CAMRT Imaging Equipment and QC Questions and Answers 2 — Questions and Answers
Question 1: Annual QC testing shows the X-ray tube HVL is below acceptable minimum. What does this indicate?
- Tube output too high
- Insufficient beam filtration increasing patient skin dose (Correct answer)
- Collimator misalignment
- Focal spot too large
Correct answer: Insufficient beam filtration increasing patient skin dose
Low HVL indicates inadequate filtration, allowing too many low-energy photons that increase skin dose.
Health Canada Safety Code 35 specifies minimum HVL values per kVp. The tube must be removed from service until filtration is corrected.
Question 2: What is the purpose of collimator light-to-radiation field alignment testing?
- Verify tube output consistency
- Ensure the light field accurately represents the irradiated area (Correct answer)
- Check AEC chamber positions
- Measure detector uniformity
Correct answer: Ensure the light field accurately represents the irradiated area
Alignment testing verifies the collimator light accurately indicates X-ray field boundaries.
Misalignment must not exceed 2% of SID per Safety Code 35. For 100 cm SID, each edge must be within 1 cm.
Question 3: A fluoroscopy unit ABC is increasing kVp beyond limits. What is the likely cause?
- Degraded image intensifier input phosphor (Correct answer)
- Patient too close to receptor
- Collimator too wide
- Grid removed
Correct answer: Degraded image intensifier input phosphor
II input phosphor degradation reduces conversion efficiency, causing ABC to compensate by increasing technique.
QC testing measures the II conversion factor. A decrease over 20-25% from baseline indicates replacement is needed.
Question 4: How should the anode heel effect be utilized in clinical practice?
- It causes uniform exposure; no positioning needed
- Higher intensity on cathode side; position thicker body parts toward cathode (Correct answer)
- Higher intensity on anode side; thicker parts toward anode
- Only affects mammography
Correct answer: Higher intensity on cathode side; position thicker body parts toward cathode
Greater intensity on the cathode side due to self-absorption in the anode. Thicker parts go toward the cathode.
The cathode side receives 20-25% more radiation. Example: AP thoracic spine with thicker lower thorax toward cathode.
Question 5: CT QC shows water measures consistently +8 HU instead of 0. What is the significance?
- Within normal limits
- Calibration drift affecting diagnostic accuracy; recalibration needed (Correct answer)
- Detector array needs replacement
- Tube nearing end of life
Correct answer: Calibration drift affecting diagnostic accuracy; recalibration needed
Water accuracy should be 0 plus or minus 4 HU. +8 HU indicates systematic drift.
Causes include detector degradation, beam hardening errors, or tube aging. The scanner requires recalibration. Recent examinations may need review.
Question 6: What is the purpose of the wire mesh test in mammography QC?
- Measure radiation output
- Evaluate screen-film contact or detector uniformity (Correct answer)
- Calculate average glandular dose
- Assess compression paddle accuracy
Correct answer: Evaluate screen-film contact or detector uniformity
The mesh test identifies areas of non-uniform image quality.
For film-screen, poor contact appears as localized blurring. For digital, the test evaluates dead pixels, gain non-uniformity, and spatial artefacts.
CAMRT Imaging Equipment and QC Questions and Answers 2
Annual QC testing shows the X-ray tube HVL is below acceptable minimum.
What does this indicate?