Calcified Tissue International

, Volume 56, Issue 1, pp 19–25 | Cite as

Factors influencing short-term precision of dual X-ray bone absorptiometry (DXA) of spine and femur

  • K. Engelke
  • C. C. Glüer
  • H. K. Genant
Clinical Investigations


In this study we analyzed the effect of variations in bone area size, baseline soft tissue composition represented by the R-value, and bone region of interest positioning on the precision in vivo of bone mineral density (BMD) and content (BMC) as measured by dual X-ray absorptiometry (DXA). The posterior-anterior (PA) spine, decubitus latcral, and femur modes were evaluated. Eleven (PA-spine), 9 (dec-lat), and 14 (femur) postmenopausal women were scanned twice on a Norland XR-26 with repositioning to determine short-term precision of BMD, BMC, AREA, and the R-value. Phantom precisions (CV[%] of 10 consecutive scans) for BMD (BMC) were PA spine: 0.66% (0.57%), neck: 1.1% (1.2%), and trochanter: 0.55% (1.0%). Precisions in vivo (CV[%]; two consecutive scans averaged over all patients) were PA spine: 0.9% (1.0%), dec-lat: 7.1% (18%), neck: 1.3% (1.9%), and trochanter: 2.5% (4.9%). BMD precision could be fully explained by BMC and AREA variations. However, BMC alone was a particularly poor predictor of BMD in the dec-lat (r2=0.05) and in the neck (r2=0.13) modes. AREA was a strong predictor for BMC precision explaining between 41% and 88% of the BMC changes. Changes in soft tissue composition contributed significantly in explaining the BMC changes in the dec-lat projection. A higher dependence of BMC changes on AREA changes resulted in a larger difference between BMC and BMD precision. Thus, particularly in the femur and in the decubitus lateral modes, the use of BMD is advantageous compared with BMC.

Key words

DXA In vivo Precision Soft tissue 


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Copyright information

© Springer-Verlag New York Inc 1995

Authors and Affiliations

  • K. Engelke
    • 1
  • C. C. Glüer
    • 1
  • H. K. Genant
    • 1
  1. 1.Department of RadiologyUniversity of California at San Francisco, Osteoporosis Research GroupSan FranciscoUSA

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