CRI Equipment Calibration & Maintenance 2 — Questions and Answers
Question 1: What is the primary purpose of a step wedge (penetrameter) in radiographic calibration?
- To measure radiation dose to the operator
- To verify the density range and contrast sensitivity of the imaging system (Correct answer)
- To align the X-ray tube with the film cassette
- To filter low-energy scatter radiation
Correct answer: To verify the density range and contrast sensitivity of the imaging system
A step wedge penetrameter verifies that the radiographic system can resolve the required density range and detect small thickness changes.
Question 2: How often should radiation output constancy checks typically be performed on a fixed industrial X-ray unit in active use?
- Once per year
- Before each major inspection campaign or after servicing (Correct answer)
- Only when images appear darker than expected
- Every five years per regulatory requirement
Correct answer: Before each major inspection campaign or after servicing
Output constancy checks should be performed before each major inspection campaign and after any repair or servicing to ensure reproducible exposure conditions.
Question 3: Which parameter is directly adjusted when performing kV calibration on an X-ray generator?
- Film processing temperature
- Peak tube voltage accuracy (Correct answer)
- Focal spot size
- Collimator blade position
Correct answer: Peak tube voltage accuracy
kV calibration verifies that the peak tube voltage output matches the set value, ensuring correct radiation energy for the intended application.
Question 4: A radiographer notices that images from a gamma-ray source appear consistently underexposed despite using standard exposure charts. The MOST likely equipment-related cause is:
- Incorrect film type selection
- Source activity decay beyond the exposure chart's reference date (Correct answer)
- Darkroom safelight contamination
- Film cassette pressure irregularity
Correct answer: Source activity decay beyond the exposure chart's reference date
Gamma sources continuously decay; if the exposure chart was created at a higher activity level, the source may no longer provide sufficient dose rate for the standard time.
Question 5: What does 'focal spot size' affect in radiographic image quality, and why is it periodically verified?
- It affects image density; verified to control radiation dose
- It affects geometric unsharpness; verified because it can increase with tube aging (Correct answer)
- It affects penetrating power; verified because it changes with kV settings
- It affects film speed; verified to maintain processing consistency
Correct answer: It affects geometric unsharpness; verified because it can increase with tube aging
The focal spot can enlarge as the tungsten anode erodes with use, increasing geometric unsharpness and reducing image definition.
Question 6: Which test tool is used to verify the resolution capability of a radiographic imaging system?
- Densitometer
- Wire IQI or hole-type penetrameter (Correct answer)
- Dosimeter badge
- Collimator test jig
Correct answer: Wire IQI or hole-type penetrameter
Wire IQIs and hole-type penetrameters assess the minimum detectable discontinuity size, confirming the system meets required sensitivity thresholds.
Question 7: When calibrating a densitometer used for radiographic film evaluation, the reference standards used should be:
- Freshly processed unexposed film strips
- NIST-traceable calibrated density step tablets (Correct answer)
- Manufacturer-supplied plastic density cards
- Digitized scans of previous known-good radiographs
Correct answer: NIST-traceable calibrated density step tablets
Calibrated density step tablets traceable to national standards (NIST) ensure the densitometer readings are accurate and auditable.
CRI Equipment Calibration & Maintenance 2
What is the primary purpose of a step wedge (penetrameter) in radiographic calibration?