DEXA DEXA Quality Assurance & Equipment Calibration 1 — Questions and Answers
Question 1: How often should daily phantom QA scans be performed on a DEXA system?
- Every day before patient scanning (Correct answer)
- Once per week
- Once per month
- Only when error alerts appear
Correct answer: Every day before patient scanning
Daily phantom scans must be performed every day prior to patient scanning to verify system accuracy and detect drift.
Question 2: What is the primary purpose of a spine phantom (e.g., Hologic or GE Lunar phantom) in DEXA QA?
- To calibrate the system and detect BMD measurement drift (Correct answer)
- To test patient positioning aids
- To measure radiation output levels
- To verify detector pixel alignment only
Correct answer: To calibrate the system and detect BMD measurement drift
Spine phantoms are used to calibrate the DEXA system and monitor for measurement drift over time.
Question 3: A DEXA system's daily QC phantom result falls outside ±1.5% of the long-term average. What is the correct action?
- Do not scan patients; investigate and contact the manufacturer (Correct answer)
- Scan patients and document the variance
- Repeat the phantom scan 10 times and use the average
- Reset the system and proceed normally
Correct answer: Do not scan patients; investigate and contact the manufacturer
A phantom result outside the ±1.5% control limit requires halting patient scans and investigating the cause before proceeding.
Question 4: Which statistical tool is typically used to track DEXA daily phantom data over time and identify trends?
- Shewhart control chart (QC chart) (Correct answer)
- Histogram
- Scatter regression plot
- Kaplan-Meier curve
Correct answer: Shewhart control chart (QC chart)
Shewhart control charts plot daily phantom BMD values and visually flag drift or sudden shifts in machine performance.
Question 5: When should a DEXA system's cross-calibration be performed?
- After major repairs, software upgrades, or detector replacement (Correct answer)
- Only at initial installation
- Every 5 years regardless of changes
- Before every patient scan
Correct answer: After major repairs, software upgrades, or detector replacement
Cross-calibration is required after any significant hardware or software change to ensure continuity of serial patient measurements.
Question 6: What does a sudden step-change (shift) in the daily QC control chart most likely indicate?
- A hardware or software change affecting system performance (Correct answer)
- Normal day-to-day measurement variability
- The phantom needs to be replaced with a newer model
- Patient volume has increased significantly
Correct answer: A hardware or software change affecting system performance
A step-change in QC data typically signals a discrete system event such as a detector swap, software update, or phantom replacement.
DEXA DEXA Quality Assurance & Equipment Calibration 1
How often should daily phantom QA scans be performed on a DEXA system?