Computed Tomography Test Computed Tomography Science 2 — Questions and Answers
Question 1: Which term describes the ability of a CT system to distinguish between two objects with very similar attenuation values?
- Spatial resolution
- Low-contrast resolution (Correct answer)
- High-contrast resolution
- Noise index
Correct answer: Low-contrast resolution
Low-contrast resolution (contrast resolution) measures the system's ability to differentiate objects with nearly identical attenuation coefficients.
Question 2: In CT, the process of reconstructing an image from projection data using mathematical algorithms is called:
- Iterative refinement
- Back-projection
- Filtered back-projection (Correct answer)
- Fourier synthesis
Correct answer: Filtered back-projection
Filtered back-projection (FBP) applies a convolution filter to raw projection data before back-projecting it to form the image.
Question 3: The Hounsfield unit (HU) value of cortical bone is approximately:
- +1000 HU (Correct answer)
- +400 HU
- +100 HU
- +200 HU
Correct answer: +1000 HU
Cortical bone typically measures around +1000 HU on the Hounsfield scale, with water at 0 HU and air at -1000 HU.
Question 4: Which detector configuration in multi-detector CT (MDCT) acquires data simultaneously from multiple rows, allowing faster volume coverage?
- Single-row detector array
- Xenon gas detector
- Multi-row detector array (Correct answer)
- Photomultiplier tube array
Correct answer: Multi-row detector array
Multi-row detector arrays allow simultaneous acquisition of multiple slices per gantry rotation, dramatically increasing volume coverage speed.
Question 5: What effect does increasing the pitch in helical CT have on patient dose?
- Increases dose proportionally
- Has no effect on dose
- Decreases dose by reducing overlap (Correct answer)
- Doubles the dose
Correct answer: Decreases dose by reducing overlap
Increasing pitch means the table moves faster per rotation, resulting in less beam overlap and a reduced effective dose to the patient.
Question 6: The term 'isotropic voxel' in CT means the voxel dimensions are:
- Larger in the z-axis than in-plane
- Equal in all three dimensions (Correct answer)
- Larger in-plane than in the z-axis
- Variable depending on window settings
Correct answer: Equal in all three dimensions
Isotropic voxels have equal x, y, and z dimensions, enabling high-quality multiplanar reformations in any orientation.
Question 7: Which artifact appears as a dark band between two high-density objects in CT images?
- Ring artifact
- Partial volume artifact
- Beam hardening artifact (Correct answer)
- Motion artifact
Correct answer: Beam hardening artifact
Beam hardening causes dark streaks or bands between dense structures because lower-energy photons are preferentially absorbed, shifting the beam spectrum.
Computed Tomography Test Computed Tomography Science 2
Which term describes the ability of a CT system to distinguish between two objects with very similar attenuation values?