ARRT Image Quality 3 — Questions and Answers
Question 1: Which window setting is most appropriate for evaluating pulmonary nodules in the lung parenchyma?
- Window width ~1500 HU, window level ~-600 HU (Correct answer)
- Window width ~400 HU, window level ~40 HU
- Window width ~200 HU, window level ~80 HU
- Window width ~3000 HU, window level ~300 HU
Correct answer: Window width ~1500 HU, window level ~-600 HU
Lung windows use a wide width (~1500 HU) and negative level (~-600 HU) to display the full range of lung attenuation from air to soft tissue.
Question 2: Partial volume averaging artifact in CT is BEST minimized by:
- Using thinner slice collimation (Correct answer)
- Increasing the reconstruction matrix
- Decreasing the tube current
- Using a smoother reconstruction kernel
Correct answer: Using thinner slice collimation
Thinner slices reduce the z-axis extent of each voxel, decreasing the chance that multiple tissue types are averaged into a single voxel.
Question 3: Adaptive statistical iterative reconstruction (ASIR) improves CT image quality primarily by:
- Reducing image noise while maintaining resolution (Correct answer)
- Increasing spatial resolution beyond filtered back projection
- Eliminating beam hardening artifacts
- Improving temporal resolution
Correct answer: Reducing image noise while maintaining resolution
ASIR uses statistical modeling to reduce noise, allowing diagnostic images at lower dose without proportional loss of spatial resolution.
Question 4: The pitch value in helical CT is defined as:
- Table travel per rotation divided by total beam collimation width (Correct answer)
- Gantry rotation speed divided by table speed
- Slice thickness divided by detector row width
- kVp divided by mA
Correct answer: Table travel per rotation divided by total beam collimation width
Pitch = table distance traveled per 360° rotation ÷ total collimated beam width, and values >1 indicate gaps in data coverage.
Question 5: A CT image shows ring artifacts. The MOST likely cause is:
- A malfunctioning or miscalibrated detector element (Correct answer)
- Patient motion during scanning
- Incorrect kVp selection
- Too low an mAs setting
Correct answer: A malfunctioning or miscalibrated detector element
Ring artifacts appear as circular bands centered on the isocenter and are caused by a single detector element producing consistently incorrect readings.
Question 6: Increasing the CT reconstruction matrix from 512×512 to 1024×1024 while keeping FOV constant will:
- Decrease pixel size and potentially improve spatial resolution (Correct answer)
- Increase pixel size and reduce spatial resolution
- Decrease image noise
- Reduce scan time
Correct answer: Decrease pixel size and potentially improve spatial resolution
Doubling the matrix halves the pixel size (FOV/matrix), which can improve displayed spatial resolution but also increases image noise and data storage requirements.
Question 7: Which CT image quality parameter is measured using a modulation transfer function (MTF)?
- Spatial resolution (Correct answer)
- Contrast resolution
- Temporal resolution
- Noise power spectrum
Correct answer: Spatial resolution
The MTF quantifies spatial resolution by describing how faithfully the CT system reproduces objects of varying spatial frequencies.
ARRT Image Quality 3
Which window setting is most appropriate for evaluating pulmonary nodules in the lung parenchyma?