Osteoporosis International

, Volume 17, Issue 9, pp 1303–1308

Comparison of BMD precision for Prodigy and Delphi spine and femur scans

  • J. A. Shepherd
  • B. Fan
  • Y. Lu
  • E. M. Lewiecki
  • P. Miller
  • H. K. Genant
Original Article



Precision error in bone mineral density (BMD) measurement can be affected by patient positioning, variations in scan analysis, automation of software, and both short- and long-term fluctuations of the densitometry equipment. Minimization and characterization of these errors is essential for reliable assessment of BMD change over time.


We compared the short-term precision error of two dual-energy X-ray absorptiometry (DXA) devices: the Lunar Prodigy (GE Healthcare) and the Delphi (Hologic). Both are fan-beam DXA devices predominantly used to measure BMD of the spine and proximal femur. In this study, 87 women (mean age 61.6±8.9 years) were measured in duplicate, with repositioning, on both systems, at one of three clinical centers. The technologists were International Society for Clinical Densitometry (ISCD) certified and followed manufacturer-recommended procedures. All scans were acquired using 30-s scan modes. Precision error was calculated as the root-mean-square standard deviation (RMS-SD) and coefficient of variation (RMS-%CV) for the repeated measurements. Right and left femora were evaluated individually and as a combined dual femur precision. Precision error of Prodigy and Delphi measurements at each measurement region was compared using an F test to determine significance of any observed differences.


While precision errors for both systems were low, Prodigy precision errors were significantly lower than Delphi at L1–L4 spine (1.0% vs 1.2%), total femur (0.9% vs 1.3%), femoral neck (1.5% vs 1.9%), and dual total femur (0.6% vs 0.9%). Dual femur modes decreased precision errors by approximately 25% compared with single femur results.


This study suggests that short-term BMD precision errors are skeletal-site and manufacturer specific. In clinical practice, precision should be considered when determining: (a) the minimum time interval between baseline and follow-up scans and (b) whether a statistically significant change in the patient’s BMD has occurred.


DXA Least significant change Osteoporosis Repeatability 


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Copyright information

© International Osteoporosis Foundation and National Osteoporosis Foundation 2006

Authors and Affiliations

  • J. A. Shepherd
    • 1
  • B. Fan
    • 1
  • Y. Lu
    • 1
  • E. M. Lewiecki
    • 2
  • P. Miller
    • 3
  • H. K. Genant
    • 1
    • 4
  1. 1.Department of RadiologyUniversity of CaliforniaSan FranciscoUSA
  2. 2.New Mexico Clinical Research & Osteoporosis CenterAlbuquerqueUSA
  3. 3.Colorado Center for Bone ResearchLakewoodUSA
  4. 4.Synarc, Inc.San FranciscoUSA

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