DEXA Scan Operation & Technique 3 — Questions and Answers
Question 1: How should the technologist handle a patient who has received an oral contrast agent (barium) within the last 7 days before a DXA scan?
- Proceed with the scan; barium has no effect on DXA
- Reschedule the scan until contrast has cleared the GI tract (Correct answer)
- Double the scan time to compensate for artifact
- Scan the forearm instead
- Scan the forearm instead
Correct answer: Reschedule the scan until contrast has cleared the GI tract
Barium contrast in the GI tract overlaps the lumbar spine on a DXA image and will falsely elevate BMD; the scan should be rescheduled.
Question 2: What is the recommended action if the femoral neck region of interest (ROI) is placed incorrectly during analysis?
- Accept the result because software auto-corrects errors
- Reposition the ROI manually and reanalyze the scan (Correct answer)
- Rescan the patient immediately
- Use the trochanter value as a substitute
Correct answer: Reposition the ROI manually and reanalyze the scan
Manual repositioning and reanalysis of the ROI is required to ensure accurate femoral neck BMD measurement without repeating radiation exposure.
Question 3: When performing a forearm DXA scan, the 33% radius (one-third site) is measured at what anatomical landmark?
- One-third of the distance from the ulnar styloid to the olecranon
- One-third of the ulnar length from the wrist
- One-third of the radius length from the wrist (Correct answer)
- One-third of the radius length from the elbow
Correct answer: One-third of the radius length from the wrist
The 33% radius site is located at one-third of the total radius length measured from the ulnar styloid (wrist) proximally along the radius.
Question 4: A technologist notices the DXA table laser alignment light does not activate during startup. What is the correct response?
- Continue scanning; the laser is only for convenience
- Document and report the malfunction; do not scan until serviced (Correct answer)
- Manually estimate patient positioning without the laser
- Replace the laser module immediately and continue scanning
Correct answer: Document and report the malfunction; do not scan until serviced
Malfunctioning positioning lasers should be reported and the unit should not be used for clinical scanning until the equipment is serviced and verified.
Question 5: Which scan acquisition parameter most directly affects the radiation dose delivered during a DXA scan?
- Table height setting
- Scan speed / mode (e.g., fast vs. high resolution) (Correct answer)
- Room temperature
- Patient gown thickness
Correct answer: Scan speed / mode (e.g., fast vs. high resolution)
Scan mode determines beam on-time and detector sampling rate, which directly affect the dose delivered; higher-resolution (slower) modes deliver more dose than fast-array modes.
Question 6: On a lumbar spine DXA scan, what structure should the inferior border of the L4 vertebral body align with in a correctly positioned image?
- The iliac crest
- The top of the scan field
- The L5–S1 disc space visible at the bottom of the image (Correct answer)
- The bottom of the lumbar lordosis curve
Correct answer: The L5–S1 disc space visible at the bottom of the image
A correctly acquired lumbar spine scan shows the L5–S1 intervertebral disc space at the lower margin of the image, confirming full L1–L4 inclusion.
Question 7: What is the effect of residual metal (e.g., an IUD) in the lumbar spine scan field during DXA?
- It has no measurable effect on the scan
- It attenuates the X-ray beam and artificially increases BMD at that region (Correct answer)
- It decreases BMD values by absorbing photons
- It only affects the scan if it is larger than 2 cm
Correct answer: It attenuates the X-ray beam and artificially increases BMD at that region
Metal objects attenuate the DXA beam more than bone, causing the software to overestimate BMD in the overlapping region.
DEXA Scan Operation & Technique 3
How should the technologist handle a patient who has received an oral contrast agent (barium) within the last 7 days before a DXA scan?