ARRT Equipment Operation and Quality Control 1 — Questions and Answers
Question 1: Which daily CT quality control test verifies that CT numbers (Hounsfield Units) remain accurate and consistent?
- Noise index measurement
- CT number accuracy/linearity test (Correct answer)
- Slice thickness verification
- High-contrast spatial resolution test
Correct answer: CT number accuracy/linearity test
The CT number accuracy/linearity test confirms that scanned materials produce the expected HU values, ensuring diagnostic consistency.
Question 2: What is the primary purpose of performing a daily air calibration (warm-up scan) on a CT scanner?
- To test the table weight limit
- To calibrate detector channels and normalize dark current (Correct answer)
- To verify gantry tilt accuracy
- To measure patient dose output
Correct answer: To calibrate detector channels and normalize dark current
The daily air calibration normalizes detector channel responses and corrects for dark current drift, maintaining uniform image quality.
Question 3: Which CT quality control phantom is most commonly used to evaluate CT number accuracy, noise, uniformity, and spatial resolution?
- AAPM CT performance phantom (Correct answer)
- Alderson Rando phantom
- Leeds TOR phantom
- MOSFET dosimetry phantom
Correct answer: AAPM CT performance phantom
The AAPM CT performance phantom contains inserts for testing multiple image quality parameters including HU accuracy, noise, and spatial resolution.
Question 4: On a CT scanner, what does image uniformity testing evaluate?
- The consistency of CT numbers across the field of view in a homogeneous phantom (Correct answer)
- The ability to visualize small high-contrast structures
- The accuracy of the patient table indexing
- The linearity of dose output versus mAs
Correct answer: The consistency of CT numbers across the field of view in a homogeneous phantom
Image uniformity testing measures whether a homogeneous phantom (e.g., water) produces consistent HU values across the entire reconstructed image.
Question 5: Which factor is evaluated by the modulation transfer function (MTF) in CT quality control?
- Low-contrast detectability
- High-contrast spatial resolution (Correct answer)
- Image noise levels
- CT number linearity
Correct answer: High-contrast spatial resolution
The MTF describes how faithfully the CT system reproduces spatial detail, directly measuring high-contrast spatial resolution performance.
Question 6: What is the recommended frequency for performing a full CT equipment performance evaluation by a qualified medical physicist?
- Daily
- Weekly
- Annually (Correct answer)
- Every five years
Correct answer: Annually
ACR and AAPM guidelines recommend a comprehensive CT performance evaluation by a qualified medical physicist at least annually.
Question 7: When a CT scanner undergoes a tube replacement, which quality control step is mandatory before returning the unit to clinical service?
- Slice sensitivity profile measurement only
- Full calibration and acceptance testing (Correct answer)
- Low-contrast detectability test only
- Gantry tilt angle verification only
Correct answer: Full calibration and acceptance testing
After a major component replacement such as an X-ray tube, full calibration and acceptance testing must be performed to ensure the scanner meets all performance specifications.
ARRT Equipment Operation and Quality Control 1
Which daily CT quality control test verifies that CT numbers (Hounsfield Units) remain accurate and consistent?