DEXA DEXA Quality Assurance & Equipment Calibration 2

Question 1

Which measurement is used to evaluate in-vitro precision of a DEXA scanner?

Accepted Answer

Root mean square coefficient of variation (RMS-CV%)

Answer

RMS-CV% quantifies the percentage variability of repeated phantom or patient measurements and reflects scanner precision.

Question 2

What is the recommended minimum number of repeat scans used to calculate an in-vivo precision assessment for a DEXA technologist?

Accepted Answer

30 patients scanned twice or 15 patients scanned three times

Answer

ISCD guidelines recommend 30×2 or 15×3 repeat scans on real patients to calculate a clinically valid precision error.

Question 3

A DEXA technologist calculates an in-vivo spine precision of 1.8% RMS-CV. What is the least significant change (LSC) at 95% confidence?

Accepted Answer

~5.0%

Answer

LSC at 95% confidence = 2.77 × RMS-CV; 2.77 × 1.8% ≈ 5.0%, meaning a change must exceed ~5% to be considered real.

Question 4

Which factor most directly degrades technologist repositioning precision in spine DEXA?

Accepted Answer

Inconsistent patient positioning and ROI placement between visits

Answer

Repositioning errors from inconsistent patient setup and ROI placement are the leading cause of poor in-vivo precision.

Question 5

A DEXA facility is switching from one manufacturer's system to another. What must be done before comparing serial BMD results?

Accepted Answer

Perform cross-calibration using ISCD-recommended methods and ideally rescan patients on both systems

Answer

Different DEXA systems are not interchangeable; cross-calibration studies are required to establish BMD conversion equations.

(DEXA) DEXA Bone Density Scan Certification Practice Test