DEXA Scan Operation & Technique 4 — Questions and Answers
Question 1: During a serial DXA exam, which factor is MOST critical for ensuring valid comparison to a prior scan?
- Using the same scan technologist
- Replicating the same positioning, ROI placement, and scan mode as the baseline (Correct answer)
- Scanning at the same time of day
- Using the same patient gown
Correct answer: Replicating the same positioning, ROI placement, and scan mode as the baseline
Reproducible positioning and ROI placement on the same DXA system and mode are essential for detecting true BMD change versus measurement error.
Question 2: A patient has a hip prosthesis on the right side. Which scan should be performed?
- Right hip only, excluding the prosthesis region
- Left hip, and note that left was scanned due to right prosthesis (Correct answer)
- Bilateral hips with metal artifact reduction mode
- Lumbar spine only; hip scanning is contraindicated
Correct answer: Left hip, and note that left was scanned due to right prosthesis
The contralateral (left) hip should be scanned when a prosthesis is present on one side, and this substitution must be documented.
Question 3: What minimum time interval is generally recommended between DXA serial scans to detect clinically meaningful BMD change?
- 3 months
- 6 months
- 1 to 2 years (Correct answer)
- 5 years
Correct answer: 1 to 2 years
A 1–2 year interval is recommended because it allows enough time for detectable change to exceed the machine's precision error (least significant change).
Question 4: Which of the following correctly describes 'short-term precision' in DXA?
- The difference between two different DXA machines' T-scores
- The coefficient of variation from repeat scans on the same patient under identical conditions (Correct answer)
- The long-term drift of a DXA system over years
- The accuracy of DXA compared to DEXA phantom values
Correct answer: The coefficient of variation from repeat scans on the same patient under identical conditions
Short-term precision is expressed as the coefficient of variation (CV%) from repeated scans performed close together under the same conditions to quantify operator and machine variability.
Question 5: When scanning the total body, which of the following patient instructions is MOST important before starting the acquisition?
- The patient should hold their breath for the entire scan
- The patient must remove all metal objects and lie still with arms at sides, palms down (Correct answer)
- The patient should cross their arms over the chest
- The patient's feet must be elevated on a footrest
Correct answer: The patient must remove all metal objects and lie still with arms at sides, palms down
Metal objects create artifacts, and the arms-at-sides palms-down position with stillness ensures accurate whole-body composition and BMD analysis.
Question 6: What does a 'spine phantom' primarily verify during daily DXA quality control?
- Patient radiation dose levels
- System stability in BMD accuracy and precision over time (Correct answer)
- Correct positioning laser alignment
- Network connectivity of the DICOM system
Correct answer: System stability in BMD accuracy and precision over time
Daily spine phantom scans track system BMD accuracy and precision, allowing detection of drift or malfunction before clinical scans are affected.
Question 7: A DXA operator performing a hip scan notices the greater trochanter is partially cut off at the image edge. What is the most appropriate action?
- Proceed with analysis; the femoral neck is the primary region
- Reposition and rescan to ensure the full proximal femur is captured (Correct answer)
- Crop the image and reanalyze
- Add a note to the report and sign off
Correct answer: Reposition and rescan to ensure the full proximal femur is captured
The full proximal femur including the greater trochanter must be within the scan field for valid total hip ROI analysis; incomplete images require repositioning and rescanning.
DEXA Scan Operation & Technique 4
During a serial DXA exam, which factor is MOST critical for ensuring valid comparison to a prior scan?