ARRT Equipment Operation and Quality Control 2 — Questions and Answers
Question 1: What does the term 'detector efficiency' refer to in CT scanner performance?
- The speed at which the gantry rotates
- The ability of detectors to capture and convert X-ray photons into usable signal (Correct answer)
- The number of detector rows in the system
- The FOV coverage per rotation
Correct answer: The ability of detectors to capture and convert X-ray photons into usable signal
Detector efficiency describes how effectively CT detectors absorb incident X-ray photons and convert them into electrical signal, directly affecting image quality and dose.
Question 2: In CT quality control, 'low-contrast detectability' refers to the system's ability to:
- Resolve fine structural detail in bone
- Distinguish objects with small differences in attenuation from background (Correct answer)
- Measure exact CT numbers for each tissue type
- Determine the maximum scan field of view
Correct answer: Distinguish objects with small differences in attenuation from background
Low-contrast detectability measures the scanner's ability to visualize objects with subtle attenuation differences, which is critical for soft-tissue diagnosis.
Question 3: Which of the following best describes the purpose of the CT table indexing accuracy test?
- To confirm the table moves the correct prescribed distance between scan acquisitions (Correct answer)
- To verify the table weight tolerance
- To measure the table speed during helical scans
- To evaluate gantry isocenter alignment
Correct answer: To confirm the table moves the correct prescribed distance between scan acquisitions
Table indexing accuracy testing ensures the patient couch advances exactly the specified distance, which is critical for accurate slice positioning and volume coverage.
Question 4: The 'noise' measured in a CT image is quantified as:
- The mean CT number in a region of interest
- The standard deviation of CT numbers in a uniform region of interest (Correct answer)
- The difference between maximum and minimum CT numbers in the image
- The number of image artifacts present
Correct answer: The standard deviation of CT numbers in a uniform region of interest
Image noise in CT is quantified as the standard deviation of HU values within a uniform phantom region; higher standard deviation indicates greater noise.
Question 5: Which generator component is responsible for converting AC power to the high-voltage DC supply required by the X-ray tube in modern CT systems?
- Filament transformer
- High-frequency inverter generator (Correct answer)
- Autotransformer
- Rectifier diode bridge
Correct answer: High-frequency inverter generator
Modern CT systems use high-frequency inverter generators that convert line AC to high-frequency AC, then rectify it to produce a near-constant high-voltage DC supply for the tube.
Question 6: On a CT system, what does the term 'isocenter' refer to?
- The center of the X-ray beam at the detector plane
- The precise center of gantry rotation where the X-ray beam and detector array intersect (Correct answer)
- The center of the patient table surface
- The midpoint of the scan field of view display
Correct answer: The precise center of gantry rotation where the X-ray beam and detector array intersect
The isocenter is the exact point at the center of gantry rotation where the X-ray beam is focused, and proper patient centering at this point optimizes image quality and dose.
Question 7: What is the primary reason CT scanners use slip-ring technology?
- To improve detector quantum efficiency
- To allow continuous gantry rotation by eliminating the need for cables to wind and unwind (Correct answer)
- To increase the kVp range of the X-ray tube
- To synchronize gantry rotation with patient respiration
Correct answer: To allow continuous gantry rotation by eliminating the need for cables to wind and unwind
Slip-ring technology uses electrical contacts that rotate with the gantry, enabling continuous 360° rotation without cable entanglement, which is essential for helical/spiral CT.
ARRT Equipment Operation and Quality Control 2
What does the term 'detector efficiency' refer to in CT scanner performance?