ARRT ARRT CT Artifacts and Troubleshooting 2 — Questions and Answers
Question 1: Which technique is most commonly used to reduce metal artifact in CT imaging of patients with hip prostheses?
- Decreasing kVp
- Metal artifact reduction (MAR) software (Correct answer)
- Increasing slice thickness
- Using a smaller FOV
Correct answer: Metal artifact reduction (MAR) software
Metal artifact reduction (MAR) algorithms replace corrupted projection data near metal with interpolated data, significantly reducing streaking artifacts.
Question 2: A starburst pattern of streaks emanating from the edge of the patient's shoulders during a neck CT is most likely caused by:
- Detector malfunction
- Beam hardening from bone and soft tissue interfaces (Correct answer)
- Incorrect windowing
- Gantry tilt error
Correct answer: Beam hardening from bone and soft tissue interfaces
Dense cortical bone at the shoulder causes beam hardening, producing characteristic streak artifacts that radiate into adjacent soft tissues.
Question 3: Quantum (photon) noise in CT images is most visible under which conditions?
- High mAs and thin slices
- Low mAs or large patient size (Correct answer)
- High kVp and wide window
- Fast pitch and narrow FOV
Correct answer: Low mAs or large patient size
Quantum noise increases when fewer photons reach the detectors, which occurs with low mAs settings or when X-rays are attenuated by a large patient.
Question 4: The windmill artifact seen in helical CT is most commonly associated with which acquisition parameter?
- High pitch values (Correct answer)
- Low kVp
- Large detector collimation
- Small reconstruction FOV
Correct answer: High pitch values
Windmill artifacts appear as alternating dark and bright streaks rotating around structures and are caused by the under-sampling that occurs at high pitch values.
Question 5: Which of the following best describes an out-of-field artifact in CT?
- Streaking caused by anatomy extending beyond the scan FOV (Correct answer)
- Noise from low mAs
- Ring caused by detector failure
- Blurring from respiratory motion
Correct answer: Streaking caused by anatomy extending beyond the scan FOV
Out-of-field artifacts occur when part of the patient's anatomy lies outside the calibrated scan FOV, causing truncation of projection data and bright peripheral streaks.
Question 6: A horizontal band of decreased attenuation passing through the posterior fossa on a head CT is a classic example of which artifact?
- Beam hardening between the petrous bones (Correct answer)
- Motion artifact from cardiac pulsation
- Ring artifact
- Partial volume artifact
Correct answer: Beam hardening between the petrous bones
The dense petrous temporal bones cause preferential absorption of lower-energy photons, producing a dark band across the posterior fossa known as a beam hardening artifact.
ARRT ARRT CT Artifacts and Troubleshooting 2
Which technique is most commonly used to reduce metal artifact in CT imaging of patients with hip prostheses?