CRI Equipment Calibration & Maintenance 3 — Questions and Answers
Question 1: Which condition would cause a radiographic system to produce images with excessive fog density even when exposure parameters are correct?
- Tube current (mA) set too low
- Darkroom light leak or expired film (Correct answer)
- Source-to-film distance too long
- IQI placed on the wrong side of the part
Correct answer: Darkroom light leak or expired film
Darkroom light leaks or radiation-fogged expired film raise base-plus-fog density, masking true image information and indicating a maintenance issue.
Question 2: During acceptance testing of a new X-ray unit, linearity of output is checked by:
- Comparing images taken with different IQI types
- Measuring radiation output at multiple mA settings while holding kV and time constant (Correct answer)
- Verifying the source-to-film distance with a tape measure
- Confirming the generator manufacturer's serial number
Correct answer: Measuring radiation output at multiple mA settings while holding kV and time constant
Output linearity testing ensures that changes in mA produce proportional changes in radiation output, confirming the generator behaves predictably.
Question 3: A collimator on an X-ray unit is primarily maintained and calibrated to ensure:
- Correct film chemistry temperature
- The radiation field aligns accurately with the intended exposure area (Correct answer)
- Adequate source-to-detector distance is maintained
- The X-ray tube is properly cooled
Correct answer: The radiation field aligns accurately with the intended exposure area
Collimator calibration ensures that the visible light field coincides with the actual radiation field, preventing unnecessary exposure and ensuring correct coverage.
Question 4: A gamma radiography projector (camera) is found to have a cracked or damaged guide tube connector. The correct action is:
- Continue use at reduced source-to-object distances only
- Remove from service immediately and quarantine for repair (Correct answer)
- Tape the connector and document in the log
- Use only with a backup dosimeter present
Correct answer: Remove from service immediately and quarantine for repair
Damaged guide tube connectors on gamma projectors create a radiological safety hazard and the unit must be removed from service until properly repaired.
Question 5: The half-value layer (HVL) measurement of an X-ray unit is used to assess:
- Film processing speed consistency
- The beam quality (effective energy) and filtration adequacy (Correct answer)
- Focal spot drift over time
- Timer accuracy at short exposures
Correct answer: The beam quality (effective energy) and filtration adequacy
HVL measurement characterizes the beam's penetrating quality; a change from baseline indicates filtration problems or voltage calibration drift.
Question 6: Film processor QC monitoring typically involves daily processing of a sensitometric strip exposed to a standard light source. This practice primarily verifies:
- Film emulsion batch consistency
- Developer temperature, replenishment, and chemistry activity stability (Correct answer)
- Darkroom safelight wavelength
- Fixer solution pH only
Correct answer: Developer temperature, replenishment, and chemistry activity stability
Sensitometric strips processed daily reveal shifts in developer activity, temperature, or replenishment rate that affect film density and contrast.
Question 7: Which statement about geometric unsharpness (Ug) and its control through equipment maintenance is CORRECT?
- Ug increases as the source-to-object distance increases
- Ug increases as the effective focal spot size grows due to anode wear (Correct answer)
- Ug is unaffected by source size and depends only on film type
- Ug decreases when higher kV is used regardless of focal spot condition
Correct answer: Ug increases as the effective focal spot size grows due to anode wear
As the tungsten anode wears, the effective focal spot enlarges, directly increasing geometric unsharpness and reducing image sharpness.
CRI Equipment Calibration & Maintenance 3
Which condition would cause a radiographic system to produce images with excessive fog density even when exposure parameters are correct?