title: Comparison of BMD precision for Prodigy and Delphi spine and femur scans.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiology, University of California, 185 Berry Street, Ste. 350, San Francisco, CA 94143-0946, USA. john.shepherd@radiology.ucsf.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Shepherd
authors.forename: B
authors.initials: B
authors.lastname: Fan
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: E M
authors.initials: EM
authors.lastname: Lewiecki
authors.forename: P
authors.initials: P
authors.lastname: Miller
authors.forename: H K
authors.initials: HK
authors.lastname: Genant
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation*; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D005260:Female; D005269:Femur / Q000502:physiology*; D005272:Femur Neck / Q000502:physiology; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000175:diagnosis; D017698:Postmenopause / Q000502:physiology; D015203:Reproducibility of Results