Computed Tomography (CT) Basics Flashcards

Which CT scan artifact appears as a dark band between two high-density structures and results from the x-ray beam becoming increasingly hard (filtered) as it passes through dense tissue?

Answer: Beam hardening (cupping) artifact

Beam hardening occurs when the lower-energy photons are preferentially absorbed by dense tissue, leaving a harder (higher-energy) beam. This causes the center of dense structures to appear darker than expected.

A ring artifact in CT imaging is typically caused by:

Answer: A malfunctioning or miscalibrated detector element

Ring artifacts appear as concentric rings centered on the scan isocenter and are caused by a single detector element that is malfunctioning or requires recalibration.

In CT, the term 'effective mAs' accounts for pitch and is calculated as:

Answer: mAs / pitch

Effective mAs = mAs / pitch. It normalizes the mAs for pitch, allowing meaningful dose comparisons between protocols with different pitches. Higher pitch = lower effective mAs = less dose.

Which clinical parameter most directly affects the contrast resolution (ability to distinguish tissues of similar density) in CT imaging?

Answer: mAs (noise level)

Contrast resolution in CT is primarily determined by image noise, which is controlled by mAs. Higher mAs reduces noise and improves contrast resolution (ability to detect subtle density differences).

The ALARA principle in CT specifically encourages radiologists and technologists to use:

Answer: The lowest radiation dose that provides diagnostic image quality for the specific clinical indication

In CT, ALARA means using the minimum dose consistent with the diagnostic task — adjusting technique for patient size, clinical indication, and using dose modulation tools.

Which component provides the electronic connection between the rotating gantry (with x-ray tube) and the stationary data acquisition system in a modern CT scanner?

Answer: Slip rings

Slip rings are circular electrical contacts that allow continuous rotation of the gantry without twisting cables, enabling helical (spiral) CT scanning.