ARRT Equipment Operation and Quality Control 3

Question 1

Which CT quality control parameter is most directly affected by X-ray tube focal spot size?

Accepted Answer

High-contrast spatial resolution

Answer

Image noise

Answer

Low-contrast detectability

Answer

CT number uniformity

Question 2

What is the role of the bowtie (beam-shaping) filter in CT equipment operation?

Accepted Answer

To equalize X-ray flux across the fan beam, reducing dose at the periphery and minimizing detector saturation

Answer

To harden the beam and remove low-energy photons uniformly across the beam

Answer

To collimate the beam to the prescribed slice thickness

Answer

To increase photon energy for improved tissue penetration

Question 3

During CT scanner acceptance testing, which test verifies that the displayed scan field of view (SFOV) matches the actual reconstructed area?

Accepted Answer

Geometric accuracy/distance accuracy test

Answer

Noise power spectrum test

Answer

Detector crosstalk measurement

Answer

Bowtie filter attenuation test

Question 4

In CT quality control documentation, what is the purpose of establishing 'action limits' for QC measurements?

Accepted Answer

To set thresholds that, when exceeded, require investigation and corrective action before clinical use

Answer

To define the maximum patient dose per study

Answer

To determine the minimum number of QC tests per week

Answer

To establish the contrast media injection rate limits

Question 5

Which type of CT detector material is most commonly used in modern multi-detector CT (MDCT) systems due to its high conversion efficiency and fast decay time?

Accepted Answer

Gadolinium oxysulfide (GOS) solid-state scintillators

Answer

Xenon gas ionization chambers

Answer

Sodium iodide (NaI) crystal detectors

Answer

Bismuth germanate (BGO) crystals

Question 6

What does 'afterglow' (or 'ghosting') in CT solid-state detectors cause?

Accepted Answer

Residual signal carried over from prior projections, causing streak artifacts

Answer

Increased image noise due to photon starvation

Answer

Reduced spatial resolution due to detector cross-talk

Answer

Ring artifacts from a single failed detector channel

Question 7

Which ACR-recommended CT quality control test should be performed if visual image artifacts are noted during clinical scanning?

Accepted Answer

Perform artifact analysis using an appropriate phantom and document findings before continuing clinical use

Answer

Immediately repeat the patient scan at higher mAs

Answer

Switch to a different reconstruction kernel and continue scanning

Answer

Reduce the scan FOV and repeat without QC evaluation