
Correct answer: View reconstructed images in coronal, sagittal, and oblique planes from axial data
MPR uses isotropic or near-isotropic volumetric CT data to generate reconstructions in any desired imaging plane without additional scanning.
Question 6: The concept of isotropic voxels in modern multi-detector CT (MDCT) means that voxels are:
- Equal in all three dimensions (x, y, z) (Correct answer)
- Larger in the z-axis than x-y plane
- Round rather than square
- Variable depending on reconstruction kernel
Correct answer: Equal in all three dimensions (x, y, z)
Isotropic voxels (e.g., 0.5 × 0.5 × 0.5 mm) allow high-quality MPR and 3D reconstruction in any plane without staircase artifacts.
Computed Tomography Test CT Image Quality and Reconstruction 2
What is the primary advantage of iterative reconstruction over filtered back projection (FBP) in CT?