Image Quality Flashcards

Which window setting is most appropriate for evaluating pulmonary nodules in the lung parenchyma?

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.

Partial volume averaging artifact in CT is BEST minimized by:

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.

Adaptive statistical iterative reconstruction (ASIR) improves CT image quality primarily by:

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.

The pitch value in helical CT is defined as:

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.

A CT image shows ring artifacts. The MOST likely cause is:

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.

Increasing the CT reconstruction matrix from 512×512 to 1024×1024 while keeping FOV constant will:

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.

Which CT image quality parameter is measured using a modulation transfer function (MTF)?

Answer: Spatial resolution

The MTF quantifies spatial resolution by describing how faithfully the CT system reproduces objects of varying spatial frequencies.